96 Yukon starting problem

[gmchevy]

I have a 96 Yukon that isn't very dependable right now. ~Year ago changed fuel filter and fuel pump. Not fun! Recently it is not wanting to start, like it is not getting gas. If you turn it over it won't start then stop then hit the key again and most of the time it will start. It has been getting worse over time. I just changed the fuel filter again to see if it helped and it did not make any difference. Is there anything to check, maybe fuel pressure while it is turning over? I really want to fix it myself and not take it in. Any ideas??

Thanks

[gmchevy]

Well, I purchased the fuel pump today but I hate to drop $200 plus go through the hassle if this may not be it. I should do it this weekend. Any ideas before I jump into it?

Thanks

[maxwedge]

A routine check of the fuel pressure will confirm if the fuel pump is bad, basic diagnostics can save lots of money and time.

[gmchevy]

Where can I plug in and test the fuel pressure? I don't see a test tee any where in the fuel line but maybe I am not looking in the right spot. I lowered the tank a little bit and checked the electrical plug and it looks fine with no obvious signs of shorting out. That is what one guy told me to look for.

[gmchevy]

Okay, I checked the fuel pressure and it is 53psi. I checked the wiring harness and I have a good ground plus when it is cranking over I have power to the plug at the fuel pump. I also changed the fuel pump relay to rule that out. What else could it be? I just don't think it is the pump. After I changed the relay it started right up 5-6 times in a row and I thought maybe that was it. Then I tried it again and it wants to fire up but just can't quite get there. Couple of more off and on's and it finally started. So basically I just wasted $12 bucks on a relay. HELP ME!!

[2000CAYukon]

Fuel pressure is suppose to be 60 - 65 for your engine. It could be the regulator but you have to take the upper intake off to even see it. Normally, you plug the vacuum line going to the regulator and the pressure from the pump will be max. I am not sure if there is a vacuum line to your regulator or if it plugs into a port on the intake.

Bottom line, the fuel pressure is too low.

//2000CAYukon

[gmchevy]

One thing I just noticed. When you turn it off and I have the hood open, I hear this weird ratcheting type sound coming from under the intake. Any ideas? Could this be the fuel regulator? It kinda goes on twice after you turn off, it is real quick noise. My wife said she has never heard that truck do that before.

[gmchevy]

The latest: Figured what the noise at the intake was. Little thing attached to the carburator that has a plug going to it. Solved. I see the fuel pressure regulator right to the right of the carb and it has a really small vacuum line going to it and the hose coming off the top goes to the PVC. How do you know if the fuel pressure reg is bad?
Okay last night dropped the fuel tank replaced the fuel pump reinstalled the tank. Put 5 gals of gas in the tank and it started right up. But I checked the fuel pressurre and it is about 55psi now. Before it was 53psi. I checked a few ignition things and they look pretty good. I will drive it today and see if I get stranded.
I was reading the service manual and it talks about a fuel pump test terminal in the engine compartment. DOES anybody where or what this looks like?

Thanks for all the help.

[gmchevy]

Drove the truck this morning and 1/4 mile down the road it quits. Restarted it and quickly turned around and when I pulled in the driveway it quits. Parked it! Runs great when its running. Will run non stop sitting in the driveway. Anybody got any ideas on whats next besides the repair shop?

gmchevy

[MT-2500]

Originally Posted by gmchevy

Drove the truck this morning and 1/4 mile down the road it quits. Restarted it and quickly turned around and when I pulled in the driveway it quits. Parked it! Runs great when its running. Will run non stop sitting in the driveway. Anybody got any ideas on whats next besides the repair shop?

gmchevy

Here is some guide lines for fuel pressure testing.
Run the test and Post back readings.

Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.

[gmchevy]

I don't have all the answers to the previous questions but here is what I have done. Borrowed a new MAF and MAP sensor and the truck runs great. Fuel pressure is up at 60psi. No leak down. When the truck revs up it is a little higher pressure. So I am guessing that it was either the MAF or the MAP. It did stall on me right after I put the new parts on but hasn't stalled as of yet. I will drive the crap out of to put it through a good test. If it doesn't stall then I guess it is all done.

Thanks
gmchevy