Cadillac Seville / Cadillac Eldorado Forum Discussion, Slight stumble under light load - 1995 ETC in Past Cadillac Vehicle Discussion; U tested alt but still are using it. It's a pain but u could replace the alt. I did and ...
I actually removed the alternator last week to get it tested at a specialized repair shop. During the test, it was in good working order.. so I putted the thing back in the car.
I also disconnected the lead wire, and plugged a external power source on the alternator's lead connection, so I could regulate the voltage of the alternator myself. But even without the car controlling the alternator, the lights are still flickering. So I don't think the lead wire is the problem.. or did i miss something?
The alternator in my car is not a AC Delco one by the way, it's a (pretty new looking) WPS alternator. Should that be any good or is a branded alternator the way to go?
FINALLY! With some help of a alternator specialist, the flickering lights are gone! It turned out I had the wrong type alternator, which needed two wires on the black plug instead of one. The missing wire was for a 'charging light', which has a constant 12V. So a additional wire from the battery to the alternator solved this problem.. and the car drives SO much better now.
But.. the stumble is still there. It's a lot better now, but the car stays stumbling between 80-120 km/u (50-75mph), only when the car is in low revs in the fourth gear. In that case it stumbles pretty bad. When I manually shift back to third gear at those speeds, the stumble is almost gone. When I disconnect the EGR valve, the stumble is also gone.. pretty weird I think?
Oh, and the idle is slightly rough.
This is the list of things I did so far, trying to solve this problem;
- New spark plugs (Delco's)
- New spark plug wires
- New coils (all 4 of them)
- Cleaned the throttle body
- Cleaned the EGR valve and passages
- Checked all vacuum hoses (no leaks)
- Checked the FPR
- Checked the engine block ventilation system and valve, all OK
- Changed engine oil and oil filter (has nothing to do with the stumble, but the oil was REALLY dirty.. and so was the filter..)
With my 'old skool' car knowledge (I always worked on fairly simple cars), my feeling leans towards the ignition for a possible culprit. Could it be the ignition control module under the coils? I didn't find any method to test it; is there any? Or do I have a leak somewhere in the EGR circuit (because the stumble is gone when I disconnect the EGR valve). This problem is driving me pretty crazy..
Oh, and no significant trouble codes either. Only a S code for a 'suspension solenoid shorted to ground/open'. And until a week ago, the P052 (transmission speed input sensor) code sometimes popped up, but it seems to be gone after I re-isolated a part of the wiring loom. So I only have the suspension code now.. nothing else.
Automobile(s): 2002.5 F55 STS, 2014 Explorer XLT 4WD
MD Eastern Shore
Re: Slight stumble under light load - 1995 ETC
EGR is always "turned on" when the engine changes to closed loop emissions control after many sensors and conditions are monitored and the PCM/ECM shifts operating conditions.
EGR is a variable exhaust gas bleed back into the intake ports used to dilute the incoming fresh air and thus slow the combustion process. A sticky or stuck EGR valve will cause driveability problems as well as possible light spark knock upon acceleration or part-throttle acceleration as if to pass another vehicle. EGR is locked out and the PCM takes direct control of ignition timing (significant retard from full advance) during WOT
Automobile(s): White Diamond '03 DHS (with DTS floor shift)
Re: Slight stumble under light load - 1995 ETC
Originally Posted by jonkheer
Hmm, that could also be the problem.. Do you also know when the EGR is on? Because I noticed that the car stops stumbling when i use the cruise control :S
Being an OBDI car, I think you can monitor when the EGR valve is activated, but I don't have the diagram. You'll have to enter overrides and watch the ICONs. EGR is not used at idle or under high loads. I don't know the exact definition that GM uses for high loads, but my guess would be that there is no EGR used during acceleration either, period. I suspect it is in the FSM, but I'm too lazy to go dig it out. So what I'm saying is that I think EGR is only used during cruise.
Ok, I tested the EGR valve last Friday and it turned out to be bad.. (tested it with the Chilton manual procedure). Ordered a new EGR valve and mounted it yesterday.
The car still stumbles, although it seems to be less harsh..
I found the method to disable injectors, so I tried it - with no success. I can feel the engine hestitate when disabling every separate injector. If the ICM is broken, does it usually break one coil pack connection or all of them?
I also noticed that I only have two vacuum hoses on the top of my throttle body, instead of three. The TPCV (Tank Pressure Control Valve) hose is missing, and the gap for that hose is plugged. I also cannot find said hose in the engine bay - is that normal?
Oh, I cleaned the old EGR valve before and that didn't make any difference. That's why i ordered a new one last week
The hose I mean should be connected to the top of the throttle body, in that rubber clamp which has 3 vacuum hose connections in it. The Chilton manual describes those three hoses as following;
1. is for Cruise Control and Body
2. to Tank Pressure Control Valve (this one is missing on my car)
3. to EVAP solenoid
So.. this hose should be present? I'm trying to find out where the TPCV valve should be located, but searching doesn't show up much results. Do you have any clue?
Yes, thanks very much! My hoses are exactly like on that diagram. That's definitely a thumbs down for the Chilton manual..
Oh, and the P056 (transmission speed input sensor) code is back.. but only at idle. On idle, the code is current. If I drive away, the code disappears (and so does the service engine light). It's only the code and light popping up, the car doesn't drive or shift differently at all :S