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Unread 09-29-2011   #1 (permalink)
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Default 1990 Mustang GT FP/ECU Problems/Questions, Plz Help.....

I am having engine problems with my 1990 GT 5.0. I took it to a electrical shop where the mechanic diagnosed the problem as being the ECU/Computer. He advised me that I can go to junk yard and get another one as long as the numbers matched. I went to pick-a-part and they told me to get a computer out of a car of the same year with the same characteristics. They printed me out a paper with similar ID #'s that I can pick from (I attached a copy of that paper to this post). I bought one and the mechanic told me that he needed to program coding to computer in order for it to work with my car. Please take a look at the video and tell me if any of you think the problem would be my ECU. My question is does the computer need programming? Can I program it myself since the mechanic wants to charge me $145? Or could the problem be a relay or the fuel pump? Take a look at the video and any advice would be greatly appreciated.
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1990 5.0 Engine Stall video by mjay2020 - Photobucket
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Unread 09-29-2011   #2 (permalink)
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If you got the new computer from the same year and model (same transmission, same computer code), and your motor is stock, you should be able to just plug it in. It's memory would have been cleared between the removal and installation, so you shouldn't even have to clear its memory.
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Unread 09-30-2011   #3 (permalink)
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Thats what I was thinking mustangbradley. So what I did is I took my old comp. out and I plugged in the new one and when I went to start the car the car started to turn over and then it just stopped but it stopped like you didnt hear the noise of the car turning over. it sounded electrical like "neeeeeeee". Its hard to explain but when I turn the ignition to start it goes "rorh, rorh, rorh...." like 2 or 3x's and the no "rorh, rorh". just an electrical sound like "neeeeehh". So i took the new comp. out (of course with batt disconnected when necess) and I put the old one back in and the same problem. It wouldnt start. Prior to swapping them, the car started and performed like the video in my post. What do you think it could be?
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Unread 09-30-2011   #4 (permalink)
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That "neeeeh" sound is probably the fuel pump. Did you tighten the bolt holding the big plug into the computer all the way? Can you confirm you have the same computers? Do they both have their tags on them still?

How did you get the "new" computer? Are you certain it is in working condition?

It makes no sense for two computers, exactly the same, to not perform the same.

Check fuses.

I'll think about this some more and maybe something will spring to mind. The others will jump in too and point out something I have overlooked/missed/F'Up.
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Unread 10-02-2011   #5 (permalink)
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Since I swapped them, I am having a cranking issue. Its not doing what it was originally doing in the video. I charged the battery but havent had a chance to start it yet. I also have the stock air cleaner. the serial code from j/y comp is:
EEC-IV SFI-MA12A A9P
E9ZF-12A650-CA G
61SM12AF03 22302-209 0L01
I will post code for the original comput in a couple hours. I had autozone charge the batt yesterday. So you guys think nothing is wrong with org. comp? I will post video of exactly how the car is cranking in a couple of hours.
Thank you
Ok here is the serial code for the original comp in my mustang:
EEC-IV SFI-MA12 A9L
E9ZF-12A650-A2A G
60SM12AF01 19600 - 1679
THIS MORNING I tried to start and I am gonna post video on the symptoms. Its acting different but it sounds a little better. watch the video you guys please and any advice will be greatly appreciated....


PB010018.mp4 video by mjay2020 - Photobucket
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Unread 10-02-2011   #6 (permalink)
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The A9P is for an automatic, while the A9L is for a manual. I found this in the archives:

There is a hardware difference between an auto processor & a manual processor. The difference is because of the way the NDS [neutral drive switch, manual trans] & the NSS [neutral safety switch, auto trans] are wired. They are both wired to the same pin#30 but the auto trans wiring grounds the pin to the starter solenoid & the manual grounds to signal return, during crank mode there is a voltage spike sent to pin-30 so the auto trans processor has a diode on pin 30 where as the manual processor doesn't, most of the time this won't cause a problem unless you get into a prolonged crank condition. Long cranking can burn the "signal return" (pin #46) trace in a manual trans EEC.

I've been warning people about converting an auto to a manual and using the manual EEC with the auto wiring harness; those that want to convert their automatics to manuals, and swap the ECM, need to clip the wire going to pin 30 or else the ECM could fry the trace.

Here is the link to the thread:

http://www.allfordmustangs.com/forum...s-a9l-a9p.html
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Unread 10-03-2011   #7 (permalink)
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I did put the original EEC back in the car and the problem is cranking, but if u watched the video,

PB010018.mp4 video by mjay2020 - Photobucket

underneath the air filter is a relay that is making noise, either the fuel rail or the injectors are making some kind of vacuum/air noise, and some times when u put key in and turn to "Run" the fuel pump will either prime or it will stay on until I turn off ignition. I am gonna run codes early this morning and I will post my results. Car is 5-speed.


Why do u think it is doing this?
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Unread 10-03-2011   #8 (permalink)
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Is someone using a leaf blower in the background? That is the dominant sound, and I can't hear anything going on with your car. Sorry.
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Unread 10-03-2011   #9 (permalink)
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Ok this is the latest
I did most of the stuff on the "Surging Idle CheckList". and take a look at the video and this is whats going on.

PB020019.mp4 video by mjay2020 - Photobucket

I tried to run codes but when the ignition is set to run, my OBD1 wont go into test mode. Its just got one long beep sound.
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Unread 10-03-2011   #10 (permalink)
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Are you sure that sound is not from one of the accessories? You can confirm this by starting the car without the belt on. Remove the belt, crank up the car and let it run for about 30 seconds. Don't go much longer than that since the water pump is not turning.

If you don't hear the sound, then one of the accessories is the cause.

Can you determine where that clicking sound is coming from? I heard your friend mention smoke. Was that just an exhaust leak? That may be the problem, but probably not since it should be constant instead of coming in and out. I am just throwing guesses out since I am not there to hear it for myself.

That sound was not like anything I've heard before, but that could be because of the video.
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Unread 10-06-2011   #11 (permalink)
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88 gt is doing the same thing. i converted to mass air and she just decided not to start on me one day about two weeks ago. i have the A9L computer as well. My fuel injectors aren't getting fuel into the cylinder with good fuel pressure and great spark. my buddy told me that the injectors have a "switched ground" rather than a body ground. meaning the ground for the injectors go through the computer. my new computer hasn't come in yet so i can't know for sure yet. Just my thoughts, I am just as lost as you though.
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Unread 10-06-2011   #12 (permalink)
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Yes some idiot had a leaf blower. Im sorry. Ill re-record tomm. ok mustangbradley i did forget to mention this prior to all this happeneing, my water pump started to show signs of failing. Could the water pump failing be the solution to my problem now?
I've also had people tell me to change the fuel filter. Do u think the fuel filter could be the solution to my problem now?
Travix could u keep me posted on what you did to solve ur problem.
Thank you
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Unread 10-06-2011   #13 (permalink)
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Did you remove the belt and start it up? Without the accessories turning, that takes a lot of things that CAN make noise out of the equation, and will let you narrow the causes down some.

That second video you posted worked. I just can't determine where the sound is coming from.

If your waterpump is filled with the broken vanes, I guess it could sound like that. We'll find out when you pull the belt off.
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Unread 10-12-2011   #14 (permalink)
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here is the latest videos on my car. Please view them and I would appreciate any advice or help. Thank you.


PB100082.mp4 video by mjay2020 - Photobucket


PB100083.mp4 video by mjay2020 - Photobucket
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