Engine/Transmission (1998.5 - 2002) Fuel Pressure-Towing

[jeepit]

While towing 7,000 lbs this weekend I had the following numbers: WOT-8lbs, cruising 10 lbs. I believe this to be normal? My question is this. Does my stock ECM and stock fuel system defuel when my boost and egt's start to max out thus giving me the 8lb reading at WOT?

 

[RustyJC]

Defueling happens internally and downstream of the VP44 - it shouldn't affect your supply pressure readings. 8 PSIG at WOT is the least I would want to see. I'm still on the original lift pump and see 16+ PSIG at idle, 14-15 PSIG at 70 MPH cruise and 11 PSIG or so at WOT when towing our 5th wheel (see signature).



Rusty

 

[PC12Driver]

The VP44 (injector pump) sucks harder as load and/or RPMs increase. The lift pump puts out a fixed amount of fuel. So, at WOT the demand for fuel increases but the lift pump is still providing the same amount (roughly), and the pressure will drop in the lines between the LP and the VP44, which is where your FP sender is at. The harder the engine works, the lower the fuel pressure.



Like Rusty said; defueling happens in the VP44 and reduces fuel to the injectors (the same as backing off the throttle). If the VP was defueling for whatever reason (overboost or rpm redline, not egt since there's no egt information going to the computer) you would see an increase in fuel pressures since the engine would be unloading.

 

[DieselLady]

This is exactly the same pressures I had while pulling a 13000 lb 5th wheel with my 99 with a stock lift pump. 8psi is just fine especially with WOT. J&S injection shop in Las Vegas, says as long as you are at positive pressure you would hurt any thing. I personally like over kill so I have installed the FASS system. but mine usually ran between 12 and 8 psi depending on load and conditions.

 

[GBrock]

Just returned from towing my 13,000 lb boat throughout the hill contry of central and west texas. My fuel guage also showed 8 at WOT while under load... . unless I went to O/D, then the pressure would increase to 10. But with O/D on, she simply wouldn't go so I had to tow with it off.