Low fuel pressure-need suggestions-long post

[Dr. Matt]

About a week ago as I was driving my L started to feel sluggish. I looked at my wideband and it was going lean off the scale and my fuel pressure was down to about 22#'s and the needle was dancing up and down on my mechanical gauge. Low pressure was intermittent that day and always corresponded to AFR going lean. Problem became costant over the next 2 days.

The pressure doesn't bleed down right away when I shut the truck off like a leak in the tank and it doesn't leak anything outside. Fuel system hasn't been touched (other than filters) for 2 years since I put in a set of Walbro's with new submersible line, new steel "Y" fitting, Larger filter and bracket, and 60# injectors all about 10,000 miles ago.

Started by doing the obvious which was replacing the filter-no change

Checked the resistor and it looked good, but temporarily bypassed it anyway-no change

Bypassed fuel pump and high pressure relays-no change

"Deadheaded" the pumps from under the truck like JJ suggested with my wife looking at the fuel pressure gauge and the relay jumped. She reported that the gauge didn't jump up so I dropped the tank, checked everything out, all looked good and put in a new set of Walbro's-no change

Deadheaded the pumps again and the wife reported no change on the gauge, then pointed to the AFR gauge and asked if it was the one she was supposed to watch. Decided to disconnect the return line by the filter and plug it with a line going to a seperate gauge I could watch from inside the truck, turned on the key and both pressure gauges went right to about 85-90#'s. Hooked the retun line back to the tank and again, very low pressure.

I unplugged the wiring going to the pumps near the tank, took a fully charged group 27 marine battery under the truck, and ran juper wires direct to the pump harness. Still low pressure!

I thought it has to be the regulator and unpluugging the regulator with the truck idling doesn't change the pressure. Even though a vaccum pump hooked to the regulator showed no leak, I replaced it since it was the only other possibility- STILL NO CHANGE

Oh and since they are cheap I just went ahead and replaced the relays too and as you probly guessed, no change.

So it doesn't appear to be electrical since I totally eliminated the L's electrical system by using a battery hooked directly to the new pumps. It doesn't appear to be a leak since pressure holds when the key is turned off. It doesn't appear to be the pumps since they will make 90#'s of pressure when the return is eliminated. Replaced the regulator already so what's left? The only other parts in the system are the rails and fuel lines.

I am about frustrated enough to yank the rails off my fathers F150 and salp them on and if that doesn't fix it then his fuel lines, but I'd rather hear from somebody that there is something simple I've missed. I was planning on going to the track this weekend and shooting for a new PB but that's not going to happen now, maybe in July.

Any input/suggestions?

 

[fuelonempty]

When you turn the key to the on position and the pumps come on, what psi are you seeing? and does it stay constant?

 

[Dr. Matt]

When I turn the key on it goes to 39#'s for a few seconds, then drops to about 36. If I turn off the key it will hold 35#'s for a long time. However, if I start the truck the pressure drops slowly down to about 24#'s at idle and if I give it a little throttle the pressure drops as load increases until I get into the transition between vaccum and boost at which time the pressure jumps to about 38#'s.

Matt

 

[LSUstang05]

I haven't seen a Walbro pump myself, but isn't there a filter in the tank on the pumps? I know there is on the stock ones and when I had this problem it turned out to be that the little filter in the tank on the pumps (or in the line or something) was deteriorating and causing fuel starvation. You may have already looked at that, though :shrug:

 

[Dr. Matt]

I haven't seen a Walbro pump myself, but isn't there a filter in the tank on the pumps? I know there is on the stock ones and when I had this problem it turned out to be that the little filter in the tank on the pumps (or in the line or something) was deteriorating and causing fuel starvation. You may have already looked at that, though :shrug:

Actually I reused those filters when I put in the new pumps. I was wondering if even though they looked fine they might be clogged and therefore the cause of my problem. My next plan is to remove the tank again and try unplugging the pumps one at a time and seeing if they both work, then remove those filters and try running the pumps without them. I think you may be right about those filters being the problem. I'll pos up what I find.

 

[Dr. Matt]

Well both pumps work & I had no change in pressure when run without the inlet socks. Next I bypassed the fuel hose from the filter to the rails and I FINALLY GOT NORMAL FUEL PRESSURE! So apparently there is a collapse or something in the line somewhere. No visible kinks or crushed spots in it but bypassing it solves my low pressure issue and my truck runs normal again. So for those of you who PM'd saying you have the same problem, mine turned out to be the fuel line between the filter and the rail. Dealership quoted me $312.73 for the hose assembly. I'm going to cut the end off of it and see if a local business can make me a new braided stainless hose for a little less.

Matt

 

[LSUstang05]

Awesome man! I know when I was having fuel issues it was such a pain and so much stress just trying to figure out what could possibly be wrong. I'm glad you got it fixed and figured it out :beer:

 

[Dr. Matt]

Hose end fittings from local junkyard. - Free
New hose and ends crimped on at my local Parker store - <$10
Wasted money on new pumps, regulator, & relays - $300
Having my L back running - Priceless

 

[Dr. Matt]

Well crap. Bad news. I put the tank back in, got my new custom fuel line ran, fired up the truck and it was showing good pressure and AFR in the mid 14's. I backed it down out of the garage and off my ramps. While getting my computer out to hook up for some datalogging of the race tune, pressure dropped back to 22#'s and the truck went so lean it would barely idle. I was barely able to get it back in my garage and up on the ramps. I reloaded my street tune and while it was loading I can hear the pumps running at full speed but only had about 36#'s of pressure again. I guess it wasn't the line after all. &^%*!

 

[Dr. Matt]

Well I'm about out of ideas. I'll sum it up here. To eliminate a flow resriction I've replaced the inlet socks, pumps, in tank hose, inspected my stainless Y, ran hose direct from the Y to the third fuel filter I've put on, new hose from the filter to the rails, and installed a set of stock L rails off a friends L with the third pressure regulator.

To eliminate the electrical system I took a seperate battery and hooked power and grounds from it directly to the pumps bypassing the entire electrical system including the hat wiring. I've bypassed the resistor and pressure comes up just like it does when I'm running the resistor and load the motor enough to go into high pressure cycle with the resistor in place. I've replaced the pump and high pressure relays too.

Pressure is still low and the truck runs lean. I can see no other option than I had bad pumps and got new bad pumps. Only thing I can think of now is to put my stock pumps back in and see how it runs. My pressure gauge is hooked to the passenger side rail and my wideband is hooked to the drivers side so both banks are having the same problem. If I do bypass the resistor it idles like normal and runs fine at part throttle because I get 40#'s of fuel pressure and before this problem I had 38 at idle/light load. It doesn't smoke like I have an injector stuck open or miss like one cylinder is flooding.

Oh and when I test the power at the harness going to the pumps I get the same voltage as the battery has.

 

[wydopnthrtl]

After reading your posts.. IMO you have either; an internal bleed, air trapped in the top 1/2 of the system, or a faulty pressure regulator.

1) First thing I'd do is to make sure the fuel rail doesn't have air in it. Tilt the truck so that your bleeder valve is highest in the system. Then bleed it by running the pumps and a clear hose running to a container. If the hose to bleeder fitting is tight you should see no aeration after the hose is filled.


2) Secondly, I'd bench test the lower 1/2 of the system. Take the pumps -to- filter part of the system out of the truck. Get a clear container that has enough windshield washer fluid in it to act as a "tank". Now run a **small** clear hose back to the container. **This hose must be smaller / more restrictive than everything else before it**
If there is a leak in that 1/2 of the system you'll readily see it squirting out **or** you'll see an aeration of the "fuel" returning back to the container. It should neither leak nor have air in the line (once primed).
Once your satisfied it's work well.. run some gas through it to flush out the windshield washer residue. (so it doesn't get into your injectors)

This second step will do two things. It'll prove that half of the system is working properly. Hopefully you can put it back in the truck and not have to worry about them ever again.

If that checks out good.. IMO it's gotta be the fuel pressure regulator or air trapped in the upper 1/2 of the system.

Rich

 

[01subaru]

regulator!

 

[Dr. Matt]

Well you know the old saying, "Once all other possibilities have been eliminated, whatever remains, no matter how unlikely, has to be the answer."

Ater talking to Paul from totalinduction.com this morning, (what a great guy by the way callling me back on Memorial Day and spending over a 1/2 hour on the phone trying to help when I've never bought anything from him) I went out to my garage and put a pressure gauge right after the pumps. I started the truck and pressure there was 22-24#'s. I pinched off the return line and again fired up the truck and no increase in pressure. Next I disconnected the return line and put it into a gas can (of course taking off the vise grips I pinched it off with) and watched flow. NO FUEL FLOW. So I put my stock pumps back in, hooked the return back to the tank fired it up and it sat there idling with 36#'s of pressure and responded to light throttle like normal. Just for the heck of it I disconnected the return, put it in the can and started the truck to watch flow. It looked like a garden hose at full bore.

So in the end, after all of this, it looks like my pumps went bad and I got a new defective set of pumps.

Because I thought the possibility of 4 bad Walbros was so remote, I replaced the rest of the system from the socks to the rails. The whole time I had a good set of stock pumps in the garage I could have tried and confirmed the true problem.

Lesson: Never assume any new electrical part is good.

JJ I'll be calling about the pumps tomorrow.

 

[Rook]

thatz crazy. i hope you get it this time. good luck.