Limp Mode Problem - PLEASE HELP

[bronco2v8]

Check your oil pressure sending unit and/or oil level sending unit.

I'm assuming that a low oil pressure issue is putting your car into limp mode. It appears to be the only sensor you haven't replaced several times, and in 'go fast, turn left' racing oil starvation can be a big problem because oil is always forced to one side of the sump.

What's your on-track oil consumption look like? Oil temperature? What type of oil are you using?

I have an aftermarket gauge, so the stock sending unit isn't even hooked up. I run about 90psi under load & 50psi at an idle. Not sure of the oil temp. I use Mobile1 5w-30 synthetic & change it every other race.

 

[bronco2v8]

Are you running a thermostat? Are you looking at temps on the gage or those provided to the ECM? I know it seems like your problem is temperature related based on your description but I have a hard time believing that could be the case. It just doesn't seem plausible.

JHC13 asked about oil consumption. An important question to ask. Because I'm wondering if you're overpowering the crankcase ventilation system. If you are sucking oil into the combustion chambers, the knock sensors will go insane because of the resultant detonation with the result being retarded timing until that doesn't work and then countermeasures will be implemented (limp mode).

Also, how much gas are you carrying when you go out on the track? Half full, quarter full, just enough to complete the session?

Additionally, I've got to ask what may be a dumb question but you're talking of swapping out ECM's and you're talking about using OBDI and OBDII versions. Really? I just can't imagine that the wiring is going to be compatible between those two. Same connectors? Wires running from the same cavities to the same sensors? Seems implausible. My plausibility meter really goes off the chart when you say you have used ECM's for both manual and automatic transmissions.

You're speaking of a conversion harness. What exactly does that allow for? I have an idea of what the purpose is but would you tell us exactly?

Also, you have removed a number of sensors and the VSS for certain and perhaps the EGR concern me. What in the ECU has been done to compensate for their being removed? You could probably easily fool the system into thinking an EGR is present (there may not be any feedback to the ECM for EGR operation so this may not be an issue at all) but the VSS? That's a pretty critical sensor.

For the purposes of fixing your problem, one thing you should do at this point is remove any preconceived notion of what the problem is. It's good to suspect something then eliminate it and move on but feeling that it absolutely has to be "x" can really get you chasing your tail. And truly, you've thrown enough parts at it that you've been chasing your tail.

Sorry, but I keep adding things as I think of them. You say you have never had a code set. Does the ECM have power when the car is off? Does the master switch (assuming the sanctioning body requires one) kill power to the ECM?

No thermostat. We can not have antifreeze in our cooling systems on the track & last year my brand new thermostat rusted up & caused the motor to blow a head gasket, so this year I'm not running one.

My crankcase vent doesn't go into the intake tube anymore, instead I run it through an oil catch can, the it vents out of the catch can through a hose under the car. I got tired of the oily mess inside the air tube.

We were running half a tank of gas last year, but this year we keep the take full all the time with 92 octane gas & some octane booster.

I purchased a conversion harness online & then went through it with a wiring diagram from a OBD1 car & a diagram from my OBD2 car. I thoroughly researched every single wire & as far as I can tell everything is 100% correct in the conversion harness. My car is a red-headed step child of the preludes. In 1996 they had to switch to OBD2 for the USA, but Honda wasn't ready to come out with the next gen of Preludes, so they made the 96's a really base OBD2 system. The car only has one O2 sensor instead of 2, and some other differences I don't remember. So essentially the OBD1 & OBD2 systems for my year car only are the same. It is very expensive to find a 1 year only OBD2 ecu, but it's really cheap & easy to find 4 year produced OBD1 ecu. Someone stole the original ecu out of my car before I purchased it, so it took me awhile to find an OBD2 ecu.

The EGR is still plugged in, it's just not attached to the intake anymore. The ecu never gives me an EGR code, so I assume it's not causing the problem. The VSS used to be hooked up, but then I had issues with it causing the car to to idle extremely high after hitting the accelerator. When I unplugged it, the car returned to a normal idle & I just never tried plugging it back in since I don't have the stock speedometer anymore.

I would have to say yes the ecu has constant power. I have a battery shut off switch, cause we're required to have one. My OBD2 ecu is an automatic, so it always sets the lock-up code. When I kill the power from the battery via my switch, wait a few days, then turn it back on, the lock-up code is still stored in the ecu's memory, but if I use my scanner to clear the codes, then try again, the code goes away until I start the car up again.

 

[bronco2v8]

A few more tidbits....
My idle air control solenoid quit working earlier this year, I have replaced it many times with know working ones & every time the coolant temp reaches about 175 the idle starts going up to 2500rpms, then drops dramatically to 600rpms, then back up to 2500rpms, then back down to 600rpms. I have checked the wires numerous times, every thing is reading fine as far as I can tell, but I'm not entirely sure why it keeps doing this, so in order to make it stop, I unplugged the IAC, removed the spring inside it & put a dowel in to keep the plunger open. The car idles like it has some huge cams, but it's a lot better then extreme surging it was doing before.
Now the IAC did not do this last year & the car still had the limp mode problem, so I know that the IAC is not causing the limp mode. However I do not know if whatever sensor is causing the limp mode has gotten so bad now that it could also be affecting the IAC operation now?
Yesterday I purchased a new O2 sensor because when I was viewing the live readings of the ecu during my test drive, it didn't appear that the O2 sensor was doing anything. It wasn't, so now with a new O2 sensor I've noticed that the fuel trim is now working. At an idle the fuel trim is at 0%, but when you rev up the motor to about 4500rpms, the fuel trim goes up to 65%. Seems like an awful lot to me. Also the coolant temp sensor reads 175 degrees, but my air temp sensor is only reading about 126 degrees. Shouldn't those 2 sensors have readings a little closer together?

 

[Zenmervolt]

Its how the rev limiter works on a Honda. If the idle valve is stuck open then there is no idle control.

When the idle valve is stuck there is too much air going in to the intake.

So when the revs get to high the PCM cuts the injectors to drop the idle.

If you have a scan tool you can watch it happen.

Injector pulse width will drop every time the revs go up and then go up when the idle speed drops.

Same thing happens on Nissans when the the electronic throttle valve loses its calibration.

1) That's not a rev limiter. That's a backup idle control. That operates only when the throttle is closed.

2) The OP's condition is happening at WOT; the effect of a stuck idle control valve at WOT is exactly nothing.

3) The OP's car does not have an idle control valve (he has removed it).

4) If the problem were that the engine was attempting to control idle by cutting the injectors because there was no idle control valve, the problem would be happening all the time, and at idle -- the OP has said that the car idles fine and that the problem is not constant.

ZV

EDIT: I typed this up before the OP's last reply. The surging he experienced before disabling the IAC is what you describe. It is not the same as the rev limit he's experiencing as another problem.

 

[JCH13]

CLT and IAT have very little to do with each other, don't worry about that.

Any idea why you're going through O2 sensors like crazy?

 

[Zenmervolt]

A few more tidbits....
My idle air control solenoid quit working earlier this year, I have replaced it many times with know working ones & every time the coolant temp reaches about 175 the idle starts going up to 2500rpms, then drops dramatically to 600rpms, then back up to 2500rpms, then back down to 600rpms. I have checked the wires numerous times, every thing is reading fine as far as I can tell, but I'm not entirely sure why it keeps doing this, so in order to make it stop, I unplugged the IAC, removed the spring inside it & put a dowel in to keep the plunger open. The car idles like it has some huge cams, but it's a lot better then extreme surging it was doing before.
Now the IAC did not do this last year & the car still had the limp mode problem, so I know that the IAC is not causing the limp mode. However I do not know if whatever sensor is causing the limp mode has gotten so bad now that it could also be affecting the IAC operation now?
Yesterday I purchased a new O2 sensor because when I was viewing the live readings of the ecu during my test drive, it didn't appear that the O2 sensor was doing anything. It wasn't, so now with a new O2 sensor I've noticed that the fuel trim is now working. At an idle the fuel trim is at 0%, but when you rev up the motor to about 4500rpms, the fuel trim goes up to 65%. Seems like an awful lot to me. Also the coolant temp sensor reads 175 degrees, but my air temp sensor is only reading about 126 degrees. Shouldn't those 2 sensors have readings a little closer together?

OK, first of all, it feels a bit like every time you post you mention another "repair" that really should never have been performed. Unplugging the sensor doesn't solve the problem, it only cripples the ECU's ability to handle the problem.

In all honesty, at this point, the only real way I see to get to an engine that we know will run well is for you to have the engine completely rebuilt with a custom EMS (like a MegaSquirt or a Wolf V4X) that has been tuned properly on a dyno. Right now there are so many hacks in your engine's history that I don't really see this issue being resolved by performing more hacks. It's time to go back to square one and do things properly.

Second, yes, 65% fuel trim is incredibly high. This is normally expected to be under 5%. It means you're leaning out catastrophically at higher RPM (or that your code reader is misinterpreting the information it's seeing). You are either getting s shit-ton of un-metered air into the intake from somewhere or something is preventing the ECU from being able to make its normal enrichment. Bottom line, there is a HUGE underlying problem with your engine if that 65% fuel trim is accurate. Also, if the 65% fuel trim is accurate, that leaning out would absolutely cause enough misfires to trigger a limp mode.

Finally, no, the water temp and air temp should not be closer together. Under normal operation the water temp should be around 180 degrees. Significantly higher is bad because you start to have it boil off and significantly lower is bad because it means the engine is too cold to work properly. Intake air temperature should be as cold as you can possibly get it, but normally this is between 10 and 30 degrees above ambient (when the car is in motion; intake air temp can get much higher at idle with the car sitting still). On a 70 degree day, I would expect intake air temps in the 85-105 degree range when the car is in motion, though racing will tend to increase temperatures.

ZV

 

[Mark R]

A few more tidbits....
My idle air control solenoid quit working earlier this year, I have replaced it many times with know working ones & every time the coolant temp reaches about 175 the idle starts going up to 2500rpms, then drops dramatically to 600rpms, then back up to 2500rpms, then back down to 600rpms. I have checked the wires numerous times, every thing is reading fine as far as I can tell, but I'm not entirely sure why it keeps doing this, so in order to make it stop, I unplugged the IAC, removed the spring inside it & put a dowel in to keep the plunger open. The car idles like it has some huge cams, but it's a lot better then extreme surging it was doing before.

Sounds like the ECU is going into "IAC solenoid failure" safe mode. The ECU tries to close the IAC, but for some reason it doesn't close - so the rpm rises, the rpms get to about 2500, the ECU switches to its IAC failure program which controls the idle speed by cutting fuel (so you get a sudden drop in idle, then the ECU restarts fuel).

You say, you'd already replaced the IAC, but this didn't help. The only other explanation is a major air leak somewhere - e.g. disconnecting a PCV and using an "open breather" can create a major air leak if the "neutral" crankcase breather isn't disconnected from the intake.

 

[JCH13]

How do you know that your fuel pressure is staying at 45psi under high RPM/throttle conditions?

Have you ever flow benchmarked your whole fueling system?

Are you using any octane boosters that contain lead or something else that might damage an O2 sensor?

ZV is probably right, if you 'do it right' then you'll have a much more reliable car at the end of the day.

 

[Zenmervolt]

ZV is probably right, if you 'do it right' then you'll have a much more reliable car at the end of the day.

It also makes it much easier to diagnose issues that come up. What we have here seems like a situation where a problem comes up and, instead of that problem getting fixed, what has happened is that another problem is introduced that has the opposite symptom. So the symptoms roughly cancel each other out, but now there are actually two problems instead of the original one. Even though the engine seems to be running better than it did with just the one problem. Then, when a new problem arises, it's not always easy to tell that it's actually caused by one of the pre-existing problems that had previously seemed to be canceling each other out.

It's a bit like that Simpson's bit where Mr. Burns goes to the doctor and they find out that he has every single disease in the world, but no symptoms because they all cancel each other out.

ZV

 

[bronco2v8]

Ok, I built this car from scratch 2 years ago. Motor was completely rebuilt & when I first put it on the track last year it was cold & wet cause it's the Pacific NW & the car did excellent, no problems. Until about May when the temps started increasing & we were racing harder, then this weird limp mode started happening.
At first I thought it was sputtering, like running out of fuel, so I put on an adjustable fuel pressure regulator with a Glowshift digital fuel pressure gauge inside the car. I could see that the fuel pressure was always dead on, even when it would have it's little problem.
So then I replaced the TPS & it still did it.
Then I switched from the manual OBD1 ecu I was using to the automatic OBD2 ecu I had just gotten & it still did it.
Replaced the OBD2 crank sensor on the oil pump & the OBD2 distributor, still did it.
Then I switched back to the OBD1 ecu & bought a new OBD1 distributor, still did it.
Replaced the head gasket, the coolant temp sensor, cleaned the intake, new plugs, new wires, new MSD coil, new map sensor, new air temp sensor & relocated the crankcase breather. None of it worked.
So by this point I was really getting frustrated, so I just started eliminating things.
Anything that I removed or unplugged made absolutely no difference in when it would activate the limp mode.
What did help, raising the back of the hood about 5" so that cooler air could get in. When I did that, the car wouldn't hit the limp mode nearly as often as before.
So I got a new radiator, new hoses, new fans & about that time the thermostat stuck on me & blew the head gasket.
Race season was over with, so the car got parked until January this year. I pulled the motor, rebuilt it again, new stage 3 clutch, new flywheel & everything inside the engine was new, crank, rods, pistons, valves, springs, cams, oil pump & water pump & a balance shaft eliminator kit was installed & a gates racing timing belt.
I did nothing to the electronics, just put the motor back in & when I started it up everything was sounding good. Until the engine temp reach 175 & the IAC started doing that surging thing I described above, so I put a quick fix to that.
Then this race season started & everything was working perfect, no limp mode problems at all, until May arrived & the temps warmed up & we started racing harder & now the limp mode problem is back, just like last year.
It's not that I set out to make a mess out of this, it's just that I'm to the point where I can't do anything but go with the process of elimination, unplug, change resistance, move sensors, whatever it takes to figure out why the car is acting this way. Also, once again, my race friend's completely bone stock, untouched car is doing exactly the same thing as mine, which makes it even more frustrating because I know we can't be the only 2 on the whole internet experiencing this problem, but yet it seems as though we are, so we've both been left struggling to find answers any way we can.
If I ever figure this out I will certainly start putting things back to right, but at this time I just don't see the point of doing so right now when the source of my main problem has not been found yet.

 

[Zenmervolt]

It's not that I set out to make a mess out of this, it's just that I'm to the point where I can't do anything but go with the process of elimination, unplug, change resistance, move sensors, whatever it takes to figure out why the car is acting this way.

I know you didn't set out to have this happen. But the fact remains that whether you wanted to be here or not, you are here.

My honest recommendation at this point is to scrap the entire stock/semi-stock ECU setup and invest in a custom EMS like the Wolf V4X (with the "wire in" option so you have a whole new engine wiring loom) or one of MegaSquirt's "Pro" offerings. That should give you some data-logging capabilities as well as allow you to create fully custom fuel and spark maps that are suitable for racing (you may need a professional race shop with a chassis dyno to get this done if you're not experienced with creating complete ECU maps from scratch). There are a couple of Wolf dealers in Western Washington (one in Vancouver and one in Sammamish) as well as one in Burnaby, just outside of Vancouver, BC.

If you can't do that, I would focus on heat, not on a sensor. It seems relatively clear that your issue is somehow heat-related. Raising the back of the hood doesn't let cold air in so much as it allows hot air out and decreases the overall air pressure in the engine bay, which allows more flow of air. I still don't think it's a sensor. I still think there's an underlying reason why the ECU thinks something is wrong enough to go into limp mode and that this is related to an overheat scenario for at least some part of the engine (lean mixture causing misfires, etc.).

All I can say though is that, if this were my own car, I'd be looking at pulling the whole engine wiring harness and starting fresh with a new, custom, EMS.

ZV

 

[boomerang]

Is there a passenger seat in the car? Can you rent the track? Get some guys together to rent it to reduce the cost if need be. Connecting a scan tool that can record history has just got to tell the tale. Get a passenger that can trigger the recording if it's too much to drive and do that too. (Small button and you've got gloves on, you know what I'm saying.) You say that when it happens that the sensor input goes all haywire but a careful analysis of that may point you in the right direction.

If you can get some guys together to rent the track, be sure to invite the top dog. You may be surprised to find that he's willing to share some knowledge. A guy that really likes to race, really likes to win, but also wants real competition. The top dog is never going to share all his secrets but he just might be willing to help you with this.

I thought ZV was giving great advice from the beginning. I really like the idea of a brand spanking new harness and an ECU that can be tailored to what you're doing. But you would know best if that ECU is legal in the class you're racing in.

You've gotten a lot of very good advice in this thread and I don't envy you trying to figure out which is the best course of action. That's why I suggest trying to get help from within the racing community.

 

[michal1980]

Is there a passenger seat in the car? Can you rent the track? Get some guys together to rent it to reduce the cost if need be. Connecting a scan tool that can record history has just got to tell the tale. Get a passenger that can trigger the recording if it's too much to drive and do that too. (Small button and you've got gloves on, you know what I'm saying.) You say that when it happens that the sensor input goes all haywire but a careful analysis of that may point you in the right direction.

If you can get some guys together to rent the track, be sure to invite the top dog. You may be surprised to find that he's willing to share some knowledge. A guy that really likes to race, really likes to win, but also wants real competition. The top dog is never going to share all his secrets but he just might be willing to help you with this.

I thought ZV was giving great advice from the beginning. I really like the idea of a brand spanking new harness and an ECU that can be tailored to what you're doing. But you would know best if that ECU is legal in the class you're racing in.

You've gotten a lot of very good advice in this thread and I don't envy you trying to figure out which is the best course of action. That's why I suggest trying to get help from within the racing community.

wouldn't it be cheaper to just get a stand alone ECU and pay for tuning before renting a track?

 

[bronco2v8]

I would love to get a nice, tunable ecu, but the fact remains that the track rules strictly forbid chipped or programmable ecu's in my class of racing. So basically I need to make this thing run right on a stock ecu or I just have a very expensive pile of crap sitting in my shop.
Renting the track is an option, but a dyno is a more affordable option, plus the track doesn't allow passengers any more cause of insurance reasons. We try & test it around here, usually late at night, sometime we can trigger it, other times not.
My car is the top dog, & my friend & his dad are the second & third, we all have 4G Preludes with the H23A1 motors. Only 2 of our cars are having this issue, which makes it really strange.

Since changing the O2 sensor made the fuel trim start working again, I decided to throw more money at it today & went out & got a new air temp sensor.
I replaced it, started the car, let it warm up to 175 degrees again & started reving it to 4500rpm's. To my utter surprise the short term fuel trim didn't go any higher than 5% this time, even when I held it WOT, bouncing off the rev limiter for 20 seconds, the highest the short term fuel trim went was 12%.
I can't be sure, but it seems like I might be getting closer to solving my problem.
Also the map sensor says 19 at an idle & drops to 9 under a load, is this ok?
My timing fluctuates between 22 degrees - 28 degrees, is this an acceptable amount?

 

[Zenmervolt]

Also the map sensor says 19 at an idle & drops to 9 under a load, is this ok?

19 what? Without a scale that's meaningless. 19 bar would be horrifically wrong. 19 PSI would be very wrong. 19 mmHg would be very wrong. But 19 inHg would be about right for hot idle.

Also, what do you mean by "under load"? At wide open throttle you should see 1.5 or lower if you're reading in inHg (for a non-turbo/non-supercharged engine). At partial throttle but under load, 9 inHg could be right depending on how much load and how much throttle opening. 9 inHg at wide open throttle though would indicate a pretty massive obstruction somewhere in the intake.

With the key "on" but the engine off, what is the reading from the MAP sensor?

ZV

 

[bronco2v8]

19 what? Without a scale that's meaningless. 19 bar would be horrifically wrong. 19 PSI would be very wrong. 19 mmHg would be very wrong. But 19 inHg would be about right for hot idle.

Also, what do you mean by "under load"? At wide open throttle you should see 1.5 or lower if you're reading in inHg (for a non-turbo/non-supercharged engine). At partial throttle but under load, 9 inHg could be right depending on how much load and how much throttle opening. 9 inHg at wide open throttle though would indicate a pretty massive obstruction somewhere in the intake.

With the key "on" but the engine off, what is the reading from the MAP sensor?

ZV

Sorry, it was 19inHg at an idle & under a load was 9inHg, holding the throttle about half way, with it in gear & the ebrake on with wheel chalks. The key on, engine off reading was 30inHg.

 

[Zenmervolt]

Sorry, it was 19inHg at an idle & under a load was 9inHg, holding the throttle about half way, with it in gear & the ebrake on with wheel chalks. The key on, engine off reading was 30inHg.

OK. That's interesting to me.

30 inHg is roughly 1 atm, or atmospheric pressure at sea level. The fact that it's reading that with the key on but engine off would seem to indicate that it's reading absolute pressure.

However, if that were the case, then at hot idle it should read about 11 inHg (30 inHg for atmospheric minus 19 inHg of vacuum for 11 inHg absolute pressure). And if that were the case, getting on the throttle would make the reading go higher, not lower.

19 inHg is pretty much spot-on for relative vacuum at warm idle though, and 9 inHg for part throttle with light load seems about right to me as well for a relative vacuum reading.

So, taken together, my best guess is that the ECU reports in relative pressure when the engine is running but reports absolute pressure when the engine is not spinning. On that assumption, those readings are within what I would expect for a naturally aspirated car.

ZV

 

[bronco2v8]

Excellent!! Well I should know for sure if the limp mode problem is solved tomorrow, we have another race & it's going to be a 75 degree day.
Thanks for all the help & I'll let you know if the O2 sensor & air temp sensor solved my problems.

 

[boomerang]

Well, I have not really provided anything of any value but I will add some more thoughts although they are not related to your immediate problem.

You said something about fuel additive and it was brought up that you could be fouling your O2 by using that. I guess I'm wondering why you need a fuel additive? If you're trying to raise the octane, is there no higher octane fuel available in your area? If the additive contains lead as was brought up, you're going to be going through a lot of O2 sensors.

I think you're going to be having to deal with your cooling system. You may need to restrict the flow of coolant with a restrictor in place of the thermostat. It's something you'll have to experiment with. Do you have an electric radiator fan in place? I can't imagine that you could get away without one. With no thermostat, (and I fully understand why you removed it and don't disagree) the water will not remain in the radiator long enough to be cooled sufficiently and your water temp will just keep increasing.

Anyway, those are my thoughts for the moment. I really wished I could have contributed something worthwhile but I'm really enjoying the thread and hope you'll keep posting to let us know how things are working out. Personally, I would enjoy some pics of the car too. I've not been involved in racing for well over 15 years (would have to put some thought into coming up with the actual number) and that was as a crew member but I still like the nitty gritty of it all. In the end of my involvement we were racing nationally in the Speedvision World Challenge series and after even that degree of involvement, watching it on TV or from the stands just doesn't hold my interest.

 

[bronco2v8]

There is no lead in the octane booster, it's actually not even "octane booster" that I'm using. I add 1 gallon of 109 race fuel to 4 gallons of 92 pump gas. The race gas burns so much better than just straight up pump gas. I don't know about other states, but around here the pump gas has so damn much ethanol in it that I have to add something in order to get it to burn otherwise just straight pump gas constantly fowls out the spark plugs & makes the car chuggy. Some people use a can of Seafoam in their tanks every race, which also helps.
I actually haven't had any real cooling problems yet, but we're not quite at our hottest time of year yet either. I have a brand new 3 core aluminum radiator with two 1750cfm electric cooling fans. The car turns one fan on & off, then there's a switch inside the car to turn on the second fan in case it's needed.
Pics....I've got lots of pics. Here you go.

 

[Zenmervolt]

I add 1 gallon of 109 race fuel to 4 gallons of 92 pump gas.

109 octane race gas? I'm familiar with Sunoco's 260 GT Plus which is an unleaded 104 octane fuel by US (RON+MON)/2 pump octane standards but I can't think of any race gas off the top of my head that's 109 octane. Sunoco Standard is 110 octane, but it's leaded.

It's possible that you're either inadvertently using leaded fuel or that you're not getting quite the octane boost you think you are which could affect whether you're getting detonation. Or maybe I'm just used to what's at Pacific Raceways and your track sells different fuels.

Pump gas here in WA has up to 10% ethanol, but I've yet to have that create any running issues in my own cars (one of which is 28 years old and was definitely not designed for ethanol blended fuels) nor has it created any issues in my 32-year-old motorcycle. I'm very skeptical of claims that ethanol would "foul the plugs" since the stoichiometric ratio for ethanol is slightly richer than for "pure" gasoline. That means that increased ethanol percentages make the engine run slightly lean (since it's metering fuel based on "pure" gasoline's leaner stoichiometric ratio instead of based on the slightly greater amount of fuel needed when you're running ethanol), which would not foul plugs but instead burn them.

"Pure" gasoline burns perfectly at 14.7:1. Racing engines will typically run richer than that, of course. But ethanol has its perfect burn ratio at 9:1. That's far richer than even race engines run on pure gas. If the plugs are fouling, it's because the engine is running rich and an increased ethanol amount in the fuel won't cause the engine to go rich, it'll cause it to go lean.

Ethanol can cause issues with degrading old rubber seals or corroding old metallic fuel system parts, but I've not seen it cause plugs to foul.

ZV

 

[boomerang]

Pics....I've got lots of pics. Here you go.

:thumbsup:

 

[JCH13]

I'm still voting for lead in your fuel or something that's screwing your O2 sensors, and the O2 sensor malfunctions are screwing up your fueling.

If you can't do that, I would focus on heat, not on a sensor. It seems relatively clear that your issue is somehow heat-related. Raising the back of the hood doesn't let cold air in so much as it allows hot air out and decreases the overall air pressure in the engine bay, which allows more flow of air. I still don't think it's a sensor. I still think there's an underlying reason why the ECU thinks something is wrong enough to go into limp mode and that this is related to an overheat scenario for at least some part of the engine (lean mixture causing misfires, etc.).

ZV

I'm going to call BS on this. The seam where the windshield and hood meet is a high-pressure zone. Raising the back of a hood, i.e. an 'extractor hood,' is a commonly-believed 'fix' for reducing under-hood temperatures in the Miata world, but it doesn't work as intended. I've seen testing videos where strings were affixed to the back edge of a raised hood once at speed (30-40mph) the strings get sucked into the engine bay because the high pressure air at the base of the windshield is forced into the engine bay. Air flow into the back of the engine bay will tend to increase air pressure inside the engine bay and reduce flow from the radiator fans.

Thread: http://www.miataturbo.net/general-miata-chat-9/highly-lame-hood-risers-59623/

Video: https://www.youtube.com/watch?feature=player_embedded&v=aF-UPdfHEzU

TL;DR - Some people think they get cooling help when STOPPED because hot air can vent out of the engine bay. When MOVING a raised rear hood edge will push air behind the radiator and reducing cooling capacity.

Since changing the O2 sensor made the fuel trim start working again, I decided to throw more money at it today & went out & got a new air temp sensor.
I replaced it, started the car, let it warm up to 175 degrees again & started reving it to 4500rpm's. To my utter surprise the short term fuel trim didn't go any higher than 5% this time, even when I held it WOT, bouncing off the rev limiter for 20 seconds, the highest the short term fuel trim went was 12%.
I can't be sure, but it seems like I might be getting closer to solving my problem.
Also the map sensor says 19 at an idle & drops to 9 under a load, is this ok?
My timing fluctuates between 22 degrees - 28 degrees, is this an acceptable amount?

Imagine that, with working sensors your engine is happy! Seriously, you need to figure out how/why you keep destroying oxygen sensors. 109 octane fuel has to have some sort of additive, and I'd bet its lead. Please link/cite your source for this fuel, for the sake of diagnosing your issue I want to see an datasheet or MSDS that says "no lead" or "oxygen sensor safe."

Why are your using octane boosters/drag racing fuel on a stock ECU/stock engine anyway? You're just throwing money away unless you're playing funny games with base spark timing.

 

[Zenmervolt]

I'm going to call BS on this. The seam where the windshield and hood meet is a high-pressure zone. Raising the back of a hood, i.e. an 'extractor hood,' is a commonly-believed 'fix' for reducing under-hood temperatures in the Miata world, but it doesn't work as intended. I've seen testing videos where strings were affixed to the back edge of a raised hood once at speed (30-40mph) the strings get sucked into the engine bay because the high pressure air at the base of the windshield is forced into the engine bay. Air flow into the back of the engine bay will tend to increase air pressure inside the engine bay and reduce flow from the radiator fans.

You're right. I wasn't thinking it fully through and was assuming it would work similarly to extractor vents in the middle of the hood. I had a complete brain fart about the high-pressure area at the windshield base when at speed. I've been around enough old racers with cowl induction that you'd think I wouldn't do that.

ZV

 

[bronco2v8]

I could be wrong on the whole octane thing. I was just making a guess, It's probably 110.

As for the ethanol part, yes it does affect the way ALL my vehicles run & has at one point or another affected every car in my racing class. The cars start running rough, chugging during acceleration & everyone always thinks it's the fuel filter. I usually take about 4 cans of seafoam to the track each time & someone always needs one. Pour a can in & run the car for a few laps & it always clears up. Time & time again I've done this & it always works. I've been told that it's the high ethanol content in the fuel that gums up the fuel lines & injectors.

I run higher octane gas in my car because that's what my machinist recommended. He knows way more about that stuff then me, so I don't argue with him, I just do it.

Now, the car did absolutely perfect on saturday, never went into limp mode, but my friend's car did. I did 4 things to mine, new O2, new air temp sensor, raised the back of the hood & unplugged the ABS computer. I have no idea what actually solved the problem, but I'm so very happy that the problem seems to be fixed. It appears that one of the wires for the o2 sensor got damaged & when I took the sheathing off the wires I found one that was cut in half. I have no idea when or how this happened, but the new sensor wires are zip tied out off the way, so I shouldn't have that happen again.

Thanks for everyone's help, I'm so very happy that the car is finally running correctly & I hope other people who experience this problem will find all this info as useful as I did.