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dallenpetersen
It all fun and games anyway.
Do you have a battery charger? If so, then pull the battery out and give it a long slow overnight charge. Tomorrow you can take the battery to your Autozone (or generic equivalent) and they can do a load test. My local autozone will even charge mine up if it needs it before load testing. I finally bought a load tester like last month just because I wanted one.... not sure it's worth it as far as a useful tool but I can now die with another tool.
Anyway - after the battery gets charged you can try starting it; or you can try starting it by jumping. Either way; once it starts take a voltage reading at the battery terminal at idle and share what the voltage reads. Optimally it should be in 14.3 vdc range ..... we can then go from there.
dallenpetersen
It all fun and games anyway.
Do you have a battery charger? If so, then pull the battery out and give it a long slow overnight charge. Tomorrow you can take the battery to your Autozone (or generic equivalent) and they can do a load test. My local autozone will even charge mine up if it needs it before load testing. I finally bought a load tester like last month just because I wanted one.... not sure it's worth it as far as a useful tool but I can now die with another tool.
Anyway - after the battery gets charged you can try starting it; or you can try starting it by jumping. Either way; once it starts take a voltage reading at the battery terminal at idle and share what the voltage reads. Optimally it should be in 14.3 vdc range ..... we can then go from there.
I’ll make sure to do that! Thanks again for the help
Just saw your start video. Do you have a fuel pressure gauge? Or a place to install one? That video leads me to believe it's not your battery. Do you know what ECM is controlling your EFI?
Just saw your start video. Do you have a fuel pressure gauge? Or a place to install one? That video leads me to believe it's not your battery. Do you know what ECM is controlling your EFI?
I do have a fuel pressure gauge, it’s right next to the air filter on the engine block. I’ve looked EVERYWHERE for which ECM it has and I’ve found nothing. Idk where else to look anymore
dallenpetersen
Just saw this.... that looks like a fuel pressure gauge. What does it read when you turn the key to ON (not START, just ON)?
Keep an eye on it while starting..... if the pressure drops away as soon as it starts we'll be onto something.
It's been ages since I had a 730 ecm but if I remember correctly they had some interface with oil pressure ..... oil pressure had to be valid or the fuel pump would cut out (don't quote me on that ..it's been about 20 years since that ecm)...... but check what happens with that fuel pressure.
Put the key to ON.
check fuel pressure (write it down).
while watching the gauge go to START ( may need assistance).
report what happens to fuel pressure.
Last edited by carriljc; Mar 11, 2025 at 11:23 PM.
dallenpetersen
Please pull that air cleaner off and let's see if we can identify that Throttle Body..... but the fuel pressure readings and that will help us move along
dallenpetersen
Please pull that air cleaner off and let's see if we can identify that Throttle Body..... but the fuel pressure readings and that will help us move along
20 psi before the key turn and then dropped to 15 after.
If you turn the car to the "ON" position, do you hear a relay click, and the fuel pump run? Can you locate that relay? Do you see any fuel pressure?
I agree, cutting out like that sounds like fuel pump, or ECM issue.
Is there an oil pressure switch somewhere inline with the fuel pump? Or an impact detection switch*? Perhaps there are some clues in the original EFI system instructions, that show what safety measures they added, or modifications they made to the fuel system.
In a pinch, you could always run the fuel pump manually.
20 psig seems a bit low for shutoff pressure in ON.
Do you know where your fuel pressure regulator is?
That sure looks like a first generation GM knockoff with 27 PSIG injectors & the first gen TPIs ran at 43 PSIG..
I suggest you adjust your fuel pressure to read 43 PSIG with the key in on.... you can tweak it again once you get it running.
IF I remember right (it's been ages) the inertia switch would even let the pump start (but, again, don't quote me on that....)
Seems like a fuels delivery issue to me. from the sounds of how it gradually got worse id say you have a possible plugged fuel filter inline somewhere or filter sock in the tank.
Pick up a can of carb cleaner at your auto store. Make sure it is the old style that is combustible. Some of them are not. Spray some of it down the throat of the intake manifold. Try to start the car. If it catches and runs for a few seconds, the problem is fuel related. Could be clogged fuel filter, bad pump, bad sender, bad relay, bad gas etc. If the car does not catch and run, focus on your ignition system. Engines need fuel, air and ignition to run. Jerry
I saw a problem very similar to this one back a few years ago when I left my 1988 C4 parked for a couple of months. The fuel pressure was okay when tested but the engine shut down very quickly after starting like yours is doing. I use gasoline with Ethanol in it because that is all that is available to us here in Northern Virginia.
On the C4 the fuel pump was able to make pressure but the engine cut right off. After watching the fuel pressure drop immediately after cranking the engine I was suspicious about the fuel delivery. I removed the factory line to the EFI system and measured the fuel volume that came out in 15 seconds into a graduated container. Then I ran a new hose from the fuel pump outlet directly to the EFI system. The difference was amazing and it was obvious that there was a major delivery problem. It turned out that my fuel line was very restricted in the volume of fuel and this led to the engine shutting off. With the bypass hose the engine would purr for hours and run at speed.
Gasoline with ethanol is "hygroscopic" and will attract moisture like brake fluid does. It seems that the ethanol caused the fuel supply line to get rusted shut, Internally, with no evidence of any corrosion on the outside of the line. There was just enough of a hole inside the line to allow the restricted fuel to be pressurized, just not enough volume for the car to run. To be able to work on the fuel systems you will need a fuel pressure gauge with a long hose so you can attach it to the windshield while operating the vehicle. On the C4 the fuel supply line runs under the passengers door area below the sill. The spot that rusted shut was right at the turn towards the front of the car which just happened to be the lowest point in the fuel system.
Any time you leave a vehicle with gasoline and ethanol in it I always add a Ethanol treatment to prevent this type of damage from occurring again. Steel fuel lines DO Corrode, internally and externally. When a catalytic converter gets plugged up the engine can start but will not rev which is similar to what you have going on but you don't have a catalytic converter on your Corvette.
How high the voltage goes after starting the car with a fully charged battery would really depend on the alternator's rated "output". If you had the 63 amp original alternator my car came with it might not push it to 14.5 right away. On the same car with a 125 amp alternator that would be a different story as it would push the voltage up faster. Now we see 150+ amp alternators on C3's and that just blows my mind. They will be pushing so much current and charging the battery at too high a rate which will have a bad effect on the battery and it longevity. If you do this on a plain-Jane Flooded lead Acid battery then you would be adding water to the electrolyte more often as it would use more at the higher charge rates. So what will happen to a "maintenance free", "valve regulated" or even the "AGM" battery that gets that much current pushed into it? Does a C3 Corvette really need 20+ amps of charging power at idle? A valve regulated battery would likely be charged until it pops open the vent to prevent it from rupturing, then it looses vital materials that help the battery recombine the electrolyte. You Don't want any valve regulated battery to "pop open". If your car uses 80 amps then use a 100 amp alternator. I have 2 electric fans, an EFI system and the basic loads from a very simple C3 and I don't need to use a huge alternator. Instead I use a Deep Cycle battery in my C3 because I have the fans running after the engine shuts down for a few minutes.
The Flooded lead acid deep cycle battery is a great product for use in a C3 when you have plenty of power consuming accessories and a "normal" charging system, the battery is recharged within minutes of the starting of the engine with my 105 amp alternator. The 63 amp alternator could even operate my Corvette without too much of an issue, it would take a bit longer to charge it up.
For a quick check to see if you can manually rotate the engine, use a 15/16 socket (typical) on the alternator nut. If the pulley slips under the fan belt, tighten the belt and redo. If you can't rotate at the alternator, loosen the belt to check again to make sure that the alternator is not locked up.
For a quick check to see if you can manually rotate the engine, use a 15/16 socket (typical) on the alternator nut. If the pulley slips under the fan belt, tighten the belt and redo. If you can't rotate at the alternator, loosen the belt to check again to make sure that the alternator is not locked up.
Engine turns over on battery power fine.. its not getting fuel from the sounds of it
