85 GT Auto - ECM conversation

[MetalBlue85GT]

85 GT 3spd Auto.

I have this: Shutter, Jitter, spudder, during cruising when the TCC locks just as I hold the throttle not accelerating not slowing.

Here is what I know:

- New fuel pump no help ( fixed my stalling after an hour though)
- new plug wires didn't help
- putting the old ones back in didn't either
- New coils no help
- old coil back in no help
- New plugs no help, new plugs again no help.
- new distributer no help (found old distributor had cracked Magnet and couldn't find jut the magnet)
- new ICM no help
- other old ICM no help
- TCC recently changed (was stalling - fixed that but no help to this)
- Transmission fluid flush no help

So in talking to Charlie, I borrowed the 86SE Computer (auto trans too) and installed it. right off the bat I got a Check engine light (34 map sensor). The Acceleration was not correct either. It was shifting really slow and taking too long to shift to 2nd (with low power). But I did not get the jitter, shutter, spudder that I was getting I think.

So the question is should I even mess with this 86 SE computer is there something so different with it controlling my 3 speed verses what I think is a four speed Auto?


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[Fierofool]

If you have the stock Fiero trans, it's a 3-speed with overdrive.  The ECM from the 86 has lost it's memory when it was disconnected from power.  The car would need to be driven for about 10 minutes at road speed to learn the vehicle systems.  With the code popping up, makes me wonder if your old ECM isn't bad. 

After driving it, disconnect the ECM power connector near the battery to clear codes and try it again to see if the code pops up again.

[MetalBlue85GT]

I will try that this week some night and let you know how it goes.

The power and shifting delay has me skeptical a little. But I can do it. Now I need a Map Sensor too. side bar troubleshooting


Add to the list -

02 sensor (I did that and forgot to list it. I had a new one laying around. )

[MetalBlue85GT]

RESULTS:

Removed 85 ECM installed 86 ECM drove freeway speeds for 15 miles; the computer did adjust but it is not quite right yet (but probably for other reasons where I need to do the timing the old way with #1 TDC. and see where the mark is.) it seemed to bog down at highway speed during acceleration and either Back fired or fired forward. (a fluff sound near intake)

So....

Successes - Studder sputter chugs are gone.

Issues - Got two codes with the 'borrowed' ECM 34 (MAP sensor) and now 54 (low power fuel Pump relay)

For CODE 34 - I bought a second MAP Sensor installed it :: Disconnected power for 20 seconds and restarted the Car.  The code is still there so I went to drive it for a little bit the code is still there.
 
For CODE 54 - I think I am going to take the car to Advance and check the battery and ALT - it seems to be starting slow so the battery may be low and I wonder if it may be that the Alt isn't putting out enough power.

OK - so here is another question - If the engine in the 86SE was not a stock 2.8 could it be that the computer I am using is not a match?

how could I tell?

just a thought

[MetalBlue85GT]

Some other research I have done:

http://www.exatorq.com/ludis_obd1/fieroprom.html

Looks like the 85 Auto has its own Part number - I may be chasing a ghost 

Edit: The ECM is from a Camaro - Service # 1227302 (Guess I should have looked at that first.)

Oh well back to the drawing board.

I will wait to hear what people think.

[Fierofool]

First, this is on the assumption that the old ECM was bad and the new one is good and didn't have a custom tune.  There would really be no need for that.

The ECM will still operate the engine, even though the engine has been changed out in the 86.  I'm running a 3.4 with a stock ECM.

The new ECM picked up a faulty MAP.  That could have been giving poor information to the ecm to help control the injectors properly.  The backfire or cough could be a result of a fuel pump reacting slowly.  Do a vacuum leakdown test on the line from the map to the fuel pump or as f85gtron did, give a puff on it with your mouth to see if you taste fuel.  A sure indicator of a leaking fp diaphragm. 

If you can secure a dial indictor to insert into the cylinder, checking TDC would really be a good place to start.  Timing it with a slipped balancer ring could be a bit difficult.

[Fierofool]

I'm not sure as to why the 85 has a different ECM number, but this is just pure speculation on my part.  The 85 V6 ECM had the capability of a knock sensor, though that wasn't energized in the programming.  So it might be with the 85 automatics, too.

The Camaro ECM would probably have to be from an early year when they first switched to fuel injection?

We discussed putting the 88 Formula Fastback 5-speed up for sale with proceeds to go toward the Warrior Project car.   

[f85gtron]

If this helps,
I've learned that the 85 ecm is different than the others. It has knock sensor capability, just needs to be enabled in the prom, and can be aldl monitored without going into diagnostic modes....just plug into it and it starts spitting out data. I think the hp ratings published are a little higher than the remaining years because of different a/f mapping and so on. 
Somebody please correct me if I've misspoke.
I can pull my ecm model no. if that will help

Ron
Ron
Ron

[Fierofool]

I think you're correct.  I don't know about the reason for the different HP ratings but one reason I've heard is that it was because of the insurance industry starting to classify the car as a sports car instead of an economy car with the introduction of the V6.  If you look at the specs for different years, you'll see that the HP is derived at a different rpm.  All were the same engines, except the 88 was a little smoother and in actuality may have produced a few more horse if all were rated at the same rpm. 

[MetalBlue85GT]

The 85GT ECM I have is  Service # 1226869. Which matches what I should have as stock. The one out of the 86 SE is Service # 1227302 (Camaro when I search the Internet)

Everything that I was chasing with the second ECM is a ghost. So I am starting from ground zero.

85 GT has a studder at cruise and you can feel it more when the TCC sole is locked.

[f85gtron]

If you bring the car to the picnic, i can hook up the aldl and read the 85 computer, save a log, and see what's happening in its head.
Have you tried blocking off the egr valve to see if its allowing too many exhaust into the intake at cruise and part throttle?  A cut up coke can will do in a pinch.
Ron 

[Raydar]

The stock 85 ECM is a 6869. The stock 86-88 ECM is a 7170.
As long as you keep the correct prom with each ECM, they are pretty much interchangeable.
I ran an 85 ECM (with appropriate prom) in my 88 with a 3.4. Worked just like the original.
I have no idea about the Camaro ECM. I would expect that there are some differences, but I don't know that for sure. 

[MetalBlue85GT]

I have a plate that I took off and put an a new EGR - I can try that.

Here is why I fixed the EGR system. Does anyone have any experience that is different?

http://floridafieros.org/osg/EGR.html#info6

This basically says that I will start running rich, and that the car will lose gas mileage - before I took off the plate it was definitely running chokingly rich and it was getting about 17mpg. after the plate was taken off it balanced out on fuel burn and I am getting about 20mpg.

Anyway - I think I would rather have it not studdering.

So I will put the plate on as a test.