Help! Scratching my head on this one.

[Jb77]

If anyone can help me it would be appreciated, i bought my 88 last year off my brother in law, it was just sitting in his driveway for 4 years untouched. I have replaced the fuel pump, filter, oil and filter, plugs, wires, battery, and even siphoned out old gas and put in 5 gal of premium with an octane boost. I am getting pressure, spark, and compression. I did a noid test on injectors, all firing, and all ohm'd out at 16-17. I am at a loss of what to do next because the engine fires for 3-5 sec then cuts out. I'm thinking that it might be electrical but no idea. In theory i have everything an engine needs to run, but it wont. Any help or ideas would be appreciated

 

[Jb77]

ps

and i am getting oil pressure also

 

[TedC]

Jb77, Did the vette run 4 years ago before the long storage? Do you have the FSM? Now is a good time to pick one up. Shade tree advice... I would verify injector fuel flow by cranking and then remove easy to get at plugs. Do they have a strong spark? Verify spark plug wiring order. The stock coil is pretty decent and can jump my spark tester even when set at 50,000 volts. How about the timing? A non-functional IAC (Idle Air Control)? Try cranking at 1/4, 1/2, and full throttle. Try cranking with MAF disconnected.

 

[geekinavette]

Did the vette run 4 years ago before the long storage

That would be my first question also...

 

[TWISTERUP]

There is a oil pressure switch which controls the fuel pump on top of the engine behind the distributor.....symptoms would be like yours in that when first cranking you'll have fuel pressure for a few seconds and then if the switch doesn't "see" oil pressure (so to speak) the fuel pump will stop running. I'm not saying you do or don't have oil pressure..the pressure switch itself may be bad JMO

 

[bradfordsvettes]

I am wondering if you are having a security issue? you could also do a fuel drop test on the injectors to make sure none are clogged from sitting just my 2 cents Steve

 

[Jb77]

thanks for all the ideas, i'll try everything and get back with the results, and yes it did run before it sat, he just got lazy and i hated seeing a perfectly good car go to waste

 

[vetteoz]

if the switch doesn't "see" oil pressure (so to speak) the fuel pump will stop running.

Switch is wired in parallel to relay and acts as backup should relay fail.

 

[geekinavette]

Switch is wired in parallel to relay and acts as backup should relay fail.

I don't believe that is correct...at least in '84 that is not how it operates, I don't have '88 diagrams tho. The idea is to shut the engine down in case of loss of oil pressure. The ECM will energize the FP relay for a few seconds to get the engine started. Once the engine is running the ECM signal shuts the relay off, leaving the only path for current to the FP through the oil pressure switch. If oil pressure is lost, the switch opens, fuel pump shuts off killing the engine. True they are connected in parallel (the oil pressure switch and FP relay contacts), but it is not as a backup, it is to prevent the engine from running with no oil pressure.

It doesn't make a lot of sense that this scheme would have changed from 84 to 88.

 

[vetteoz]

I don't believe that is correct.. The idea is to shut the engine down in case of loss of oil pressure. .......they are connected in parallel (the oil pressure switch and FP relay contacts), but it is not as a backup, it is to prevent the engine from running with no oil pressure.

Common misconception amonst Vette owners
Do a search , I know you will find different.
http://forums.corvetteforum.com/c4-...t-is-the-function-of-oil-pressure-switch.html

Corvette OP switch operates at 4psi. By the time that opened your engine would be dead especially if at revs
OP switches to save engines are typically around 15psi

 

[TWISTERUP]

Switch is wired in parallel to relay and acts as backup should relay fail.

agree 100%...I just pulled up the wiring diagram and it is wired to work that way. I'll say this though.. using the engineers logic on this circuit I'm surprised there's not a backup relay and maybe a backup fuel pump Seems like they didn't have much confidence in the relay and/or wiring. lol

 

[geekinavette]

Hmmm well gonna have to get the 'ol meter out and verify that!