Problem came on suddenly while driving on a trip. I can run up to 80 mph if I ease up very slowly, but motor will die anytime, even at idle, if i crack throttle enough to drop vacuum to zero and get boost.

New battery (guages had been sweeping on start-up for a while before problem developed), one new coil (found a bad coil a few days before problem developed). I have since changed fuel filter and fuel pump relay in underhood panel andfuel pump resistor at inner cooler pump.

Also tried returning PCM to stock programming also incase program had been corrupted. Have new y fitting ordered and plan to drop tank and swap in the stock pumps I pulled out of my other L and change Y fitting this Saturday if I can not figure anything else out before then. Just do not want to do all that work and discover that is not the problem either. Any diagnostic help would be appreciated.

 

i remember about 2 months ago someone posted similar problems, they discovered they had a bad alternator and the vehicle wasnt making enough volts to power the truck under a load. i would try to test your charging system and maybe you have the same problem. it sounds electrical to me..
good luck

 

check/clean all the power and ground connections on the main bettery cable. it connects the battery terminals to the starter solenoid on the firewall, the starter and the engine chassis grounds.

when it dies, does all the power on the truck cut out? like gauges, radio, lights, etc.

 

the main thing that i can tell you is that your computer seems to be re-setting itself everytime your gauges sweep. which is why i brought up the bad alternator/battery problem..

 

Bet you that its a fuel pump.
Ordering the Y is the smart bet.
If you have a fuel pressure gauge, check to see if your fuel pressure increases or drops when you give it gas.

 

The battery was replaced and the coils are firing while the motor is dying, should be lack of fuel. Bought a mechanical fuel pressure test gage tonight and will check fuel pressure before pulling the tank.

Checked for codes and found none. The sweeping of gages on start-up went away with installation of new battery, problem did not. It has been driven several hundred miles in this state, so alternator is not a problem.

Thanks for the suggestions.

 

Update - The plastic Y was intact, but the hose between the y and the high pressure pump had slipped almost off the pump discharge outlet. Some residual bend in the hose was keeping it on, but looks like when the pump would kick on, the pressure would lift the hose enough to cause complete pressure loss and then the hose would drop back down when the pump was off and thus seal well enough to keep some pressure. Something a little different. Have spare SS and plastic Y's should I ever need one again.