To start with my car will start and run for a second or two and then die immediately. It does not do this every time I start the car, only sometimes. If I give the car some gas while cranking it, it will start and run rough. When I accelerate it will be okay(but not great), but as soon as I let off the tach starts jumping all over the place and the car starts to buck, but does not die. I have used the prime wire on the fuel pump and the pump comes on and runs at 42 psi, but when it is running it only has 34 psi(with the line on). Why the difference? Also my pump does not prime every time I turn the key on. If I turn it on it will prime and if I shut it right back off it and then turn it back on 10-15 seconds later it will not prime, is this normal? I checked a buddies 95 Z28 and it turned on and primed every time he turned it on.

Does this sound like a bad fuel pump? Opti has 2k on it, ICM has 500 miles on it( and I checked it with a known good one and still did this), 2k on wires, new plugs TR6s, 500 miles on coil, 2k on fuel pump. BTW pump is a Walbro 255. If it is not the pump what else should I check into?

 

The difference between priming at the pump connector with the engine off and having the engine running is there is no vacuum at the FPR when you simply primed it with the prime connector.

Perhaps the regulator has a problem giving you the low pressure? Since you want pressure to be about 42 pounds when running, I would have to say 34 is too low.

 

Okay I have a code 16 low resolution code set. The car has been missing pretty badly and sometimes will not start or starts and then just dies immediately. Is this a bad opti. It has a new opti harness on it and the wiring harness is a painless unit so I have checked both of those. I nkow that some people say this can be caused by a low voltage problem and I checked the battery 12.6 volts off, alternator 14.4 volts running. I did not check the cranking voltage but if I need to I will. The car always starts right up and then just dies immediately. It does not do this al the time and it seems as the problem will come and go.

Should I just put a new opti on and be done with it? Or do something else?


BTW thank you speedy for always helping me with all my electrical problems.

 

Could be an opti problem since it has to deal with the low res feed back signal from the opti to the PCM. Could also be a wire / connection issue and rarely it's a PCM issue.

 

You want 42psi when there is no intake manifold vacuum..... e.g. at WOT. 34psi at idle with full vacuum is low but not unacceptable with good vacuum from a stock cam. Rail pressure is seldom 42psi under normal driving conditions. The ultimate test of fuel pressure is what it reads at max load/max RPM.

I'm assuming "giving the car some gas" means you are opening the throttle slightly to start the engine. With the electronic fuel injection, you are not providing any more fuel, just allowing more air into the engine. Put the throttle completely on the floor, and the PCM enters "clear flood" mode, cutting fuel to the minimum.

 

Did you rosolve the problem? I am having the same problem, I have a 95 Z-28 convertible. My husband bought a new LT-1 motor and somehow managed to get it installed with help from a friend of his. It was good for a while, but now when I start try to start it it will fire and then die. If i hold the key on and give it gas it will start but then run really rough. If i continue to feed it gas slowly and the rpms go up it will smooth out and everything is ok until i turn it off again. My husband is guessing and i am afraid he will change a bunch of parts until he finds what fixes it. That can get very expensive.
Speedy Gonzales you seem to know it all maybe you can help me.