Mustang Foxbody ECU Inspection - Things to check if you suspect your ECU is in need of repair

[@warrenlucier5796]

Great information on the Fox Mustang ECU and a big thanks for sharing this.

[@wbrockstar9550]

Great video man.I had always thought the capacitors were the cause of the continuously running fuel pump so it's great to finally hear/see the true cause.Showing how to externally test pin 46 instead of squinting while trying to look for the burnt/ open trace on the board itself.Thanks for the great job,

[@Adrenacyde]

This was VERY well done!

[@Mustang5L5]

Thank you!

[@krisf5247]

Great video! Thanks for sharing

[@dntlss]

Man you are a great teacher,very concise video, no music, no BS, just knowledge, i have been around these cars for decades and have 2 of them Ive had forever,on my 91 i have had some issues here lately, i do have a new engine in it and ive been having idle issues and I'm very familiar with them, when i installed my new engine i basically bought everything new, not because i like to throw parts but because ...new engine=new parts, why install a new engine with a 20 year old distributor or sensors etc ? that kinda thing. Here recently i pulled my computer for the very first time and there are a couple of capacitors that look like hell, since ive checked everything and everything is basically new with oem Ford parts i'm guessing the computer could be at fault and its time for a rebuild? i also have a very very weird problem,when it rains the car will run like crap, i dont have to drive it in the rain,just the fact it rains its enough to throw it into a a abyss of bucking and dying etc, you ever hear of a computer going crazy due to moisture? Its not the distributor, or the plugs or the mass air or the distributor boot or the oxygen sensors or the ECT or ACT or any of those things, that has all been triple checked, codes have been pulled, no codes except for a 31 and 85 which are emission related,those are the only 2 codes,thank you for any input you might have,im in the process of purchasing a used PCM that needs rebuild so i can have a spare one but mine is getting rebuilt too.

[@Mustang5L5]

I haven’t heard of too many instances of moisture affecting the ECU but doesn’t mean it can’t happen. For the most part they are somewhat isolated in the kick panel, so they aren’t as exposed. However the caps should probably be replaced in general due to age, especially if they look terrible I have heard of moisture being an issue with ignition parts, specifically the PIP in the distributor. No codes, no other signs of issue but distributors should be looked at carefully, especially with the latest aftermarket parts for them being of poor quality. I wouldn’t discount ignition yet as the source of your problems

[@dntlss]

Yeah that distributor is new but like you say these aftermarket parts are normally not very good specially electrical ones, the distributor was one of the few things i could not get OEM,they are hard to find these days, thank you so much for your input@@Mustang5L5

[@bennyhill3642]

Great Info, Thank You!! 😇🙏👍👍👍👍👍+

[@matthopkins1107]

Have to subscribe after this video

[@jamjr5132]

Good video!!

[@adamcartwright6220]

I have a car that won’t start with a constantly running fuel pump. I have no clue how to fix it so unfortunately I’ll most likely be going to a TerminatorX even though I really don’t want too. Thanks for the video. Very informative and I greatly appreciate the knowledge.

[@Mustang5L5]

You could always send it in to ECUExchange for a rebuild. 9 times out of 10 the constantly running fuel pump is that capacitor off to the side on the edge of the board.

[@adamcartwright6220]

@@Mustang5L5 Thank you! That’s great to know. I worry about sending it out and never getting it back or paying out the rear for it to be fixed. Thank you for the information.

[@Mustang5L5]

@@adamcartwright6220 while I’ve never used them, lots of folks have. They seem to be a pretty trustworthy operation

[@adamcartwright6220]

@@Mustang5L5 Thank you. I may just have to try it because I do want the option to go back to stock

[@49Fordproject]

Very very helpful, at least from a visual standpoint. I am about to do a capacitor replacement. 92 t-bird X2P. The pinouts are different than the A9P A9L. I have an alleged A9P but the decal is gone. Is there another way to tell the code? I set it aside for now. I got it from a foxbody friend. But I'm not confident of A9P or even MAF at this point. I love these "deep in the weeds" projects. My project is a '49 Ford F1 with an Explorer 5.0 running EEC IV MAF not a drag car, just a cool old truck!

[@joshuacielinski3597]

On my car we checked continuity between 46 & 40/60 like you stated. Test came back good, but we are hesitant to open up the case because the car was tuned years ago and it appears as though when the chip was burned in and cut into the side of the box and is sticking out. Before opening it, is there anything else I can test for with just the pins?

[@nickpanhead7209]

Wow, great video. Really got into detail with it all to make me understand I have a question, maybe you could answer, I have a1987 ford f150 No start issue, it cranks. I have spark when I spray starting fluid into the intake. She starts up but stalls, My truck is equipped with 2 fuel tanks. When I turn the ignition on I can hear the fuel tank pump prime itself for either tank i have selected. Can this computer? Be causing that no start issue with the fuel. Like I said, I could hear everything kicking in it's just not starting. I would appreciate if you could get back to me if you feel this is my issue and maybe let me know where to look the computer. For my issue. Thank you so much

[@Mustang5L5]

I don't think i'd immediately suspect the computer yet. I'd still look at the fuel system and troubleshoot that like checking for fuel pressure on the rail. I'd be looking to see if the pump can supply pressure to the engine, and if the injectors are getting signals to spray fuel. Could be a wiring issue, could be a failed fuel line from the tanks? Could be several things but I wouldn't blame the ECU just yet. In fact, with it priming the pump for 1-2 seconds and stopping, it's likely not the ECU unless it's a fuel injector issue. Still, i'd have to troubleshoot wiring first. On Mustangs, i've seen a similar issue causes when the little S-hose on the fuel pump splits in the tank. Pump primes, but no pressure at the rail.

[@nickpanhead7209]

Thank you so much for getting back to me, I just not sure what the actual computer does for my issue. But reading your text back to me kinda helps me out. I'm glad that you feel. Maybe it's not the the computer.I'll look elsewhere, I change the fuel pressure regulator and the truck started, but I think it was because it still had some starting fluid in it.From the last time I tried to start it, but it wound up dying on me and wouldn't start again after that

[@BruceWayne-te5bv]

i dont have a smog pump anymore.you think i could put that transistor in place of my fuel pump one? great vid btw most informative one yet

[@Mustang5L5]

The transistors for the TAD/TAB are the same p/n as the fuel pump transistor. They should interchange, but I’ve never done it so I can’t say for a fact if it would work.

[@heffytomad4741]

I got some questions about cel always being on, can't retrieve and codes

[@Mustang5L5]

Strong indication there is an ECU issue, specifically a burned out trace for pin 46. You can pull the ECU out and check for continuity between pin 46 and pin 40 and 60.

[@matthopkins1107]

Do you recommend certain capacitors to replace these with brand wise?

[@Mustang5L5]

I don't have a preferred brand but my preferred Vendors are Digikey and Mouser. I typically get all my electronics components there vs Amazon or Ebay. It's a little more $$$ but I feel better about the quality of the components those vendors sell.

[@matthopkins1107]

@@Mustang5L5 even chasing idle issue for 3-4 days then after running just crank no start. Pulled ecu and capacitors are leaking 👌👌👌

[@Mustang5L5]

@@matthopkins1107 At this point, i just assume every ECU that hasn't been repaired, probably should be repaired as a proactive measure. Good luck!

[@g0e2real46]

I recently purchased a 89 5.0 5 speed convertible with a bad computer the number is E9ZF-12A650-A2A is that the correct computer for this car? And which should i replace it with if? Thanks in advance

[@Scrapla1]

Whats the best method for cleaning off the J port at the bottom to install a chip? I have a old style chip with my tune on it and need to install it onto my new ECU which still has that coating on it.

[@Mustang5L5]

I believe the proper term for it is “conformal coating”. If you search on here for “conformal coating removal” there are a few videos showing methods and solvents to use.

[@MiguelSanchez-kl9bt]

Where can i get the transistor?

[@Mustang5L5]

It's an 04S74 transistor. I haven't looked for replacements for this so I don't know at this time

[@nothanks81]

You ever make a thread on these, noticed alot of the old big brand remans A9l's I've opened have components you normally don't see on the factory boards, traces that are normally empty with components on them. but haven't had much luck finding what they used as donors.

[@Mustang5L5]

I never did one on that topic. I’ve had the same curiosity. A lot of the components inside are obsolete and tough to find the exact replacements and need to locate substitutes. I’ve just never had my hands on any of the remains to take a good luck at what was used.

[@nothanks81]

@@Mustang5L5 I posted a board pic in the tfi guts thread of an old 90's town car ecu on SN.. Boards appear identical, but with more components and some chips differ but what I think the used as a core on some from others remans I've seen cracked open

[@wbrockstar9550]

Interesting, I've got one in my 342ci 91LX hatch and have never bothered to pull it open simply out of curiosity, I haven't noticed any issues with it in regards to proper operation.

[@dntlss]

Hey i wanted to ask a question if i may,i finally sourced a computer I'm gonna send off to have overhauled,its a A9P and from what i can tell someone replaced the capacitors however the capacitor closest to the main harness plug is different from the other 2, its really small in size from the other 2,I'm no electronics expert but sometimes i wonder why people just dont replace things with the same instead of monkeying around but again maybe it was a good idea? Also, on the big black processor on the board, they removed that rubber coating around it and i guess they were going to replace it but didn't, why would anyone do that? the reason i dont think they replaced it is because it still has the OEM processor, it doesn't look bad and the solder points look fine,the pin 46 trace is fine also, i just checked it. The guy that sold it to me is not a electronics guy, he just had a few for sale but he told me this computer comes up as a "constant prime" which I'm familiar with,he told me if its not repairable he will refund my money but as good as ECU xchange is im sure it will be fixable,i was just curious about the capacitor discrepancy and why they removed that coating of the processor? thank you for your input, i was just curious.

[@dntlss]

These computers are now in their 3rd decade plus of operation with capacitors that were normally good for 15 years so most are on borrowed time,i have a 89 and a 91 and I'm trying to find at least a couple and have them rebuilt for spares,if you are planning on keeping your car act now cause they get more and more expensive and hard to find every day,you could buy them for 100 bucks all day long a few years ago, now most people want 6\700 dollars for them rebuilt @@wbrockstar9550