I tried to start my Vette the other day and it died on me.
The engine turned over and ran for about a minute and then died.
Now when I try to start the car it turns over and catches for a second or two before it dies. Anybody have any ideas what is wrong?

All the eletronics work fine, and the engine does turn over, but it seems like it's not getting fuel. Has this happened to anyone here before, and if so where is the first place to look for a problem? The fuel pump or the line? Any help is greatly appreciated.

 

When you start a C4 the fuel pump comes on for 2 seconds and goes off. If the engine catches and runs, a switch operated by the engine oil pressure turns on at 4 psi and supplies power to the fuel pump allowing the engine to continue to run. Most likely your engine runs on the pressure provided by the 2 second run and your oil pressure switch is not coming on, so the engine runs out of fuel and stops quickly after being started. You can prove this by measuring the voltage on the fuel pressure switch and starting the engine. If you see 12v for two seconds, the engine starts and then quits while the fuel pump fuse only sees 12v for 2 seconds, then your oil pressure switch is defective. You could also jump 12v to the fuel pressure switch and start the engine. If it runs continuously after starting, you have a defective oil pressure switch.

 

Thanks for the help! One more thing, could you recommend a good repair book or diagram that would show me where the oil pressure switch is?
I've never worked on a Vette of this vintage.

 

just a guess it's behind the distrib. or down by oil filter.Helms is the best manual

 

Correct.

 

while sitting in the car, above your right knee is the ALDL..some still have the plastic cover..some don't. If you look you'll see a 12 pin connector. the configuration top row first is;

FEDCBA that's from left to right, on the bottom row there are six other slots, but only one has a pin..pin G, directly below pin F,

so the lay out looks like this;

FEDCBA
G. . . . .

take a wire, and jump it from the battery(positive post) to pin G, this will allow the fuel pump to run...until the wire is disconnected.Try it and report back.

 

If the pump runs after terminal G is energized, your circiut/FP relay/connection is good and it will run until you remove the wire from the terminal. It does sound like it could be a bad oil pressure switch. The switch is a back up for the FP relay and runs the pump after 4 psi of oil pressure is meet. If the fuel pump doesn't run after you energize terminal G then there could be a problem with the relay/fuse/circuit. You can use a test light on the FP fuse when the key is turn to the on position and it should light up for 2 sec as the pump is primed then shuts off. Give it a try as Rick suggested and get back. Further troubleshooting is needed.

 

I agree the problem does sound like fuel, but, this (above) is NOT how it works. When the key is turned to "On", the ECM runs the fuel pump for approx 2 seconds, via the fuel pump relay. When the engine starts cranking, the ECM senses the pulses from the distributor and reactivates the fuel pump relay. As long as the ignition is "On" and the engine is turning, whether cranking or running, the ECM keeps the fuel pump running. When the oil pressure reaches approx 4 psi, the oil pressure switch closes and sends a redundant, 12 volts of power, along a parallel circuit to power the fuel pump, directly, in the case of a fuel pump relay failure.


This is still wrong. The "hot" side of the N.C. oil pressure switch will be hot any time the ignition is "ON". It will not lose power after 2 seconds. It would be possible for the negative (load) side of the oil pressure switch to have 12 volts during the 2 second priming period as feed back through the parallel circuit from the pump as energized by the ECM via the fuel pump relay. If you see 12 volts on the "load" side of the oil pressure switch for the 2 seconds, the relay has proved itself. If fuel pressure then falls, after 2 seconds and there isn't 4# of oil pressure yet, it is a problem with the distributor pulses reaching the ECM.


AND a defective fuel pump relay.

The best tests are to start testing long after the last attempt to start the car. Hook up a fuel pressure gauge and observe. Next, turn the key to "On", don't crank it yet. What has happened to the fuel pressure? Did it go up? Does it stay up or does it begin to drop fairly rapidly? It should go to somewhere near 40# and hold? If so, the ECM is triggering the relay and the relay AND the pump are working. If not, there is a problem with either the pump or the relay (not likely to be the ECM). It is worth it to note, that the 2 seconds of priming can only take place after the ignition has been "Off" for at least 10 seconds. If you wish to re-energize the fuel pump via the 2 second ECM/relay power up, you need to be sure the ignition has been off for at least 10 seconds.

These steps will get you going on the trouble shooting. Get back to us with your results and we can direct you further, if necessary. The very best book in the FSM (Factory Service Manual) which is printed by Helm Inc. and available direct through that blue link. It is the ONLY manual with trouble shooting charts to track down the cause of the various codes, and for problems, exactly like this one.

RACE ON!!!

 

Thanks for the help guys, this is Dale's husband, I've started to run the troubleshooting on the car as you suggested. (in between rain showers too) Here is what happened.

The car has been sitting for a week and this is the first time we've tried to start it since we discovered the problem.
The battery volt meter was reading about 10 volts, so I connected it to my pick-up to get it to 12.4
I then ran another wire from the positive terminal on the battery into thte car. After connecting the wire to terminal G, I heard the fuel pump activate. At least that is what I believe it was. The sound was a mechanical whir that came from behind me in the direction of the gas tank.
The car would not catch at all this time.

Unfortunatley we do not own a fuel pressure gauge so I can not run the other test that was recommended.

After searching our bacement I found the GM shop manual we got from the previous owner.

Thanks again for your help and patience.

 

I realize you posted this before my post, but it DOES perpetuate the false info flying around.

Energizing terminal "G" in the ALDL does not prove the condition of the relay.

The key idea here is, BACK UP. If everything else is good , BOTH the fuel pump relay AND the oil pressure switch would have to be bad, as one backs up the other.

RACE ON!!!

 

Yep, that sounds correct...the noise was the fuel pump. Unfortunately, you're gonna have a heckava time further trouble shooting without a fuel pressure guage...about $30-40. at any auto parts store. Glad you have the FSM..it will help, but only if you have the equipment, you see, now we've heard the FP running, but is it reaching the fuel rail..or is the fuel filter plugged? without the guage we can't tell. BTW, you should hook that battery up to a charger and let it charge til completely charged, or you may be replacing an alternator soon.

Just read the above, according to the wiring diagram in my 87 FSM from the power terminal behind the battery a fusible link runs to a point where it branches off, one branch goes to the oil switch, the other to the fuel pump relay...if the link blows, both lose power.And that would be the first place to trouble shoot, rather than condem both components.

 

Thanks for the clearing that up CFI, and as Rick stated a fuel pressure guage will be needed to go anyfurther with the fuel problem. Since you have the "FSM I assume", it will be easy to find the problem.

 

You have proved the pump, the pump wiring and the fuse, all to be good. What you describe WAS the fuel pump running. If you left the pump running while you were cranking it and it wouldn't start, I would move on...temporarally. It is possible to have a blocked filter, a bad regulator, or a few other items, but the car not starting with the pump running answers a lot. Before I would ask for you to invest in a fuel pressure gauge (which ought to be on your "wish" list) I would check for spark. Maybe now that you've found the book, you won't need us anymore. Let us know how it turns out.

RACE ON!!!

 

Good point. It is almost inconceivable that both the fuel pump relay and the oil pressure switch would fail simultaneously. However, it is possible that one failed and it wasn't noticed until the second went out. Your's is probably the more common C4 wiring scheme. In my '84 book, there is a 1.0 mm red, wire running from terminal 17 of the 24 terminal plug of the ECM that runs to terminal "A" of the fuel pump relay. Piggybacked in terminal "A" of that plug, is a second, 1.0 mm red, wire running to the hot side of the oil pressure switch.

RACE ON!!!

 

Started to rain again, this will have to wait.

Nah, this is too much fun!

 

After the rain has stopped, you can try this..with caution (rags and safety glasses) on the passenger side, back toward the distributor you will see an object that looks like a tire valve, take the cap off..go turn the igniton switch to ON, after you hear the fuel pump, turn the key off and carefully, observing from the side, rags in hand supress the valve, just like you would to let air out of a tire..gas should spew out of the valve...this should tell us if adequate fuel is reaching the rail..replace the cap.

I'm really at this point concerned with the health of your battery...and this may just turn out to be the culprit, 10 volts ain't gonna get it, sometimes even trying to jump it as you did is not sufficient.

Glad our rain is finally gone and now we're in the high 80s.

 

The battery is brand new. I just put it in last month and the car ran great for weeks before this problem developed.

When we first encountered the problem with the car we thought that there might be moisture in the line so we kept trying to start it, and start it, and start it. This is because the car was in the middle of the driveway and blocking our other cars. After doing this for a while I think we began to wear the battery down. Without the car running the battery, obviously never recharged. In the end we had to push the car (up hill) out of the way.

 

Charge the battery and check for spark. I have my own way and may differ from others. I use a spare spark plug and remove the spark plug wires (remember/label which is which or do one at a time). Put the plug in the wire and hold it 1/2" from the exhaust while someone cranks on the engine. You should see a blue spark and test all 8.

A quicker way is to put your finger in the wire end and crank, but more painful.

 

hold it hell mannnnnnnn I've been zapped good doing that ONE time , should be able to disconnect the plug wire, put an old plug in place of it and LAY it on the manifold, you should easily be able to see it fire. RRT, do you have a little sadism in you

 

That doesn't make sense. The ECM term 17 goes to the low side of the relay? And a wire connects from this circuit to the switched 12V side (when >4psi) of the oil pressure switch? I know the ECM has a 12V input to see fuel pump voltage...

Can you clarify?

Also, the reference pulses, do these come out of the module inside the distributor?