fuel pressure bleed off

[Facime]

Ok, so I installed a brand new Walbro255 and my A/F is all over the place. Right after starting it, it is reasonable at around 12 then slowly rises to 15's, then eventually wants to die. When I shut off the engine the FP drops to nearly zero very fast.

Is my new pump defective and the check valve is bad? The AFPR is brand new Aeromotive as well. Is there some other way the pressure could be bleeding off? Could an injector bleed off that pressure that fast if it was defective or cracked?

Edit: I just played around with fuel pressure and throttle responce. When I start it, like I said its rich, pretty quickly rises to the 15's and off the chart within about 1 minute. If I goose the throttle a little in little quick short bursts I can bounce the A/F from 12's to 16's, but as soon as I let it return to idle it jumps up off the chart again. I have tried fuel pressures from 20 up to around 60. The A/F is obviously affected by this but even at 60 its still doing it, and I dont dare run more pressure than that.

 

[pimptrizkit]

jump fp to e1 in the diag box under the hood, note how fast pressure falls off after you pull the jumper pin, it should hold atleast 25psi for over 5 minutes.

ive seen mine hold 40psi for over 10minutes and take over almost an hour to hit zero..

ninja edit, make sure you set your fuel pressure correctly, are you runing any sort of piggy back?


i think i have my fuel at 32psi @idle with vac, and 38psi with vac off, and when you start boostin, it increases the fuel pressure even more.

 

[Facime]

As I mentioned, as soon as I shut the car off (or pull the jumper) fuel bleeds off very quickly to zero.

Also for testing purposes I put the Stock AFM back on in place of the LS400 one. A/F got richer by only a little, and same as before, the A/F rises slowly and the car starts to sputter, then goes off the chart and the motor acts like its starving out.

Also, no codes.

 

[Facime]

As I mentioned, as soon as I shut the car off (or pull the jumper) fuel bleeds off very quickly to zero.

Also for testing purposes I put the Stock AFM back on in place of the LS400 one. A/F got richer by only a little, and same as before, the A/F rises slowly and the car starts to sputter, then goes off the chart and the motor acts like its starving out.

Also, no codes.

Im wondering if putting the stock pump back in would be worth a try to test. Maybe I got a bad pump right out of the box.

 

[pimptrizkit]

Im wondering if putting the stock pump back in would be worth a try to test. Maybe I got a bad pump right out of the box.

i bet you do.. is it the real deal or a knock off pump?

i heard alot of the knock off's suck and aren't worth the money, yet i have one in my car and works perfect.. though it is on the back of my mind when i start pushing for bigger numbers..

will the car run fine with the jumper in? i wonder if the ecu is shuttin off the fuel pump thinkin it's not seeing a ignition signal?i dunno just thinkin aloud..

 

[Facime]

Thats a possibility, I was able to get it to remain at idle with the jumper in place. Time to do some electrical diag.

and no, its a real deal Walbro.

 

[theDon]

did you do a 12v constant mod to the fuel pump?

 

[Facime]

yeah I tried that as well. I can keep it running now, its supplying a constant feed of fuel. I hooked up the SAFC and tuned a little. Im definately unhappy with my car, but Im pretty sure I have my question answered here on this topic. Im going to try putting the stocker back in.

 

[jetjock]

That's a lot of work for a guess Weez. Does the return line deliver a minimum of 1 liter into an open container in 30 seconds? Does it do the same at the inlet to the rail? What does fuel pressure do with the regulator vac hose off during a snap throttle test? How much does it drop? Got a meter that'll handle over 6 amps? If so stick it across FP and B+ in the diag block in place of the jumper. What do you get?

 

[Facime]

Well first of all, Ive had the tank out a couple of times now and I can drop it in less than 15 minutes. I consider that to be less work than digging my way to the fuel lines on the rail to do a flow test. Besides, Im not sure what that would tell me as the major concern is the lack of any pressure 30 seconds after I shut off feed.

And lastly, Im really just too disgusted right now to even think about that fucking car. I appreciate the help guys, but I gave up on this issue hours ago. Im out of money, out of time, out of patience, and out of heart.

The car can sit and rot for all I care right now.

 

[jetjock]

The lack of rest pressure shouldn't cause drivability symptoms unless the cold start injector is at fault or one of mains is stuck open and in that case the a/f should be rich. You appear to have a flow problem. Sounds like the pump relief valve might be opening. That'd explain both issues but the root cause may not be the pump. But OK, sounds like you're tired of it for now. And roger that...there comes a time when a break in the action is good.

 

[pimptrizkit]

true dat jj,

i have had pumps go on me where they would run, idle, and get around, but no top end, i riped the exhaust off, thinkin i had a clogged cat, vac test's, compression, and so on, did some fuel test's and i had a low flow problem, it would build pressure, but couldn't maintain it. almost like a clogged fuel filter, but it was the pump. ie replaced the filter first and didn't fix the problem one bit, drove me nuts for a week.

 

[drjonez]

check V @ pump @ WOT.....sounds like ye olde walbro is demanding more current than your 20 yr old wires can handle....

 

[Facime]

they are all great ideas, but is everyone just ignoring the fact that Im mainly concerned about the pressure dropping to zero? I was trying to find the answer to the question: "is a bad check valve in the fuel pump the only way pressure can bleed off that fast?" or am I missing something. Is there another area I can look at?

Im pretty sure the pump is junk, and Im pissed because I bought it a long time ago and have no recourse on it. Im gonna have to fork over another $100 for a replacement.

 

[drjonez]

they are all great ideas, but is everyone just ignoring the fact that Im mainly concerned about the pressure dropping to zero? I was trying to find the answer to the question: "is a bad check valve in the fuel pump the only way pressure can bleed off that fast?" or am I missing something. Is there another area I can look at?

Im pretty sure the pump is junk, and Im pissed because I bought it a long time ago and have no recourse on it. Im gonna have to fork over another $100 for a replacement.

still unsure why this is such a concern....

 

[Facime]

well if the pump is bad for that reason, it would need to be replaced anyway. If thats the case then doing further testing on the fuel system would be unneccessary until the pump is replaced. Or is this logic flawed?

Also like I said before Im only mentally reapiring the car. I am out of time and patience with it. It needs to go on a trailer to TX real soon and I have other things to worry about right now.

The only thing Im going to do to the car is a combustion leak test, and a cooling system flush. Im able to keep the car running long enough to pull it on and off a trailer, thats pretty much all I need atm.

 

[Doward]

I would check and verify the pump is the problem, before just replacing it.

When you jump the Fp terminal, what is your fuel pressure? Does it hold steady?

If you are bleeding the fuel pressure off as fast as you're saying, you're either dumping fuel down the intake (stuck injector) or back into the tank (relief valve).

Find out where your fuel is going, before going nuts with it. Check back by the fuel filter, too, make sure you're not leaking there

 

[Facime]

Car has a blown head gasket...fuel is now the least of my worries. Thanks for all the idea and useful comments. We can let this thread die now.