Hey all,

I have an issue that is beyond me... I suspect it is an ECU related issue, but if it is not, I may have to move this thread to another board.

My Camaro which was running nearly perfectly up until last weekend, and is now not drivable... and seems to be getting worse...

Here is what I know so far:
- I changed out my torque converter from stock to an Edge 2600 stall last fall. (likely unrelated)
- I installed a trans temp gauge over the winter, and found I was running a bit hot after the new converter. (likely unrelated)
- I installed a secondary trans cooler last Saturday with low temp, hi pressure bipass. (likely unrelated)
- Car was running great Sunday when I ran some errands, and pushed it a bit as a test
- Also, on Sunday I noticed the passenger fan stopped working it seems like at all, I know it is controlled by the computer and by the temp switch in the passenger side header
- Wed morning, car started fine, backed out of the driveway fine, but when I first pushed the throttle past a couple percent, the engine started to shutter. It felt like it was starting and stopping abruptly at a certain throttle input. I thought at first it was the torque converter locking and unlocking repeatedly, but this was before the engine even had a chance to warm up, so torque converter lockup is disabled at that temp.
- I had been experimenting with torque converter lock up parameters prior to installing the cooler, so I reverted back to my previous map which I had used for weeks with no issue, this made no difference.
- Tonight, I started searching deeper. This time it did not start up as smoothly, and as I was backing out of my driveway, it was already stumbling and surging, once I made it to the curb it died in reverse. I restarted and pulled right back into the garage. (This is when I started my datalog I will try to attach) I found it was stumbling and surging even at idle now, giving any throttle only made it worse and made it nearly die.
- Near the end of my testing it seemed that my computer was no longer able to connect to my ECU similar to when I needed to replace my ECU previously.

Ideas:
- The think that I am thinking may be possible, is that the ECU is just failing. I had my original one that allowed the engine to run fine but I was unable to data log from, and someone suggested swapping it out for a new one, and that allowed me to start datalogging. So something in there was failing... It was an off the shelf version from O'Riley Autoparts. This was a year or two ago. I wonder also if somehow the failure of the one fan, somehow was an indication of the beginning of the ECU failure?
Thread about previous ECU swap: **SOLVED** No one can get my Moates Xtreme ALDL Connected to ECU - Pics! - Third Generation F-Body Message Boards
- It seems like I occasionally hear louder than normal sucking, but when the engine is surging, and the hood is up it may just be the air coming through the air filters. I did trim the basket out from under the filter elements, so they are now exposed, and louder.

I'm at a loss... what do you all think? What else should I be checking? It's just bazar because it seems like it came out of nowhere, and installing a trans cooler should have no effect like any of this... Can anyone spot anything out of the norm in the data log???

...OK, I'm going to need some help on how to share the data log, the forum is saying it is not an acceptable file type.

 

You will get "millions of opinions". It can be "millions of things".

What have you checked so far? You have not mentioned anything but assumptions.

Not "bazar" at all... things brake, degrade and fail. One day it works, the next it does not.

Be nice to have the log attached.

Need to attach the .XDL file only. Zip it first and it will accept it.


​​​​​​I assume it's a 1991 Camaro, 5.7L TPI with '7730 $8D ECM/Mask? All stock?

 

yes ypur assumptions are correct
More details in my sig. I'll zip the file and post it shortly.

Another symptom I forgot to mention. CEL is on and flashes at times when the engine struggles to run, but when I try to check the codes with a paperclip in the top right two terminals, it does not show me any, the CEL just stays on steady. Also the drivers side fan turns on, shouldn't it be both fans in this mode?

Thanks!
-Eli

 

Data Log zipped and attached.

One additional test I did was disconnecting the battery for 30 sec to reset the ECU then starting back up, and it continued to surge and stumble immediately after restarting.

Ah, one of the strangest things I almost forgot, first three times I slammed the hood the engine revved up on its own for a couple of seconds, then the third time it stumbled and almost died... I tried banking on things by hand, and lowering the hood slowly and quickly, but without slamming, and nothing created this result, aside from actually slamming it closed.

 

i would start with the basics... fuel, air, spark

to kick it off with fuel
- what is your fuel pressure reading... ie get a gauge on the fuel line and determine if you have appropriate fuel pressure ~40 psi... get an extended length hose gauge and you can watch the fuel pressure while you take a short drive
- if you have fuel pressure issues think about when did you last replace the fuel filter, check the FPR, what is the life of your fuel pump... any of these could cause what you are seeing
- if fuel pressure a-ok, what is the history of your injectors? i have a 91 Z28 vert i ordered new with only 7K miles now on it and a couple years ago the injectors needed replaced even though the z28 is basically new... 4 of the injectors were at the point that the z28 would barely start when warm... use an ohm meter to see if you have failing injectors... if they are original they are likely a potential problem. also if injectors ohm ok, use a noid light to see if firing pulse getting to injector

some quick ideas to think about on fuel

also here is a bonus one, what does your coolant temp sensor read... if it is failing it can read really cold but maybe not to the point of tripping the code... if it is reading really cold you will be running way rich and difficult start / driving

 

Sounds like its in and out of limp mode. Try the screwdriver test on the ECM.

 

Again, try the ECM screw driver tap test

 

Replace the ECM, it is toast (intermittent).

I see data logging, is any PROM burning/tuning being done by the OP? If not, then this is DFI & ECM, NOT DIY_PROM.

RBob.

 

Looking at your log, a few things stick out like a sore thumb. But I can't really tell you what is the cause(s)

I assume the engine was fairly warm because CT indicates 160Deg.F. at start of log
The IAC taps out and goes to zero, can't maintained commanded idle of 650rpm
SA gets low to 14* during the event (I would have to see your BIN to see why it's so low. I suspect ECM pulling 5* trying to bring down idle)
O2 sensors swings are on the rich side
BLM goes to 108 which stabilizes INT
There is a code #33 stored: MAP sensor high
Commanded AFR, open loop and closed loop seems to work ok
Voltage is normal
MAP seems normal

Inconclusive at this point for me.

You could try an ECM swap to eliminate it as the cause. If it does not work, then, like others say, fuel, spark, compression, etc... EGR could be acting up. Injectors (if original multec) could be toast, ICM, pick-up coil, EPROM, fuel pump, etc... etc...

 

Took some videos today while doing some tests...

 

If this needs to be moved to another section that is fine, I am doing some tuning to the Prom, but it was relating to torque converter lockup. I didn't know if it had any effect.

I was able to get my hands on another ECM from Oriley, but its the same as the one I have now, I hope I'm not going to have to go through this every two years... Especially when they only have a one year warranty...

I do have some data to report as well:

When I started up the car to do these tests, the car seemed to idle smoother, maybe because it was cool. Also, the CEL was not on before or while the engine was running or at all through any of the tests in the videos previously posted.

They are OE multi tec injectors. I plan on an engine rebuild this fall, with new heads and a cam, so I will be getting new injectors then, I hope I don't need to get new standard flow ones now, only to replace in a few months...

(Resistance in Ohms)
Passenger Side Drivers Side
Rear
22.7 23.3
23.0 23.3
23.4 23.5
23.3 23.3
Front

Fuel Pressure:
36 PSI vacuum line connected
44 PSI vacuum line disconnected

Time to go out and try the new ECM, fingers crossed!!! I'll report back...

 

Please explain this ECM screw driver test???

Is post #2 what you're talking about?
VSS output signal from ECM - Third Generation F-Body Message Boards

 

While running the engine tap on the ecm case with a screw driver handle. See if it runs different or stalls .

 

Ohhhhhhkay....

I'm still processing this all, but I just tried the screwdriver test and yes, the engine rpm dropped, and it went into this low rpm undulation. So that indicates the ECU was bad.

I swapped out the ecu, started the car, which took a while of cranking the first time, but eventually it started. Was not perfectly smooth at first then smoothed out. I revved the engine and again around 2000 rpm, it started missing...

THEN I HAD THE THOUGHT, why does this sound almost like the engine hitting a rev limiter, so perfectly at 2k rpm. Then I remembered, wait my ignition box has a rev limiter put in, and I vaguely remember messing with it years ago. I looked at the box and it was set to 2k rpm. So, I flipped the switch I had that I thought I had wired up as a manual fan switch, and suddenly it revved freely, no more stumbling, missing. Oh man, I'm a moron, it came back to me that I had rewired my fan switch as a rev limiter switch for launching at the drag strip a couple of years ago... I went for a drive and everything was perfect! Even my secondary fan started working again. Idle went back to being just as smooth as it was before this whole incident...

In the end it sounds like I totally forgot that I had a rev limiter enabled at 2k rpm and that is why it would start missing right at 2k rpm and was unable to exceed this engine speed. But also, my ECU did go bad causing the very unstable idle, the passenger side fan to stop working, and caused the ECU to fail the screwdriver test...

My only question is, could my accidentally engaging my rev limiter have burned up my ECU? If I recall correctly, the rev limiter functions by sequentially cutting spark to different cylinders.

Thank you all for your help, and sorry for sort of wasting all of your time...

 

TURNS OUT ITS NOT SOLVED! HAAAA!!! SO MUCH FOR MY AUTOX EVENT THAT STARTED 5 MIN AGO...

I'm starting to think this a more general electrical gremlins issue... if you need to move the thread that's fine...

Now when it can get started, and it has a hard time, never did before, it sounds like a top fuel car, missing frequently, I smell lots of gas.

When i first started trying to start this morning, the fan relay was randomly clicking on and off for the drivers side fan. It seems to have stopped doing that now though...

Also heard noises, continuous random sounding chatter, coming from the idle air controll valve with ignition on and engine off. Only while having the two diagnostic ports connected, so maybe that is normal?

I tried the jumper thing again and got a code 12. So that doesn't mean much. I even tried plugging in the old ecm and no change...

I'm starting to think ignition control module (ICM) in the distributor... thoughts on that one, given the symptoms???

Super bummed, this was to be my first event of the season...

 

Well... just finished replacing the ICM, and everything seems back to normal now, even with the original ECU. But honestly I don't really trust it, I'll have to do some closer to home trips, before committing to my next race...

 

The slamming the hood stuck out to me, battery cables clean and tight on both ends ?

 

How did you edit the thread title?
Thanks

 

When you edit your response, there's a go advanced tab. Click on that then edit away

 

You can't trust either ECM. Intermittent as they are. What is to say that the replacement you grabbed is any good?

RBob.

 

Thanks!
But that is to edit your response post not the thread title. I should have said, How does an OP edit the thread title, not the post title?

 

Yup battery terminals are tight... i did do a slam test again yesterday with the new ICM, and the engine speed did not change at all, so maybe the circuitry in the icm was being chaken by the hood slamming?

 

I think I found you have to go advanced while editing the first post of the thread, not a subsequent one...

 

So what do you suggest, both new and old ECM's were Cardone remans 77-7730. Different serial numbers and some different ID numbers on the board itself, but interestingly quality inspected by the same person, or at least same code...

Are certain ECM sources more reliable than others? Do some people convert completely to a holley unit or something altogether different for improved reliability?

 

Took a 45 min round trip drive yesterday, starting out taking it easy, then getting more aggressive as I went, and had zero issues. As this point it looks like the ICM was the fix.

I really wish I know why it went bad. I had another one go bad a few years ago, and at that time replaced the whole distributor including ICM with a D.U.I. unit that was supposed to be high quality... I did have issues in the beginning, and I believe also with the previous distributor, where I was getting oil finding its way up through the distributor tube into the Rotor/CAP/ICM area, which may have effectively washed away some of the thermal paste, causing the ICM to overheat and fail over time. I did contact the company and they instructed me to drill an additional relief hole for oil higher up on the tube, which I though worked at the time, but there was still definitely "some" oil in that area as I was changing out the ECM this time... Not sure what do about that one. I would prefer to not have to change out my ECM ever few years, seems like that part should have a much longer lifespan...

 

Look at the posts by vorteciroc. Might be something relevant there?
https://www.thirdgen.org/forums/elec...ar-option.html

 

NEW ICM FIXED IT? Could a bad ICM cause my '89 IROC Z LB9 305 TPI, to NOT communicate with my TWO, known good, Scanners?

I tried a different, working ECU & MEMCAL, still no communication.

 

It looks like you are still running those old Rochester/multec injectors. Change them, as they are notorious for shorting out, sometimes intermittently, and they will cause you no end of trouble. It's well established that Ethanol in the fuel today breaks down the insulation in the coils of those injectors, so it's not a matter of if they go bad but when.

 

I have driven the car a number of times since my last post. Then 2 hrs round trip to an autox event, that I did 7 runs at yesterday, and not a single issue! Seems the ICM was the problem all along. For the record, I'm still using the ECU from before all this began so it was fine all along... Seemed to be the newest of the three I had.

Mike, can't tell you for certain, but it's possible the ICM could fix ypur problem, they're cheap, and if it doesn't fix it, you now have a spare... make sure ypu clean off the mounting surface and use the thermal compound...

Regarding the injectors, I know they are notorious problem points, but here they were clearly not the issues, I plan on building a new 383 soon, so I'll get new larger injectors then, no reason to spend the money on stock size ones now when these are still functioning acceptably...