Okay. I'm not sure I understand this one.

Dave's car has been acting goofy for the last month and I think we finally fixed it. It's been shutting off during normal driving and when getting on it (even marginally - not full boost). It'll just studder and die. Popping the clutch always brings it back, but it'll like crap out again within a minute or so. The last time we took it out, it died 4 or 5 times in about 2 miles.

Last night we replaced the EGR valve and pipe with blockoff plates. Dave found something in the service manual that pointed several times to this sort of problem being caused by a defective EGR valve. After putting the plates on, we drove the car for about 20 minutes and the car ran perfectly. What I don't understand is, why a defective EGR valve would cause the car to die. Any insight? Maybe it's a fluke and we didn't really fix it yet....?

Jesse

I think the EGR should be shut unless the car is boosting. If it's stuck open all the time, I can see how things would get messed up, but only while cruising (vac pressure).

I think it's just a fluke.

Have you hooked a logger to his car to see whats happening? Don't remember if Dave said he checked/tried another ECU or not.

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06 Blue EVO 9

I dont have my logger. I gave it to Josh to use for awhile.

I pulled his ECU and put mine in. Same problem so its not the ECU.

I was under the impression the EGR worked backwards of what you said. When the car is boosting, the valve is closed and doesnt allow exhaust gas into the intake. When its in vacuum, its open and allows exhaust gas into the intake. ? Or maybe that's what you said and I read it wrong.

Jesse

Actually, that makes more sense. If the valve were open under boost, you'd be loosing manifold pressure into the exhaust whereas under vacume it'd suck exhaust in to be reburnt.

Bingo.

I'm going to assume maybe his EGR valve was just "stuck" in either open or close position? So, lets try and determine what might happen then.

If its stuck CLOSED, then it's no different than running and EGR blockoff setup right? No exhaust gases would get sucked into the plenum under vacuum nor under boost. I dont see how a stucked CLOSED valve could cause ANY problem on the car.

If its stuck OPEN, then exhaust gases would get sucked into the intake during vacuum as per normal operation. During boost, air that would otherwise enter the intake, MAY be getting pushed out the exhaust because of the open valve and cause you to lose boost. This would probably cause him to run excessively rich too wouldnt it under WOT? Would this stuck OPEN valve be enough to cause the car to crap out and die repeatedly under ANY boost though? I dunno... Sure seemed to be the case last night.

Jesse

Obviously yes in this case. Kinda like when your y-pipe blows off, only there's no vac leak, just a boost leak. One could test this by taking their EGR valve and modifing it to stay open all the time. Hmm...

Even if the car wasn't a turbo if would have idle and running problems with a stuck open EGR.

The EGR should only be open at partial throttle.

If it opens at WOT or idle the car can stall.

The purpose of the EGR is to cool the combustion during closed loop driving when the default fuel mixture is leaner. It does so by displacing incoming oxygen filled air with low oxygen exhaust gases.

EGR has a two part benefit it reduces combustion temperatures during part throttle operation and it reduces NOx emissions because of lower temperatures, and less nitrogen and oxygen.

Many types of cars have over heating problems if they remove the EGR and block it off or it is stuck closed. I

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So how does it regulate that? WOT is easy (boost pressure pushes it shut), but what about idel?

I think Greg is right on that one. I can't see how the EGR would be open at normal cruise (vacuum), but not open at idle (vacuum). I would think it would be open anytime there's vacuum regardless of idle or throttle.

Looks like we all learned some cool shit about EGR today.

I tell you guys this. Fixing Dave's car I think rejuvinated him as to liking his Stealth again He had fun when we took it out last night, he drives like he's 16 again, LOL. On top of that, maybe the convertible Mustang will stay in the garage more often now.

Hey Jesse,

Was it hard starting up his car when it was cold? This kinda sounds like my problem. My car starts up, but then dies right away. It idles really low and dies when i stop at stop signs, i wonder if my egr valve is staying open....

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Drive it like you stole it!

91' VR4 - Stillen Air Intake, Stillen downpipe, custom 3" exhaust piping, 8.5mm wire plugs, 20% window tint
96 Pontiac Trans Am - SLP Loud Mouth Exhaust, 5% window tint
02 Chevy Avalanche

Jeremy G,
That doesn't sound like an EGR issue to me. I would think that has more to do with the idle itself. I know you can adjust the idle on these cars and there's some control mechanism for it, but I forget what part it is. It's on the throttle body somewhere. Greg can probably shed more light on this for you. Ask him at the gathering tomorrow.

Jesse

You need to raise your idle a tad. Turn the BISS screw on the throttle body out a hair. If that doesn't help you may have to adjust your TPS or replace your ISC.

If that makes no sense you might want to research it a little.

later,
Curt

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To answer a few pepoles question, this is how the egr can remain closed during idle.........there are 3 vac ports on the TB.

1 - boost only
2 - Vac and boost
3 - off idle vac and boost

The egr valve is opened by vacuum and controlled by #3 above, therefore it will only open during off-idle driving.

If an egr valve (any egr valve) opens during idle, the car will die as if it has a huge vacuum leak. (the air follows the path of least resistance, ie, big hole in plenum, not small crack in throttle plate)

If you are driving, the throttle is open (along with the egr valve) and pulling enough air through the mas to operate properly.......or something along those lines

Which is why our cars run a little richer with it removed. That makes sence.