Engine/Transmission (1994 - 1998) What lift pump pressure is good?

[SEmerson]

I have had 35 # max since I installed my guages on my 12v. It is down to 10-20 now. and 0 at wot. What should I have?

 

[Andy Redmond]

18-24 psi @ idle



24-34 psi @rated rpm.



Have you gently squeezed the rubber return line to see if pressure rises? If so likely the overflow valve is worn out.



Good luck

Andy

 

[SEmerson]

Where would I crip it off? And where is the overflow valve?

 

[SEmerson]

I found the overflow valve. I took it out and disasmbled it. it looked ok. I gave the spring a little pull and put it back in. Great pressure now. I'll see how it drives in a litttle bit.

 

[illflem]

Stretching the spring is a stop gap measure, once the spring has lost it's push your FP will creep down again. I'd keep a new OF valve on hand for the next time your pressure drops.

 

[WadePatton]

I just got around to checking my pressure. I used the TST adapter and a Briar Hopper gauge. It is 17 at idle and slowly rises to 25 at 2000rpm.



Is that good enough?



Where is the best price on the overflow valve?



Is the slow change in pressure characteristic of this system or is it that itty bitty hole in the adapter? I bled the line to see if it would respond quicker, but it didn't.

 

[Joe G.]

I stretched the spring a little thinking it was a temporary fix. That "temporary" fix has worked for over 120K miles.



Fuel pressure should be about 21 PSI at 2000 RPM with no load. 18 PSI is probably ok, but anything below that is low. O PSI under any condition I would think is a problem. Pressure about 40 PSI may occur during decelleration from highway speed. Running with steady pressure above 40 PSI is a problem.

 

[illflem]

Originally posted by WadePatton





Where is the best price on the overflow valve?

Precision Diesel Injection and Turbo Inc.

Marty Tompkins

toll free 888-734-7349

$20 + $5 shipping and handling.

 

[WadePatton]

If pressure is good, the the valve is good, right?



Bear with me I'm new to the p7100.



But learning fast.

 

[illflem]

You can really only tell if it's good by monitoring the pressure in the cab while driving, under the hood isn't always correct. What happens as the OF valve ages is the spring weakens when the fuel gets hot lowering your pressure.

 

[WadePatton]

Okay so I drive it--after some hose adaptations, how should the pressure look? On a 24v it's real easy, you get the max at idle and watch for the lowest number you can pull.



Here the pump is increasing supply as RPM increases--gosh what an idea.



Am I still looking for minumum under load. I'll come back with numbers Friday. Gotta hunt in the morning and don't want to wear #2 to dinner after a quick shot at readings.

 

[DBrickel]

I would like to install a incab mount fuel preasure gauge. I can only find them for the 24valve cummins, aren't they available for the 12 valvers? would it be a problem to do this? Where would be the best spot to tap the line for this? Sorry for all the ????

 

[DMC]

I was reading through this thread and got to thinking about the overflow valve. And had a brain storm. Why not put a needle valve in the return line in place of the overflow valve, and regulate the fuel pressure that way? Of course if you do this you need a fuel pressure gauge to set the valve and monitor the pressure. This would put an end to the high cost of overflow valves. And might improve fuel mileage as a result of steady higher pressure at higher rpms.



Any body got any pros or cons on this?



Thanks



Don

 

[illflem]

Originally posted by DMC

I was reading through this thread and got to thinking about the overflow valve. And had a brain storm. Why not put a needle valve in the return line in place of the overflow valve, and regulate the fuel pressure that way? Of course if you do this you need a fuel pressure gauge to set the valve and monitor the pressure. This would put an end to the high cost of overflow valves. And might improve fuel mileage as a result of steady higher pressure at higher rpms.



Any body got any pros or cons on this?



Thanks



Don

It won't work to have a valve in the return line because the flow of fuel varies with rpm.

Ay high rpm the pressure will be way too high if the valve is set to the recommended pressure at idle.

 

[AKnight]

I've got a 2002 24 valve 6 speed. It is stock except for K & N air filter. I called Genos to order the Westech fuel pressure guage. He said the 0-16 psi guage would be okay for stock. I am not planning to do any modifications to the engine. Also what pressures should I have. Thanks

 

[wbrown02]

You can get a fuel pressure gauge from Genos Garage... It is a mechanical gauge that takes the fuel pressure from a fuel line attached to a diaphram that stays under the hood. . on the other side of the diaphram you fill it with anti freez and run the line into the cab to the permanent gauge... . Works great and no fuel in the cab This system is on my 95 12valve.

 

[WadePatton]

Welcome Aboard AKnight

Originally posted by AKnight

I've got a 2002 24 valve 6 speed. It is stock except for K & N air filter. I called Genos to order the Westech fuel pressure guage. He said the 0-16 psi guage would be okay for stock. I am not planning to do any modifications to the engine. Also what pressures should I have. Thanks

But your engine is a 24v and this is the 12v engine/transmission forum. In the 2G (Second Generation) we have two distinctly different fuel injections systems. The p7100 on the 12v engine 94-98. 0 and the VP44 on the 24v engine 98. 5-02. The supply pumps for these injection pumps are different and make very different supply side pressures.



Now to answer your question--(I have both). You were told right. The 16 PSI gauge is fine for the 24v setup. I use the Westach electric gauge on my 2000 truck and picked up the fuel pressure by removing the core of the schraeder valve at the inlet to the VP44. I then slipped fuel line over that fitting and to the sender. Mounted the sender on a custom little bracket sent to me by the guy I bought it from. I can shoot a photo if you like.



It was changed slightly when I eliminated the stock fittings.



Hope that helps. And check out the "search" function. It's a bit quirky but will help you find many many hours of reading here. Hint-when you get 459 results, simply check the box "search titles only" to narrow down the results. You can also search by specific forum.



Enjoy

 

[WadePatton]

Hey Bill,



I did a road test on mine today. It runs 15-20psi most of the time. If I keep it from upshifting and run the R's up there it'll go over 20. WOT from a 15# it'll hold there, but won't climb until I lift.



It idles 13-15. Guess I'll chuck a valve in and seef it gets better.

 

[illflem]

I certainly would, $25 is an easy bullet to bite.

 

[WadePatton]

Just because I still had the pressure gauge on there, I pulled the OV and stretched the spring. When I got through looking for leaks, I notice that the 30psi gauge was pegged.



I drove it around some and it would come back down to 28-30. And I can rev it now and hear the OV tick tick tick.



I have another noise I'm trying to hunt down. That's another reason why I messed with it.



Going to order new OV.