sudden drop in fuel pressure?
10-05-2008, 04:27 PM
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sudden drop in fuel pressure? When I first got the sts kit and racetronix PnP kit installed, the fuel pressure was 61-62psi at idle. For the last couple of months it's at 57-58 at idle. Just now when I go full throttle it drops to 50psi and my AFR which was always below 11 is now at 11.4. I checked the fuse for the harness and it seemed fine. The only other thing I found was with the battery bolt I had on the battery. The second little bolt that holds any loop terminals on, had backed out and was causing the fuel pump harness to not get enough juice and have intermittent starting problems. I just checked the power wiring underhood and it seemed fine. Could this be the sign of a fuel pump going out? I did just seafoamed the fuel system and know I need to change out the filter but I wouldn't think it would cause that big of a blockage it's been on a year and a half or so.
10-06-2008, 07:17 AM
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i would bet that your filter is clogged up. if it was fine before i would go back to the last thing you did. seafoam would loosen up and junk in the fuel system and the filter would catch it. also maybe your battery is not hold the same voltage. those pumps are 62.5 psi at 13 volts i think,
10-06-2008, 08:18 PM
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just changed the filter, no change in fuel pressure at idle or at WOT. According to dash battery voltmeter, voltage stays over 13V the whole time at WOT. Where to start next? should I start at the fuel source (tank/pump) and move forward? AFR is fine at idle and slightly leaner than I remember (used to be below 11), now at 11.3 at WOT and which corresponds with the dip in fuel pressure (about 49-50psi at full throttle).
Last edited by HossinatorSS; 10-06-2008 at 10:12 PM.
10-07-2008, 01:57 PM
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Is there a way to check the voltage at the pump without dropping the tank to read the relays at the top? The pump and harness is the racetronix plug-n-play setup so I believe it's a walbro.
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10-19-2008, 08:48 PM
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i don't believe so. there is a fuel pressure sensor that mounts to the tank but as far as I know, the PCM is "dumb" to fuel pressure as far as controlling the engine (it may still set off a SES light). My understanding of the fuel system is that the pump is always on, always running, pushes fuel out the tank, through the filter and into the "Tee" on the driver side rear wheel well. The fuel goes forward to the fuel rails, some gets used, some goes back through the return line and into the tank where it is met by the fuel pressure regulator. if the pressure is below what it should be (58psi) then the regulator opens letting the return line fuel in, and thus relieving the pressure to the point it reaches 58psi.
10-21-2008, 09:44 PM
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Well, I just replaced the flexible hose from the pump to the tank wall with high pressure in-tank fuel hose. I am still loosing pressure at WOT (about 49-50psi) but now when I prime the system, the pressure goes to 40 and then slowly CLIMBS to almost 50psi. Idle pressure is like 58psi. I just ordered a new fuel pressure regulator (found a place that sells delphi ones without buying the whole fuel pump assembly) I did notice that the pressure dips when (at idle) I have the stereo on and crank the base on the subwoofer up. I'm starting to think that it might be electrical. Any ideas?
10-21-2008, 09:46 PM
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Also, forgot to ask, where/how did you check the voltage on the pump? did you just connect the leads to the disconnected connector and and just read the priming voltage? I'm not sure how to check the voltage while the pump is running.
