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Discussion Starter #1
I have a 95 Cougar with what I am beginning to suspect is a fried PCM. I also Have a 94 thunderbird parts car standing by waiting to help test my theory out. Before I go swapping car brains all Willy nilly, are there any differences between these two cars that would make these PCMs different? Are there any hidden dangers lurking within my plan? I don't want to toss a transmission on a hunch, or buy a fresh 200$ non-returnable PCM without some kind of evidence. Noid lights sound fun, but a quick PCM swap is cheaper and requires no tool rentals.
 

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If remember correctly the 95 A5W0 is a better calibration but something has to be updated in the trans. You can use the 94 PCM in the 95 without a problem but it's not optimal.
 

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Thanks, the car is in the shop right now (and has been for 4 days without a diagnosis) because its hot is AZ and I got sick of sweating. But I'm going to get my keys back monday, make a noid light and get to testing. The LTFT bank 1 is -.8 while bank 2 is at 25. Timing advance is at 22 degrees at idle, so I'm thinking bad brains or a hanging injector.

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I'm willing to bet its a bad injector rather then a bad PCM.
 

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94 PCMs were known for hanging an injector open, and the 95s have he same issue to a much lesser extent, but if that happens, your main complaint is going to be a misfire and raw fuel out the exhaust, not just a fuel trim issue. If you do have an injector hanging open, swap it out for one on another cylinder and see if the problem follows the injector or stays where it is. Also a cheap and easy test if you don't have a noid light is to hold the tip of a long flat-head screwdriver against the injector and put your ear to the end of the handle. If the injector is pulsing, you will hear the clicking of it going on and off through the screwdriver.
 

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Discussion Starter #7
I will definitely give the screwdriver idea a shot if I can't get a noid light. There is a strong fuel and eggy smell and I can hear what I think is a miss in the exhaust. I have a parts car so when I head to the shop ill make sure to bring a few injectors, screwdriver, noid light, an ECM and the required tooling

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Discussion Starter #8
Also, if the PCM does hang an injector, should I replace the injector as well? If so, is there an upgrade you would recommend for my humble stocker?

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You can test this. If the PCM is drawing the injector open you'll have ground on your 12V line all the time. The 12V holds the injector closed - ground opens it. My PCM shorted internally for cylinder 2 thus keeping the injector open constantly.

Also - the 95 PCM has a better tune for the transmission as the 94 trans tune backs off line pressure (eating 3rd gear and overdrive) in an effort to save fuel economy. There's a TSB on it. Search for: TSB 95-8-3

I have a 1994 SC with a 2003 Mustang 4R70W that does this. The previous trans died a horrible 3-4 death. I've been considering the '95 SC PCM for some time now. Finding one is the problem.
 

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You can test this. If the PCM is drawing the injector open you'll have ground on your 12V line all the time. The 12V holds the injector closed - ground opens it. My PCM shorted internally for cylinder 2 thus keeping the injector open constantly.

Also - the 95 PCM has a better tune for the transmission as the 94 trans tune backs off line pressure (eating 3rd gear and overdrive) in an effort to save fuel economy. There's a TSB on it. Search for: TSB 95-8-3

I have a 1994 SC with a 2003 Mustang 4R70W that does this. The previous trans died a horrible 3-4 death. I've been considering the '95 SC PCM for some time now. Finding one is the problem.
in the TSB is a very important warning.

"CAUTION:
THE PCM RECALIBRATION OR REPLACEMENT AND TRANSMISSION MAIN CONTROL ASSEMBLY CHANGES MUST BE DONE TOGETHER OR TRANSMISSION OVERDRIVE BAND DAMAGE WILL RESULT. DO NOT USE THE 1994 MAIN CONTROL ASSEMBLY WITH THE 1995 PCM CALIBRATION, OR THE 1994 PCM CALIBRATION WITH THE 1995 MAIN CONTROL ASSEMBLY."
 

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I read that too Clint. Need to do some research to find out what part they're referring to. As it is now the car only does it when driving in really warm summer conditions (90 degrees plus outside). Am thinking about a transmission cooler. It never does it on wide open throttle, just normal driving. I've learned to manage the throttle to minimize the slip/oddness that comes from it.
 

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Discussion Starter #12
So testing for PCM by swapping my 94 parts car unit into the 95 is probably not the best idea. Good to know! Luckily the Napa down the road rents Noid lights so I can check the PCM that way.

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Discussion Starter #15
Update: noid light test shows all injection connectors pulsing. I did not have enough time to swap injectors before the place closed. I could have just taken the car home, but I like the idea of something being done with it while I'm at work. I need this thing running quickly because i need to swap lifters on the wifes jeep before the semester starts

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Discussion Starter #16
Shop says all the injectors are fine as well, they are at a loss. This is ridiculous, I'm swapping to 5.0L car the first chance I get. I never have this kind of trouble diagnosing the OHV engines.

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there is a PCV hose that crosses under the intake at the back of the engine, check to make sure that didn't split and collapse. that would cause missing and fuel trim problems. My 94 I got because the guy gave up diognosing the problem which was the PCV line the whole time.
 

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Discussion Starter #18
Nice! I told the Aamco guys about it, they said they would smoke it again. It wouldn't show on an intake smoke would it?

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Discussion Starter #19
Update: the Aamco guys have had the car for coming up on 3 weeks and aren't very good at listening to customers so I have no idea what happened with the PCV hose. They decided the only place left to look for problems is behind the timing cover (I've recently replaced the tensioners and guides but it had no effect on engine operation) , so They re-timed the cams and I'm SUPPOSED to get the car back tomorrow. But I was also SUPPOSED to get it back last Thursday. I have a feeling their timing theory didn't pan out.

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