I found a different ecm in the wrecking yard from a 91 Rodeo. all the pins match. I took the box apart, the board looks Identical to my Trooper board. The truck still stays in limp mode. I think I need to start looking at the emission components. Can any of you tell me where to start. Which ones would turn off the ecm? Thanks Stan

What's your rig doing?

There is (or should not be) an ECU driven "limp" mode. For the AT, the TCM can default into a limp home mode, but I think you have an MT.

Your rig is not going to run without an ECU. No ECU, no go.

So, let's get back to the basics. Is it running? If so, what is it not doing correctly?

Michael

Yes the Trooper is MT. It runs. In fact it doesn't even miss. Trottle response is very slow . You can floor board it going up a hill in second, it won't cut out. I shift down to first just to get up an average hill. On take off in first, unless you give it lots of gas it well stall and die. You can tell it is in some kind of shutdown. When I start it it does not rive like it used to when cold., just sits in idle and slowly starts to die. then will catch and go back up to idle speed between 8 and 11rpms. I have checked all the emission lines by the book and pics I have seem on here. I am going to recheck again today. I thought if it is one of the emission components it would at least sound ok when it starts, then act up a little later.

It was a sudden change I pulled off the street to take a phone call. I turned off the engine. When it restarted it was imediately sick. the ecm popped a few times engine light came on two or three different times, Now engine light does not come on any more. except when I start it.

My Chilton book says if the ecm is bad the truck will go in to a default mode or limp in. The truck can barely get to 4th on a flat road. Possible both ecms I tried are bad I suppose. The pins sure did match though. I can't find an exact match year for year, model for model yet. I will keep looking though. If you need more info let me know. I'm not sure where to start looking at this point. Thanks alot, Stan

This may sound silly, but did you check the bulb in the instrument cluster? (oops, it does come on). If the CE light lights when you start it, then the ECU should be considered functional. That is part of the self-test. If the ECU is dead, then the light will not work. Or at least that is how it should go.

I am still not convinced that these ECUs have a true backup mode. They may have some back up maps for when a sensor goes south, but the truck will not run if the ECU is toast or not powered. I think you are confusing a "limp" mode with a poorly running engine.

I also don't quite trust the quote in Chiltons. 1) It is Chiltons, 2) I would almost bet that paragraph is in every version of Chiltons. I am also very concerned with the "popping". ECU's should not do that and there are no parts in an ECU that should allow that to happen and for it to work at all.

What happens when you jumper the diagnostic link? Do you get any codes at all? 12?

With two ECU's and Occam's Razor, I would be more inclined that there is something else wrong, not two bad ECU's.

I know you have troubleshot this thing to death, but is may be time to start back with the basics. To some degree, what you describe sounds like a timing issue or it could be a fuel delivery problem. It also could be something like a clogged cat. It could be a TPS or IAS (or whatever it is that gets adjusted on the 2.8 family of engines). Engine temp sensor, especially with the change in cold idle. Just some ideas.

So, there are a few things that should be checked. It could be that whatever is wrong toasted the 2nd ECU, but that again is not quite as simple as something extra-ECU as being the source of the problem.

Good Luck,
Michael

PS. What did the old ECU "smell" like? Did it smell burned? It will be pretty obvious if something did fry.

Gees I screwed up again by discribing the sound as popping, it was clicking. I have taken the ecm boxes apart to compare them. No smell. No signs of a meltdown.

I got one code, 42. We had just set the timing. That code has to do with what we were doing. It does blink 12 so that part has to be ok.

Let me back up a little here, I was in a rush this morning. The engine lugs down whenever I turn on accessories like blower, headlights and lighter. I'm sure you are thinking what I am. Probably the alternator. I did a test on it when this first happened. I had 12.98v at the battery. About 11.95v at the alternator when in idle with nothing else running. It dropped about .25v each time I turned on an accessory. I thought as long as the battery was good the engine should run ok until the battery go's. Am I wrong here? I understand that alternator should be putting out around 14v. I am on my way to retest and will let you know what I am getting now.

This happened on the test drive after I installed the new distributor. Ran fine at first, However I had not used a timing light yet. I didn't have the distributor tightened real tight yet. I just went by my marks. I thought it had turned a little when this happened. When I got it home after stopping a few times to readjust it. I put it on the timing light. It was at +20. I have it set to the spec at +10 now.
Thanks Stan

I just tested the alternator. It turned out 14.48 and under load it was 14.38. That should be fine, I think. Maybe the coil next if you think. Tomarrow I well start going through all the emission stuff. What's the most likely. I can look back on what you already sent to me. I well start there. I have to say the truck idles much better with the new ecm, doesn't drive any better though. You are a great help, it is appreicated.

Regardless, the ECU should not be making any sounds.

Did the setting of the timing fix the problem. I can't figure out if you did that before, or right now.

Are we still dealing with an issue? Sorry, I can't quite figure out the time line.

I would suggest fixing the alternator. It is not functioning properly. Who knows what amperage it is putting out. The engine does require power to run and if there is low voltage (and maybe even less at higher RPMs) it may not allowing the electronics to function correctly.

Good Luck,
Michael

As an aside, and for others in the future, if you are getting code 12 out of an ECU (and the CE light cycles at startup), there is a pretty darn close to 100% chance the ECU is not fried.

OK Michael, We are deteriorating here. I have never said the ecm is fried. I have corrected myself each time and called it clicking. I had the console off so it was easy to hear.

At 14.48v idle and 14.38v under load, that does indicate according to Chiltons it is functioning OK. I set the distrubutor at +10 and tightened the bolt after I had the problem. So it was set while it was in shutdown mode (running bad). Yes we are still dealing with the same issue.
Thanks Stan.

Don't worry, Stan, we are doing fine.

But...take a peek at the title of your thread? Then read your first post. "ECM Quit" and "Are ECMs fixable?" imply "fried." We operated for quite a while on the premise that the ECM gave up the ghost. But, no problem.

Your alternator seems to be working. Your voltages are fine, but you might still want to consider getting it tested as voltage is one thing, amperage is the other. I doubt you possess the equipment to load test the alt. Now we need to start looking for other things.

We are left with the basics:

Check the timing again.
Check the fuel pressure.
Consider exhaust obstructions.
Stuck EGR valve?
Stuck PCV valve?
Intake leak?
Spark plugs gapped right?
What do the wires look like?
Cap, rotor?
Is it running rich?
ECT sensor?
IAC and TPS adjusted correctly?
O2 sensor?

Driveshaft? Sorry, saw that one one time where it really felt like a miss, until everything smoothed out when the driveshaft exited the vehicle. <img src="/forums/images/graemlins/smile.gif" alt="" />

What does the spray pattern look like on the injectors. You can do this in the dark with a flashlight. They should be pretty and even between the two. These engines like to clog injectors sometimes and it can cause headaches. If they look bad, just buy new ones. Cleaning/rebuilding usually costs more than new.

Other than that, we are then down to a compression test to see if there are worse problems.

It is up to you at this point. I am pretty darn sure there is something mechanical causing your problem, but that is my full assessment sitting here on the other side of the internet. Chasing gremlins is not fun, but you gotta knock down the obvious things first instead of hunting and pecking.

Good Luck,
Michael

OK Michael I need a few days to get thruogh all this stuff. I will need to find out what ECT, IAC and TPS is, and where they are first.

In my mind the ecm did give up the ghost if there is such a thing as Chiltons default mode. It is operating exactly as they discribe.

I did change the heading of my tread. The thinking being it would be more up to date as to where I am now. Mistake I guess.

I'll let you know when I make some progress with this problem. I well get your list done and get back on here.

Stan

Stan, here are some links for you.
Link 1

Link 2

Link 3

Link 4

TPS=Throttle Position Sensor
IAC=Idle Air Controller
ECT=Engine Coolant Temperature sensor.

From what I can tell, your problem could very well be associated with the TPS or IAC. Adjusting them both, at the least, will take them off the potential problem list.

Good Luck,
Michael