Hello,

I have a problem with poor top end. I have a boost gauge and a fuel pressure gauge.

The fuel pressure gague does not suck down, but I did notice some small variations. It will idle at 6-7 psi. If I revv the motor, it will dip 0.5 psi or so and then increase a little. If I disconnect the fuel line at the injection pump and wait a few minutes and reconnect it will idle at almost 8 psi. If I revv the motor, it will not dip at all and increase to about 9.5 psi. I wonder if some air is getting trapped in the system?

As far as max boost... if I'm travelling down the road at 65 at 5 psi and floor the accelerator, it will move up to 12 psi (it doesn't get there immediately, it takes about 2 seconds) and fuel pressure doesn't decrease. However, if I am going downhill in 4th, and floor it, it will get up to 15 psi and briefly dip the fuel psi gauge to 4 psi as it does it.

This does not seem right. It seems I should be able to get 15 psi if I floor it uphill. I think if it did, I wouldn't be having any problems.

What do you all think may be the problem?

Brian

 

Are you sure you are getting full throttle? With the stock injectors and the pump turned up I could suck my lift pump to 3 pounds WOT.

 

I've checked having another person in the truck and do get full throttle.

Brian

 

The other two things:

1. I've noticed is that if turn off the truck, then try to start it up again right away, it doesn't start instantly like it would when its cold - it needs to turn over a couple of times first. I'm not sure if that is a problem or not as I've never tried when was looking for problems.

2. When I turn off the truck, with the fuel pressure gauge still powered, fuel pressure decreases to zero. Is this normal or should it hold pressure for some amount of time?

Brian

 

My diaphram pump would drop off pretty quickly, but the piston pump holds pressure longer. Check for a leak somewhere between the VE and the tank. I've not needed to do this yet, but someone here knows a way to put in a clear plastic line to check for bubbles. I think it goes between the fuel line and the pump, but I'm not sure.

 

I've replaced the tank sending unit and the fuel line from the tank to the lift pump. I don't see much of any air in the line when I splice in a clear plastic fuel line in front of the lift pump.
Brian

 

You should see no (zero) air flowing in your fuel. My fuel pressure readings have been generally inversely proportional to boost since I turned up the pump a little a few months ago. Boost goes up (for more than a few seconds), fuel pressure goes down. It seems to hold at a minimum of around three psi fuel press on a long hard run, but I think that is way too low.

 

A few very small bubbles occassionally is pretty much all I see. For all pratical purposes there is no air. When I got 15 psi of boost the fuel pressure definitely reduced. Maybe I should retard the timing and see what happens. I'm not sure why it maxes out at 12 psi most of the time.

Brian

 

well when i hold'er and when boost maxes out i see 22# with the stock 21cm housing and stock everything else

 

Your fuel pressure gauge sounds normal to me.

The boost behavior sounds odd, though. You ought to be able to make boost much easier in 5th on the highway than going downhill in 4th. The pump is not fueling very hard under load for some reason - and it's not lack of fuel supply. The problem has got to be internal to the pump. Is the AFC tube intact and not leaking? Pull out the AFC cone and look down the bore. Does the fuel pin pop out if you pull the throttle lever?

 

I have to wonder about the fuel psi gauge. Its shows pressure - but couldn't it be fuel and air together? What if there was an air leak AFTER the lift pump? I wouldn't have seen it in with the clear fuel line.

This afternoon messed around with the fuel lines and got it to act WORSE than before - pedal harder to push, just feeling lethargic. Flooring the truck in the 50-60 MPH range would do no better than 9 psi. Then I messed around some more and took it for a spin on the freeway. If I got on it it would accelerate past 85 MPH and the fuel pressure gauge would dip as low as 3 psi climing grade and I would get 15 psi in 5th. As I climbed grades the fuel psi would dip down some as boost went up. I need to do more testing. I was keeping it at speeds faster than I normally drive for this. Typically I will drive about 78.

I wonder if its now just as simple as making a timing adjustment to retard the timing a little down from 1.6 to about 1.4

Brian

 

We had a cold front come into town and it dropped from the 50's to the low 20's overnight. This morning I fired up the truck and it ran for a few seconds and then started acting very rough like it was going to stall out. I popped the hood to see what was going on and maybe I needed to reconnect my KSB. I saw fuel dripping drip-drip-drip from the WIF sensor wires. I was in my office clothes so I didn't poke around too much to see exactly where it was coming from, but appeared to be either the WIF sensor itself or the fuel heater. In recent days I changed the fuel heater o-ring and made sure it was snug. I may go to filters w/ out WIF's just to eliminate this failure possibility.

Anybody ever have a WIF sensor go bad?

Brian

 

Fuel from anywhere above will drip off the wires. It's easy enough to throw a FS1221 on there, though. If it stops you know it was the WIF sensor leaking.

The pedal gets harder to push? Is there any chance you've got some sloppy linkage that is binding occasionally?

I think your fuel pressure gauge is correct and the fuel supply is good.

 

What's a FS1221?

I tried to buy a FF5018 but it rolled to a FF42000 which is the new style made of black plastic. It does have some neat user-friendly features such as a 1/2" square drive fitting on the bottom designed so it will slip before it gets overtightened and the o-ring fits into the filter rather than on the stub.

Brian

 

FS1221 is the longest filter I could find for our trucks. It has a drain in place of the WIF sensor hole.