Car is stalling while driving, please help!

[MrSpock53]

Vehicle in question: 1998 GMC Yukon 4x4

Lately the truck has taken to stalling while driving. Both times it happened in the same place, going down a moderate incline, braking up to a stop sign. The power steering goes out, I pull over to the side, and the instrument panel simply has a red battery and a "check gauges" light. First thing I did was to check and make sure the vehicle wasn't overheating. Luckily it wasn't, 170 deg. F. I then noticed that the voltmeter on the dash was displaying about 9 volts(?). I'm pretty sure the battery and alternator are fine, since the car started right up both times with a voltage of 14 after looking under the hood. The A/C was on at the time, if it helps.

Though I honestly don't feel I did anything that could have contributed to this problem in any way, here's some stuff I've done to the vehicle lately:

-air filter
-replaced automatic tensioner
-replaced thermostat (170F seems abnormally low, supposed to be ~195F)
-replaced idler pulley

The tensioner and idler pulley were replaced previously becuase the car has a constant squeal from under the hood. Didn't solve the problem, and after I started the car back up after stalling, I thought I saw what looked like some wobble in the bottommost pulley (attached to the crankshaft I believe?). I was sure the belt was on properly, I checked the routing and felt along the pulleys to make sure the belt was in the grooves properly. When I got it back home, I disconnected the belt, pushed and pulled the pulley for looseness (none), and started it up. I figured if the squealing was still there and there was wobble in the pulley, I had found my problem. Everything was fine, nice and quiet, and not wobbling.

A day before the stalls I also had my check engine light come on. Checked the code at advance auto, it said my EGR valve was malfunctioning(valve 2?). Being a $150 part, I figured I would reset the light and see if it came back. They told me it would just cause the car to lose some mileage and maybe run rough, not stall on me. Perhaps the EGR issue is related?

I have a digital camera, so I can take pictures of anything if it will help at all. Thank you for taking the time to read all this!

 

[nakedfrog]

It sounds like a fuel starvation issue to me, how much gas has been in the tank both times?

 

[MrSpock53]

Originally posted by: nakedfrog
It sounds like a fuel starvation issue to me, how much gas has been in the tank both times?

The fuel gauge reads about 3/4 full.

I also just noticed that the battery light and the "check gauges" light came back on, as well as the service engine soon light. I'm going to look into getting the code pulled.

Edited to add: voltage reads low again

 

[Quiksilver]

What EGR Valve Get's Me...

 

[Demon-Xanth]

Check your battery cables.

Edit:
There's also likely a plug that goes to your alternator to control the regulator, check to make sure those connections are good.

 

[alpineranger]

Stalling going from a engine loaded to low load condition (such as coming to a stop) is a classic EGR problem - I didn't have to read past the first two sentences to think EGR. Sometimes it doesn't throw a code but it can still give problems. In your case, with a code, it is probably barely working. There are several types of EGR codes typically, find out which one it is. Often times you can repair the egr valve by cleaning it out.

The quick and dirty solution if you don't want to stall anymore is to unplug it. The engine computer will recognize it is disconnected and compensate for it (you'll get a check engine light for this). You do lose efficiency and emissions will increase slightly, but it won't stall anymore.

Edit (clarification): don't physically remove the valve, but do remove the electrical connector going to it.

 

[MrSpock53]

Originally posted by: Demon-Xanth
Check your battery cables.

Edit:
There's also likely a plug that goes to your alternator to control the regulator, check to make sure those connections are good.

Battery cables are screwed on nice and tight, no problems there.

The alternator had two cables going into it. One has what looks like a plastic housing that snaps in, the other was tightened on a threaded bolt sticking out, don't think it's a connection issue. Would checking these with a multimeter be possible?

What EGR Valve Get's Me...

I'm starting to wonder if it is in fact the EGR system. The check engine light lit up again

 

[MrSpock53]

Originally posted by: alpineranger
Stalling going from a engine loaded to low load condition (such as coming to a stop) is a classic EGR problem - I didn't have to read past the first two sentences to think EGR. Sometimes it doesn't throw a code but it can still give problems. In your case, with a code, it is probably barely working. There are several types of EGR codes typically, find out which one it is. Often times you can repair the egr valve by cleaning it out.

The quick and dirty solution if you don't want to stall anymore is to unplug it. The engine computer will recognize it is disconnected and compensate for it (you'll get a check engine light for this). You do lose efficiency and emissions will increase slightly, but it won't stall anymore.

Edit (clarification): don't physically remove the valve, but do remove the electrical connector going to it.

Is there any way to test this while in park, or should I take a quick drive to see if it will stall?

 

[alpineranger]

Not easily. Just drive it around.

 

[MrSpock53]

Back from the test drive. I tried running it with the EGR plugged in first to make sure it was the problem. It figures, the one time I wanted it to stall I couldn't get it to :laugh:

At this point I'm thinking I should get the code first, and go from there. I could take it for another test drive I suppose.

Is the engine supposed to run rough when the EGR is bad? It doesn't seem to be rough or have a lack of power from what I can tell, this whole thing is pretty confusing

 

[alpineranger]

It depends if it's stuck open or closed. EGR is supposed to be open at cruise only, because it affects the engine idle and low rpm operation (this is the stalling and running rough you've seen), and it limits power at high load. If it's closed, you just never get the benefit from it, which is cooler combustion temps / increased fuel economy / lower NOx.

 

[AMCRambler]

EGR is vacuum operated I think. As you throttle up it gets more vacuum and the diaphragm inside opens up and lets the intake pull exhaust gas into the motor to be burned again. Helps reduce emissions on the car. Because it's pulling exhaust gas though it can get filthy with soot and carbon deposits and start sticking. You can take it off and clean it out with carb cleaner and a tooth brush. Make sure you can operate the valve without any sticking and then put it back on and see if you still have the problem.

 

[exdeath]

If it's throwing EGR goes I would naturally suspect that first. EGR is not supposed to be operating at idle or wide open. Idle and falling to idle (dashpot) are the hardest states for the computer to control. Any foriegn and/or unanticipated "extra stuff" getting in from an open EGR, vacuum leak, bad idle valve, fuel pressure problems, etc will cause the engine to run rough or stall because the computer can't do anything to compensate for something it has no control over.

There are usually two main parts to the EGR system: the EGR diaphram itself which on the intake manifold (has a heavily oxidized and heat shielded metal hose going to the exhaust manifold) and a EGR solenoid that commands the EGR on and off via pulse width modulation that controls the amount of vacuum to the diaphram to open and close it. The computer has a built in test routine and feedback system for monitoring commanded EGR position vs actual EGR position, and when there is a big enough difference, it flags the EGR failure.

As to how EGR could cause a stall? If you lift off the throttle as you approach a stop and allow the engine to dashpot to idle, it will seem smooth as the computer is "hands off" until it passes idle, but with the mixture in a unanticipated state from the open EGR it wont recover fast enough and it will overshoot the idle threshold and stall.

 

[Bignate603]

I would cruise on over to autozone to get a free reading. If you've got an EGR code it's pretty obvious what's going on. However, I still think your battery may be a bit low (though it's probably not what's causing you to stall). A 9 volt reading is lower than normal. 14 volts is normal for when the alternator is spinning, which indicates that your alternator is doing ok.

 

[Mermaidman]

Crankshaft Position Sensor

 

[alpineranger]

I believe the computer tests the egr in several ways: 1) looking for an inductive kickback from the solenoid coil. 2) monitoring the intake manifold pressure for a change when the egr valve is opened. The first test checks if the egr is even there / connected. The second tests is a proxy for the egr flow rate.

For obd2 cars with egr (like yours), I believe the feds require egr performance to be monitored as an emissions parameter. When the flow rate drops below a certain amount, then the check engine light must be set. Of course, if the computer doesn't even sense the egr there it will fail it by default. Usually the valve defaults to the closed position, which will let the engine idle / drop to idle properly.

 

[MrSpock53]

Sorry for the late update everyone, I've been doing some reading on the net and found some interesting info.

I took the vehicle to an Advance Auto and had the code scanned, it turned out to be P1404. Typing this into google leads to tons of information on the code. This code seems to come up when the computer commands the valve to go to the closed position, but the valve fails to do so. This meshes perfectly with the symptoms I've been having, and several of the suggestions in this thread.

This error seems to be caused by two things, debris that keeps valves from operating properly, and possibly a calibration error.

I plan on going to a parts store in a morning and purchasing a new fuel filter and EGR gasket and clean the valve. As far as I know the fuel filter has never been replaced, a clogged fuel filter probably wouldn't help much with my stalling issue

For removal of the EGR valve, are there any precautions I need to take, or is it simply a matter of unplugging the EGR valve, unbolting it, cleaning it, and putting it back in? Also, should I spray some carb cleaner in the manifold to try and clean up some of the crud that tends to build up, or is that best left alone?

Thanks again to everyone offering advice for my issue. Without your help, I don't think I would've got this far! :thumbsup::thumbsup:

 

[alpineranger]

Unbolt it, clean it out with carb/intake cleaner and wire brush. Please update to let us know how it went.

 

[AMCRambler]

Originally posted by: alpineranger
Unbolt it, clean it out with carb/intake cleaner and wire brush. Please update to let us know how it went.

What Alpine said. You might be able to get away with spraying some carb cleaner down the intake with the engine running without killing anything. If any crud built up in there and breaks loose you could cause a problem. Best bet for cleaning the intake manifold is taking it completely off and soaking it. That way the crud doesn't end up in your motor. That involves getting gaskets, taking the throttle body off as well as all the rubber hoses that can split and crack on an older car, so it's best left alone until you have a problem.

 

[MrSpock53]

Originally posted by: AMCRambler

Originally posted by: alpineranger
Unbolt it, clean it out with carb/intake cleaner and wire brush. Please update to let us know how it went.

What Alpine said. You might be able to get away with spraying some carb cleaner down the intake with the engine running without killing anything. If any crud built up in there and breaks loose you could cause a problem. Best bet for cleaning the intake manifold is taking it completely off and soaking it. That way the crud doesn't end up in your motor. That involves getting gaskets, taking the throttle body off as well as all the rubber hoses that can split and crack on an older car, so it's best left alone until you have a problem.

I actually took off the EGR valve on saturday(edit: it was Sunday ) and tried to clean it. I was surprised to find that the valve wasn't all that dirty. I lightly pressed the valve up and down with a screwdriver, and there wasn't any stickiness or grittiness in the motion. I looked inside the valve and there weren't any carbon chunks, the valve and the insides just had a light carbon coating covering them. I tried using carb cleaner and a toothbrush for maybe 15 minutes, nothing was really coming off so I just put it back on.

I just took it on another drive to the hardware store to pick up a bucket and some wire brushes. Should I take it off again tonight and try soaking it for a while, then giving it a more thorough scrubbing?

If any crud built up in there and breaks loose you could cause a problem.

I was afraid of that . There was definitely some buildup on the walls, not enough to block the passageway or anything but it was there. Would a can of Seafoam or BG 44k be a good idea to clear some of that up?

Still haven't replaced the fuel filter yet, I'll try to get to that tonight.

 

[alpineranger]

I probably wouldn't bother. Usually the egr valve is totally caked with carbon deposits, but if it isn't, then cleaning the passages once more is probably not going to improve things. That said, if you haven't gotten any more check engine lights (or stalling), then you're golden.