fuel pressure flucuation

[gnturbo]

I have had this problem for a while and have not found a reason or cure...her it goes,If I start the car up cold set the pressure at 45psi,when the car warms up the pressure will drop 3-5 psi.Sooooo I have had to set it at 50 psi so when the car warms up it will settle down to 45 psi.Ny ideas? my volts remain the same at start up and through out the drive and I have a racetronix walbro 340 fp set up.No biggie just wondering if this is normal.

 

[2QUIK6]

Maybe once the car is warmed up, its pulling a greater vacuum, which causes the fp regulator to reduce pressure.

 

[QuickWE4]

I have found the same to be true.

I used to set my FP after simply letting the car idle for a while to warm up. I found that if I drove it around for an hour or so, I'd come back and the fp would be too low. I have found that the only way I can accurately set mine is to drive the car for a while and then come back and set it.

Thus, I have always felt that the car runs a little fat when it's cold (could be a symptom of the 009's), but it's the only way I can compensate for the drop in fp after it's hot. And I've never been able to really pinpoint why this happens either.

Rich

 

[azgn]

if you set the fuel pressure with the vac line off.....it makes no difference what it reads with the vac line attached....just make sure it tracks lb for lb under boost (from the baseline vac off setting)

 

[Whtlightning]

I have the same problem. My readings (static) actually drop 6-7lbs after making a run or so. Once they drop they stay put so I haven't worried too much, but I'm still curious. Anyone else have any ideas?

 

[azgn]

if your fuel pressure is tracking with boost from your 0 vac setting.....there is no problem

for example, with vac line off, set at 43.....at 20 lbs boost, your pressure should read 63

makes no difference what it reads otherwise

 

[QuickWE4]

But ultimately, what is the cause of the variation then? Let's assume that it tracks fine as boost increases. And let's assume that I set it line off as most do. What then, is the cause of the difference in fp at different times on different days, assuming that the fp gauge is good and in working order? Let's also assume no vacuum leaks....

I know it's hard to pinpoint, but I guess that's the real question...

Rich

 

[azgn]

well, who cares?

it isn't hurting you.....

my guess would be some kind of vacuum problem (as in leaks)

of course it could be something much worse like a wiped cam, blown head gasket etc