Engine/Transmission (1998.5 - 2002) truck dies when hot at intersections

[Shamp]

My brother in laws truck is a 98. 5. He is complaining to me that his truck will sometimes die at intersections once the truck is warm. 400k ish miles on his truck, his vp was replaced about 6 months ago from a donor truck with 125k ish. He has a basic upgraded lift pump with idiot light. He says he changes fuel filters every 5-6 months. That is the background of the truck, the dieing problem started after he had a mechanic install +40hp injectors. If we assume injectors are not faulty and mechanic is not to blame, my thoughts to him were injection pressure. Injectors with larger holes in addition to a vp-44 with unknown wear and tear. Perhaps his injection pressures were already on the low end of acceptable for stock injectors and with the larger orafice there is not enough pressure for for proper atomization? He says the 40hp injectors are new. I was thinking maybe adjusting the injector pop pressure might help. I am not sure with the vp if pressure is controlled by the pump or shiming in the injectors. I own a CR rig and do not follow the earlier gens as closely to give him much help on his fueling problems.

 

[Bob4x4]

All injectors are not created equal,I think I would pull the injectors and have them tested,not much money involved there. That being said over 100k on a used pump of unknown history... ... ... If it is a manual trans truck I have seen the apps not being able to keep a good idle.

 

[JR]

Is the truck triggering a cel when it stalls out? If so he needs to get the codes pulled with a scanner that will probably give a direction to start looking. 40 horse injectors shouldnt be enough to cause the truck to stall when idling, but if they havent been pop tested it is a possibility. Also tell him he really needs to put a fuel pressure gauge on his truck to monitor lift pump pressure. The idiot lights usually dont trip until 3-5 psi, at that pressure he will be burning his pump up. Vp44's have two chronic weaknesses - running them on low pressure and the ecm. The pumps are lubricated and cooled by fuel, he needs to be having a minimum of 12 psi to the pump. I personally run closer to 20 psi at idle, and this is my reasoning. The overflow valve on the return line of the vp44 is set at 14psi. So anything below that and your only supplying fuel to the injection pump. Keep your pressure up above 14psi and the overflow valve opens and now your supplying a constant flow of cool fuel through the vp, keeping it as cool as possible. Vp44's have an ecm mounted to the top of the pump and heat soak is a major factor in how long the ecm lasts. So all in all, by keeping the higher pressure Im supplying more than enough fuel to the pump and Im keeping it as cool as I possibly can. Again, this is just my theory and I havent tested it long enough to know if it will prolong the life of my inj pump, only time will tell. But he should be keeping it above 12 psi at a minimum, to be safe.

Let us know whether or not your brother in law has any codes, and we can go from there.