When you turn the ignition to the "ON" position, the fuel pump turns on and primes the system. Once the fuel pump cuts off, how long should the system stay pressurized?

Back story: Went for a drive yesterday after two months of the car sitting (it's been so hot and my FMIC setup makes it hard for the radiator to keep the engine temps down). Once the car fired up, she drove fine as she warmed up for 2-3 miles. After she was warm, I got on the turbo a bit and then when I got back to cruising, she surged, stuttered and died. I couldn't get the car to start but I also was driving on a pretty weak battery Got a tow home and I got my battery charged and the car started up the first time I tried last night. I am still troubleshooting the fuel system just to be safe. I bypassed the fuel relay in the diagnostic port (Connect F/P to Ground) to see if my pump was running (which it is). When I do that, I see my fuel pressure rise to a steady ~35 psi (it's a solid 40psi when running). As soon as I disconnect the bypass and fuel pump cuts off, the pressure drops to zero pretty quick. Is that normal? Some of the feedback on my facebook post about this issue is that I have a fuel leak, a bad fuel pressure regulator, or a stuck injector. I trust this site more than I trust the facebook collective though. Here is a video of the issue - the clicking is the relay firing to turn the pump on and off:


Thoughts?

 

Update: I spoke to Bryan @ Rotorsports Racing and he said if my car were stock, it would bleed off pressure slowly but with a different FPR and Pulsation Damper, it going to zero so quickly isn't uncommon and said its better because you dont want pressurized system if the car isn't running. Still curious what other peoples thoughts/experiences are.

 

There was a thread recently about this, some of the aftermarket FPR's just don't maintain pressure after shutdown. If you can jump the F/P and GND connectors and it holds pressure while trying to start the car that's not the problem.

See if you can find the thread about FPR's and pressures bleeding down, it was a few months ago. Went into great deal on the topic, someone was troubleshooting the same thing you are. That will at least educate you on how that system works and how it should work.

Dale

 

A stock system will drop over time (like 30 mins or so?). Not sure how the aftermarket stuff will behave. Theres been a lot of talk recently about the submerged hose from the pump in the tank leaking with aftermarket installs, maybe worth a look.

 

That’s normal, mine goes to 10 quickly and bleed to 0 shortly after, and I have an Aeromotive FPR. As Dale mentioned, pressure after shut down is not important, as long as it holds pressure when the car is running you are fine. You can also adjust it to make sure it holds higher pressure just to be on the safe side, I test mine to base plus a couple psi above max boost with the car off, also a good time to check leaks when the pressure is high.

 

Awesome. Thanks for the replies. I’ll look for the old FPR posts. Based on my issue, Bryan suspects I might have a bad alternator since the FPR seems to work as intended. Going to pull it off and have it tested. A bad alternator and weak battery could cause all sorts of low voltage issues including a fuel pump that’s couldn’t deliver fuel properly that could have caused stuttering and surging. At least that’s the theory....

 

OSomeone of the Facebook group claimed he was holding pressure and still had a leak. That being said, I don’t smell gas when my pump is jumped to run but the car isn’t started...at least none my nose can find.

 

If you have an external leak you would be able to smell it for sure. A leak inside the gas tank is another issue - if there's a split or leak on the line going from the fuel pump to the outlet pipe on the top of the hanger, the gas will spray back into the fuel tank. A leak there can result in lower pressure or lower volume. You may have enough fuel flowing to maintain pressure at a static or idle test, but at full load with the injectors wide open there may not be enough flow to maintain pressure.

Definitely want to start with the charging system, if your alternator isn't up to the task you'll have all sorts of odd problems. Warmed up at idle you should see around 13.5v measured at the battery terminals. Anything under 13v is a problem. The number may be in the 14's when the car is cold.

Dale

 

I was referring to external leak, for internal leak you’ll have to pull the hanger to check, but if the leak is bad enough you might see issue if you do do the high pressure test.

 

had the alternator tested at two different auto parts store and it passed. Ugh. Back to the drawing board.

 

that was me. I forgot to tighten one of the hose clap when installing a new fuel pump. fuel was spraying on to the top hat and seep out onto the tank. I still had pressure, my fuel lab fpr with the FFE fuel kit held pressure after prime. I have noticed that pressure drop was much slower after I fixed the leak. I was holding a 43.5 fuel pressure with that leak.