91 beretta 3.1 rough idle and dies

91 Beretta dies after running anywhere between right away/15seconds and 5minutes.

Sometimes it runs fine, sometimes it runs rough. Cannot drive the vehicle at all because of how bad it runs.

Swapped the IAC Valve with a working beretta, no change. Also have changed/checked/swapped: computer, crank sensor, knock sensor, upper + lower intake gaskets, ignition module (and had NAPA test new one), swapped the coil packs, new ($130 stinkin dollars) crank sensor to ignition module wire harness, spark plugs, wires.

Also checked for vacuum leaks.

Kind of at a dead end here. No lights/codes at all.
Have a snap-on modis to do diagnostics with.

Ideas?

Check for loss of spark and fuel pressure when it dyes.
What is fuel pressure readings?
Go from there. That old snappy Modis should be able to help you out.
Is it doing anything like losing RPM signal or injector pulse?
What is fuel trim and block learn on it?
Give that computer the old tap/twist test.
Tap and or unplug Maf sensor?
MT

OLD snappy modis? thing is brand new :P

Going to check for spark and fuel pressure again. Very sure fuel pressure is AOK.

As far as the computer tap/twist test... we have 2 computers now.. original and replacement.. neither makes any difference.

Will also check MAF sensor per your suggestion as well as the other items.

Just so we're sure on this... the car does all of this idleing in the garage... without even trying to drive or move it at all.

Car is a 1991 Beretta 3.1L 5spd-man.

Will keep post updated with findings

OLD snappy modis? thing is brand new :P

Going to check for spark and fuel pressure again. Very sure fuel pressure is AOK.

As far as the computer tap/twist test... we have 2 computers now.. original and replacement.. neither makes any difference.

Will also check MAF sensor per your suggestion as well as the other items.

Just so we're sure on this... the car does all of this idleing in the garage... without even trying to drive or move it at all.

Car is a 1991 Beretta 3.1L 5spd-man.

Will keep post updated with findings

10-4 on the modis
Good scanner.
Watch the rpm signal close. The crank sensor can lose rpm signal.
Also there has been a lot of prom updates on them.
Can you post scanner ID on prom and pcm service no. and engine code?
MT

We are losing spark.. Varies from almost immediately to several minutes...

Doesn't matter if the engine is cold or hot.. same response. No difference in amount of time it takes to lose spark either.

Not losing RPM signal or injector pulse.. Fuel trim short +long term are in spec. Belive the block learn was 128..???

MAP sensor voltage and HG is in spec, but have 0 volts on barometer and 0 HG on barometer.

There is no MAF sensor on this motor.

Info you requested:

Engine code: M1G3.1V8XGZ6

PROM: AUXY3828
Serv. no: 01227730

Sounds like an ignition module and/or a crank sensor. Both very common on 3.1 motor. can take the module off and get it checked for free at most any good parts store, ie. Advance, NAPA, Autozone. When warmed up they both can show their hind end.

Thanks for replying

As I said in my first post.. the crank sensor has been replaced.

We have 2 ignition modules. Have been tested @ napa on their bench and show as being good.
(Test was run 9 times, passed with flying colors)

Update: Just learned that the tech that took the modules to get tested went to autozone, not NAPA.

Do not depend to much on off the car module testing.
Do have the trouble shooter cartiage for the Modis?
You might want to run a voltage check on the ign module.
Also if it has a tach on it disconect it.
Post back vin and built date and prom Id 4 digit no.
And I will do some digging.
Certain one had a know ign module problem and a lot prom updates on the PCM to.
MT

Also
If the modis has the lab scope built in it on it get in there and there should be some test in the lab scope part to test the ign module and other sensors.
Let us know how it goes.
MT

Hi, im new on here. I saw this and had to write! My beretta is doing the same thing. Did you ever get it figured out? PLease let me know of anything. this thing is driving me crazy! Mine is a 92 3.1. Please help! Thanks a lot JP

what is your fuel pressure? Loss of fuel pressure will shut the ignition off. My 91 Cavalier 3.1 did the exact same thing you Beretta is doing, and it was a bad fuel pump. Occasionally it would pop a MAP sensor code when it died. IT would start and idle, sometimes rough, and die as soon you touched the gas in gear. That factory ECM number was fairly problematic, so if it's original, it may be your issue also. The lack of trouble codes makes me lean toward the ECM.

I havent actually measured the fuel pressure, but I just put a fuel pump in it (I thought that would fix it) and it will spray a foot and a half up in the air at the schrader valve at the intake.

I havent actually measured the fuel pressure, but I just put a fuel pump in it (I thought that would fix it) and it will spray a foot and a half up in the air at the schrader valve at the intake.

How many lbs to the foot of spray does that add up to?:grinyes: :lol:
That is not really the safe and right way to check fuel pressure.
Put a gauge on it and post back the fuel pressure readings.
MT

I figured mine out. 1 bad injector shuts the whole fuel injection system down.