Updated: I thought my knock sensor was bad (and it still is), turns out I used regular oil rather than synthetic.

[TurtleCrusher]

I've seen alot of people get good advice here so tada! Here it goes..

I have a 1994 Subaru Impreza L 1.8L AWD. It has 209K (bought at 203K just 3 1/2 months ago) and has a minor oil leak and a torn CV joint. Those problems I'm not too worried about. What I am worried about is my Knock Sensor.

I entrusted my father to work on my car. About a week ago I was running an errand on my break and as I tried to start my car to go back to work it hesitated really bad. I sat there more a minute trying to get my car to finally turn over and fire up. Well after a minute or two it fired up and I was on my way.

When I got off work the problem persisted and the car wouldn't fire whatsoever. I tried for over a half hour. I called my brother and we put a multimeter to my battery and it only read 5V. I thought i wasn't getting enough spark as my lights dimmed when i tried to fire up. The new batter I bought powered at the correct charge (approx 16V) so that wasn't the problem. We then tested if the spark plugs were getting power during ignition and after a few shocks to my brother we concluded it was.

So then I bought the book to my car and had my father run more testing on it. After about a day of testing he said that the only part that doesn't work properly is my Knock Sensor. He said after testing that it powered 0hms, which it should be at 6-700ohms (IIRC, i'm no expert) and that the part needed to be replaced.

What does this part actually do? And why is it preventing me from starting up?

I use plus grade gasoline and a high quality 10-30w Castrol Synthetic Oil in the engine. IDK if these are factors and I'm not sure if Subaru engines are made for it.

Does anyone have any ideas where to get this part cheap or if it has nothing to do with my problem?

EDIT: Video added. http://www.youtube.com/watch?v=_aCUVaNuYNM

New EDIT: So today I decided to change the oil in the car. The Oil light as well as the engine and the battery light popped up on failed startups. I already bought a new battery, so the oil was next. I was unaware that the oil I used to change the oil a few days prior to all of this mess was some shit chevron 10w-30 oil. I went back to Castol Syntec (10w-30 high performance, $6.49 quart) and my car fires back up again. Although there is a minor hesitation, all seems well. It's been bad without a car!

I'm going to be turning it on each day for the next week before I'll trust it for a trip again.

Would the temporary regular oil cause any long-term problems?

 

[exdeath]

Knock sensor detects detonation and lets the computer know to retard timing to protect the engine. It does not affect starting or running whatsoever. Detonation is the premature and violent explosion of the mixture before the spark goes off, and can seriously damage the engine.

As long as your car is not modified and you are using premium fuel you have nothing to worry about except possibly on very hot days accelerating uphill or something like that (detonation makes a muted sound of marbles shaking around in a can, sounds similar to the clacking of a diesel engine). By hot I mean 110+ AZ heat. If the knock sensor isn't working, the sound won't go away as soon as you hear it, and you'll need to lift off the throttle or downshift so there is less of a load on the engine.

None of your problems have anything to do with the knock sensor. It sounds like you need to have your alternator checked out. A new battery should be 12.6v and about 14 volts with the car running. 16v is way too high.

 

[brblx]

knock sensors contain some kind of piezoelectric material which senses a certain kind of vibration caused by detonation in the combustion chamber. upon recieving this information, the ECM typically retards ignition timing to try and stop it.

600-700 ohms sounds like a reasonable value, but i don't think there's any way a defective knock sensor could measure zero ohms. at the least, it's not bloody likely. i suspect your father may have measured wrong.

that said, it has nothing to do with startup.

what do you by 'hesitated really bad'? ran badly, or just cranked slowly? i guessing if you tried to start your car for thirty minutes, it was cranking (otherwise you just spent the most futile half hour ever). a car battery showing 5v would not crank your engine over. you should also never seen 16v in a car's electrical system, max charging voltage should be in the 14v range, and a new battery should read around 12.6v. i would be highly suspect of your DMM if you got those readings.

is the check engine light on? that car's not OBDII, but surely it has some kind of diagnostic system that would generate codes for any kind of faulty signal from an engine sensor or control.

 

[TurtleCrusher]

Originally posted by: exdeath
Knock sensor detects detonation and lets the computer know to retard timing to protect the engine. It does not affect starting or running whatsoever. Detonation is the premature and violent explosion of the mixture before the spark goes off, and can seriously damage the engine.

As long as your car is not modified and you are using premium fuel you have nothing to worry about except possibly on very hot days accelerating uphill or something like that (detonation makes a muted sound of marbles shaking around in a can, sounds similar to the clacking of a diesel engine). By hot I mean 110+ AZ heat. If the knock sensor isn't working, the sound won't go away as soon as you hear it, and you'll need to lift off the throttle or downshift so there is less of a load on the engine.

None of your problems have anything to do with the knock sensor. It sounds like you need to have your alternator checked out. A new battery should be 12.6v and about 14 volts with the car running. 16v is way too high.

Its a bit odd you say that. It was 109F here in Portland and the problem did begin at about 1800, the hottest part of the day.

I was running a bit low on oil the few days before and the engine was making some sort of a clicking noise (somewhat close the the chug chug chug a diesel engine makes). It would only make that noise while load was being applied to the engine. The day after the oil was changed the sound slowly went away while driving nearly the whole day. It was still 105-107F if that matters. Two days after that was when my car started acting finicky. The sound had completely gone away but it wasn't starting up.

Originally posted by: brblx
knock sensors contain some kind of piezoelectric material which senses a certain kind of vibration caused by detonation in the combustion chamber. upon recieving this information, the ECM typically retards ignition timing to try and stop it.

600-700 ohms sounds like a reasonable value, but i don't think there's any way a defective knock sensor could measure zero ohms. at the least, it's not bloody likely. i suspect your father may have measured wrong.

that said, it has nothing to do with startup.

what do you by 'hesitated really bad'? ran badly, or just cranked slowly? i guessing if you tried to start your car for thirty minutes, it was cranking (otherwise you just spent the most futile half hour ever). a car battery showing 5v would not crank your engine over. you should also never seen 16v in a car's electrical system, max charging voltage should be in the 14v range, and a new battery should read around 12.6v. i would be highly suspect of your DMM if you got those readings.

is the check engine light on? that car's not OBDII, but surely it has some kind of diagnostic system that would generate codes for any kind of faulty signal from an engine sensor or control.

To the bolded part, would that be related to above?

And the battery read about 13V after retesting. I remembered it being above 10 but must have misread it.

When I say it hesitated, it was trying to turn over but didn't. I can see the engine moving around but there is nothing happening. I can hear it making the normal ignition sounds before it usually would fire but it doesn't.

The day after the incident the car turned over just fine. Kind of weird. It ran for over and hour without issue. I then took it out for a drive to run an errand (round trip, no turning off the car of course) and it was fine. No engine clicking or anything. I didn't trust it so i left it there for about 5 days. Yesterday I went to use it because my ride was not showing up and I was going to be late for work and the same startup difficulty occurred. I could hear and see the engine trying to turn over and start but it didn't and hasn't since.

The check engine, oil and battery lights pop up during the process for about 5 seconds then go away. The battery light does persist though, even with a brand new battery. I'm certain my father checked the alternator and he said it works just fine.

 

[brblx]

what are 'normal ignition sounds?'

i feel your terminology might be a problem. by turning over, i mean can you hear the engine cranking and making compression (chugachugachug)? if so, it's not battery related and means you have either an ignition (spark) or fuel issue. if it isn't cranking, your problems are all likely related to a low battery, probably caused by issues with either the alternator or wiring.

by your description, it sounds like perhaps you did experience some detonation. this could be related to your no start, probably being a problem in the ignition system. i would take a look at the plug condition first. IF it is indeed turning over but not hitting.

 

[TurtleCrusher]

Originally posted by: brblx
what are 'normal ignition sounds?'

i feel your terminology might be a problem. by turning over, i mean can you hear the engine cranking and making compression (chugachugachug)? if so, it's not battery related and means you have either an ignition (spark) or fuel issue. if it isn't cranking, your problems are all likely related to a low battery, probably caused by issues with either the alternator or wiring.

by your description, it sounds like perhaps you did experience some detonation. this could be related to your no start, probably being a problem in the ignition system. i would take a look at the plug condition first. IF it is indeed turning over but not hitting.

I certainly hear the chugchugchug sound, but it just doesn't fire up. And by plug condition, like my spark plugs?

EDIT: Attempted startup video added. This was 10 minutes ago.

 

[brblx]

your video's hard to hear. is that the normal sound you get before the engine starts and you release the key?

if so, the two places to go are basically fuel and spark. if the fuel rail has a shrader (tire) valve, you can use a $10 harbor freight gauge to check it. if not, you may need specialty tools. factory pressure is probably somewhere in the range of 25-40psi. pull the spark plugs and see what they look like. they should be dry and some shade of grey or brown. black (oil and/or carbon fouled) or white (burnt) plugs could be the issue. also look at the electrode, the part in the middle of the porcelain opposite the ground strap, and check the gap. usually, that little electrode in the middle is the first part to get burnt up. if they look okay, get a spark tester (again, maybe $10) or just pull a plug, connect it to the plug wire, and hold it against the engine (to ground it). look for a fairly bright regular spark while cranking. if the spark is erratic of very faint, you probably have a distributor or ignition coil problem.

 

[TurtleCrusher]

Originally posted by: brblx
your video's hard to hear. is that the normal sound you get before the engine starts and you release the key?

if so, the two places to go are basically fuel and spark. if the fuel rail has a shrader (tire) valve, you can use a $10 harbor freight gauge to check it. if not, you may need specialty tools. factory pressure is probably somewhere in the range of 25-40psi. pull the spark plugs and see what they look like. they should be dry and some shade of grey or brown. black (oil and/or carbon fouled) or white (burnt) plugs could be the issue. also look at the electrode, the part in the middle of the porcelain opposite the ground strap, and check the gap. usually, that little electrode in the middle is the first part to get burnt up. if they look okay, get a spark tester (again, maybe $10) or just pull a plug, connect it to the plug wire, and hold it against the engine (to ground it). look for a fairly bright regular spark while cranking. if the spark is erratic of very faint, you probably have a distributor or ignition coil problem.

Thanks. The beeping of the car is normal. I don't think the sound is out of the ordinary. I will be passing along this information to my father. If anyone else has opinions feel free to extend or offer other possible solutions.

 

[kami333]

I thought the EJ18 did not have a knock sensor?

 

[joutlaw]

A knock sensor will make your car use more fuel and not run that great.

My understanding is if the ECU doesn't get a good value from the knock sensor it will use fail safe timings and fuel maps. This means your car will run pig rich and not have a lot of get up and go off the line.

I have a mazda millenia with 120K miles with a knock sensor that has been out for 30K or so miles. I get about 17-18mpgs but replacing the sensor is a PITA. You have to remove the intake manifold to get to it.

 

[TurtleCrusher]

Updated ^^^^^

 

[jlee]

Switching oil type should have no effect on the engine.

 

[LTC8K6]

The oil wouldn't have anything to do with any problems you noted, nor would it harm anything at all.

 

[DivideBYZero]

For short periods, oil is oil.

 

[Zenmervolt]

Originally posted by: joutlaw
A knock sensor will make your car use more fuel and not run that great.

My understanding is if the ECU doesn't get a good value from the knock sensor it will use fail safe timings and fuel maps. This means your car will run pig rich and not have a lot of get up and go off the line.

I have a mazda millenia with 120K miles with a knock sensor that has been out for 30K or so miles. I get about 17-18mpgs but replacing the sensor is a PITA. You have to remove the intake manifold to get to it.

Bullsh*t. Pure. Unadulterated. Bullsh*t.

Yes, the ECU will use failsafe maps if the knock sensor dies (on turbocharged cars with electronic boost control it will also reduce boost pressure), but this will never make the car "run pig rich" unless there are other problems as well. A failed knock sensor should have no significant effects on either driveability or fuel mileage.

Frankly, most people will never notice a a failed knock sensor.

ZV

 

[fbrdphreak]

Originally posted by: LTC8K6
The oil wouldn't have anything to do with any problems you noted, nor would it harm anything at all.

Indeed. And your "high performance" 10W-30 oil is a waste unless you beat the snot out of the engine in high heat staying at high RPMs for long periods of time. Its a 200K mile 1.8L Impreza. Good car, sure, but hardly needing anything beyond 87 octane and plain jane dino oil.

With that many miles, maybe your catalytic converter is clogged up. I believe (someone double check me?) that would inhibit startup. No clue why it would suddenly start up though.

 

[exdeath]

Still chasing a start problem? Start with the basics: spark and fuel. None of the things you are doing are going to have any affect on starting or hesitation.

The oil light comes on during cranking because oil pressure is extremely low while cranking. Battery light comes on during cranking because the alternator output is low. Both of these are normal when the engine is below idle speed, as when cranking. You have an intermittent ignition or fuel problem, and starting after the oil change was purely coincidence.

If it's only having problems starting after it's been sitting for a while, the usual suspects are fuel pump (internal check valve), fuel pressure regulator, or engine coolant temperature sensor. If it's totally random and depends on the phase of the moon, it's usually an electrical issue with the ignition or fuel system, often as simple as a relay.

All the electronics and computers aside, the combustion engine remains the same crude and primative device after 100 years. If you have pressure at the fuel rail (and correct injector signal) and spark at the plug wires, it WILL start and run. Any other infinite array of problems with sensors or computers failing or whatever you can imagine doesn't really matter, because ultimately all it's going to do is result in disruption of fuel and spark at the end of the line.