Help! can't get C4 running

[garyg]

Problem started when I got an OBD code 36 indicating Mass Air Flow sensor, so I cleaned it with CRC remounted it and resulting codes are 12, which is normal. Next car would start but shut down immediately, I could tell it wanted to fire. I suspected the fuel filter ( tackle easy things first ) I replaced it.
Still, Vette won't fire up. I tested the fuel pressure at the fuel rail with a gauge, reading with only the ignition on is 40 lb. If I spray starting fluid in intake car will fire up strong then shut down. I am getting no other codes on the OBD except 12.

I would appreciate input from a more experienced Vette owner.

 

[joe j]

I had a similar problem - it turned out to be one of the 8 fuel injectors. Try checking them with an OHM meter, should be around 15ohms.
If you see one at .7 or .8 that's the problem. If you disconnect that one the car should start.

 

[garyg]

Thanks, I am at wits end.

 

[DonB]

Also here a little information to help your diagnosis. The injectors get a constant positive to one pole on the injector when the key is ON. The ECM switches and completes the circuit by connecting the other pole to ground. Thus opening the injector. 40 PSI at the rail is adequate.

 

[garyg]

I tried again spraying starting fluid into intake manifold and the Vette fires up strong but shuts down. I then tried removing the MAF unit and again, same thing with starting spray, starts up strong then shuts down. The only readings I get on my OBD readout is 12, normal, which surprises me.

I will say that I didn't drive my Vette parked outside for a month during the 100+ days and I wonder if the fuel injectors are "plugged".
But why I don't get any problem code readings is a puzzle.

 

[Otter]

I had a similar problem - it turned out to be one of the 8 fuel injectors. Try checking them with an OHM meter, should be around 15ohms.
If you see one at .7 or .8 that's the problem. If you disconnect that one the car should start.

^yeahthat..Had a similar problem on an 89 I had and turned out to be a bad injector. Note: You say you are the original owner and if it's the original injectors, replace them all; I found it to be a real PITA job. Also note that I am not an 'experienced vette owner' but I can follow the methodologies for diagnosis in the Factory Service Manual.

 

[ecss]

I tried again spraying starting fluid into intake manifold and the Vette fires up strong but shuts down. I then tried removing the MAF unit and again, same thing with starting spray, starts up strong then shuts down. The only readings I get on my OBD readout is 12, normal, which surprises me.

I will say that I didn't drive my Vette parked outside for a month during the 100+ days and I wonder if the fuel injectors are "plugged".
But why I don't get any problem code readings is a puzzle.

Any signs of rodents have been under the hood or in the interior of the car?

More likely the fuel injectors are not being pulsed by the ECM.

If you rent a noid light you unplug one of the fuel injector connectors. Insert the noid light and
crank the engine. The noid light should flash indicating the injector is being pulsed.
No flash verify there is 12 volts on one one of the injector connector wires to the negative battery terminal
when the ignition is On.

No 12 volts verify INJ1 and INJ2 fuses are good. INJ1 Fuse should be good because you say the Service Engine Soon indicator works.

You can also pull spark plug number 1. With the spark plug removed, continually crank the engine.
You should see and smell fuel being pumped out of the spark plug hole. If only air comes out of the spark plug hole I'd say the VATS Decoder module could be defective.

When you insert the ignition key in the key cylinder and turn the ignition On the resistance of the key pellet is read. If it reads the proper resistance the starter enable relay is enabled and a 30 hertz square wave signal is sent to the ECM telling it to pulse the injectors. If the ECM does not receive the fuel enable signal the ECM will never pulse the injectors and there is no code to detect that failure.

You say you are located in Annapolis, MD.
I'm off of Forest Drive and Spa Rd.

Send me a private message with your contact information if you want me to stop by.

 

[garyg]

I have found the problem to my starting problem, after removing the fuel pump I used a battery powered siphon and have excessive water in my tank. I will have to completely drain the tank.

 

[Hib Halverson]

I have found the problem to my starting problem, after removing the fuel pump I used a battery powered siphon and have excessive water in my tank. I will have to completely drain the tank.

No doubt that will do it.

Also, if the water has been in the fuel system for a while, all 8 injectors are suspect because it was not until the mid-90s that Delphi changed the design of their injectors to make them more tolerant of moisture.

In short, the injector internals are prone to rust.

 

[garyg]

We ran a test meter on all eight injectors and they indicated normal, the car would fire up strong briefly once I sprayed starting fluid mist into the intake. We used a computer to do readouts on all elements. I then resorted to pulling the fuel pump from the tank.

 

[garyg]

Update on C4 not running. A test of the fuel pump indicated 40 lb. pressure, the pump was removed and all the gas ( 18+ gal ) was removed. I fitted a new gasket and reinstalled the pump with all correct connections. I put in 5 gal of new 93 octane fuel saw the fuel gauge reading correctly however with the fuel pressure gauge connected I got zero fuel pressure when trying to start the car. The OBD readout is showing 12.

Is it possible the problem is the fuel pump relay? The fuel float did indicate the correct level in the tank.

 

[garyg]

Further follow up, I replaced the Fuel Pump Relay still no pressure reading on pressure gauge, also I can not hear the pump running. I have ordered a new pump and pump filter to install in the fuel pump assembly.

 

[DonB]

Are you getting power to the pump? Throwing parts at it can get real expensive. Get a FSM and use the troubleshooting guide. Are all your fuses, fuseable links and grounds good? There are power and grounds going places you'd never expect. For instance, If the 5 amp LCD fuse is bad the fuel pump won't work, too. The courtesy fuse is another that can(and does) wreak havok. Check every fuse and link with a test light to be sure you are getting power. Also be sure you are getting ground to the pump.
Take a couple jumper wires and go directly from a battery to the pump + and - to check the pump. Use caution to avoid sparks! Boom!

You said earlier that you were getting 40psi at the rail. So the pump is doing it's job. When you turn the key to ON(NOT START) the pump should run for 2 seconds and quit. This is normal. Did you check the oil pressure lock-out switch? NORMALLY, If the engine does NOT have oil pressure after 2 seconds(or you should lose o/p) the switch will (tell the ECM to) turn off the pump. There are 2 oil pressure senders buried behind/below the distributor. The short single wire one is for the o/p gauge and the multi-wire switch (that looks similar to a 3/4" deep socket) is the oil pressure lock-out switch. These switches have been known to STICK after getting old and sitting for a while. It gets gummed up by the oil and after it sits in the OPEN position for extended periods it'll stick.

Definitely check this before getting to crazy. Sometimes, It's best to pull the distributor, otherwise you can't hardly even see it. Like I said, It's buried. Check the wires too. They get old and brittle and mice like to chew on them too. TRUST ME! You "Never Know" with these old Vettes. I'd post my schematic, but I have a '90 and there are a few differences and I don't want to confuse the issue.

 

[garyg]

Thanks for your insight, all the relevant fuses checked out. To recap the no starting problem:
1. Car was running OK with a code 36 (MAF indication).
2. I cleaned the MAF with CRC, OBD code read 12. Car then wanted to fire up strong but wouldn"t run.
3. Sprayed starting fluid into intake, car would start strong but die.
4. I installed a new fuel filter to no avail.
5. Ran a fuel gauge pressure check, 40lb reading, perfect.
6. Suspected water in tank ( car had 18 gal of hi octane SHELL ).
7. Removed the fuel pump assembly and siphoned out all the fuel.
8. Pump assembly "looked OK" reassembled and put 5 gal of new hi octane SHELL gas in tank.
9. Now fuel pressure gauge reads "0". I can not hear the pump running with ignition in on position.

A Corvette Action Forum member that lives near bye came over (before I pulled the fuel pump) with a lap top and test diagnostic reader ( we had checked the fuel injectors then and all eight read perfect. That is when we suspected water in the fuel.

 

[DonB]

Well, if the pump ran before and now it doesn't; reverse engineer everything you did. Also is the pump NOT running due to lack of POWER or a ground? That will lead you in the right direction. Have you tried to "hotwire" the pump out of the car. Do NOT run it for an extended time with out it being submerged in fuel. It'll fry. Just verify it works.

 

[garyg]

Well, if the pump ran before and now it doesn't; reverse engineer everything you did. Also is the pump NOT running due to lack of POWER or a ground? That will lead you in the right direction. Have you tried to "hotwire" the pump out of the car. Do NOT run it for an extended time with out it being submerged in fuel. It'll fry. Just verify it works.

My plan is to tackle that tomorrow. Thanks for your input

 

[garyg]

I plan to check that out tomorrow. Thanks for the input.

 

[garyg]

New follow up to "fuel pump not running, C4 won't start". I had just replaced the fuel pump relay, I reinspected all the connections at the fuel tank and I then bridged the connection with a jumper wire at the OBD unit under the dash, connecting A to G and ... nothing.

I now have a new Bosch elect. pump which (I guess) I will install in the pump assembly. I don't know what else to check.

 

[Hot Rod Roy]

Are you getting 12 v. at the fuel pump connector? Testing first is much better than throwing parts at a problem!

 

[garyg]

Are you getting 12 v. at the fuel pump connector? Testing first is much better than throwing parts at a problem!

I plan on testing the connection at the pump today before having to remove it... again.