tallzag

Posted some of this in the "longer starting" thread but don't think many people saw it so will post in it's own post.

First off, have a 1998.5 24v 2500 5 speed. 220k miles on it and have a fuel pressure, pyro, and boost gauge, all isspro. The fuel pressure gauge comes off the top of the fuel filter and it has an isolator in the middle. Also have a Smarty box on the lowest setting.

A little over a year ago I put in gauges on my truck just before putting in the Smarty, wanted to make sure everything was working right before boosting it. After putting in the gauges the truck would run at 10 psi at idle then immediately drop to 1-2 psi after getting on it at all. I replaced the lift pump with another stock type pump from the parts store (I believe it had been replaced once before as well before I owned it). This fixed the problem and I've had 9-12 psi ever since.

A couple of weeks ago I noticed the pressure start to drop while driving it, at idle it went down to 5-6 psi and although it wouldn't really go down after getting on it I knew that wasn't good. I got my last replacement pump warrantied but this time they gave me the Airtex lift pump. The replacement was very easy and I went ahead and changed out the fuel filter at the same time. Problem is this didn't fix my problem, still have the 5 psi fuel pressures. Well now it is down to 4 psi when I start it and this morning it started to run rough and actually died on me in my parking lot. Obviously want to get this fixed.

Couple more things, seem to be having some electrical issues with the truck as well, put in some HID headlights and have been getting a lot of interference with the radio from them as well as everytime I run the wipers. My trailer brake controller keep on flashing at me too and no trailer is hooked up, not sure if this has anything to do with anything but thought I'd point it out.

Any suggestions? I know people are going to say just put in a FASS which is what I will probably do later but why is the pressure down? It was fine with the old pump until it went down. The new pump didn't change anything so I'm thinking it isn't the pump. Do I maybe have air in the lines from changing the pump and filter? Clog in a line? My injection pump going out? Not even sure where to start looking. Thanks for any input.

rightwinger

Even with the pump "working" 9-12 PSI is not enough, you need 14-15 psi at idle, anything less and you could possibly be harming your VP

AggieJustin

Considering some of your other electrical related issues, you may want to check the voltage going to the lift pump. Could be a bad ground or other issue causing lower voltage which would decrease your output.

tallzag

Quick update, still don't know what the problem is but have tried a few things. Put direct power to the fuel pump and it still will only go up to 5-6 psi. If I am putting direct power to it shouldn't the pressure go above that? Fuel pump sounds like it is working fine.

Went through and cleaned up all the terminals, made sure the batteries had a good charge as well. The pump doesn't seem to build pressure when I put it into accessory with the key but it does when I put direct power to it (but still only 5-6 psi). Keeping at it.

tallzag

Little more info:

When you first turn the key the fuel pump primes to 2-3 psi but only for about a second then goes back down to zero. Truck starts fine, no long starting or anything and pressure then goes up to 5-6 psi and stays there. It will not keep going after you crank either. What would keep the pump from priming? It seems like the grid heaters go on everytime too no matter if it is hot or not, could that be related?

Checked the voltage at the pump and it has plenty of juice.

tallzag

Could the problem be the ECU is not providing enough voltage? Any way to test this?

Lary Ellis (Top)

Sounds like a bad pump...sometimes you get a bad one right out of the box with those El Cheapo's. The VP 44 can pull some on it's own which will likely show more pressure when it is running but it isn't enough and will cook the Injection pump if you keep running it that low on pressure.

Also as stated before check all your grounds!