94 Metro Code 51 EGR Problem ... AARGH!

[wetback1]

Hello Fellow Geophytes;
I have a 94 Metro 1.0 with a constant code 51 (EGR). I have done all the Chilton diagnostics - wiring, ECM, solenoid, modulator and EGR valve are all working as designed. I have tried cleaning the EGR passages as some others have suggested - there wasn't much in them and when vaccum is applied to the EGR valve I can almost stall the engine so I have no reason to believe anything is plugged. A brand new solenoid from Rock Auto has the same resistance as the old one (36 ohms) so this isn't the problem either.

Chilton mentions that the ECM will intermittantly 'try' the EGR and look for a manifold pressure drop to confirm operation. Any chance the MAP sensor isn't quite 'with it' enough any more to confirm this? I have no other codes and when the ECM is reset the 51 comes back within 5 - 10 km (this is a Canadian car).

Has anyone got through this one???

[91Caprice9c1]

Well I appreciate the preliminary work you have done and the detail with which you have described your predicament. I do not believe your MAP is the culprit here, as it would certainly have some noticeable detrimental effects to the vehicles driveability.

With the engine at operating temperature, operate the throttle by hand, under the hood and while watching the EGR's diaphram (sounds personal doesn't it?) it should visibly pull back with some 1/4-3/4 quick throttle snaps. If it doesn't there is something wrong with the vacuum to the EGR, the solenoid, the wiring, the EGR valve, or the driver in the ECM. If it does move accordingly, you have a clogged passage(s).

When the ECM checks the system it wants to see a specific quantitative range in pressure change.

Originally Posted by wetback1

I can almost stall the engine so I have no reason to believe anything is plugged.

I think this deserves some further investigation. You SHOULD be able to stall the engine with little difficulty when the EGR passages are clear. The fact that you can't (or almost can) stall the engine by manually opening the valve tells us that what is probably happening is that there isn't enough EGR to get the pressure change in the range that the ECM is looking for.

So, what now?! The EGR passages as you probably already know, start at the exhaust manifold, go through the head, through the intake manifold, to the EGR, then back through the intake manifold. Be sure the EGR valve itself, is clean enough as to not impede airflow, and after that you must (as painstaking as it is) clear all the passages - because this is most likely your problem.

-MechanicMatt

[wetback1]

Hi Matt;
Your reply made me stop and think this through a bit more - the forest for the trees thing... I rechecked and discovered no ground signal was coming from the ECM (green wire) to operate the solenoid. Upon removing the ECM and opening it up I found a fried 3.9ohm resistor just off the 5th pin that connects to the green wire - hence the problem. Have made repairs and things seem to be working fine now. I miss the days of points and carburetors...

Thanks so much for your help and clarity on this one!

[91Caprice9c1]

Excellence! Impecable diagnostics! Stick around the forum bud, ingenuitive minds are welcome.

-MechanicMatt