Installed Walbro 255HP - Fuel Pressure WAY Too High Even w/ AFPR

larsrya8 · 03-14-2006, 11:39 PM

Just finished installed my Walbro 255HP fuel pump. Install went well, didn't break any fittings or anything. I used DSMLink to turn the pump on with the engine off to check the fuel pressure.. everything seemed fine. Then I started the car.

Fuel pressure was sitting at about 62 psi. I panicked. So I turned the car off and hooked up the battery charger to get some better voltage with the engine off. Now the fuel pressure sits at 55 psi. I turned the adjustment screw all the way out, and the pressure stayed at 55 psi. I unbolted the AFPR from the brake fluid resevior and moved it around to make sure the rubber return line wasn't kinking; pressure stayed at 55 psi. I removed my gas cap; pressure stayed at 55 psi.

Other details: My gas tank is reading 1/8th full because I didn't want any gas spilling into the car. The pressure gauge seems to be working fine; it will read 0 psi after I turn off the pump with the adjustment screw completely out. The AFPR was working just fine with the stock pump. If I turn the screw in I can get the fuel pressure to climb to 70+ psi (without leaks too). The Import Evolution FPR kit also uses the stock rubber line that attached to the stock FPR... could this be the problem? Also, the fuel pump is not rewired.

The three things I can think of are:
1. My return line is kinked/dented somewhere under the car. It was cold, and I didn't feel like jacking it back up to check, so I just went inside and had some hot soup.
2. There is some sort of blockage in the return line. How would I go about finding or fixing a blockage?
3. Somehow... I haven't thought of anything yet... I managed to do something to the return line while installing the new pump. Maybe something on the assembly inside the tank, or maybe to the rubber or hardline connected to the assembly.

Has anyone else had this happen by simply changing the pump... with an AFPR installed? My fuel pressure at idle is worse than what most people have when still using the stock FPR. I'm fairly sure my pressure regulator is not at fault, because it was working fine beforehand, but I won't rule it out completely.

I plan on checking on the return hardline underneath the car tomorrow, but if anyone has any other ideas/experiences to share, I'd love to hear them.

larsrya8 · 03-15-2006, 11:48 AM

I know I'm not supposed to bump, but I really need help on this quickly. The lines under the car seem fine, so how would I go about finding and clearing a blockage in the return line? I searched but couldn't find anything.

weith1111 · 03-15-2006, 12:01 PM

Sorry I can't help much. Only thing I can think of is to put in the stock pump and see what psi you are at. Maybe there is something wrong with the pump, defective? If you don't see anything to fix, it's usually best to undo the change that caused the problem and start from there.

larsrya8 · 03-15-2006, 12:13 PM

Quote:

Originally Posted by weith1111

Sorry I can't help much. Only thing I can think of is to put in the stock pump and see what psi you are at. Maybe there is something wrong with the pump, defective? If you don't see anything to fix, it's usually best to undo the change that caused the problem and start from there.

I'll put the stock pump back in and see if it gets back under control. I'm not sure what could be wrong with the Walbro... flowing way too much? I'm afraid the thing that needs fixing is a return line blockage, but I can't see it and I don't know how I would fix it. My only idea so far is to apply compressed air to the line where it connects to the regulator, and have a container in the back to catch any gas/etc that sprays out. The compressor I'd have to use is a huge standalone that holds at 120psi... Is this a bad idea? Any other ideas?

weith1111 · 03-15-2006, 12:20 PM

I might not be thinking straight here, but the FPR goes at the end of the fuel rail, which I'm assuming you did correctly, and your gauge would be on the line coming in, so...if there was a blockage in the return it would be in the section of line between the FPR and the tank and wouldn't interfere with the pressure in the rail. I'm assuming the FPR doesn't let pressure backfeed it at all. Does that make sense?

We'll see what happens when you switch pumps.

edit: If it turns out it's not the pump and it's the line, I wouldn't F with it, just replace it with a new line from the FPR to the tank.

boosting_laser · 03-15-2006, 12:24 PM

Just throwing this out, but is there a 1-way valve (check valve) leading to the tank on the return line? If so, maybe that could be causing your problem?? Good luck.

larsrya8 · 03-15-2006, 12:26 PM

Quote:

Originally Posted by weith1111

I might not be thinking straight here, but the FPR goes at the end of the fuel rail, which I'm assuming you did correctly, and your gauge would be on the line coming in, so...if there was a blockage in the return it would be in the section of line between the FPR and the tank and wouldn't interfere with the pressure in the rail. I'm assuming the FPR doesn't let pressure backfeed it at all. Does that make sense?

We'll see what happens when you switch pumps.

edit: If it turns out it's not the pump and it's the line, I wouldn't F with it, just replace it with a new line from the FPR to the tank.

I'm assuming the problem is in the line between the regulator and the tank. My gauge is mounted on the regulator. The line isn't letting enough fuel flow through it so the FPR can't bypass enough fuel to keep the pressure down.

Yeah, I'll get on that stock pump in a few. Just gotta eat some lunch.

gixrman · 03-15-2006, 02:17 PM

What kind of AFPR is it? My Aeromotive regulator did the same thing when I installed it. It ended up being the boost signal nipple binding with the spring inside. I had to grind off some of the nipple for it to work properly.

larsrya8 · 03-15-2006, 02:38 PM

Quote:

Originally Posted by gixrman

What kind of AFPR is it? My Aeromotive regulator did the same thing when I installed it. It ended up being the boost signal nipple binding with the spring inside. I had to grind off some of the nipple for it to work properly.

It is an Aeromotive... I'll look into that.

And for an update: I got the pump assembly out of the car. Funny thing is, even though I only have about 1/8 of a tank of gas, the tank seems to be full. The gas is level with the bottom of the gasket for the pump assembly. Is that normal? The VFAQ says I should have "preferably 1/2 tank".... but I think if I had any more it would spill everywhere.

Anyway, I'll put the original pump back in and see if the pressure is fixed. If it's not, I'll start looking at the regulator. Still no ideas on how to troubleshoot a clogged return line?

femmeDSM · 03-15-2006, 02:58 PM

What are your vacuum readings at idle? High vacuum readings will cause fuel pressure to drop - so by logical deduction, Low vacuum (caused by improper vac line setup, vacuum leak, whatever) would cause the fuel pressure to read abnormally high.

Also, I wouldn't be so sure about that gauge - gauges that have been knocked around during install or even normal driving conditions can be damaged and read incorrectly. I would try a new gauge if you can get your hands on one, just to be sure.

larsrya8 · 03-15-2006, 03:20 PM

Alright I got the stock pump back in. With the adjustment screw turned all the way out the pressure was at about 22 psi. I turned it in until it was at 43ish, and it's holding. What does this mean? Should the pressure have been 0 psi with the screw turned all the way out?

As for the gauge, I'm 99% sure that it's working correctly. It reads 0 when there's no pressure, and when I turned in the adjustment screw all the way with the "hard spring" it read 60 psi, which is what it should read because that's the max base pressure the hard spring can support. It did this with both the 255HP and with the stock pump.

All of these readings are with the engine off and with the vacuum hose off, using DSMLink and a battery charger (to supply higher voltage to simulate the motor running). While the car is idling my vacuum is between 18in/Hg and 20in/Hg, so that shouldn't be the problem. I'm assuming the reason the pressure was even higher with the engine running is because the pump was getting more voltage than the battery charger could provide, and therefore flowing more, and therefore overrunning... something.

edit: I looked at the fuel pump assembly while I had it out of the car. Both the "line to the other side of the tank" and the "return line" feed into a single off-white thing on the assembly. The hole on the bottom of this "thing" is really small. Like, pin-hole small. I'm wondering if I were to remove that plastic thing and just have both lines dump straight into the tank, would that fix my problems? Having the fuel go through that thing does result in it dumping at the "bottom" of the assembly, but I don't think that's protecting anything, like the electrical connections or anything. What do you guys think? Give it a shot? Or does it serve some purpose that repair manual isn't showing me?

larsrya8 · 03-15-2006, 04:30 PM

Well after letting the engine run a bit, I checked the "lowest" fuel pressure I could get with the engine off. It now has risen to 33 psi. That's what it's supposed to be with the engine at idle. So... does this mean my regulator is defective, or my lines are clogged?

larsrya8 · 03-15-2006, 08:26 PM

Ok I think I found and fixed the problem.

I took the white-ish thing off of the pump assembly and found a piece of dirt blocking the return to the bottom of the pump assembly. After cleaning that out and reinstalling the Walbro, my fuel pressure at idle is 35 psi. I don't think I can get it to go any lower, but I didn't really try. I was just happy it was running again.

If I can't get the pressure down though, what might happen when I install my high-flow fuel filter? Will the pressure climb again? Or is the stock fuel filter not making that big of a difference in this case?

boostyGST · 03-16-2006, 04:23 AM

with a 255hp and 680cc inj, with a aeromotive FPR, what should the idle FP be set @, and with mods should the FP still sit where is it normally does stock, I am running a G50 turbo with only a SAFC2 for tuning. Just give me the Pressure's that you all are running on your 2G's

Stapl3 · 03-16-2006, 04:45 AM

There is no right answer for your question. There are different ways to go about it.

larsrya8 · 03-16-2006, 06:05 AM

Quote:

Originally Posted by boostyGST

with a 255hp and 680cc inj, with a aeromotive FPR, what should the idle FP be set @, and with mods should the FP still sit where is it normally does stock, I am running a G50 turbo with only a SAFC2 for tuning. Just give me the Pressure's that you all are running on your 2G's

The base fuel pressure should be 43.5 psi, and with 20in/Hg of vacuum at idle the fuel pressure should be around 33.5 psi. (2in/Hg ~ "-1 psi")

Boiler2 · 03-18-2006, 04:08 PM

I am late to this thread, but for others who have this problem and are searching the threads ... you can detach the return line hose from the AFPR and run a separate open hose from the return of the AFPR into a 5 gallon bucket. Make sure it is secure and will not flail around once gas flows. Plus make sure you have enough gas in your tank.

Start the car, then see if you can lower the fuel pressure with the AFPR. If you can, then it is more than likely the return line is restricted with a kink or dirt in the line, etc.

Also, FYI, at one point my fuel pressure was bouncing rapidly +/- 4psi. It ended up being an old fuel filter. After changing it, the pressure was steady.

larsrya8 · 03-18-2006, 04:14 PM

Quote:

Originally Posted by Boiler2

I am late to this thread, but for others who have this problem and are searching the threads ... you can detach the return line hose from the AFPR and run a separate open hose from the return of the AFPR into a 5 gallon bucket. Make sure it is secure and will not flail around once gas flows. Plus make sure you have enough gas in your tank.

Start the car, then see if you can lower the fuel pressure with the AFPR. If you cannot, then it is more than likely the return line is restricted with a kink or dirt in the line, etc.

If you can't lower the pressure w/ the AFPR dumping into the bucket, wouldn't that mean that the problem is the AFPR (a.k.a. Not the return line)?

Boiler2 · 03-25-2006, 07:48 PM

Quote:

Originally Posted by larsrya8

If you can't lower the pressure w/ the AFPR dumping into the bucket, wouldn't that mean that the problem is the AFPR (a.k.a. Not the return line)?

Oops! Thanks for the catch. Thread edited.

mirkoelek · 03-25-2006, 09:00 PM

it doesnt make any sense that could be fp problem. if he cant lower the fuel pressure by adjusting the afpr, how could be the fuel pump. The pump doesnt know are you changing fuel pressure on afpr and adjust it self so it would keep the same fuel pressure. I would like to have that kind of pump so i wouldnt need afpr.