Significant Intermittent Power Problem

[dennisst99]

Hello and thanks in advance for looking at this. Sorry for the length but I'm stumped!

 

I have a 1999 Chevy 1 ton express van with a 5.7l engine auto transmission. The van has 183000 miles on it but up until recently has run like a top.

 

I am having 2 problems with the van (both are new problems) :

 

1. It will not start in the morning without starting fluid (sometimes in the afternoon it needs a shot as well)

2. On hot days it looses power to the point of not being able to move more than a few inches (yes inches) a second. (I can keep it running but it is a struggle!) When I press on the accelerator it just seems to be sucking wind and it has an occasional backfire but mostly just no power.

 

What I have done:

1. Pulled OBDII codes and found that there was an egr and o2 sensor issue. I pulled the egr and it was indeed stuck open so I replaced it and the o2 sensor. I have no more codes pending or set. (no difference with starting and as I found today no difference with power issue when hot.)

 

2. Just so I could say I did it I replaced the fuel filter.

3. Hooked up a fuel pressure gauge and found pressure to be between 55-60psi. While the vehicle was in it's failure prone state I took it up a couple of hills and the problem occurred but there was no drop in fuel pressure. (It actually rose a bit.) Pressure will also hold for over 20 minutes before dropping.

4. I have cleaned the MAF sensor. After cleaning (with an aftermarket spray solvent) I drove it with a OBDII scanner plugged in and recorded MAF sensor output against throttle position and both tracked as expected with no hint of the signal bouncing around on either sensor.

5. While in the failure state I pulled off the road and sprayed the ignition module with some freeze spray to try and see if it was perhaps acting up when hot. At first this actually seemed to help but I couldn't reproduce the results later in the day so I'm skeptical.

6. Swapped the coil with a known working vehicle.

7. A friend who is a mechanic told me that he had seen problems with the composite intake manifolds on these vans. According to him they can crack and develop a vacuum leak. His suggestion was to carefully spray brake cleaner around the manifold to see if I notice any difference in RPMs or performance. So far I haven't.

 

An interesting event happened this afternoon during a particularly bad power-loss episode, I stopped for gas and to just think things over a bit and that is when the idea for cooling the ignition module hit me. As I said previously, this actually seemed to work but then it dawned on me that 2 things had actually changed- the temperature of the module and I had gone from 1/8 tank to a half. Once again, as I already stated, the fuel pressure readings seem to not point in the direction of a pump or other pressure problems and I can't really duplicate the success with the ign. module.

 

As an aside I replaced plugs, wires and the distributor cap less than 15,000 miles ago.

 

Any help would be greatly appreciated.

 

Dennis