I have a 95 Z M6 and have a little problem. Once running it runs like a champ but getting it running is the hard part. The longer that it sits the harder it is to start. It cranks over just fine but won't fire. I have a new optima battery, new alternator, new NGK plugs and 8.8mm wires. Because of this problem I have replaced my fuel filter, fuel pump (put in a Walbro pump) and checked my fuel pump relay under my dead petal. also, no fault codes came up using tunercat Could a stuck open injector, a bad coil or opti be my causing this headach of mine??? I'm getting tired of poking around... any Ideas?? Thanks.

 

When it takes long to crank, verify if you have spark during that time. You should also check the fuel pressure with a test gauge. A leaky injector or regulator could be an issue.

 

Is there any way to tell if a injector is sticking open? when I ran data master I was running much richer than before I changed my fuel pump??

 

If fuel pressure bleeds off quickly after the engine is off, that could be caused by a leaky injector, regulator, fuel pump check ball. Further isolation tests can be made. Verification of a leaky injector has to be done visually with the injectors pulled up out of the manifold and the system pressurized.

 

How long should LT1's keep pressure in the lines? Yesterday I got it started and about a half of an hour after I shut it off I disconnected my fuel filter and there was no pressure in the line.

 

Spray some starter fluid in the throttle body. Then try to start it. That would be my first check.

Jeff D.

 

Hey Shoebox and Poorman, thanks for the replys. I'm going to head out to the gerage now for some more troubleshooting. Thanks for your help. I'll post how it goes later.

 

Definitely should be some pressure left in that short of time. I think my pressure stayed the same for at least an hour. I left my gauge on overnight and still had half the pressure 12 hrs later.

Here is something I had already written up for checking the system:

When you have a gauge connected and the pressure looks initially good and then bleeds off quickly, you can do a couple of tests to help you figure out where the pressure loss is.

What the factory manual says to temporarily install, is a set of "fuel line shut off adapters" (probably something the normal guy is not going to have available). You remove the fuel lines from the rail and connect these valves in between. This lets you shut off either side of the lines for testing.

You can do the same thing by pinching the flexible line to shut it off, but risk breaking it. You could probably do it relatively safely (your risk) by using a needle nose vise grips and putting some scrap hose as cushions on the jaws. Then use that to clamp off the line just enough to seal it.

You can use the fuel pump prime connector for pressurizing the system (jumper 12v to it to run the pump).

Watch your gauge as you jumper the prime connector. When you have good pressure remove the jumper and clamp off the fuel supply line (3/8 pipe). If pressure holds, you have a leak on the feed line somewhere before it gets to the clamp or at the check ball in the pump.
If it still goes down, release your clamp. Pressurize the system again, then remove the jumper and this time clamp the return line (5/16 line). If pressure holds, then the regulator is faulty. If pressure does not hold, you need to locate leaky injector(s).

If you can't tell a leaky injector from reading the plugs, you can look and see if injectors are leaking by removing the fuel rail screws and pull the rail and all the injectors up a little. Leave them over the injector ports. Pressurized the system and look under the injectors to see if any are dripping.

 

Good thinking that should cover all the basis
Kudo's shoebox!

 

Hey, thanks for all the info Shoebox! I've been tinkering with the problem some more today and hooked a fuel pressure guage to the car and am getting 0 psi with the key in the ON position. I'm also getting 0 psi when trying to start the car. I had the car running yesterday with the new fuel pump in it and it ran good. Now, again I am having really hard starting issues and even with the ignition in the start position I am getting 0 psi. Can a bad fuel pressure regulator cause 0 psi? ( the guage is brand new.)

 

i dont mean to jack your thread tuff lt1. but i've got a similar problem and i need to know if a lazy fuel pump could be causing my problem thats like this. like my fuel pump doesnt pump up enough pressure while its priming, and i have a hard start problem because it waits for my oil pressure switch to turn it on when it hits 4 psi? also i kinda have a hesitation when the car is in gear like it takes it takes the fuel pump awhile to catch up to a sudden demand when i blip the throttle. around 3.5 or 4k i get all my power back until the red line. if feels like a nitrous hit because its such a dramatic change. but like when it goes into passing gear it'll just not really respond to the throttle for a couple of seconds and then it takes off like always. this hesitation was noticeable only a week ago, and its only gotten worse. no access to a fuel pressure gauge as of yet so i'm having to just guess. but if i can locate one what should the fuel pressure be @ and is there a procedure for testing it.

thanks in advance.

 

I think it would. I just changed my pump because of this problem and before it acted like it was starving for gas when I got the RPM's up around 5500 or so. This condition proceeded to get worse until suddenly the car starded having the starting problems. After installation of the pump yesterday I actually got my car started and it ran better than I ever can remember it running. So I think that the pump was starting to go bad and causing that problem. Now I think that my fuel pressure regulator has crapped out on me at almost the same time as the pump. ( lucky me ) You should be able to fine a fuel pressure gauge at any normal autoparts store. I purchased mine today for $36. Your PSI on a 97 and earlier should be between 41 and 47. On a 98 and up should be 55 to 60 psi. Good luck and hope that helps.

 

Make sure you are getting the gauge on fully. If you need to, use the prime connector to run the pump for testing purposes. The regulator would have to leaking very badly to cause no pressure. There would be lots of gas in the vacuum hose if it was.

 

Hey Shoebox, I thought that the regulator would have to be leaking pretty bad to cause that to have 0 pressure. I thought that the gauge was on fully but maybe it wasn't. I thought that I could hear fuel surge into the gauge when I first turned on the ignition. Maybe I got a bad gauge from the parts store I'll check the vaccume line for fuel. It will have to wait till tomorrow though, time for bed. Thanks again

 

Ok, I got the gauge to working now and when I turn the key to the ON position I got 37 psi. With the after cranking the engine over the gauge went to 40 psi. It is supposed to be between 41 and 47 psi. After about 40 min of just sitting the pressure dropped about 4 to 5 psi. I did a resistance check on the injectors and all checked good. once I get some help I'm going to check the power to the injectors with a test light to see if they all are getting good power. Would 37 to 40 psi with the key in the on position cause the car not to turn over? Already changed the filter and the fuel pump so it would almost have to be a bad or clogged regulator right? Thanks for your advice.