Fuel Pressure DROP!!

[MARKO]

My 86 GN has a problem with the fuel pressure droppin when
it builds boost or at WOT. I have a 255lph pump which is a month
old. Adj reg, hotwired pump and green stripe injectors. With a fuel pressure gauge I set it to 44psi with the line off. The pressure would build upon acceleration and the drop once it was boosting for a while back to 39-40psi roughly. I took the vacuum line off and plugged it and bumped my pressure up to 59psi to see if it would bog under full boost (15psi 94 octane)
Same thing again! Could it be a voltage drop or my fuel pump?
I'm not sure if my regulator is faulty or not? Anyone be able
to tell me how I could monitor my voltage to see if it drops off
underboost. The pressure probably drops 10-15 psi when it
leans out. Thx for any info

 

[Fuelie600]

Doubt it's your regulator.
Doubt it's the voltage, being how you mentioned it's hot wired, unless your volt reg is not working properly or you used too small of a gauge wire to your pump.
Possible your pump is insufficient if the wiring and voltage checks out, but I don't know your combo so it's hard to tell if your running out of pump.
What I suspect, is a kink in your fuel line or a collapsed fuel sock. Later Brian

 

[S10xGN]

Change the fuel filter!

 

[87GN_70GS]

Easy to test the voltage at simulated WOT conditions. Hook a good digital voltmeter up at the rear connector - as close to the pump as possible. Get some long wires or leads so you can read the meter at the front of the car. With the engine idling, crank the fuel pressure up to 65 or so (if it doesn't stall) and watch the meter. If it doesn't drop, it's not your wiring.

 

[granatl]

When you shut off the car, does the FP quickly drop to zero? If so, the little piece of fuel line that you used to replace the pulsator (I'm assuming you did this), might have split, so a good % of your gas is just dropping back into the tank.

 

[Royal-T-Ltd]

When was the last time you had your regulator off? Had this problem looooong time ago - checked everything, fuel filter, fuel pump, changed pumps just in case, blew compressed air through fuel lines, etc, etc. All along my new Accufab regulator must of ingested an extremely small piece of o-ring from the rail. Took the regulator off, flushed it out, new oring [with globs of petroleum jelly] and been drivin' fast with class ever since. Just my experience.

 

[MARKO]

Maybe I'll try that. The car did sit for over 2 years, but I took
the tank down cleaned it, new pump, filter etc... Just need
to make sure voltage is alright. Also I might try a different
chip and see, Yesterday I had a code 51 (faulty ecm prom chip)
Thanx for all the help guys!!

 

[XLR8]

If you "cleaned" the tank and installed a new fuel filter, the new filter could be clogged from disturbing the junk in the tank. I would try replacing it. It's less than $15.00 and 15 minutes of work.

 

[postal]

I had a walbro 340 that was doing the same thing to me. Boost would build and fuel pressure with it, to a point, then the boost would keep climbing and the FP would start droping. This pump didnt have 500 freaken miles on it!
Every body told me all the other stuff to check but it was a faulty pump in the end.

HTH: Jason

 

[granitestategn]

me too, I think

Originally posted by postal
I had a walbro 340 that was doing the same thing to me. Boost would build and fuel pressure with it, to a point, then the boost would keep climbing and the FP would start droping. This pump didnt have 500 freaken miles on it!
Every body told me all the other stuff to check but it was a faulty pump in the end.

HTH: Jason

Postal,

I think I've got the exact same problem. Exact same symptoms. Pressure rises w/ boost then drops off. I've been through everything except the pump, fuel sock or the little piece of rubber hose at the pump. I just received a new pump yesterday. I wasn't going to drop the tank w/o a new pump to install. Too much of a PITA. Walbro 340 hotwired. Two years old but less than 500 miles. A few runs down the track and a couple of cruises and that's it. Bought a new pump for $99 from Full Throttle Speed. I can't wait to get the thing running right with the new injectors.

 

[MARKO]

I think my fuel pump is screwed. I tried checkin everything.
I unhooked the hotwire and checked the voltage and it was
at 11volts. With the hotwire it was just over 13volts. Ran
2 wires into the car so I could monitor the voltage and it
stayed at 13.2-13.4 volts and the fuel pressure still dropped.
The pump was changed 300 miles ago with new f/filter.
Anyone have any other ideas?

 

[Fuelie600]

MARKO, Have you checked for kinks yet? Hows your fuel pump sock?

 

[MARKO]

I haven't check for kinks. Are you talking about the lines on top
of the tank? I guess I'll have to drop the tank to check. The
sock should be ok cause I changed it when I put the new pump
in 300 miles ago? Anything else I should look for?

 

[87GN_70GS]

Sounds like debris is blocking something. Remove and clean the regulator, filter, etc. Disconnect and try to blow out the lines with air or fuel.

 

[Hunter Dog]

I just noticed similar issue for first time two days in a row. The car initially ran great for maybe two short drives a week or so back, now seeing the boost build and drop back to almost nothing. This is just going from 30-50 or 40-60 mph, not able to get it any faster unless its a slow increase w/o getting on the gas at all. From reading this thread the one thing we did not change was the fuel filter. Otherwise not sure where to look. Since it ran great a few weeks ago, the changes made were a new solenoid as the nut kept coming off as the threads were really bad on a new starter. We also put new positive and negative battery cables on from Caspers. We put in new fuel pump, hot wire kit, 60lb injectors and TT chip a month ago and it ran great on a couple of short trips around the area. Now got an issue. Any thoughts out there? I am no mechanic but trying to learn how to get by on my own..lol