Help! Fuel pressure low, 25 PSI, then zero.

[Guitared]

With a fuel pressure gauge installed, the pressure reads about 25 PSI for 2 seconds then drops to zero, ignition on, without starting . I expected the pressure to last only 2 seconds as described in the factory service manual but the pressure is well below 41-47 PSI and it is my understanding it should hold up for some time. I've replaced the fuel pump and the pressure remains low. Following the troubleshooting steps I need a specialty tool, J 37287, to insert in the fuel line. I can't find it anywhere. The engine runs rough and the exhaust smells "funny" with a slight bit of white-ish smoke.

I've come to a crossroads. I really don't want to let someone else work on her but I need her back. Any advice would be greatly appreciated.

 

[Aurora40]

The pump only runs for two seconds, but the pressure should be closer to 50psi and it shouldn't bleed off like that. I'd think you either have a huge leak, or the pressure regulator has problems? You could try clamping the return line under the fuel filler cap cover assembly maybe? See if the pressure will build up higher than 25psi? If so, at least it means the pumps are capable of more pressure, and I'd guess it's the regulator that isn't working properly.

You might also check the vacuum line for fuel, a lot of FPR's fail and start dumping fuel into the vacuum line, which might be why you aren't running horribly lean, yet are running crappy.

Just thoughts.

 

[Guitared]

Thanks for giving me some ideas. I forgot to mention I also replaced the FPR with no help. I think you're right though. I do have a leak somewhere and with no gas coming out of anything I'm thinking it might be an injector is stuck open. This car only has 60K on it and hasn't been driven more than 5K in the last year. Maybe the problem is not enough miles. I think I'm going to bite the bullet and buy some new O rings for the injectors so I can take them out and clean them and make sure thay are all working well. Can't hurt.

Thanks again for your help and if anyone could point me in the direction to buy some of these GM specialty tools I'd greatly appreciate it.

 

[Aurora40]

What specialty tools are you referring to? What are you trying to do? You don't need any GM tools to remove the injectors. You really don't need new o-rings either if you just want to pull them to look at them.

 

[Hib Halverson]

The tools to which "Guitared" refers are part of Kent-Moore's fuel injection test kit. Typically, only dealers, big independant shops or "well-heeled" DIYs will own that kit which consists of a K-M fuel pressure gauge and other diagnostic tools necessary for fuel supply system work.

I'm going to guess that this engine has one or more leaking injectors. If the existing injectors are stock, I'll also guess that most of the leakers cannot be "fixed" by cleaning because of internal rust.

Having them cleaned may or may not repair that problem, but when the shop doing the cleaning runs them on their test bench, they should be able to see any "leakers".

Regardless of price, the best replacements are RC Engineering injectors. Next best, if they're available for the LT4, are Accel's "disc type" injectors. The main difference between the two is quality. RCs will flow within about half a percent of each other. Accels usually flow within one or 1.5%.

Lastly, I just noted the first post was in the ZR-1 forum but the car listed for "Guitared" is a 96 LT4. What I say above applies to both LT4 and LT5.

 

[Guitared]

Hib and Aurora40,

Thanks so much for your replies. Just to show you how inept I am, I just learned about, and purchased at Checker, a tool that is commonly available to remove the quick disconnect fuel lines. I had no idea. I haven't done any car repairs in many years and am not up on current technologies. I made a commitment to myself when I bought my LT4 that I would service it personally as much as I could. Probably a mistake but I feel it is part of the experience when you own a Corvette. This forum is awesome and I definately need the advice.

After reading your comments I spoke with Wayne at RC Engineering. I cannot say enough good things about Wayne. He told me that I could actually clean these injectors myself if I had a way to energize them, which I do. He was very helpful and really laid it all out for me. RC Engineering will do a far better job than I cleaning them and I will probably send them out to them. He was most helpful.

Thanks again for all your comments. I'm waiting on new O-rings and clips from Art's Corvettes. I'll follow-up after the work is done.

By the way, is there a way to move this thread to LT4?

 

[Hib Halverson]

All the people at RC are like that. Russ Collins seems to have not only a knack for injectors but, also, hiring good people.

I've known Collins since his days driving the BME Top Fuel Dragster and he's been my "injector guy" since the early 1990s. No doubt, RC Engineering can be a bit high on price, but you're getting good value...not only with the parts, but in the service from Wayne and the others there.

 

[Jeffvette]

He told me that I could actually clean these injectors myself if I had a way to energize them, which I do. He was very helpful and really laid it all out for me. RC Engineering will do a far better job than I cleaning them and I will probably send them out to them. He was most helpful.

Save your money. The cleaning of the injectors is garbage.