Is this amount of fuel pressure drop normal? (Page 1/2)
windex42 OCT 06, 02:45 AM
Hi everyone,
I hooked up a fuel pressure gauge to see how things were looking, and I saw that the fuel pressure was dropping faster than I expected.
I don't know anything about fuel pressure, but could you check my video, and let me know if this is a normal amount of fuel pressure drop, or does it look like there's a leak.
Youtube Video

Also, I was checking for regulator leaks and fuel injector leaks, I didn't find any leaks.
When I pulled off the intake manifold, i did smell a lot of gas, but maybe that's all normal, i don't know.

Thanks for all your help.
Have a great day!
-==-
Nick
Patrick OCT 06, 02:56 AM

I'd say your fuel pressure is dropping way too fast.


quote
Originally posted by windex42:

Also, I was checking for regulator leaks and fuel injector leaks, I didn't find any leaks.



How were you actually checking the injectors for leaks?
windex42 OCT 06, 04:16 AM
Thanks for your reply, Patrick

Regarding your question about how I was checking the injectors for leaks,
I tipped the fuel rail out of place so that the tips of the injectors were no longer completely in the holes.
I had my wife turn the key to prime the pump while I looked at the tips to see if anything leaked out.

Thanks for verifying that the fuel pressure is dropping too fast.
I would assume if it's dropping, it's either
A. leaking out of the injector tips - doesn't appear to be
B. leaking out through the vacuum port of the regulator - doesn't appear to be
C. leaking through the cold start injector - might be harder for me to check, advice would be welcome
D. leaking back through the return line to the tank - I heard this can be tested by pinching off the return line while monitoring, but I can't find any rubber section, advice would be welcome
E. leaking back to the tank through a faulty check valve in the supply line - again, not sure how I could test this, advice would be welcome
F. leaking to the ground through a broken fuel line - I have not seen any indication of this.
claude dalpe OCT 06, 07:41 AM
Have you checked to see if it's the check valve on your fuel pressure gauge that's leaking?
A little water and soap on the valve to check if the check valve is tight
Hudini OCT 06, 09:03 AM
The fuel lines should have a rubber hose between the hard metal lines and the fuel rail.

Pinch the supply line after prime to check the fuel pump check valve. If pressure holds the problem is the fuel pump. If the pressure drops after the first check then the issue is either an injector or the fuel pressure regulator. My guess is the FPR. Either busted diaphragm or maybe some trash holding it open.
theogre OCT 06, 11:22 AM
F-pump valve test is just careful pinch a rubber section of feed line.
Regulator problems to same for return line.

Warning: Do Not pinch a line w/ F-pump On for more then a few seconds. Fuel is coolant and lube to the pump and blocking flow can cause pump failure.

So pump valve test is Pump On, Pinch, and quickly turn off power and watch the pressure.
Most Return issues Pump On, pinch return enough to see a spike then release the pinch. But If reg valve leaks,,, to same as pump valve.

If pressure still drops after those then isn't a "valve" problem.
Pump valve fail mostly mean just a bit slower to start. Problem is really isn't pump problem but can be early sign of hose/pulsator is dying.
Injector or regulator leaks must be fix right now.

Get hose pinch tools from HF etc or make them for small hoses.
Make from old pliers etc and grind of any teeth and sharp edges. Depending on pliers to make this, May need other grinding so tool won't pinch too tight near the hinge. "Bernard Pliers" and others w/ parallel jaws, long nose Visegrips and other can work w/ little or no mods or get scrap copper tube to spit open and put on the jaws.

------------------
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(Jurassic Park)

The Ogre's Fiero Cave

windex42 OCT 07, 02:43 AM
Thanks for everyone's help.

I tried really hard, and finally found some section of rubber to clamp onto.
From the passenger side, I peeled back the rubber wheel liner, then pulled back some loom covering the supply and return lines.
I clamped onto the supply line, and discovered that the Fuel Pump Check Valve is allowing fuel back into the tank through the supply line.
I determined this by turning the key (40lb) then quickly turning the key off. I clamped onto the line, and the pressure on the gauge no longer dropped (held firm at about 30lb).

I have some followup questions:
A local shop just changed the fuel pump, then changed it again under warranty (new fuel pump lasted about a month)
Should I talk to the shop about replacing the check valve under warranty, or would that have been a separate job?

Thanks again!
-==-
Nick
Patrick OCT 07, 03:03 AM

quote
Originally posted by windex42:

A local shop just changed the fuel pump, then changed it again under warranty (new fuel pump lasted about a month)
Should I talk to the shop about replacing the check valve under warranty, or would that have been a separate job?



The check valve is part of fuel pump, it's not a separate component.

I'd hazard to guess that it may not be the check valve that's leaking. The leak might instead be coming from the flexible hose (or the "pulsator" if it's been kept) that connects the fuel pump to the hard line within the tank.
windex42 OCT 07, 03:21 AM
Thanks Patrick

I think I follow the logic there, if the pulsator is bad, or if a line is cracked within the fuel tank, it will just depressurize right back into the fuel tank, so no real harm done.

If the check valve is bad, it would probably leak back through the pump itself.

I guess I'll give the shop a call once I put everything back together, see what they say.

I'll probably start a separate topic for this soon, but can I get an opinion of if this fuel drop might be causing some other problems I'm having?
1. The car has always started rough if it's been a couple days. It will sometimes start on the first attempt, but the idle will drop down real low for a few seconds, then come back up. Runs fine after I get about a block away from home
2. Lately, if I drive into town along the interstate (20 miles), as soon as I get off the off ramp, and stop at the light, my car dies. It starts right back up again, but then dies again at the next stop. Runs fine if I let it cool down. To try to fix this, I changed my TCC solenoid, it did not help. I currently have the TCC wire unplugged, and still get the same symptoms.

Thanks again for everyone's help
-==-
Nick
Patrick OCT 07, 04:05 AM

quote
Originally posted by windex42:

I think I follow the logic there, if the pulsator is bad, or if a line is cracked within the fuel tank, it will just depressurize right back into the fuel tank, so no real harm done.



...until it looks like this.