96 gmc jimmy 4dr 4x4 cold start throttle down

[stealthprey]

this car is weird. It has had a tuneup about 500 miles ago. plugs(acdelco platniums), cap, rotor, wires. Has had new fuel pump put in. about 300 miles ago. pressure is pushing at about 63 at turn key. Has these new parts to help figure it out: tps, ambient air temp, coolant temp sensor, coil, crank sensor, cam sensor, lower intake gaskets(steel ones), upper intake gaskets. Now these are from the yard: mass air sensor, ign module and coil combo, idle air valve. Have an egr valve but have not put it on yet. grabbed an ecu but for a 99. doesnt have that plug in the middle what ever that does.

Now for the problem: if temp is over 60degrees outside fires up and runs perfect. If colder out starts runs at 1200 rpms for split second then dies. turn key again and wont start. Hold the throttle half way down it will start hold the throttle down so does not die about 2200 rpms. if hold it there for about 5 min or till warm it will be fine. It fouled out all the delco plugs already they are pitch black. changed them out.

Dont want to keep throwing that much more at it. It pulls so much vacuum at the pcv port that the valve rattles. put a gauge on it for vacuum when it is running at idle it shows about 19psi or so. The weird part is it also is showing running at anywhere between -19 degs to -35 degs. runs fine but I think that is wrong or part of the issue.

I have people saying possible fuel pressure regulator, maybe knock sensor for the timing bouncing issue.

Any ideas here?????

Thanks for any help guys appreciate it.
Chris

[ctwright]

you said pressure at 63psi turn key. you also want to do a hold test, to see that it holds pressure, i don't know what the specs are for your vehicle though for the hold pressure, but if it doesn't hold after about 5 minutes or so and is below specs, you then want to do test again and this time clamp off the line either before or after the gauge, to determine where the leak down is, if you clamp off the line before the gauge, and it still leaks down then possible leaky injectors, leak leading up to the fuel rail, or around the fuel rail, or bad pressure regulator, if you do the test with the line clamped after the gauge and it leaks possible fuel line leak in the feed line from the tank up to the gauge somewhere or bad check valve in pump.

[stealthprey]

I know when I had it good and running. It was at 63 turn key. When it started and was running it would drop to about 55 and hold stable. So reason I keep thinking fuel pressure regulator is having issues. But no idea. If I can get it running tomorrow I will try to do a leak check. I know when u turned the car off it would start going Down fairly fast. However tomorrow s temp is like 22 don't know how much luck I will have.

[ctwright]

you said when you turn the car off it would start going down fast, that is what i meant by to doing a hold test, after you shut the engine off, you don't have to wait until you get the engine running, just turn the key on, note the reading on the gauge, turn the key off and see how the pressure holds, it shouldn't leak down fast,. If you can notice the needle moving after you shut the car off it is leaking too fast, then do the clamp test to determine where it is leaking at, due to the fact that you have smoke i believe it is possible that the fuel is leaking into your cylinder(s), it may be flooding because a faulty fuel injector. After I got pressure in the system i would pull up the fuel rail to check and see if that is the culprit before getting a pressure regulator.

[Blue Bowtie]

Test the CTS resistance at a known temperature. I know the CTS was replaced, but it sounds like the PCM may think it is considerably colder than it actually is. This will cause a very rich mixture as you describe.

A leaking line set, FPR, or poppet wouldn't care if it was above 60ºF, but the CTS would. Even if the CTS is new, the wiring isn't. Since you stated

The weird part is it also is showing running at anywhere between -19 degs to -35 degs. runs fine but I think that is wrong or part of the issue

that should be a clue that the PCM doesn't know the temperature and is defaulting to full rich for injector PW.

[ctwright]

yeah i was thinking the same thing but also thinking it may just be coincidence about temp due to the fact it is colder in the morning, and warms up some during the day, and the real problem may be after the car sits for a long period of time, not the temp, and also said replaced CTS but however that still doesn't mean anything that could still be it so check it like he said. Was I right about that though, is the problem you are having like the first crank of the day then fine after that until it sits for long period of time?

[ctwright]

Originally Posted by ctwright

due to the fact that you have smoke .

I had your post mixed up with someone else.

[stealthprey]

Well not too bad out today. Yes it has leak down. U can watch the gauge drop down as soon as u let go of the. Key. Not dramatically fast but u can watch it drop. I would say coolant temp but by scanner it reads within about 4 degrees of what weather channel says it is outside. Today swapped out egr valve from the yard. Changed the fuel pressure regulator out with new one. Swapped ecu with a newer model one. Doesn't have the middle plug in it. Does anyone know what the middle plug goes to. Still has same symptoms. It acts just like the other. Person posted a faulty coolant temp dumping in too much gas. When I changed pressure regulator didn't see any spots where fuel would be leaking at least in the upper intake. The chances of every fuel injector bad is too slime I think.

[Schrade]

Static fuel pressure test:

Leak down of fuel pressure is injector pintle open, FPR bladder ruptured, leak in line, or bad check valve in pump.

DO NOT PINCH / CLAMP the gas line. You don't know for one if you've actually clamped it tight enough to hold. For 2, if you have clamped it tight enough, you will damage the line.

CAP the return line AFTER the FPR. Prime the rails, let the pressure drop, and then pull the vacuum line off of the FPR. If wet, the bladder is ruptured. Replace FPR.

If dry, look for leaks in the line from the tank to the FPR. If leaking, repair.

If no visible leaks, an injector or the check valve is leaking. Check injectors first - I don't know if you have to pull them or not to see... In vette TPI, you do.

Dynamic FP test:
Measure at idle WITH vacuum attached, with vacuum dis-connected, and pedal down.

At idle with vacuum attached, rev the motor slowly. Pressure should drop significantly, as FPR responds to vacuum - this simulates acceleration enrichment.

I'll check the other 2 conditions later - I can't remember at the moment what to observe...
edit:
one of them checks the condition of the spring in the FPR diaphragm...)

[Schrade]

Originally Posted by stealthprey

Today swapped out egr valve from the yard. Changed the fuel pressure regulator out with new one. .

A faulty EGR (carbon-fouled pintle valve) will behave like a vacuum leak. The motor will lope idle, up and down rev's, at idle.

ANY vacuum leak will cause loping idle.

[stealthprey]

no vacuum leaks to my knowledge. Did one of the old tricks with brake cleaner since i have some. When it was running like a week ago I hosed down the intake and other areas and no idle up or change. Here is something weird that I noticed. If I start it and it is pissy and I have the throttle down some what to keep it running the brake light and the ABS light remain on til it stalls out or I push the throttle up higher. If I push the RPMs to 2500 rpms light goes out then if below lights are on unless running correctly. This may help with the diagnostic. If the car is running fine then those lights turn on the brake and ABS light the car will die. It is weird I am running out of ideas. Changed the FPR today and pressure stayed up better. If the fuel pressure must remain above 55 while no pump running for about 5 ish seconds then it is alright. what is also weird is I primed the pump did a couple things for like 5ish min then pressure was still up. I decided to put the old ECU back in because the newer one primes the pump on turn off of key also. The odd part was as soon as i disconnected the battery and unplugged the ecu and swapped it back out hooked up the neg of the battery this took maybe 3 min. the pressure dropped to zero, instantly. why would the pressure of the line drop with loss of power from battery and ecu change? It was holding pressure with the newer ecu the 99 for a longer time but it primed just after turn key. The 99 ecu also sounds like it changed voltage to the fuel pump. At turn key prime it sounded lower pitch than when I turned the key to off it had a higher pitch.

This vehicle is so weird. It has to be something easy though. Only has the issue when it is cold out!!!!!! However the timing degrees still bugs me. when it is warmed up and running it runs arround -35 degrees! the closest I have seen it to zero is -10deg for a split second. People have said that the knock sensor has a mojor effect in retarding the timing. But might not be back enough to throw the chk engine light on.

Otherwise it is still the same dumping too much gas in motor flooding it out. that is why starts up with the first attempt for about 2 seconds takes it to 1400 rpms the dies. Turn key again and starts for about 1 sec takes it up to 700 then dies. After that it just crank and cranks unless u hold down throttle to let air in because the cylinders are flooded. Not one all of them. It keeps making me want to say the CTS but it is new and the scanner shows it is reading the correct temp.

Chris

[old_master]

Originally Posted by Schrade

....CAP the return line AFTER the FPR. Prime the rails, let the pressure drop, and then pull the vacuum line off of the FPR. If wet, the bladder is ruptured. Replace FPR....

If you restrict the return line and allow pressure to rise above 75psi, the fuel pressure regulator diaphragm will rupture. Also, the regulator does NOT have a vacuum line connected to it on this engine. Key on, engine off, fuel pump running, is the only pressure test for CMFI and CSFI systems. GM does not publish any "engine running" fuel pressure specs, there are far too many variables involved.

[ctwright]

Originally Posted by Schrade

DO NOT PINCH / CLAMP the gas line. You don't know for one if you've actually clamped it tight enough to hold. For 2, if you have clamped it tight enough, you will damage the line.

I've never ran into a problem doing this, you take a rag and wrap it around where you are going to clamp the line to help protect it. But if somehow you were to damage the line it's better that than the regulator.

[old_master]

There is a warning in the factory shop manual. If you're using a Chilton or Haynes manual, it wouldn't surprise me if there wasn't a warning in them. A good CSFI fuel pump should build just over 100psi. It makes perfect sense that exposing the regulator diaphragm to that much pressure would rupture the diaphragm, (the excess pressure has nowhere to go). If you're trying to check max pump output, or trying to locate the source of a leakdown issue, install the shut off valve tool at the fuel filter. You won't damage any vehicle parts.

[ctwright]

Originally Posted by old_master

There is a warning in the factory shop manual. If you're using a Chilton or Haynes manual, it wouldn't surprise me if there wasn't a warning in them. A good CSFI fuel pump should build just over 100psi. It makes perfect sense that exposing the regulator diaphragm to that much pressure would rupture the diaphragm, (the excess pressure has nowhere to go). If you're trying to check max pump output, do it at the fuel filter. If you're trying to locate the source of a leakdown issue, install the shut off tool. You won't damage any vehicle parts this way

If you look at my original post where I mentioned doing the check you will see that I said to clamp on the feed line, one check on each side of the gauge, I never said to clamp after the return line, then the other guy came back and said to never clamp a fuel line, and to cap off after the regulator, that is when I came back and said never ran into problem of hurting a line when clamping, I wasn't saying to clamp off after the regulator I agree with you on that.