Raphs50

I have been chasing an intermittent issue, where power drops off above about 5,200 RPM. I thought it was losing spark, but recently started looking at fuel pressure, and upgrading the fuel delivery system. When I first checked pressure, with a gauge connected at the Schrader valve on the fuel rail, a KOEO test showed zero pressure. After turning the key on and off 3 or 4 times, it built up to a few PSI, but still really low. When starting the car with vacuum disconnected from the FP regulator, it built up to 40 PSI within a second or two. After turning it off, the pressure bled off slowly, like I would expect. I am going to rig up the FG gauge, so I can test under load, to see if FP is being maintained (I don't have an in car FP gauge), but thought it was strange that it would not build up full pressure with one prime of the pump. I am also replacing the fuel filter, before I decide to drop the tank and replace the pump. It is a 255 lph pump, installed in 2000, so it is 15 years old. Not that many miles on it, but getting up there in age.

Any input is appreciated. Should know more after the FP test tomorrow. Street legal track day is Sunday, and wanted to get the car out for a few passes, but am concerned about the fuel pressure and potential engine damage.

mjr46

AFTER key is cycled off pressure should maintain with minimal drop of of a few psi over a 10-15 min period, if it hits 0 with in a few min or even less, you have a bleed down issue, often a faulty check valve in the pump

Raphs50

It holds pressure OK. It dropped to about 20 PSI after 15 - 20 minutes. It was the long time it took to build pressure that concerned me. 4 - 5 key cycles, with the pump running for a second or so each time, and it was still at less than 5 PSI. It had been sitting for a week or so, so I would expect 0 at first, but one maybe two cycles of the pump and I would expect to be at normal operating pressure. It didn't hit 40 PSI until 2 seconds after starting it.

mjr46

check filter for a restriction

Raphs50

Replacing the filter seems to have done the trick. After replacing it, pressure built up after two key cycles. Ran a temporary fuel pressure gauge and taped it to the windshield, so I could run at WOT and see if pressure was maintaining. No issues all the way up to 6000 RPM.

mjr46

I win

bluebeastsrt

Trouble shooting 101. Check the little things before doing the big things. Glad you got it fixed.

Raphs50

Agree 100%. Easy to get buried in a problem and forget to check all the basics. On to the next problem. Went to the track for a few passes Sunday and every pass I blew oil out the dipstick. Excessive crankcase pressure. Either my bypass valve on the supercharger has failed, or need bigger hoses running from my PCV valve and oil breather to the intake of the SC.

bluebeastsrt

Make sure your PCV valve is in good shape and not letting pressure back in the crank-case. What did you do with the line that "used" to go from the throttle body to the oil filler neck? If it's still in place, you'll get full boost in the crank-case. The line needs to be re-routed from the filler neck to the suction side of the blower. Plug the connection on the throttle body. Sounds like another simple fix good luck.

Raphs50

It's a new PCV valve, and I have the PCV and oil filler neck both routed to the suction side of the blower, though an oil separator. The two lines are connected with a tee fitting, and routed to a single line, through the oil separator to the intake side of the blower. It is only 3/8" line, so I am thinking that may not provide quite enough suction. I was thinking I would route each line separately, and see if that fixes it. The throttle body connection is plugged. Considering putting the old PCV back in, but there isn't much in those valves to fail is there? Hoping it is an easy fix.