Car starts and then immediately stops

Tiny
RIK ENDERS
  • MEMBER
  • 1994 CHEVROLET CORVETTE
  • 5.7L
  • V8
  • RWD
  • MANUAL
  • 56,000 MILES
I start my car immediately it sounds like all cylinders fire over, but then it just shuts off all. My lights work everything on the dash works. I have replaced every sensor. I replaced up to spark and still I had the same problem it starts and then immediately stops.
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Sunday, October 2nd, 2016 AT 8:17 AM

19 Replies

Tiny
WRENCHTECH
  • EXPERT
The first thing to check would be the fuel pressure. It should be 41 to 47PSI and hold within 5 PSI when shut off.
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Sunday, October 2nd, 2016 AT 11:05 AM
Tiny
RIK ENDERS
  • MEMBER
Checked it. It is good. Stayed at 42 lbs. New wires, plugs, opti spark, key tumbler, ignition, I miss, map, iac. Every electronic gadgets there is.
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Sunday, October 2nd, 2016 AT 11:44 AM
Tiny
WRENCHTECH
  • EXPERT
Do you have a security light on or flashing when you try to start it?
Have you scanned for stored codes?
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Sunday, October 2nd, 2016 AT 11:55 AM
Tiny
RIK ENDERS
  • MEMBER
No security System on the car the ODP one is not operating.
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Sunday, October 2nd, 2016 AT 1:25 PM
Tiny
WRENCHTECH
  • EXPERT
It definitely has an operational immobilizer system. That cannot be totally eliminated.
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Sunday, October 2nd, 2016 AT 1:28 PM
Tiny
RIK ENDERS
  • MEMBER
Sorry, it is a 1994 in a 1984 body using 1984 harness. No security or vats at all. Was driving and it died. Tried to start it, it turns over but dies immediately.
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Sunday, October 2nd, 2016 AT 2:20 PM
Tiny
RIK ENDERS
  • MEMBER
Fuel pressure is at 40. If I started that but starting fluid in the throttle body it keeps attempting to run so I do not think it is an electrical problem.
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Sunday, October 2nd, 2016 AT 2:22 PM
Tiny
WRENCHTECH
  • EXPERT
The only way you are going to find this problem is you are going to have to determine which function is dropping out at the moment it dies.

All "crank, no start" conditions are approached in the same way. Every engine requires certain functions to be able to run. Some of these functions rely on specific components to work and some components are part of more than one function so it is important to see the whole picture to be able to conclude anything about what may have failed. Also, these functions can only be tested during the failure. Any other time and they will simply test good because the problem is not present at the moment.
If you approach this in any other way, you are merely guessing and that only serves to replace unnecessary parts and wastes money.

Every engine requires spark, fuel and compression to run. That is what we have to look for.

These are the basics that need to be tested and will give us the information required to isolate a cause.

1) Test for spark at the plug end of the wire using a spark tester. If none found, check for power supply on the positive terminal of the coil with the key on.

2) Test for injector pulse using a small bulb called a noid light. If none found, check for power supply at one side of the injector with the key on.

3) Use a fuel pressure gauge to test for correct fuel pressure, also noticing if the pressure holds when key is shut off.

Once you have determined which of these functions has dropped out,
you will know which system is having the problem.
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Sunday, October 2nd, 2016 AT 2:23 PM
Tiny
RIK ENDERS
  • MEMBER
When I spray ether into the throttle body it will run, but stalls after I stop spraying. Changed every sensor.
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Sunday, October 2nd, 2016 AT 2:24 PM
Tiny
WRENCHTECH
  • EXPERT
Is this something you are just building or has it been operational in the past with this combination?
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Sunday, October 2nd, 2016 AT 2:26 PM
Tiny
RIK ENDERS
  • MEMBER
I have had it about a year. Ran great, then felt like I shut it off. How do I test the fuel pump? I do hear the relay, the injectors priming and the pump turn on. After it fires over and dies, I hear the pump for about three seconds.
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Sunday, October 2nd, 2016 AT 2:57 PM
Tiny
WRENCHTECH
  • EXPERT
You said you have 40 PSI of fuel pressure. The spec for a 94 is 41.0 to 47.0 psi. It will be a little less with the engine running when the regulator gets vacuum, but you should see more than 40 key on.
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Sunday, October 2nd, 2016 AT 3:06 PM
Tiny
RIK ENDERS
  • MEMBER
I tested it to get exact numbers last night in the dark. LOL when I crank it it goes up to about 47 when it starts to fire it goes down to about 38 and then when I shut the car off it stays right at 42. What is the role of the oil pressure switch? I heard that it might turn the fuel injectors off if it is given the computer a false reading. On my dashboard when I attempt to start it the fuel pressure goes up to 10 if I try to restart it immediately after that the fuel pressure goes up to 14. 14 to 15 is the max it shows when I try to crank it. And since you seem more knowledgeable than me how can I test that switch the oil one to see if it is working? And I would like to say thank you very much you are being extremely helpful.
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Monday, October 3rd, 2016 AT 4:24 AM
Tiny
RIK ENDERS
  • MEMBER
I am sorry I meant the oil pressure goes up to 10 and maximum 10 to 14.
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Monday, October 3rd, 2016 AT 4:25 AM
Tiny
WRENCHTECH
  • EXPERT
No, the oil pressure does not shut of anything but you do need to find out if the injectors are being cut off and whether it is the power side or the trigger side that is dropping out.

Now, the oil pressure switch does supply a redundant power supply to the fuel pump along with the fuel pump relay. I did have a car one time that the oil pressure switch was shorting out the fuel pump feed when it built up oil pressure. You can simply disconnect the switch to determine that. Since your pressure is not dropping off, I doubt that.

The bottom line is you need to go back to the series of tests I gave you as they will isolate the problem area.
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Monday, October 3rd, 2016 AT 5:20 AM
Tiny
RIK ENDERS
  • MEMBER
I did every thing you suggested. Cannot stay running long enough to test which side of injectors cut out. There is definitely positive power going to them when key is on. (12.47v) I will try to take off the oil pressure switch when I get home. See if it changes anything. Does the relay turn the fuel pump on for the three seconds after car is off. I can only do all this from a start to off circumstance. Do you know if it has an inertia switch anywhere? Or would it even turn over if it had a tripped one?
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Monday, October 3rd, 2016 AT 7:03 AM
Tiny
RIK ENDERS
  • MEMBER
Should my fuel pressure drop to 37-38 lbs when it briefly turns over, than go back up to 42 when it dies again? It does not spit, shake, sputter or backfire. Ours like a kitten for three seconds?
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Monday, October 3rd, 2016 AT 7:05 AM
Tiny
RIK ENDERS
  • MEMBER
Purrs. Lol
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Monday, October 3rd, 2016 AT 7:05 AM
Tiny
WRENCHTECH
  • EXPERT
The relay energizes for two seconds when the key is first turned on and resumes when the computer sees a tachometer signal. Apparently it is retaining for a couple seconds when the tachometer signal drops off. Many GM products do that.

It might be difficult to monitor which function drops off the injector plug in that split second when it dies but that is the only way you are going to get to the bottom of this. Welcome to our world.
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Monday, October 3rd, 2016 AT 7:08 AM

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