L-JET fuel pressure - HELP NEEDED -UPDATE #2
05-08-2006, 09:04 PM
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L-JET fuel pressure - HELP NEEDED -UPDATE #2
Just got and installed a fuel pressure gauge from 928 Motorsports. Very easy install, and may have finally revealed the problem.
At idle the fuel pressure is 28 lbs and it decreases to 24 lbs by 2,000 RPM. Haven't been able to check higher rpm's yet.
This seems low and I'm not sure how much the pressure should drop with RPM (if at all).
I have a new filter and tank to pump hose that will get installed next weekend. I read somewhere that the feed hose should not be clamped and the present one definitely shows signs of a clamp.
What next?
At idle the fuel pressure is 28 lbs and it decreases to 24 lbs by 2,000 RPM. Haven't been able to check higher rpm's yet.
This seems low and I'm not sure how much the pressure should drop with RPM (if at all).
I have a new filter and tank to pump hose that will get installed next weekend. I read somewhere that the feed hose should not be clamped and the present one definitely shows signs of a clamp.
What next?
Last edited by Phil Silano; 05-12-2006 at 07:31 PM.
05-08-2006, 09:09 PM
#2
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pull the vacuum line leading to the regulators . it should jump up 5psi or so.
however, there is not much vaccum that is present at 2000rpm, so i wonder why its dropping .
yes, it does seem low.
make sure your vacuum advance and the fuel reg vacuum are not reversed. check spark timing with and without the vacuum hose connected and see what happens.
Mk
however, there is not much vaccum that is present at 2000rpm, so i wonder why its dropping .
yes, it does seem low.
make sure your vacuum advance and the fuel reg vacuum are not reversed. check spark timing with and without the vacuum hose connected and see what happens.
Mk
05-08-2006, 10:34 PM
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IIRC idle pressure is ~30psi, off idle ~37psi. I would next check delivery rate (lt/min).
Is there a symptom you are looking to fix, like low power, running lean? How long since fuel filter replaced, or is there audible noise from the pump?
jp 83 Euro S AT 50k
Is there a symptom you are looking to fix, like low power, running lean? How long since fuel filter replaced, or is there audible noise from the pump?
jp 83 Euro S AT 50k
05-09-2006, 08:28 PM
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After work today I checked the fuel pressure again.
Down to 24 psi at idle and 22 psi at 2000 rpm. When the throttle is suddenly released the pressure dropped just below 20 psi.
With the vacuum removed from the regulators the pressure rose to 32 psi and was steady through rpm changes (no vacuum).
The mighty vac shows 17 inches of vacuum to the regulators at idle.
So, for some reason the fuel pressure is not behaving itself; but why? Too much vacuum?
I'm open for suggestions.
Down to 24 psi at idle and 22 psi at 2000 rpm. When the throttle is suddenly released the pressure dropped just below 20 psi.
With the vacuum removed from the regulators the pressure rose to 32 psi and was steady through rpm changes (no vacuum).
The mighty vac shows 17 inches of vacuum to the regulators at idle.
So, for some reason the fuel pressure is not behaving itself; but why? Too much vacuum?
I'm open for suggestions.
05-09-2006, 08:58 PM
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IIRC, mine was 14" at idle, but I don't think that difference matters much. Are the diaphragms in the fprs leaking? Check for fuel in the vacuum lines to the regulators and damper, or see if it leaks out of the fprs or damper when you leave them with no vacuum reference. I wouldn't think they'd leak enough to lower fuel pressure, but I guess it's possible.
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05-09-2006, 09:16 PM
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I have checked all three components on that vacuum loop. I can put 20+ inches of vacuum on them, no problem. The vacuum holds, no apparent leaks.
I wish it were that easy.
I wish it were that easy.
05-10-2006, 12:16 AM
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Pinch the hose for one of the regulators, fuel pressure should only go up slightly (5 psi or less). If you see a big increase in pressure, the regulator is bad, or the fuel return on the opposite regulator is clogged. Try this on both regulators.
05-10-2006, 08:38 AM
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By the way.
My plan for this weekend is:
remove the fuel pump, fuel filter, feed line from tank to pump, and the line between the pump and filter.
Check the inlet to the pump for debris, clean the electrical connections, then put it back together with a new filter and feed line.
My plan for this weekend is:
remove the fuel pump, fuel filter, feed line from tank to pump, and the line between the pump and filter.
Check the inlet to the pump for debris, clean the electrical connections, then put it back together with a new filter and feed line.
05-12-2006, 03:47 PM
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Had some extra time last night so I changed the fuel filter and the feed line to the pump. The old feed line had a definite flat area that was probably restricting the flow some.
Also checked the pump inlet and electrical connections.
The fuel pressure went up to 29psi when cold and 26-27psi when hot. The drop off at higher RPM's isn't so bad now either.
Tonight comes the regulator check per the WSM. more to follow.
Also checked the pump inlet and electrical connections.
The fuel pressure went up to 29psi when cold and 26-27psi when hot. The drop off at higher RPM's isn't so bad now either.
Tonight comes the regulator check per the WSM. more to follow.
05-12-2006, 07:37 PM
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Now I am really confused.
Jumpered the pump and got 34 psi, WSM says 35+/- 3 so that looks good.
Pinched off each hose to the pressure regulators and gained about 1 psi each time, per spec.
WTFO!
Is it okay to run without vacuum to the regs? That gives a constant 32psi.
Jumpered the pump and got 34 psi, WSM says 35+/- 3 so that looks good.
Pinched off each hose to the pressure regulators and gained about 1 psi each time, per spec.
WTFO!
Is it okay to run without vacuum to the regs? That gives a constant 32psi.
05-12-2006, 07:41 PM
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It should be fine. Just be sure to plug the vacuum lines (prevent leaks) and cap the vac ports on the regulators (prevent dirt and solvents from entering). You may run a little rich at idle.
