neevosh

My fuel pressure keeps dropping off under boost. I'm running a rewired Walbro pump. I checked the voltage at the relay and at the plug on top of the tank and they're both at around 14 volts at idle. My fuel pressure at idle is 40 psi and it drops to 35 psi under boost. When I jump the plug in the engine bay I don't get more then 45 psi. I've tried 3 different vacuum/pressure sources for the pressure regulator and it didn't make a difference. When I pinch the return line the pressure goes up. So is the regulator bad? I had this problem with my old rail on, so I bought another. Is it just bad luck to get 2 rails with the same problem? Or a bad pump?

HAILERS

Stock pressure regulator????? Run the car at idle. Put a vacuum hose on the fpr and suck. Did the pressure drop down to about 28psi? Now apply pressure with something like a MittyVac. On a stock fpr the fuel pressure in the rail should go to close to fifty psi if you apply ten psi to the fpr's vac hose.

neevosh

Yeah. I've been meaning to do that. Thanks for the reply.

neevosh

Well, the regulator works fine. I guess I'll recheck the wiring one more time before pulling out the pump. It seems to drop off when the secondaries come on.

HAILERS

Try putting the fuel pumps strainer in some cleaner like acetone for a few hours and blowing it off. They varnish up with a clear varnish that you might not have noticed. Might be the problem.

IF you put the fuel pressure gauge just in the delivery line just after the fuel filter, does it show a pressure like 80psi or so????? I mean with the fuel rail out of the picture. Just the gauge at the end of the line and nothing else. Like a dead end. I *think* the book says about 80psi. Just from memory. If its like that, then maybe the problem is something other than the pump???????

neevosh

Well, I pulled the pump out today. The filter was clogged. It looked like moss was growing in there or something. It only been in the car for 3 months. I could barely blow through it. I managed to get the stock filter on there. I'm still having pressure drop off. Now it doesn't happen until around 5K RPM's. So the filter did help some. I guess I'll pull it back out. Maybe some of that gunk got into the pump.

cymfc3s

Mike, you're running the vacuum line from the lower intake manifold right to the regulator right?

neevosh

It was on the bottom nipple of the 4 on the UIM. I had it on the top by accident, and when I noticed, I thought I found the problem. I also tried teeing it into the line that goes to my BOV. It didn't make a difference. And I had Steve watch my guage while I sucked and blew on the regulator line. He said pressure went up when I blew into it.

HAILERS

Maybe change the fuel filter up front along with another cleaning of the strainer in the tanK???

I'm not real familiar with fuel pressures and gauges, but.........in the past I have put a fuel pressure gauge (mechanical) tee'd in the fuel delivery line and gone for a spin while boosting. The gauge should go up from the low thirties to the high fourties depending on how much boost you have.

There's a chech in the fsm. You pull the vac hose off the fpr at idle and the pressure should read approx 35-37psi, then put the hose back on at idle and the pressure should drop to approx 28psi (I never saw less than 30 myself on three cars and two different gauges).

I'm looking in the fsm and it says if you put the fuel gauge on the outlet of the fuel filter that the pressure should be 71-92 psi (no tee, just the outlet line from the pump).

HAILERS

Looking at your problem with the fuel pressure falling off makes me suspicious about the old saw on this site that says you need to upgrade your fuel prior to upping the boost. I wonder how many apex seals went PING just because the low pressure filter in the tank was clogged, not because of an inadequate fuel pump.

I run a stock fuel pump with a catback and downpipe w/presilencer (yeah, only the 2and 1/2 inch one) and see ten psi boost and never see a sign of a lean condition on the TechEdge wideband. Runs pig rich.

neevosh

I'm running a hybrid turbo, full exhaust, intake, 1000cc secondaries, and about 10psi for the moment. I probably have enough fuel even with pressure dropping off. But this primarily a track car, so I'd rather sacrifice some power for rebiability. At least until I have the money for a Haltech and WB.

I'm seeing about 45 psi at idle, goes up to around 55psi, and then drops to about 35psi.

Thanks for the replies guys. I'll get to the bottom of it.