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Ok, dreamer your on to something. Got a F pressure tester that fits the Gm for 42$. Turn key to on position and goes to ~ 50 and drops in 2 sec when pump turns off. doesn’t hold pressure. I start it and sits right on 53psi. Specs are between 60-70. Same thing when it dies it drops and is down within 5 seconds.
Not sure where the F/P regulator is. The F/P was replaced in ’06’. The F/P relay was replaced after the lightning hit.
Any ideas on narrowing it down?1. Not in specs. running at 53psi . Specs 60-66psi. for 1997 GMC sierra 5.7 liter
2. When I pinch the return hose, when the key is in the on position the pressure bleeds quick.
3. When I pinch pressure line when key is in the on position the pressure doesn’t bleed. I see pressure drop as I release the pressure line.Summary- failing fuel pump and bad check valve in the Fuel pump.
Anyone agree?
Any other ideas on what could cause the stalling after the lightning strike? F/P is ~6 yrs old. It runs for 3 minutes and dies. No F/P sound after it dies.
Just want to do due diligence before dropping $100 on F/P and F/Filter. Wonder could inadequate voltage to the F/P cause an out of spec condition for the fuel pressure like we see. Or if it would just fail to start period.Your evidence does seem to suggest a problem with the fuel pressure regulator but I suppose it could also be a fuel pump issue. I might start with a fuel pressure regulator and then recheck as that’s the easiest thing to replace.
Yeah no connection to PCM.
Would a low voltage to the F/Pump cause low pressure? Or not to work at all? Also, if I am right about the F/P going bad, what causes the truck to die? Is there a sensor that kills it if there is low pressure, or should it run low pressure indefinitely? Cause it’s not sluggish’ing out it just cuts off and you stop hearing the F/P.
Any definitive way to test regulator? Does the theory below look correct?
Would it be more a regulator issue if:
I pressurize the line, and pinch the pressure line and pressure DOESN’T hold? Which would suggest a leak on the top side of the gauge?
TANK——F/P——F/F——(PINCH)—–GAUGE ——LEAK~~~REGULATORInstead:
FACT 1: I pressurize the line and it look like a leakdown into the tank from the check valve on the fuel pump. (This DOES hold Pressure on the gauge, suggesting the regulator to be good.)TANK——F/P~~~LEAK———–F/F——(PINCH)—–GAUGE—–REGULATOR
(also, FACT 2: Fuel pressure from pump to gauge is 53, which is out of spec 62-66.)
FYI, When I pinch the return line it leaks down, This test shows could be any of the three leaking F/P, regulator, injector.I think that your 13V reading is borderline and should be checked out, even if everything is turned on.
Quoted From el_crab:
Yeah no connection to PCM.
Would a low voltage to the F/Pump cause low pressure? Or not to work at all? Also, if I am right about the F/P going bad, what causes the truck to die? Is there a sensor that kills it if there is low pressure, or should it run low pressure indefinitely? Cause it’s not sluggish’ing out it just cuts off and you stop hearing the F/P.
Any definitive way to test regulator? Does the theory below look correct?
Would it be more a regulator issue if:
I pressurize the line, and pinch the pressure line and pressure DOESN’T hold? Which would suggest a leak on the top side of the gauge?
TANK——F/P——F/F——(PINCH)—–GAUGE ——LEAK~~~REGULATORInstead:
FACT 1: I pressurize the line and it look like a leakdown into the tank from the check valve on the fuel pump. (This DOES hold Pressure on the gauge, suggesting the regulator to be good.)TANK——F/P~~~LEAK———–F/F——(PINCH)—–GAUGE—–REGULATOR
(also, FACT 2: Fuel pressure from pump to gauge is 53, which is out of spec 62-66.)
FYI, When I pinch the return line it leaks down, This test shows could be any of the three leaking F/P, regulator, injector.Everything you say here is on target but unfortunately till you start replacing parts at this point it’s hard to say which one is at fault here without more sophisticated testing equipment such as a lab scope so you can look at the current draw of the fuel pump. If there isn’t enough pressure in the system it won’t run properly and may be the cause of the stall, it could be that the fuel pump is not getting enough voltage to run or it would be better to say ‘enough current’ but it could also be a mechanical issue such as a fuel pressure regulator that’s not maintaining the pressure OR a fuel injector that’s leaking. Here’s a video by my friend Duane about using a lab scope to monitor fuel pump operation with a lab scope.
Good video. Yeah it would be nice to have the scope… Probably less expensive to do what you said and get dirty now. Got a F/P, F/F and screen for ~100
fuel pressure on that engine is 60-65 psi. if you pinch off the return line that pump can produce 80-85 psi
key on engine off you need to see 60-65 psi if you don’t your fuel filter is either dirty or your fuel pump is suspect.
you should be able to blow through your fuel filter in the flow direction with out much restriction. I would also like
to add that if a constant 12 v is not being supplied to the fuel pump.this will affect fuel pressureC8-)Good job with your diagnosis thus far.
Here are 2 video’s for you to watch by ScannerDanner. Its not for your particular vehicle but will educate you –
GM CPI Leak –
http://www.youtube.com/watch?v=09_wQ9yQ85A&feature=plcp
Fuel pump circuit testing (covers voltage drop testing)-
http://www.youtube.com/watch?v=Q3ZiTsKCdO8&feature=plcp
Good luck and keep us posted!
glad to see the fuel pump is resolved. The pressure is still low. the next thing to look at is constant 12v
to the fuel pump. then the fuel pressure regulator. good job so farC8-)
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