96 GTP (x motor) stalling FIXED

[haro1225]

Ok, this has been going on for a little while and I can't figure it out. The car runs perfect except when slowing down to a light it stalls almost every time. Seems to happen between 40-30 mph whether or not its in neutral or any other gear. Its not too big of an issue but it is slightly annoying. Most of the sensors had been replaced due to another issue we had before when we first got it. I also can't find any vacuum leaks.

[CMNTMXR57]

Even IAC? MAP?

[haro1225]

Not the MAP, IAC is new though. And no codes.

[crash93ssei]

Can you put it in neutral and keep it running by giving it a little throttle?

[CMNTMXR57]

TPS? You've ensured that the TB is clean of EGR soot and that the blade closes, just enough to leave a little gap?

I'd say it sounds like a fuel delivery issue.

[haro1225]

TPS was changed, and throttle body cleaned. And yes I can keep it running in neutral with some throttle.

[CMNTMXR57]

Have you put a fuel pressure gauge on the fuel rail, pressurized it (don't start yet), and see if it's low? IF it isn't and it's getting pressure, that leads me to bad injectors... If you have access to a T2, while you have that fuel gauge hooked up, you should be able to do an injector balance test. Basically it'll cycle each injector. As an injector fires, fuel pressure in the rail should drop a say 5 - 10 psi. Really take the concensus of that the injectors are dropping it, and then find the one that DOESN'T drop the pressure... In this case, it sounds like it may be more than one!

[BillBoost37]

Have you considered relearning the throttle position? Might be off a smidge and closing more than it should. Since you are DBW it's also your low speed idle, you don't have an iac.

[crash93ssei]

Have you considered relearning the throttle position? Might be off a smidge and closing more than it should. Since you are DBW it's also your low speed idle, you don't have an iac.

This issue is not on his GP, but on a '96 GTP with the 3.4 DOHC V6, no DBW mess to deal with

[CMNTMXR57]

Yea, I was gonna say, all cable/pulley here.

But somewhat the same concept as I called above when I asked if the TB was free of EGR soot and whether or not the throttle blade wasn't open sufficiently at idle. But Ryan said it was cleaned and ok.

[Zeik75]

Reminds me of leaving a manual car in a high gear snd stopping, usually stalls the motor out... Idk if it applies here though.

[haro1225]

Unfortunately I don't have access to a Tech 2 but I'm going to check the fuel pressure and test the MAP sensor over the weekend. I may get a video of it happening too.

[CMNTMXR57]

Dumb question... (I'm pretty good at these).

Does it idle fine if in park, just sitting there??

If so, I wonder if a faulty vehicle speed sensor? Or possibly in the trans like a TCC solenoid not wanting to disengage...

[Zeik75]

Wfy would the vss cause it to stall?

[haro1225]

It does surge slightly at idle in park, but not all the time.

[CMNTMXR57]

Wfy would the vss cause it to stall?

If it's reading too low, it may be reverting the vehicle back to 650 - 750rpm idle setting while the torque converter may still be engaged, snubbing it similar to if you don't push the clutch in, when you brake a vehicle to a complete stop

[CMNTMXR57]

It does surge slightly at idle in park, but not all the time.

Normally I would say a post-MAF leak, which on the "X" motors, I always found it to be where the upper intake plenum meets the lower plenum, and bolts being stripped not allowing proper torque spec. Or, '96 versions GM allowed for separation of the upper intake plenum from the TB tube ('95 and earlier it was all one big PITA). That little gasket in there could be bad. Problem is, this things' PCM, being as sensitive as it is, would throw a lean code for sure. So I hesitate to say go look that way, but it doesn't hurt to have it in the back of your mind... Had they recently removed it to do the rear plugs?

Here is a pic of a '96 (mine), upper plenum removed with the TB side facing up...

[haro1225]

The plugs were changed (so they say) when they swapped the engine while it was out of the car but I'll look into that too.

[haro1225]

Ok, so I think its fixed. I took off the map sensor and tested it at work. The sensor failed but, IT WASN"T EVEN THE RIGHT ONE FOR THE CAR! when I looked it up. According to the Wells sensor book, the one that was on this car is for a Cavalier. I took the correct one from an 02 Lesabre in the junkyard and put it on. I drove it about 5 miles and it didn't stall, and the idle is stable now. I'll give it a couple days and see what happens with it.

EDIT: Its doing it again, I have no idea why it didn't do it for me but they went out last night and it stalled a few times.

[CMNTMXR57]

If you have replaced the MAP itself, and it temporarily seemed to work, but then became problematic again, I would start looking at the plug, connections, harnesses, etc... This is indicative of an intermittent problem which usually results in poor contacts in the plug.