Good Morning guys, it's been awhile.

My car has been up at my parents house since the beginning of January as I have been undergoing projects at my own house and wanted the car safe and out of the way. Went to pick it up Saturday to bring her home and noticed it had a pretty rough time starting. It had been on a battery tender so I didn't think it was the battery but had it tested anyway and all came back fine with it. Got it home and tried to do a fuel pressure test but my tester is so old it was spraying gas out of the hose . I am waiting on a new fuel pressure tester to come in from Amazon, did not like the one the local parts store had.

Anyways, the fuel pump does prime when I turn the key on. If I let the pump finish priming with the key on/engine off and then try to start it, it barely wants to fire. But! If I start the car while the pump is in the process of priming it fires right up. This leads me to believe the pressure is bleeding off somewhere, probably back into the fuel tank. I removed the vacuum line going to the FPR and no fuel came out of the line or FPR so I suspect it is still good. Weird thing is it runs great once it is running, did not give me any hiccups at all on the 1.5 hour drive home.

I am leaning toward the fuel pump since it seems to start normally if I start it while the pump is priming. For whatever reason I always have had a habit of letting the pump prime first before starting. I did replace the fuel pump back in 2015 with a Racetronix unit that got rid of the fuel pump pulsator with a piece of submersible fuel line. I am wondering if that submersible fuel line was really up to spec or is starting to possibly degrade? I am going to wait for the fuel pressure tester to come in for further diagnosis but wanted to try and gather some of your guys thoughts? Car is a 1994 LT1 6 Speed Coupe.

 

I had a bypass valve in my fuel pump fail. It would build pressure, but then drop it. You won't be able to test without a pressure gage though.

 

Is this bypass valve within the pump itself?

 

Yeah. The hose used to replace the little fuel vibratory thing was fine, but the pump itself had the leak. I had a lifetime warranty on it from the auto parts store, so a few bolts later and a trip to the store and all was cured.

I tested it by clamping the fuel lines during the prime. If the fuel feed line was clamped while priming but up to pressure the pressure would hold, if not the pressure would drop off.

 

Very cool, I am pretty sure that is exactly what is going on. Yours ran fine once started?

 

Yeah, no issues after it started. I ended up realizing after priming it a few times it would start, but I think what was really happening is I was hitting it in that right time frame where the pump was priming and hadn't started to leak back yet.