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My 1985 c4 starts runs three seconds and then dies

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My 1985 c4 starts runs three seconds and then dies

 
Old 02-24-2019, 09:07 PM
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Charles Davis
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Default My 1985 c4 starts runs three seconds and then dies

I have replaced relay's ECM fuel pump plugs and wires
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Old 02-24-2019, 09:12 PM
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CorvetteRules
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And prior to you doing that work what, if any, issues where you having?
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Old 02-25-2019, 03:54 PM
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VikingTrad3r
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the usual:

- buy/rent/borrow a fuel pressure gauge. do you lose pressure when it dies? what is pressure?

beyond that first step, agree with above, what is the story/history? can help diagnose.
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Old 02-26-2019, 04:37 PM
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playsdixie
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I could take a guess and say you're blowing the line out of the pulsator if you kept it.....A fuel pressure gauge will tell you a lot more.....
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Old 03-03-2019, 03:52 AM
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Charles Davis
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Default Still chasing demons

Originally Posted by VikingTrad3r View Post
the usual:

- buy/rent/borrow a fuel pressure gauge. do you lose pressure when it dies? what is pressure?

beyond that first step, agree with above, what is the story/history? can help diagnose.
well I have pulled filter and the injectors seems I had good pressure with low volume now it runs just trying to set it right
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Old 03-03-2019, 06:49 AM
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mazdaverx7
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What is it that you're trying to set right? The fuel pressure at the rail is adjusted by the fuel pressure regulator. What issues are you currently having?
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Old 03-03-2019, 10:11 AM
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VikingTrad3r
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Originally Posted by mazdaverx7 View Post
What is it that you're trying to set right? The fuel pressure at the rail is adjusted by the fuel pressure regulator. What issues are you currently having?
this ^

what is the pressure value in the following conditions:

key on after fuel pp primes:

while cranking:

while running:

as it dies:


after it dies:

If you have already verified pressure thats great but i wasnt sure based on your reply so i thought id better ask. there is nothing to adjust other than going through the “minimum idle set” procedure.


Have you made any adjustments to the throttle body? Don’ t. If you have, just let us know.

VT
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Old 03-03-2019, 10:51 AM
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KyleF
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Originally Posted by Charles Davis View Post
I have replaced relay's ECM fuel pump plugs and wires
Not really providing much information to help.

Are you checking fuel pressure? Could be the oil pressure switch.
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Old 03-03-2019, 11:31 AM
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Originally Posted by KyleF View Post
Could be the oil pressure switch.
I just started the car with it disconnected. Reconnected it and the car still was running, disconnected it and the car still runs.
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Old 03-04-2019, 12:46 PM
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Originally Posted by aklim View Post
I just started the car with it disconnected. Reconnected it and the car still was running, disconnected it and the car still runs.
There is actually 2, one for the gage and one for the fuel pump.

However, this is something I have been told, and never had the experience with. Had to look up a Diagram, the secondary switch is a secondary switched power source for the pump. Shouldn't cause any issues.

So what are you getting for pressure readings?

Last edited by KyleF; 03-04-2019 at 04:45 PM.
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Old 03-11-2019, 10:55 PM
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Z51BOB
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ECM holds fuel pressure regulator on for 3 seconds after start. After that, its up to the Oil pressure switch to maintain Fuel Pump power. since it starts, then dies, check the holding circuit. Either the fuse is bad or the Oil pressure switch is not working. sometimes the connector goes bad. you can check by jumping at the connector, FP should run. You can also keep FP on by jumping 12 V to the ALDL connector at pin G. (Use a heavy gage #12 fused wire)

Last edited by Z51BOB; 03-11-2019 at 10:57 PM.
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Old 03-11-2019, 11:16 PM
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aklim
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Originally Posted by Z51BOB View Post
ECM holds fuel pressure regulator on for 3 seconds after start. After that, its up to the Oil pressure switch to maintain Fuel Pump power. since it starts, then dies, check the holding circuit. Either the fuse is bad or the Oil pressure switch is not working. sometimes the connector goes bad. you can check by jumping at the connector, FP should run. You can also keep FP on by jumping 12 V to the ALDL connector at pin G. (Use a heavy gage #12 fused wire)
AFAIK, the ECM primes the pump for 2 seconds and not the regulator. After that, the oil pressure switch acts as a 2nd source of power for the pump. So if that cures the problem, I suspect something else. I have tried running without the switch. Seems to work just fine so.....
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Old 03-12-2019, 07:50 AM
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Originally Posted by aklim View Post
AFAIK, the ECM primes the pump for 2 seconds and not the regulator. After that, the oil pressure switch acts as a 2nd source of power for the pump. So if that cures the problem, I suspect something else. I have tried running without the switch. Seems to work just fine so.....
If your car stays running without the switch, then your relay is fine. This is all under the hood and not at the fuel pump though. Have you checked voltage at the pump in the rear?

I have never heard anyone state the prime being any longer than 2 seconds. Never personally used a stop watch, but it seems right.

Have you checked pressure at the rail? My 88 had issues starting/continuing to run when I had a small leak on the fuel rail (Glad I found that quickly Pressure was low, very low... even with the booster pump it couldn't supply enough volume the keep pressure up.

Have you unplugged the MAF to see if anything changes?

Is the IAC doing it's thing properly? Are the passage clean and is it moving?
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