besides a bad FPR or vacuum leak, is there anything else that would cause fuel pressure to go up and down while idling?

when I was at the track, after a couple runs, I noticed my idle was acting up a bit, and realized that my a/f was reading really lean. I checked fuel pressure, and it showed it surging up and down a bit which seemed to be causing the idle to stumble.

could this be battery/alternator related? or possibly issues with the resistor box or wiring?

 

anyone?

heres what happened tonight when I was checking things out.

I tried to adjust the regulator at idle, with the vacuum line detached, to see what happened. It seemed that the higher the pressure was(~50), the leaner the a/f got, idle started bouncing a little bit and the pressure would start to surge slightly. If I lowered the pressure(low 40s), it seemed to richen up and be closer to where it used to be at idle, and didnt seem to bounce around nearly as much, if at all. does this sound right? I would think more pressure would make it richer, especially at idle with 1000cc injectors. Someone correct me if Im wrong.

The problem comes in because Im not sure at what pressure the car was tuned at. The gauge I had took a crap shortly after my first tuning session, but it reading 50psi while at the dyno. I just dont know if it was actually reading correctly because anything close to 50 now, it is really lean and surges. And when I removed that gauge, the needle didnt move from 50.

The motor seems to be pulling the same amount of vacuum as it always has, I dont seem to have any vacuum leaks.

Im using a 255 Walbro HP pump, with maybe a few thousand miles on it, if that.

could this be pump or battery related? how would I go about checking the pump?

 

Bump i would like to know also

 

Sounds like it's the pump going out as it can't flow enough as fuel pressure rise.

 

there doesnt seem to be a problem under boost, a/f's are still where they used to be (low 11's) so I dont think the pump is taking a crap. Im gonna try to measure the battery voltage while idling to see if its spiking.

 

clogged fuel filter can cause fuel pressure to surge

 

good call, totally forgot about that, Ill replace that tomorrow.

another thing I noticed it that it only seems to be doing this after its been running awhile. it doesnt do it immediately after warming up, it takes a little while for it to start doing this.

 

I had the same issue, only did it when it has ran for a while. Trust me, its the fuel filter, i replaced everything I could. stupid me found out it was just the filter. an easy $30 fix costed me about $400 since my new pump n **** was about 3XX

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RTW DC2R &raquo;</TD></TR><TR><TD CLASS="quote">

when I was at the track, after a couple runs, I noticed my idle was acting up a bit, and realized that my a/f was reading really lean. I checked fuel pressure, and it showed it surging up and down a bit which seemed to be causing the idle to stumble.
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Is the idle going up and down. A change in intake manifold vacuum will cause the fuel pressure to change.

 

You can check for a kinked or pinched return line too, that'll cause pressure to rise.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chiovnidca &raquo;</TD></TR><TR><TD CLASS="quote">
Is the idle going up and down. A change in intake manifold vacuum will cause the fuel pressure to change.</TD></TR></TABLE>

wouldnt this show as loss of vacuum as well on my boost gauge?

no vac lines are broken/kinked as far as I can tell.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RTW DC2R &raquo;</TD></TR><TR><TD CLASS="quote">wouldnt this show as loss of vacuum as well on my boost gauge?
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I would think so. Lets start from the beginning: How much is the fuel pressure fluctuating?

 

when it fluctuates, it goes up and down a good 5psi.