Beretta dies when trying to leave from idle, help needed

[No Quarter]

HI, my 1991 3.1 has a problem the shop can't fix. It idles fine, but as soon as you push the throttle just a little, it totally dies. If you''re fast enough to let go of the throttle, it can stay alive. The shop has replaced IAC and Crank Position sender, but no change.

Any ideas? The shop seems to just replace parts at my expense until it works?

[1988GTU]

Codes? Check tps voltage readings? it should sweep pretty smoothly in values.

[No Quarter]

I doubt it has meaningful codes, besides the ones that led GM to replace the IAC, but I don't know. I myself have had the TPS off, and with a simple ohm-meter it looks smooth.
Thanks

[No Quarter]

I asked GM why they wouldn't know what to do, couldn't they see the culprit on their computer?! They say it's so old they can't see a lot. Meanwhile they replace parts at my expense.

Didn't we have someone in here that worked at GM, that I got in contact with? It's been many months since I was in here, because until now, it's just been running and running and running

[Rettax3]

I too would be looking at the TPS, but also the MAP sensor. Make sure that the little vacuum hose to it is good, and that everything is hooked up all the way to the manifold. A vacuum pump (like a Mightyvac) that is hand-held would be a good way to test the MAP sensor, watch your meter to look for voltage changes. IIRC, grey will be the 5 volt reference input, light green is the signal out, black is ground, but GM changed their color-codes right around '89 to '90 on some of those systems. Fuel pressure should also be looked at. I am not sure what resources you have where you are, but borrowing a fuel pressure test gauge would be a good free option. Watch it while bumping the throttle. Unfortunately, these cars are getting old enough now where that one in a million ECU failure is becoming one in 10 thousand. , and I have seen a few now. I would not bother with the dealership anymore -they obviously cannot handle your car. Find a good local independent shop you can trust. Good luck.

[1988GTU]

Checking it off vehicle may not expose a bad connection/harness. Re-check it while on vehicle to see what the ecm is receiving and if they coincide with each other.

[Rettax3]

@1988GTU: I agree. Typically at our shop, we back-probe into the harness at the connector to get real-life sensor signal readings. Using an actual lab-scope is even more accurate than watching a scan-tool trying to communicate through the slow OBD datalink connector too. But even a volt or Ohm meter can be useful here, if that MAP sensor has gone bad enough to cause this problem. Dito for the TPS and any other sensor. CTS (Coolant Temp Sensor) could be throwing the whole fuel mix out enough to cause the issue too, especially since it sounds like the problem gets worse when the engine is warm, but it may not even be a sensor issue...

[No Quarter]

OK, this is getting serious now, help needed. I’m beginning to doubt we’ll ever get it running again. I’ve tried all I knew, then the local garage gave up, then it was transported to GM where it was bought 25 years ago, and they had it for 2 weeks trying stuff, and couldn’t solve it! I haven’t seen their bill yet, that will be a battle. So now it’s back in my home garage, and I just try to replace stuff, after reading 50 pages in the Service Manual. And no change.

It’s a shame if we have to scrap it, it has only 65k miles on it, and no rust, so should have many miles left…
Has anybody tried something just a little bit similar? And didn’t we once have a GM Tech posting here here

Here’s an update:
--
Symptoms:
It started weeks ago where occasionally the throttle response would be bad when cold, occasionally the first 5 mm of throttle would not change rpms and then it came, and otherwise it drove fine

Then on a normal drive, it died. I restarted and at that time the throttle could be pressed 2-3 mm, so we could limp home, but now it’s worse.
Most times it can’t start. When it does start, it can idle (forever?), but the split second, and I mean split second, you press the throttle just 1 millimeter, it dies. If you’re fast enough and lucky and let go of the throttle while the engine is still turning, it’ll stay running, but mostly it’ll just die when the throttle is touched

--
What has been replaced:

Crankshaft position sensor
Throttle Position Sensor
O2 Sensor
IAC
Coolant temp sensor
ECM (had an old version, it gives exactly same symptoms, bought it when we bought the car 5 years ago because the idle was racing)
MAP sensor
Battery
Ignition module
EGR, both a new module and also just blocking passages with gasket

--
Analysis:

According to GM mechanic fuel pressure is fine, all wires rested with ohm-meter. He had a piece of equipment that he showed me that read both 500-700 rpm when trying to start and also on the same display 0 rpm, and he said that was wrong. He said that he could get the engine to run, so it must be fuel missing
I’ve tried having a plug cable tester on when idle ran, and there’s spark, and when it dies by pressing throttle or simply won’t start, there’s still spark, so it must be fuel missing
I’ve had a vacuum gauge on, 17 steady at idle, seems OK?
I’ve tested starting it while having the O2 sensor out, to test for collapsed catalyst, no change
I have a Tech 2, it only goes back to 1992 and if I select “F” and 3.1 V6 I can see data, 38 data point, but don’t know what to look for? Ideas? It had one DTC MAP wiring or something, but just had it disconnected, so probably why.

--
So what is it that happens on the fuel side? That is apparently totally malfunctioning when throttle is even touched? I’ve googled a lot, and while I found many issues with 3.1 non-start condition, I haven’t found any symptoms like mine, that it dies when touching the throttle ever so lightly.

Help needed! If you can’t help, do you know any GM gurus that might?!

Desperate…

[1988GTU]

FPR or injectors were never verified for being good?

[No Quarter]

Not sure, only thing I know is that GM mechanic said that they tested fuel pressure as good. I may have to try injectors and FPR, but takes time to get and cost $... But it's a possibility

[No Quarter]

So another frustrating morning, testing all the things I've thought of and read in the books, read here and on the web in general. Today I couldn't get it to start and idle, I could get it sometimes to fire and then run trying to find an decent idle for 1-2 seconds, and sometimes no sign of ignited combustion at all.

Today I tested as follows:
-Makeshift fuel pressure gauge , shows about 40 psi and it holds that pressure
-Had battery off, maybe a relearn (both of these things were done at GM according to the mechanic, but I'm retesting out of desperation)
-Cleaned the plugs, all were fouled, dark soothed
-Put test lamp to the two pink/black wires to the injectors, yes power present all the time when ignition on
-Put test lamp to the light blue and light green injector pulse wires, plenty of pulses of light, a bit weak, but the book says that that's okay
-Had 3 plug wires out to check they all gave spark, not just one, ok
-The mechanic said that the Tech 2 showed no rpm when cranking, and that that was a problem. He's right, I can now see it on my Tech, see pictures in the following posts, when I run the starter and it doesn't fire at all, it shows RPM=0. The times when it fires it shows RPM, but since I can't get it to keep running it soon dies, the Tech 2 continues to show RPM going down. So in my logic it's not as if it dies because this RPM signal fails, the RPM signal records the slowing of the engine. On the other hand, as stated, it shows RPM=0 until it fires. ?????????????

To me the biggest mystery (besides that I haven't pushed it off a cliff yet) is the following: An engine needs air, fuel and spark. I can see it gets spark anytime I crank it, and think/thought it likely to be lack of fuel/injector problem. But...how can the plugs then be soothy black? That indicates fuels and no spark. Could the spark be timed wrong? Am I only seeing the "waste spark"???

And how does all this work with the three different symptoms:
-No start
-Start and immediately dying
-Start and able to idle, touching the accelerator the slightest makes it stop

[No Quarter]

Here are 5 pictures of what the Tech 2 tells me, ignition on, engine off (since I can't get to run)

Do you see anything out of the ordinary?

Notice on top here the Engine speed that I talked about in previous post, and that the GM mechanic was an error

[No Quarter]

The other pictures

[No Quarter]

Picture 3 of 5

[No Quarter]

Picture 4 of 5