: Engine lugs, occasional stall



cmgrafmc
07-05-05, 05:02 AM
1989 Brougham

Some of you will remember my past thread(s) about the engine lugging down when approaching a stop. What I thought at the time was that it was shifting from 2nd to 1st LATE...thus the lugging. What I've found out now (one of those DUH kinda things) is that it's not the shifting. I was driving in 1st the other day to test it and sure enough, the problem continued.

Here is what I'm talking about specifically:

The engine is warm, the ECM is in control of the shift solenoid.
I'm in 1st gear traveling at a low speed and approaching a stop of any kind.
Just as I'm about to stop, say, a few feet away, the engine lugs down momentarily.
*NOTE* This problem does not occur when the engine is cold and the ECM is not yet "in charge."

Recently it's stalled on me and very nearly stalled a few times. I haven't had THAT problem before or in the last couple days, however, the lugging remains.

I pulled the fuse for the ECM and drove around for a few days, a while ago. I didn't have the lugging issue at all. I might try that again to confirm it.

Any ideas or questions? Sorry if I'm not totally clear in my explanations.

N0DIH
07-05-05, 02:03 PM
Sounds like the TCC solenoid. TCC is not engaged or active when in open loop operation of the ECM.

Does it do it when the brake is applied? The power for this circuit is:

+12v from battery through brake pedal switch, to the TCC solenoid, then ground path goes to then to the third gear switch (TCC never can apply in lower than 3rd gear), then to ALDL connector Pin F (you can measure it here or trigger it manually here, see my thread on this elsewhere in the 4.9L or Deville forum), then to the ECM where the transistor driver grounds it as the ECM commands.

So the solenoid is HOT all the time with +12v, then grounded by the ECM. If you short pins A and F on the ALDL, it will engage anytime the brake is not applied and the 3rd gear switch is engaged.

Try this, when warm, drive in second gear (don't go too fast, keep under 50 mph) and does it give you any problems? Or when you are decelerating, drop to 2nd gear around 30 mph, does it then give you any problems?

By pulling the ECM fuse you disable the ground to the TCC Solenoid through the ECM. If it is bad and grounding all the time, it will engage too early. You can check the ECM with a DVM in pin F of the ALDL. Again, the thread I posted on in the other forums has some detail on this testing proceedure.

cmgrafmc
07-05-05, 07:02 PM
Unfortunately, the solenoid seem to be ok. I've had it replaced twice. The first time was to correct a much more severe form of this problem, which it did. Then my ECM was "reconnected," because somewhere along the line it was disconnected all together. (And yet I had no problems...) After the ECM was wired to the fuse panel, this problem developed. I had the solenoid tested and replaced at no charge and it hasn't corrected the problem. SO...I suppose it could be the actual clutch itself, not the solenoid.

Or am I off base?

The solenoid responded normally during our last round of tests. Traveling at highway speeds in Drive, you feel it slip into OD. You depress the brake slightly and you feel it shifting back into 4th, out of 4.5 (OD). So it would seem the solenoid works. I'll call a tranny shop to see if they think it's the clutch...if so, I'm looking at a total rebuild, something I can't do for a while. heh.

I might try some of the diagnostics you suggest, N0DIH, but it seems more and more like it's the actual clutch.

cmgrafmc
07-05-05, 07:04 PM
Oh, btw, I forgot to mention that the near-stalling I experienced was when I would accelerate from a stop, as though the engine was choking on gas.

N0DIH
07-05-05, 08:50 PM
Does it do it once it gets to 3rd gear, or does it do it in 1st and 2nd also?

You can stick a DMM (DVM) into the ALDL, Pins A (black) and F (red). Note the reading when it is high and low (around +12v, and around +2v or less). Drive normally and note at what time, what gear, what "mode" (open loop, closed loop) the ECM is in that the voltage is high or low.

http://cadillacforums.com/forums/showthread.php?t=40197&highlight=ALDL+Brake

You can also disconnect the trans connector also to disable. But this can cause trans overheating, so use for only testing and do not use OD, it will cause the converter to stall at cruise and overheat trans quickly. If you need to drive, just don't use OD unless you are over 2000 rpm cruise (likely around 80 mph....)

But monitor the voltage on the DMM. Don't use a test light, it might trigger early lockup.

Let me know if that helps diagnose. BBob might be good to ask on the mechanical side. I know the electrical side, as he might as well.

If the TCC driver in the ECM is bad (grounded all the time), it will trigger lockup as soon as you let your foot off the brake AND the trans is in 3rd gear. That will make it buck and/or chuggle. If you suspect the TCC driver in the ECM is bad, you will have it "low" voltage all the time. If it is ok, it will be +12v when cruising and not in 1st or 2nd gear and below lockup speeds.

It could be the TCC itself, I don't know the diagnosis of the TCC mechanical side. But on the electrical I do. I played with it some when I had some issues with it.

90Brougham350
07-05-05, 09:35 PM
If the TCC driver in the ECM is bad (grounded all the time), it will trigger lockup as soon as you let your foot off the brake AND the trans is in 3rd gear. That will make it buck and/or chuggle. If you suspect the TCC driver in the ECM is bad, you will have it "low" voltage all the time. If it is ok, it will be +12v when cruising and not in 1st or 2nd gear and below lockup speeds.

I had this exact problem in my 85 Parisienne, but that had a 700-R4 so it would lock up in even first or second. Exact same symptons though. I just put the pink wire to the tranny which controls lockup on a toggle switch, and hit it whenever I was on the highway, or long stretches in 3rd or 4th gear. Worked great for well over a year this way. Good luck!

Brian

N0DIH
07-05-05, 10:06 PM
You could also disable the TCC engage from the brake pedal switch. No power to the TCC from there, no lockup.

cmgrafmc
07-06-05, 04:59 PM
Hm. Well, the lockup would be nice seeing as how I need to drive on the freeway. Mileage in these isn't very good in the first place so not having OD would make things worse. =P

I'm not a mechanic or engineer so I won't be able to do much in the way of diagnostic or mechanical work on it. I was mostly trying to confirm my own suspicions, that something is wrong with one of the following: The transmission; The ECM

NOW, what I can say is that, the lockup feature works when it's supposed to. It disengages properly at cruising speeds, by slighly pressing on the brake.

The reason I think the ECM may be bad, despite glowing diagnostic results, is that my mileage is far below where it should be, it seems to affect the lockup and the near-stalling sure feels like the ECM is mismanaging the fuel/air ratio. The carb is solid and mechanically everything checks out.

That said, it still could be the transmission. If the clutch is going out, it would explain the poor mileage and improper lockup. Trying to pin down a real cause of my various problems has been an expensive and painful (because of the expense) experience...one that's not over. The car is beautiful and drives like new EXCEPT for these couple things. In fact, it hasn't threatened to stall ever before or even since those couple times last week. It could even be junk gas so far as THAT goes.

So if anyone has reason to confirm my suspicions about the ECM, let me know. Like I said, before the ECM was "reconnected" my mileage was fine and I had no problems.

Otherwise, I may be looking at that tranny rebuild. Sorry I can't give you more specific and professional clues. Thanks for all the help so far, too.