Engine/Transmission (1994 - 1998) strange fuel pressure problem

[tdubliture]

Ok I am a newbie here, I've been lurking for some time and have been able to search and find solutions to most of my problems until now. This might get a little long.

My story: I bought the truck used and the PO did a swap from a CTD to a V10. I believe that most of the swap was done poorly. I have encountered several issues. With most of them fixed I still feel like the truck isn't running correctly (low power). I just got some gauges and need some help trying to pin down a pressure problem.

PO had installed a small electric pump in line with the lift pump. (I think he was trying to fix a starting issue related to the fuel shutoff....wiring was hacked up and lets just say I'm surprised there hasn't been an engine fire.) this is all fixed now but the pump is still there.

The Problem: when I start the truck the fuel pressure immediately goes up to 30 lbs. Which is quite high for idle. When I slowly increase RPM it lowers to about 20-25 at around 2K. When I get up to 2.5K it gets back up to 30. Strange. Under load if I am on the throttle it drops pretty quick down to about 15 and sometimes less and builds to 20. I unplug the electric pump and it only drops about 2 psi at idle and everything stays the same.

I can't build more than about 20 lbs of boost and EGT maxes at 1000. The PO welded the waste gate shut and blocked off the line . The truck runs ok but feels like it should have more power. I do have the factory plate and housing moved all the way forward with 4 clicks on the star wheel.

Pressure gauge was installed on banjo nut on the pump inlet with 18" of grease hose and a needle valve. it is electric. I haven't verified with another gauge that it's correct but I feel that it is.

I pulled the overflow valve and it's a little different than I have heard others describe theirs. It has a metal "hat" instead of a different material. Is this weird? I plan on ordering the Tork tek adjustable valve but don't think it will solve my issue. I also plan on doing the heater delete and maybe replacing all fuel lines. I don't believe it is the lift pump because of the high idle pressure but maybe with a blockage it could be?

Is there anything I am missing?? Am I going the right route with this issue? Any help is appreciated

 

[JR]

I'm assuming you still have the OEM mechanical lift pump on the drivers side of the engine block? I'm not sure why anybody would install an electric pump in line before the mechanical pump but I would really consider getting rid of it. If it is a POS pump and it decides to fail the OEM lift pump may or may not be able to draw fuel through it. The mechanical pumps are solid and supply plenty of fuel volume unless the truck is highly modified. I would guess your erratic fuel pressure is likely related to the electric pump as well.

What year truck? More importantly, what year engine and what injection pump? If it were my truck I would replace the wastegate so that it works as it should. You could always install a boost elbow if you want a little extra boost out of it, but I would prefer to be able to control the point at which it wastegates. If it is an HX35 it should be capable of more than 20lbs of boost under full load but that is with the assumption everything is working properly, which is not going to happen in the current state.

 

[GAmes]

I agree that the electric pump is part of the problem. The bad thing is that it was probably installed to compensate for air leakage into the fuel supply lines between the tank and the mechanical lift pump. This article tells everything you might ask about the 12 valve fuel system. http://www.cumminsforum.com/forum/94-98-engine/58777-joe-gs-fuel-system-writeup.html

 

[JR]

The bad thing is that it was probably installed to compensate for air leakage into the fuel supply lines between the tank and the mechanical lift pump. [/url]

That was my first thought as well.

 

[tdubliture]

Ha I've read through that about 5-7 times. Lol. I was thinking the same about the electric pump at first. Then I read about a lot of people that put in small electric boost pumps to ease the duty of the lift pump. I did make some progress today. Put in the Tork Tek adjustable OFV today. Idle pressure dropped to where it is supposed to be. And reacts somewhat better to a load. What exactly would be the symptoms of fuel leaks before the lift pump. I'm considering ripping out the fuel heater pre filter assembly.

So my question for those who have 12 valves with a fuel pressure gauge. How does the pressure typically react to regular and wot driving.

 

[tdubliture]

I def do plan on fixing the waste gate eventually. I just don't understand why I can't build more than 20 lbs.

 

[GAmes]

What exactly would be the symptoms of fuel leaks before the lift pump. I'm considering ripping out the fuel heater pre filter assembly.

So my question for those who have 12 valves with a fuel pressure gauge. How does the pressure typically react to regular and wot driving.

It would be air leaks before the lift pump, not fuel. No start is the most common. Just take out the fuel heater, not the whole assy. Didn't you read Joe G's writeup 5-7 times?

Fuel pressure drops when demand increases (climbing a hill) and goes back up when the demand decreases (going down a hill).

 

[tdubliture]

It would be air leaks before the lift pump, not fuel. No start is the most common. Just take out the fuel heater, not the whole assy. Didn't you read Joe G's writeup 5-7 times?

Fuel pressure drops when demand increases (climbing a hill) and goes back up when the demand decreases (going down a hill).

yes I read it 5-7 times but was considering gutting the whole thing and put a pre-filter closer to the tank after reading several other threads on the matter. How much of a fuel pressure drop is normal under a high demand situation?

 

[GAmes]

Removing the whole thing requires a spacer for the mechanical lift pump, or a cover plate if you are removing it also. The prefilter is inexpensive, easy to clean/change, and is something I do at 100k mile intervals. I don't see how placing another filter closer to the tank makes a difference. Pressure drop is dependent on how much you are pressing the go pedal and how much weight you are pulling, but 5-10 is normal if the filter is good.

 

[tdubliture]

Removing the whole thing requires a spacer for the mechanical lift pump, or a cover plate if you are removing it also. The prefilter is inexpensive, easy to clean/change, and is something I do at 100k mile intervals. I don't see how placing another filter closer to the tank makes a difference. Pressure drop is dependent on how much you are pressing the go pedal and how much weight you are pulling, but 5-10 is normal if the filter is good.

Was planning on leaving it on the engine just capping it off. then going straight from the tank through a filter to the lift pump. Less connections less chance for error or leaks?

5-10 lbs of drop or a drop to 5-10 lbs??

 

[GAmes]

To each his own. I guess 0-10 psi drop would be more accurate, it is totally dependent on demand.

 

[tdubliture]

well sometimes I see numbers around 7 lbs if Im really getting on it in a higher gear at first. I recall reading another thread that stated the pressure should NEVER drop below 20 at WOT. Im just trying to get a baseline from people that might know. Im going to do just the fuel heater delete and clean my pre-filter today and new fuel lines over the holiday if all goes well. I'm leaning more towards a failing lift pump at this point. is that wrong? hate to just throw money at it

 

[GAmes]

I recommend that you bypass the electric pump while you are installing new fuel lines. That is the only way to determine if the mechanical one is good or not.

 

[tdubliture]

Will do. Hopefully tomorrow

 

[Missouri Mule]

When you do a fuel pressure test at idle the pressure be no lower than 20 psi. When the engine is idling squeeze the rubber return flue line with a pair of pliers. If the pressure goes up it your overflow valve, if it doesn't go up (if it was low) or goes up slowly it is the lift pump. You can check for fuel leaks by pressuring the tank with a little air.