bad FPR symptoms?

[1990LTD]

question: What does a fuel pressure regulator do (or fail to do properly) when it's starting to go bad?



relevant information: My car has always taken what I consider longer than normal to crank. Key on, turn to crank, engine cranks 3-4x and fires up. If I crank it and only let it turn once or twice (especially when cold) it won't fire, but then usually on the second attempt, first crank it will fire immediately. Makes me think fuel problem but I am a n00b.



I do not have any vacuum leaks that I could detect - No running problems either.



My entire fuel system and shortblock are stock, AFAIK. The only changes I made were the upper intake/throttle body/egr spacer. I know it's possible to test pressure at the fuel rail but I don't have the gear for it at the moment.



Don't know if this is relevant: If I play my cards right I can make it pause slightly between cranking and firing. I let go of the key just before it normally catches/fires, it sounds like a diesel somewhat for a brief moment actually, then fires. There is a definite pause between the starter motor spinning and the engine firing/running.

[1990LTD]

FWIW, I'm replacing the thing eventually anyway, this is more for my own edification than anything else.

[gadget73]

turn the key to 'on' and wait 3 seconds (or until you hear the fuel pump noise stop) before you turn it to crank. If it lights right up, the check valve in the fuel pump is weak and its simply draining pressure back down to the tank. Nothing particularly abnormal about that. If the FPR is bad, I'd expect either very lean or very rich running, depending how it failed. They are generally quite reliable though so unless you can verify the problem with a fuel pressure tester, I wouldn't go changing it just for S&G.

[1990LTD]

I always wait until the fuel pump stops whining before I crank it. Also, letting the fuel pump cycle multiple times does not seem to make any difference in cranking time.


Do you mean if it fires right away after the pump cycles, the check valve in the FPR is weak?

[86VickyLX]

I always wait until the fuel pump stops whining before I crank it. Also, letting the fuel pump cycle multiple times does not seem to make any difference in cranking time.


Do you mean if it fires right away after the pump cycles, the check valve in the FPR is weak?

There's a check valve in the fuel pump. Hook up a fuel pressure gauge and do some tests. Put the key in run once. And observe the gauge. It should be around 40-45psi. AND IT SHOULD HOLD THAT PRESSURE! If it leaks down, you have a bad fuel pressure regulator, or the check valve in the pump is weak.

To differentiate between the two, do this test. In this test you're doing the same thing, except this time you need to deadhead the pump some way (by blocking the return line somewhere). Yes it's not very good to do. But doing it once to diagnose something is not a problem. If the fuel pressure still leaks down, (it should be higher) its the check valve in the pump. If it doesn't, the fuel pressure regulator leaks down. Also while doing this test, remove the vacuum line to the fuel pressure regulator to make sure that gas isn't coming through the nipple. Because that's another way they fail. The FPR allows gas to get by the diaphragm and the vacuum line pulls it into the engine.

[mrltd]

leakdown could also be a bad injector.

Long starts can be from gunk buildup on intake valves, oil in the cylinders, etc..

[86VickyLX]

leakdown could also be a bad injector.

Long starts can be from gunk buildup on intake valves, oil in the cylinders, etc..

That's true, but I didn't mention that cause he wasn't complaining about driveability issues.

[1990LTD]

Yeah, it's not giving me any grief. the startup isn't a problem, I'm just curious about it. It has never ever failed to start except when a fender solenoid or battery connections went bad, and a screwdriver fixed that.


Motor looks pretty good under the valve covers (I know that doesn't matter much to the intake tract) and I've regularly run seafoam through a manifold vac source to degunk whatever gunk might be built up.

No signs of oil getting past rings, no oil loss or blue smoke etc....if anything it runs rich but generally only when warm assuming because I haven't replaced my o2s yet - I have them, they're just sitting on top of my bass amp right now


I will attempt to test pressure at the valve on the fuel rail once I get ahold of a pressure gauge

[86VickyLX]

My car had weird starting issues with the old fuel pump. Sometimes it would need to crank for a while. Other times it would fire up almost instantly. Now I could just hit the key and like not even a full second it will start sometimes. If it's cold it might take a second.

[1987cp]

I had a SEFI regulator start squirting fuel out the vacuum hole. That's how I figured out that one was bad.

[1990LTD]

My car had weird starting issues with the old fuel pump. Sometimes it would need to crank for a while. Other times it would fire up almost instantly. Now I could just hit the key and like not even a full second it will start sometimes. If it's cold it might take a second.

well my fuel pump is the stocker AFAIK and whines like a banshee, so it could be it. it always works but sometimes the pitch of the whine wavers very slightly, as if it's getting more/less power or something.

[86VickyLX]

well my fuel pump is the stocker AFAIK and whines like a banshee, so it could be it. it always works but sometimes the pitch of the whine wavers very slightly, as if it's getting more/less power or something.

Change in speed. That could be from the power to the pump, a loose ground, accessories in the car turning on and off. Some pumps are loud, some are quiet. Mine got louder, and that's partially why I replaced it. The other part being it didn't hold fuel pressure after shutting the car off.

[1990LTD]

I've ruled out accessories so it's probably a loose ground or bad 12v to the pump

[86VickyLX]

I've ruled out accessories so it's probably a loose ground or bad 12v to the pump

As long as it doesn't drop pressure down, I wouldn't worry about it.

[mrltd]

That's true, but I didn't mention that cause he wasn't complaining about driveability issues.

Even with the buildup it'd fun fine after startup. Might not cause any drivability issues.