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post #1 of 9 (permalink) Old 06-18-2019, 09:55 AM Thread Starter
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Question for you EFI experts

I have a customer with a donor build cobra that (randomly) will not start after it warms up. After much research I diagnosed it as a bad ecu. I swapped in a known good one and the problem went away. Sent the old one out to be repaired, re-instlled and everything was good. Started it hot at least 20 times. Customer drives the car to NH and when stops for gas it will not restart. Heres a clue. The only way to get it to restart hot is to trip the impact switch to shut off the fuel pump. Found this out by accident. I can duplicate this over and over. Why does shutting off the pump allow it to start?
Is it possible something in the ECU is still bad?
Thanks Mike

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post #2 of 9 (permalink) Old 06-18-2019, 11:38 AM
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So when you trip the inertia fuel switch, does the fuel pump run or does the car start then die as the remaining fuel in the line is consumed?
The inertia switch is independent of the ecu and they are unaware of each other. If the pump runs even with the switch tripped, there's probably a short in the switch and I'd replace it.
If the car starts then dies only after the pump is off, I'd guess a fuel pressure issue. You'd be able to replicate that by pulling the fuel pump fuse/relay.


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post #3 of 9 (permalink) Old 06-18-2019, 11:41 AM
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Can you re-start when hot by un-hooking the battery or do you have the re-set the crash switch? If you have to re-set the crash switch it may be bad.

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post #4 of 9 (permalink) Old 06-18-2019, 01:06 PM Thread Starter
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I don't think its crash switch related. My thought was it was flooding and causing it not to start. When I trip the switch it starts and runs for a second or two. It takes 2 people to restart it once this happens.
Trip the switch, one person cranks it and the other to re-energize the switch. Funs perfect after that. I was able to repeat this over and over with the same results. Very strange. This is a basic stock EFI setup. Pump runs for a couple of seconds when you turn the key on. I can hear the pump operating properly even when it doesn't start.

Mike
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post #5 of 9 (permalink) Old 06-18-2019, 02:23 PM
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Well, I'm going to ask what fuel pressure you see when this happens. If you're seeing full pressure (at least 40psi) I wouldn't be suspecting the fuel system. Are you getting spark when this happens? A lot of simple things you may have covered but not sure from the post.

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post #6 of 9 (permalink) Old 06-18-2019, 03:27 PM
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If you think it is a flooding condition, most efi systems shut off the fuel injector pulse, if you open the throttle all the way while cranking.

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post #7 of 9 (permalink) Old 06-18-2019, 03:39 PM
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I had a similar problem on my '03 silverado when the fuel pressure regulator diaphragm failed. It was pulling fuel through the vacuum line and would not hot restart. Had to let it sit until the gasoline evaporated and then it would restart. Luckily, I figured it out pretty quick and gave it an oil change, as well...

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post #8 of 9 (permalink) Old 06-18-2019, 04:44 PM
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It just dawned on me I have the same problem with an old model of the Holley Projection TBI.
It is injector leak down. To confirm this is the issue, bleed down the fuel rail on the warm engine. I use the schrader valve. Putting a rag around it and bleed the pressure off. Your symptoms sure sound like the issue I have.

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Last edited by railroad; 06-18-2019 at 07:26 PM.
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post #9 of 9 (permalink) Old 06-18-2019, 07:21 PM
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Fuel Pressure

By-pass the inertia switch completely and see if it still does this no start when hot issue . . . no effect, not the inertia switch.

The EEC does know that the pump is there (by relay coil resistance), or at least that it is energizing the relay for it . The pump won't [continue to] run unless the dizzy is spinning.

I'm leaning toward the injectors leaking down and flooding the engine.

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