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Old 12-28-2011, 07:23 PM   #1
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86 efi interior swap help

So here's the scoop, my brother in law bought a 86 stang 4 years ago, loved it but blew the tranny. And since then he's wanted to do everything to it. Being a mustang builder myself with 14 under my belt (maybe 9 builds at the time of parking) decided I'd help him through every upgrade. Now that my life story is out of the way, I'll get to my question. This is the car Johnny cash was singing about with the 58 59 60 61 62 Cadillac ... The mustang version. The 86 t top is factory efi, but had the MAF conversion done on it when he bought it. We have the interior from a 87 2.3L and a dash wiring harness from a 88 gt along with a steering column from a 91 lx ... Here's the problem ... We have no fuel pump activation when the key is turned on (figured relay, replaced, no avail, maybe fuel pump replaced no avail) we tested the wiring and there is the 12v constant and 12v key on to the fuel pump relay but nothing at the pump with the new harness... We traced all the wiring back and no breaks or damaged wiring... Tested the fuel injectors with a typical flash test and they aren't flashing, we replaced the ecu and engine wiring harness with gear from a 92 lx MAF ... Still nothing ... We broke out the Haynes manual (embarrassed to admit to that) and traced grounds, ignition switches ... Plugs everything and it all checks out ... Went out and bought every relay for the engine and harnesses even the hard to get to relay above the ecu and once again nothing ... Anyone have any ideas to what we have missed? Ps neither of us are real amateurs he's a journeyman mechanic and I just have many builds behind me ... and I've never had problems like this.. Oh and yes we even tried changing the inertia switch and ecu a couple times ... Nothing
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Old 12-28-2011, 09:31 PM   #2
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Re: 86 efi interior swap help

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Originally Posted by Abc20 View Post
So here's the scoop, my brother in law bought a 86 stang 4 years ago, loved it but blew the tranny. And since then he's wanted to do everything to it. Being a mustang builder myself with 14 under my belt (maybe 9 builds at the time of parking) decided I'd help him through every upgrade. Now that my life story is out of the way, I'll get to my question. This is the car Johnny cash was singing about with the 58 59 60 61 62 Cadillac ... The mustang version. The 86 t top is factory efi, but had the MAF conversion done on it when he bought it. We have the interior from a 87 2.3L and a dash wiring harness from a 88 gt along with a steering column from a 91 lx ... Here's the problem ... We have no fuel pump activation when the key is turned on (figured relay, replaced, no avail, maybe fuel pump replaced no avail) we tested the wiring and there is the 12v constant and 12v key on to the fuel pump relay but nothing at the pump with the new harness... We traced all the wiring back and no breaks or damaged wiring... Tested the fuel injectors with a typical flash test and they aren't flashing, we replaced the ecu and engine wiring harness with gear from a 92 lx MAF ... Still nothing ... We broke out the Haynes manual (embarrassed to admit to that) and traced grounds, ignition switches ... Plugs everything and it all checks out ... Went out and bought every relay for the engine and harnesses even the hard to get to relay above the ecu and once again nothing ... Anyone have any ideas to what we have missed? Ps neither of us are real amateurs he's a journeyman mechanic and I just have many builds behind me ... and I've never had problems like this.. Oh and yes we even tried changing the inertia switch and ecu a couple times ... Nothing
Never be ashamed of referring back to the books.
No one can remember everything and those who think they know it all never do.

You are going to have to get out the electrical tester, power the system up and use the books to help you work your way through the system, ensuring you have power and grounds to the places that need them.

You must have a pinched, broken. disconnected wire or faulty component somewhere. Make sure the power is flowing from the battery, through the wires, switches and relays all the way to the end of your circuits.
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Old 12-28-2011, 09:39 PM   #3
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Thanks for the reply ... We've spent hours crawling around with multi meters and two books ha ha I'm at a loss... So is he ... Everything tells me it's a break in a wire or a small separation Inside the Insulation somewhere .. Which is next to impossible to find without following every wire in 6" increments with the multi meter doing flow tests and that would take forever... I'm starting to think we may have to get a 89-93 write off car and just swap the harnesses ... Grrrr ha ha square one
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Old 12-28-2011, 11:07 PM   #4
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Re: 86 efi interior swap help

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Thanks for the reply ... We've spent hours crawling around with multi meters and two books ha ha I'm at a loss... So is he ... Everything tells me it's a break in a wire or a small separation Inside the Insulation somewhere .. Which is next to impossible to find without following every wire in 6" increments with the multi meter doing flow tests and that would take forever... I'm starting to think we may have to get a 89-93 write off car and just swap the harnesses ... Grrrr ha ha square one

Do you know how to use the ohmmeter testing function of an electrical tester?
If so, it should be relatively easy to identify broken wires.
Just be sure the battery is disconnected and none of the wires you test are powered up.

You said in your first post you had 12 volt power to the pump relay, but not to the pump correct?
It has to be in your harness from the relay to the pump if you have power to the relay, but not after it to the pump.
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Old 12-29-2011, 02:10 PM   #5
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Thanks Trojan I'll head over to his place tonight and giver a shot ... We may diagnose the fuel pump issue with that could you help with the injectors failing the flash test? I was thinking maybe the injectors don't turn on unless there is fuel pressure but I'm not 100% sure like I said him and I haven't come accross a situation such as this before.
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Old 12-29-2011, 05:44 PM   #6
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Re: 86 efi interior swap help

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Thanks Trojan I'll head over to his place tonight and giver a shot ... We may diagnose the fuel pump issue with that could you help with the injectors failing the flash test? I was thinking maybe the injectors don't turn on unless there is fuel pressure but I'm not 100% sure like I said him and I haven't come accross a situation such as this before.
It's likely that with the pump not running the ECU isn't receiving the signal it needs to activate the injectors. Try again after you resolve the pump issue.
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