[Bobber]

After sitting for two years my 93 Z28 will not start. The speedometer registers while the engine is cranked. I've never noticed that before. Also, mice nest material blew out of the exhaust pipe when engine is cranked. It acts like it is going to start the first time you crank it, shows no signs of life after that. Thinking exhaust may be plugged but speedometer registering (up to about 80mph) has me stumped. Car has new fuel pump and has good pressure.

 

[IVIitchell]

well maybe try to clean it up a bit like the filters and what not, see if anythings unplugged or rotted etc. Or maybe just give it some gas.

 

[cocobolo95]

Did you drain all the old gas out and put new fresh gas in. You might want to check your wiring in the engine compartment, as rodents love to chew things. Just so happens we have the 93 factory service manual available to download. Look in 4th gen section for thread titled "GM service manuals" Manual has full wiring diagrams.

 

[Bobber]

I did drain all the old gas and I've checked in the engine compartment and under dash for chewed up wiring and found none. I do have 47lbs of fuel pressure and have spark. However, since it won't run with starting fluid I'm starting to suspect the spark is not timed right. As soon as I get a chance I'm going to test the Opti-spark using the info on this site.

 

[Bobber]

Finally got back to working on the Z-28. There are no trouble codes stored in the computer. Hooked up the fuel pressure gauge again, when the new pump goes on pressure rises to about 50 lbs and stays there or a little higher while the engine is cranking. However, if you just turn the key to on the pressure stays at about 50 as long as the pump is running, then goes way down. My repair manual says that it should stay at about 47 after the pump quits running but does not say anything about what would cause it to drop suddenly. I looked at all the fuel lines and cannot find a leak.

So far I've replaced the fuel pump (checked the old one after removing and it definetly was bad), pumped out the old gas and added fresh, and replaced the fuel filter.

It will run 3-4 seconds the first time you try to start it, then no sign of life. It appears to have good spark.

 

[cocobolo95]

Things that will cause fuel pressure to drop quickly once pump stops; pressure regulator stuck partially open. Fuel injector(s) stuck open. check ball in fuel pump bad. Fuel line in tank that connects fuel pump is leaking.

If fuel pump gets good pressure when it runs then pressure falls quickly, engine will have a difficult time running because it needs that pressure to spray the fuel through the injectors.

 

[Bobber]

I put a valve in the fuel line downstream of the pressure regulator that I turned to closed. Pressure still drops almost instantly. Pulled pump from the tank and the hose from the pump appears fine, none of the fittings just outside of the tank were leaking. How can I check to see if the check valve in the new pump is working other than trying another pump?

Thanks for your help.

Bob

 

[cocobolo95]

Don't forget to pull the fuel rail up so you can check for injector leakage. If no leakage there, and none from fuel lines, then pump would be the suspect. No definitive test I know to see if check ball is good, it's just the conclusion left when other causes have been eliminated.

 

[Bobber]

Thanks for the advice. Just finished pulling all the injectors to replace O rings, so I just checked for leakage there. No problems. I also pulled the pump out of the tank again and replaced the hose from the pump to make sure it was not leaking. I guess I'll pick up another pump and hope for the best.

Bob