Tune up help - Hard starting when hot

[010175]

I have a 1999 with a 5.7 engine in it and 150,000 miles. It starts right up on the first start of the day. Last week it got real hard to start when the engine was hot. You have to turn the engine over a long time before it cachets. When it dose cachet the RPM are about 400 and then slowly moves to 600. I replaced the plugs but that did not help. I noted that the tail pipe had a LOT of black soot in it. I also have 1996 5.7 and looked in that tail pipe and saw very little soot. Any ideas on how to fix the starting problem? Any help or ideas would be great. Thanks Dave

[2000CAYukon]

My neighbor has a 97 that had the same problem. I put a fuel pressure gauge on it and when he turned off the key, the pressure dropped pretty fast. The fuel pressure regulator was bad spilling gas into the engine, flooding it and making it hard to start when warm. Overnight, the fuel would evaporate making easy to start in the morning.

The bad news is that the fuel pressure regulator is under the top half of the intake manifold.

//2000CAYukon

[010175]

Thanks for you help on both my problems. The way I understand it is I must take off the intake manifold to get to the fuel presser regulator. Is this true? I was at NAPA buying anti freeze and ask them about the soot and being loaded up when hot. They said that there is an air mixing valve part that might be bad, that is by the manifold somewhere. They said it was not a returnable part because it was electric and the cost is $89.00. I am not so sure they know too much about this, but they might. Do you know what they are talking about and might this be the problem? I have a 1997 2door Tahoe and a 1999 suburban so I could switch parts to test for the bad part if needed. Are there any other parts might be bad before I remove the manifold to replace the fuel pressure regulator? Thanks Dave

[2000CAYukon]

Originally Posted by 010175

Thanks for you help on both my problems. The way I understand it is I must take off the intake manifold to get to the fuel presser regulator. Is this true? I was at NAPA buying anti freeze and ask them about the soot and being loaded up when hot. They said that there is an air mixing valve part that might be bad, that is by the manifold somewhere. They said it was not a returnable part because it was electric and the cost is $89.00. I am not so sure they know too much about this, but they might. Do you know what they are talking about and might this be the problem? I have a 1997 2door Tahoe and a 1999 suburban so I could switch parts to test for the bad part if needed. Are there any other parts might be bad before I remove the manifold to replace the fuel pressure regulator? Thanks Dave

Dave,
I am not familiar with the air mixing valve that Napa is talking about. I suggest you get a fuel pressure gauge and verify that the fuel pressure regulator is not your problem. When I tested my neighbors 97 Yukon, the pressure dropped very fast after turning off the key. Within 30 seconds it went from 60 to 30 PSI.

Yes the FPR is under the top half of the intake and is not a fun job.

Sorry I can't help you with the air mixing valve. Could they be talking about the MAF (Mass Air Flow Sensor)?

Since you know you are running rich, it could be 02, MAF, FRP, a leaking injector. A fuel pressure test should really be done first before throwing parts at the problem.

//2000CAYukon

[010175]

I will get the fuel pressure tested next week and let you know what happend. Dave