strange ignition issue on 91 3.1
 

Hi Guys!

i'm trying to fix a buddys car: a 91 3.1L Firebird (7730 ECM & MFI)

there were some broken wires which caused a short-to-voltage on the Coolant-Temp-Sensor wire (yel). The "measuring" part in the ECM was gone, so it always monitored -40°C coolant-temp, even after fixing the wiring problem. Because of that it got always too much fuel so it was not possible to drive that car.

I replaced:
- ECM
- Coolant Temp Sens
- CTS wire (yel)

Now it runs nearly fine, but still has a small issue: At idle i can hear a slight missfire every now and then, it's not too bad, so only this missfire wouldn't be anything to worry about. But when you let it run about 5 mins. at idle, the Engine stops. That also happens while driving when you're at a red light or so, and that's the big problem here.

ok i replaced:
- EST-Module
- Pickup-Coil
and cleaned the whole distributor

With no change.

But when i re-set the ignition timing i noted something strange: with unplugged Timing Connector the Missfire isn't there anymore and the issue is gone.

So do you guys think that problem could be caused by a bad MEMCAL (it's the only old part at ECM-side)?

I hooked up a Tech2 viewing the Engine Data, theres no knocking detected, all temp's are realistic and BLM/INT are in a good range around 128, so theres nothing where i can assume a problem.

I do have a MEMCAL for a 5.7L TPI 7730-ECM, will that one work on this 6-cyl when i put a V6-Software in it's PROM? (i have Tunercat and PROM-Equipment, i'm just unsure if a V8 MEMCAL can work on a V6)

Re: strange ignition issue on 91 3.1
 

The 8 cylinder MEMCAL won't work for a 6 cylinder calibration.

For the misfire check the timing chain. These 60* V6's eat timing chains. Not sure why, but within 60K miles they are _very_ loose.

Couple other items: if it is an auto transmission an idle learn is required every time battery power is disconnected from the ECM. Can find the idle learn procedure on the V6 board here at TGO.

The injectors go bad and short out when hot. This will cause the engine to run badly and stall.

RBob.

Re: strange ignition issue on 91 3.1
 

thanks for your answer.

Meanwhile i put in new fuel injectors with no change on the problem.

The Timing Chain is a good idea.

So do you think the MEMCAL could cause this? if not, i'm going to replace the timing chain, if yes i get a new (and correct) MEMCAL first. The strange thing is, with unplugged EST-Connector there is no further Missfire, that appears only when spark advance is controlled thru the ECM.