1G 90 ECU in a 91 - misfire/stalling?

[Bouche Dag]

Like the title says - car is a 91. ECU has the words 90 Chry Laser 5SPD on it so I'm assuming it's a junkyard 90 ECU.

It's been recapped and I'm assuming the 6 and 14 pins haven't been changed.

Car runs like a champ until 4k at WOT. Bad misfire. However, if I roll on the throttle gradually and hit WOT at 5k it's not too bad. Just hesitates a little randomly till 7k. It also stalls if I'm sitting in traffic for a few minutes. But it starts right back up like nothing ever happened.

Background about the car- 91 FWD 5spd. 119k miles. "Sat for years" with bent valves according to previous owner. He also said that the TB shaft was leaking slightly. I am going to send it out soon to get rebuilt and bored. I also have a fuel filter that I have yet to put on. I figured that could be the culprit since it "sat for years," until I saw the ECU. Plugs and wires are good. BPR6ES gapped to .028 with Bosch OE wires.

Ideas? Anyone in Detroit have a good, working 91 ECU I could try running in my car just to see if that remedies the issue?

 

[1genbeal307]

I have a 90 FWd and last year i had the same problem up till 4.5K it was a beut but after that was junk bogged and stalled out and randomly it would go past the 4.5 marker... well it was the ECU, all the grounds were junk and i ended up just replacing it all together after that a good fuel injector cleaning and an oil change because there was gas in the oil from running like shit for a month like a brand new car... hope this helps

 

[Bouche Dag]

Thanks man!!! It does help. Testing a different ECU is definitely next on my list!!!

 

[Bouche Dag]

Changed out the ECU. Car still misfires. When I logged a second gear pull the O2 sensor voltage read .10-.15 during a the misfire. Fuel pressure was good though ~100 PSI.

In third gear (with no misfire) O2 voltage read .50-.60 and no knock.

The car sat for years and the fuel tank rusted and is leaking at the return line. I was thinking the fuel pump could be gummed up, but the fuel pressure is good. Could I have bad injectors? I'm lost. Help!

 

[fullCircle]

Changed out the ECU. Car still misfires. When I logged a second gear pull the O2 sensor voltage read .10-.15 during a the misfire. Fuel pressure was good though ~100 PSI.

In third gear (with no misfire) O2 voltage read .50-.60 and no knock.

The car sat for years and the fuel tank rusted and is leaking at the return line. I was thinking the fuel pump could be gummed up, but the fuel pressure is good. Could I have bad injectors? I'm lost. Help!

on the fuel note.... you could have good pressure but not enough flow, like something is clogged.

did you check your plugs?

 

[Bouche Dag]

Attached is the log.

on the fuel note.... you could have good pressure but not enough flow, like something is clogged.

did you check your plugs?

Plugs and wires are good. BPR6ES gapped to .028

Walbro 190 and a new tank are on the way. I'll report back with the condition of the fuel pump.

 

[ilco187]

100 psi fuel pressure WTF um am i missing something it should be between 36-42.

 

[Bouche Dag]

That was the value on MMCD. 100 then tapering off to 70ish @6K. I'm so lost with this vehicle. I don't understand what could be causing it to run this lean. Also there is no knock.

Is it possible my CAS is 180* off?

Do my MAF. values seem normal? Should it climb to 1500 Hz like that?

Perhaps it's my O2 sensor itself.

Any ideas? Bueller? Anyone? Bueller?

 

[Bouche Dag]

Got a new O2 sensor will post results once I get it in.

I'm pulling the O2 housing in order to replace it since it's seized in there (I think it's the factory sensor - 20 years old w/120k miles on it)

 

[TGST90]

I have kind of the same problem. I check my CAS and it was leaking a little, so I bought a new o-ring and new bolts for it. I haven't ran it yet, but ill tell you if that stopped my misfiring.

 

[Below Ambient]

did you change the pins on your harness? there are two pin differences on the 90 vs 91-94 ecu's

 

[steve]

That was the value on MMCD. 100 then tapering off to 70ish @6K.

Since there isn't a fuel pressure sensor for the ECU to read it's hard for MMCd to actually report useful data.

There are several things in MMCd 1.8 that don't really exist. The author of the later versions of MMCd was going to make a box that read additional sensors and intercepted commands from MMCd to return the values. What happens instead is MMCd reads memory locations for those commands and displays what ever is in them.

 

[Bouche Dag]

I did swap pins.

The O2 sensor did not help the misfire.

I'm running out of things to check/replace here!!!

Saturday the fuel pump and tank gets replaced. Walbro 190. Will post with the results.

 

[rizzzo29]

Leaking fuel at the o rings?

 

[Bouche Dag]

No leaks at the injectors.

The tank itself is leaking though.

 

[Bouche Dag]

Fuel pump didn't fix the issue.

List of replaced parts:
ECU (pins swapped)
O2 sensor
Fuel pump
Wires

It should be noted that I didn't change the plugs. I pulled them, they looked new and were gapped appropriately, so I reinstalled them.

I was also going to look at the ECT sensor while I'm under the hood.

Tested the coil again today. When measuring resistance at the coil connector between terminals 1 and 3 and 2 and 3 I got 1 ohm on one set and 1.1 ohms on the other, then I checked the secondary resistance again. One pack measured within spec and the other measured 10.8 ohms (which is out of spec, not by much though).

I'm thinking the high primary resistance and low secondary is the issue. Now I need to find a coil to swap/test.

 

[Bouche Dag]

I replaced both the coil and the PTU and the misfire is gone!!!!!!!!!!!!!!!!!!!!!

Final list of what I tested/replaced:
ECU - Recapped by ECMTuning (nothing was functionally wrong with the ECU upon arrival)
Tested injector resistance - passed
Compression - 120 120 115 120 (low but not too low, and all within a few PSI)
Fuel filter
Fuel tank (return line rusted out and was leaking-irrelevant to the misfire but while I had the tank out I also did the pump)
Fuel pump (walbro 190)
Boost leaks (lower injector seals(replaced), BISS oring(replaced), and a leak from behind the intake manifold, I'm thinking TB gaskets/shaft seals(not fixed, it's too cold and I was frustrated because I couldn't pinpoint the leak, will fix come spring))
BPR6ES plugs
Plug wires

At this point I was getting upset that nothing I was testing was coming up out of spec. and the parts that I was replacing wasn't helping at all. I did test the coil and one of the secondary values was lower than the other (13 on one and around 10.4-10.8 on the other) which is slightly out of spec. I figured I may as well replace it since that one was lower; however, I was worried that the coil wasn't in fact bad.

Well I found someone parting out a 91 so I snatched the coil (tested good - both secondaries at 13 and primaries around .9) and I also took his PTU that tested good. I never tested mine but I figured why not. Installed the ignition components and the car fired right up, I let her warm up and took it for a pull. VOILA. I was so surprised that less than 1 ohm out of spec on the coil could cause such a problem.

I wasn't too upset after replacing all the parts listed since I basically gave the car a complete tune up (which it probably needed anyways). Now that I have the aftermarket pump with a rewire I can crank the boost up

Thanks DSMTuners.