ejj

iTrader: (5)

Today I went to the track for the first time this year:

http://forums.maxima.org/showthread....34#post2848334

This was really the first time that I had an oppertunity to _really_ run out 1st-4th.

I noticed towards the end of the day that my fuel pressure was doing strange things. My base pressure is set at 26psi right now, and I'm boosting 11psi with a 3:1 FMU disk...so I should get:

(26/2) + (11*3) = 13 + 33 = 46ish psi

of fuel pressure, correct?

1st, 2nd and 3rd gears all got around that. No problems. So did 4th, initially. However as I got close to the redline the fuel pressure would slowly DROP to around 30psi.

At first I thought it may have been the guage, because my EGT's were still a very safe 1250F. However, on my last (and best) run of the day they got to 1400F, which is higher than I've ever gotten to boosted.

Could it be that my pump just can't flow that much for that long? Its a Walbro 255lph HP pump, so I according to its specs it shouldn't be a problem...perhaps its on its way out?

Any other ideas?

iansw

iTrader: (7)

I have a bad Fuel Pump installed right now. Any time I'm under 3/8ths tank of gas it does exactly what you describe above. Although unlike you I'm usually at 40PSI with the JWT ECU, 370's, and Walbro....

It will go to 60PSI usually at redline, but when below a 3/8ths tank of gas (1/2 way between 1/4 and 1/2) it will drop suddenly near redline to 25PSI.

My EGT's then go through the roof and I suspect if I did it often, I would blow my engine. It once happened on the Dyno and I hit a 17:1 A/F Ratio.

So be careful and get a new pump. I have a new pump but haven't installed it yet - been busy with the wedding and all lately - I just make sure to keep it above 1/2 tank and keep the Aux Pump plugged in.

ejj

iTrader: (5)

Is yours a stock one that's dying, or a Walbro?

Furthermore, why does this only happen in 4th gear? Because the pump has to sustain pressure longer than in other gears?

iansw

iTrader: (7)

It happens to me in every gear when low on fuel.

And it's a Walbro - it's been doing it ever since I first installed it.

never buy a used Walbro.

Stephen Max

iTrader: (59)

Interesting. I recently experienced a sudden leaning out of my afr at high rpm, resulting in detonation. I'm wondering if I'm having the same problem.

http://forums.maxima.org/showthread.php?t=298885

JAY25

iTrader: (38)

Your not the only one with a low pressure drop problem. I drove to New Orleans about two months ago. One my way back my EGTs jumped to almost 800 Celsius. My gas mileage was awesome . I sped up to 85MPH and my EGTs hit 800. Looked at my FP gauge and pressure dropped from 190 to 130KPA=20 PSI Lucky I brought my tool box with me. Pulled over in alabama and readjusted FP to 30PSI. I am seriously thinking of ripping that SFMU off and going back to a normal FMU and a SARD.