85 corvette starting issues

[Abarrios]

Hey guys, I have an 85 corvette that will not start. Its cranks but won't fire up. I have spark, new ignition coil, new spark plugs, new wires, and new fuel filter plus a fuel relay and still won't start. The fuel rails have pressure, the fuel pump engages as well. I'm completely out of ideas any help would be great.

Thanks

Andrew

[David Pozzi]

Is the tuned port engine? Not cross-ram dual throttle body?

Squirt a little fuel or starting fluid into the intake & see if it tries to start. If it does, you either don't have enough fuel pressure, or the cold start injector isn't firing.

[wedgehead]

Just got one of these running the other day. Had to do the VATS bypass module and then no injector trigger. Check for power to injectors, then check for trigger to injectors. Both banks are fused separate. If no trigger the purple white wire coming out of the distributor four wire connector. Momentarily touch a test light hooked to positive to the purple wire PCM should trigger injectors.

[epeterson]

David Pozzi: I am working on this project with him also. It is the tuned port engine and we did spray starting fluid in and it did start up. If its a fuel pressure issue where could the problem be?

[David Pozzi]

Kenny, I suspected the VATS at first, but on my Camaro, it kills the starter. Does VATS disable injectors on an 84 Corvette? If so, that's the most likely cause.

Epeterson, here is info on the VATS. http://www.drdetailshop.com/gmpellet.htm

[Abarrios]

David, thanks for the link, I took a look at my keys today and it seems the VATS resistor has fallen off. With the info from the link I am going to attempt to bypass the system. Thanks for your help and I'll post if I get her started.

[David Pozzi]

Thanks to Wedgehead.

[Abarrios]

Well I bypassed the VAT system and she still won't start only crank. I found out there is 0 fuel getting into the cylinders so I am going to replace the fuel pressure regulator, does this sound like a good idea or just a waste of time and money? I replaced the oil pressure sender unit as well, but still no luck.

[David Pozzi]

Test the injector plugs using a noid light to see if they are triggering. Do not just use a test light, you can damage the computer. A volt meter can be used to check if one injector wire is hot, - it should be. . The other side is grounded by the computer to fire it. I think yours is batch fire, half fire in one pulse, half in the other. You can probe from battery positive to the injector plug ground side to see if the ECM is triggering the injector. I suspect it isn't.

The pulse signal comes from the distributor module to the ECM. If this fails, the ECM won't know when the engine is running, or how fast.
You need a minimum pressure to fire the injector. Pressure should be 43.5 with a minimum of 38 PSI. If pressure drops much below 38, you won't get any fuel out of the injectors. You need to test weather it's a triggering or pressure problem.

If you clamp shut the fuel return hose, you will get full pump pressure as a quick indication of what the pressure regulator is doing. You need a fuel pressure gage to know what's going on.

You are changing a lot of parts, but doing very little to no diagnosis or testing.

[wedgehead]

Do check for trigger and power to injectors. CHECK the fuses for the injectors on this car. The in jectors will backfeed through the harness so check the fuses with a test light. Then you can check to see if the ECM is capable if triggering injectors. The purple with white wire is the signal to the ECM from the ignition module. Do the test with a test light hooked to positive and momentarily touch the terminal end. it should flash a noid light hooked to injector plug. The fuel pump should run with key on and then shut off after 3 seconds. get a pressure gauge on the test port.

[epeterson]

There were no power going to the injectors so he changed the fuses and it still doesn't work, he's got his hands full so i'm posting

[David Pozzi]

I'm thinking the VATS may not be bypassed correctly, but I have no experience with it to say where to go from here.

[epeterson]

We jumped the codes yesterday and got these errors:
Radiator coolant level error
Electronic spark timing
Mass air flow sensor error
Throttle position error

The radiator is new, and completely full with coolant. We tested the spark on every cylinder, we are getting spark but the timing might be off? Two suggestions we made with the mass air flow sensor, one was unplug it because it might be faulty and might start. It did not, the second was buying MAF cleaner and that did not work either. I know of a third gen camaro sitting in weeds with a tuned port injection engine so we might ask that guy if we can buy his mass air flow sensor for cheap and try a different one. We have no clues on the throttle error. Hopefully some of this info helps for you guys giving suggestions.

[Abarrios]

Hey guys got her running today!! After all this hard work it ended up being a bad ECM. Bought a new one plugged her in and she started right up!
Thanks for all the advice and tips very much appreciated!!

[David Pozzi]

That's great news! Check everything over for vacuum leaks. Any excess oxygen in the exhaust will be sensed by the oxygen sensor & will make the system run rich.

[gak68]

Hey guys got her running today!! After all this hard work it ended up being a bad ECM. Bought a new one plugged her in and she started right up!
Thanks for all the advice and tips very much appreciated!!

Just out of curiosity did GM program the ecm to have the service engine soon light blink once if the ecm is working properly when you first turn the key to on? I know I was having issues with my old 1996 Chevrolet and read about that feature as a quick way to rule out a malfunctioning ecm. I completely forgot about it until you said bad ecm.