ECM controlled carb trouble shoot

[cwdaniel]

Working on a 83-305-Q-jet. The car had issues before it came to us, and has sat for some time.

Work done so far: carb rebuilt including throttle shaft bushings and bench adjustments. Initial idle mixture screws are guesstimated at 2 turns out.

New coolant temp sensor/connector and O2 sensor/connector after testing out bad.

All other sensors Baro/MAP, TPS, test out okay.

EGR appears to be okay. With some difficulty I can get it started and run pretty smooth on the choke and fast idle cam for a few minutes. After it's warm it starts to get rough. pulling the choke off makes it stall. It seems to be very lean and only able to run with the choke almost shut. Once it's very warm it will idle very roughly for a short time with no choke until it seems the ECM finally kills it. The dwell test connections shows that the ECM never achieves closed loop operation.

I haven't found any real bad vac leaks, though I'm still hunting. My next move is to check all of the wiring to the ECM for continuity. Other than that I'm at a loss at what to do to make this thing happy. Pitching the carb and dist for something non ECM is close to happening, though I don't want to spend that kind of money to get it going.

Anyone have any other ideas for culprits?

 

[Bonnewagon]

I worked on an 82' Riviera that acted like that. I adjusted out the idle mixture screws useing a vacuum gauge just like a non-computer carb until it ran nicely. The computer did not fight the change, but actually seemed to adapt to it and ran fine after that.

 

[cwdaniel]

Okay I've made some improvement with 4 turns out on the mixture screws and fooling with the idle air bleed setting.
Still funky at idle but will compensate when put into gear.

But, it still will not go over into closed loop mode. The dwell reading is a constant 15 degrees. Which according to my manuals could mean bad sensors that I already have checked or replaced as good, or faulty wiring to the ECM (next on the hit list). It flashes code 44 eventually after idling awhile (indicates a lean condition).

Any ideas on what other no closed loop causes could be?

Also, it seems like the fuel pump is weak because it act like it's running out of gas sometimes. Float level is good.
Can low fuel pressure be an issue?

 

[megaladon6]

you could have a low pressure or volume problem.
also, stupid question-but it has to be asked-did you check the temp sensor or the temp sender? one is for the gauge and one for the ECM

 

[cwdaniel]

you could have a low pressure or volume problem.
also, stupid question-but it has to be asked-did you check the temp sensor or the temp sender? one is for the gauge and one for the ECM

No question I checked and replaced the ECM temp sensor.
Never a stupid question

 

[Bonnewagon]

Closed loop is MOSTLY dependant on temperature. Maybe the thermostat is stuck open? Are you useing a scan tool like a Snap-On? What is the motor temp? O2 is new but what is the oxygen sensor reading? Maybe substitute a known good non-ecm carb just to eliminate the carb. Still sounds like it could be a vacuum leak I had an annoying code 44 once and it turned out to be an air leak, a crack in the airbox was downstream of the MAF sensor. Computer cars can really drive you to drink.

 

[Blake442]

Maybe the thermostat is stuck open?

X2

 

[cwdaniel]

I think the stat is working, but that might be worth replacing just because. I've been getting some ECM specific help on another forum and it's beginning to look like the culprit.

Out of town till next year so no more progress until then

 

[cwdaniel]

Has anyone ever swapped an ECM? There's some instructions for pulling a PROM if you need to in the manual.

Will I need to? NAPA sells a reman with a core swap, do I keep the chip?

 

[Bonnewagon]

My Mom's 89' Olds needed the ECM changed several times. Each time I got a new one I swapped her chip into it.