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  1. #1

    Default 1984 mustang gt cfi aod hesitation & idle issue

    Hey guys, new to the forum. Working on a 1984 Mustang GT AOD with the CFI. The idle doesn't want to stay where it should be. This is an intermittent problem and can not duplicate it all the time. Also when the car is under acceleration it seems to hesitate for a split second then it works fine. That too is an intermittent problem. I have cleaned out the throtte body, changed the egr valve and ran a fuel treatment through it. I just purchased a TPS to install today hoping that may fix the problem. Any suggestions would be greatly appreciated. Car has sat most of its life. Only has 63,000 miles on it. Marti report in hand. I had previously owned an 85 GT but it was a carb car and I never had this issue. New to the CFI thing. Having problems finding a mechanic that is familiar with this system. I am trying not to swap to carb but if I can't figure this out, I am going to. Any suggestions would be greatly appreciated.

  2. #2
    FEP Power Member
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    You probably will not find a mechanic who will admit knowing the cfi. We probably have more people here who know it than any other place. We have experts and we have those who figured out how to work with it. Making it work (modifying)? Not so much.

    The cfi is not overly complicated but was not used lone enough for everyone to understand it. The tps is a great place to start.
    Fox Body/3rd Gen MCA Gold Card Judge
    84 SVO 24K miles, 85 Mclaren Capri Vert. 84 GT Turbo Vert.
    88 Mclaren Mustang Vert 20K miles, 89 Mustang LX Sport Vert, 92 GT Vert.
    03 Mach 1 7900 miles, 74 Mustang II, 69 Mustang, 67 Mustang, 14 Mustang CS/GT,
    15 F150 FTX Tuscany, 16 F250 Crewcab, 67 Tbird 47K miles

  3. #3
    FEP Super Member xctasy's Avatar
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    emerygt350, JACook, and any posts by them, including them. Its very structured and simple when you look at what each basic system does.

    http://vb.foureyedpride.com/showthre...Y-cold-natured

    All CFi units, Ford or Chev, are based around the throttle body working 100% the way it was designed to. Anything that alters ignition, or cold start or throttle kicking, changes the idle speed at phases during warm-up, so its not steady in the first 15 minutes of any warm up. It has ignition tip in to control idle speed, and TFi doles it in an out. EGR is electronically controlled, and fault codes indicate what to look for.

    All CFi's are not well understood at all. Relating to FoMoCo. This is due to the way Ford circulated information to only its certified technical people, and kept it out of the public arena for years.

    When it was re-introduced to the huddled masses by AutoZone et al, it was royally screwed over All the explanations, lumping them ad hoc into very badly written resource material that took way too many liberties. That was because of how complicated each version of CFi was.

    IMHO, aside form JACook, some of the best explanations came from Impco Propane literature, where full understanding and respect of the base systems was critical to getting a CARB certificate, and Impco used people like Ak Miller to write and research tech articles, which ment lovely, easy, clearly written explanations missing everywhere else on the internet.

    Re CFi, Ford actually had them for 5 years, and every year they differed, and there are around 13 different kinds,


    5.0 Standard Output (1980-1985, with EECIII for 1980-1984, then EECIV for 1984.5 to 1985)
    in 3.8 (1982-1985)
    and 5.0 High Output (All EECIV)

    5.0 HO's have no IAC valve, unlike all the other EECIV CFi's. Some were even run by a totally different EECIII in Fox Cougars and Tbirds

    They are totally different in each of the three applications, and the parts look the seam, but aren't interchangeable at all. Even O2 sensor wiring differs, and so do the base-plate gaskets, with very special TSB running changes which totally alter the tuning characteristics.

    The throttle Body part was the twin point central injections un-doing. People fiddle with

  4. #4

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    Everytime xctasy posts something I learn something new. This time it was scary. Just go slow and methodical. Get the code reader on there. I would also think about a new coil if you haven't already. A nice new motorcraft coil is cheap, and when I started working on my garage queen with 77k on it, the coil was causing some problems just like you describe.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    Hooker Super Comp Shorty Equal Length Headers
    GT40 heads, Edelbrock 3721, K&N filter in stock dual snorkel,
    Comp cams XE254H, hypereutectic pistons, catted BBK H-pipe, full custom duals.
    3.73 rear. CS5 225/60/15 on 10 holes (street) Federal 595 rs-rr 225/45/15 on 10 holes (race)
    Everything else stock and fully functional.

  5. #5
    FEP Power Member smitty54's Avatar
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    Try replacing the dashpot. If you can fine one, and there are mechanics out there who can work on CFI's, they are usually in their 50's or 60's.
    Last edited by smitty54; 12-02-2018 at 01:08 PM.
    "Have you ever noticed that anybody driving slower than you is an idiot, and anyone driving faster than you is a maniac."
    George Carlin, Rest in peace

    Rick
    84 GT Convertible
    68 Cougar XR7
    14 Ford Explorer Limited

  6. #6

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    Thank you for your response. When I change this out I will let you know how she does. Hey Smitty54, my car looks like yours but is factory sunroof. Same color. Dashpot? What is that?
    Last edited by FLETCHER4; 12-02-2018 at 09:01 PM.

  7. #7

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    Ok good to know. Will let you guys know how this pans out.

  8. #8
    FEP Power Member smitty54's Avatar
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    "Have you ever noticed that anybody driving slower than you is an idiot, and anyone driving faster than you is a maniac."
    George Carlin, Rest in peace

    Rick
    84 GT Convertible
    68 Cougar XR7
    14 Ford Explorer Limited

  9. #9

  10. #10

    Default

    holy cow. Don't touch the votm. it has nothing to do with idle. and wow is that expensive.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    Hooker Super Comp Shorty Equal Length Headers
    GT40 heads, Edelbrock 3721, K&N filter in stock dual snorkel,
    Comp cams XE254H, hypereutectic pistons, catted BBK H-pipe, full custom duals.
    3.73 rear. CS5 225/60/15 on 10 holes (street) Federal 595 rs-rr 225/45/15 on 10 holes (race)
    Everything else stock and fully functional.

  11. #11

    Default

    Wasn't trying to insult anyone with the garage queen comment. Just wanted people to know she is my daily driver. Even took her on a road trip over 3 states. If I had your car she wouldn't be out in the rain either. Car is too nice. I do have a garage queen, she is my viper. That car only goes out on sunny days.

  12. #12

    Default

    oh, I just meant that when I bought the car it was stored and actually parked for 10 years or so (thus the new gas tank). Now it is only during the winter where it gets to know the spiders.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    Hooker Super Comp Shorty Equal Length Headers
    GT40 heads, Edelbrock 3721, K&N filter in stock dual snorkel,
    Comp cams XE254H, hypereutectic pistons, catted BBK H-pipe, full custom duals.
    3.73 rear. CS5 225/60/15 on 10 holes (street) Federal 595 rs-rr 225/45/15 on 10 holes (race)
    Everything else stock and fully functional.

  13. #13

    Default

    TPS didn't work. Problem still there. On to the dashpot.....

  14. #14

    Default

    That is till today. Toys for Tots run with viper and parade. On way home it started raining. You know what, I am glad I am the first to drive it in the rain. Was worth it to get toys to the kids who do not have any. Looking forward to my next rain cruise.....

  15. #15

    Default

    Don't mess with the "dashpot", actually the votm. That is only for kicking off high idle, air conditioning kick up.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    Hooker Super Comp Shorty Equal Length Headers
    GT40 heads, Edelbrock 3721, K&N filter in stock dual snorkel,
    Comp cams XE254H, hypereutectic pistons, catted BBK H-pipe, full custom duals.
    3.73 rear. CS5 225/60/15 on 10 holes (street) Federal 595 rs-rr 225/45/15 on 10 holes (race)
    Everything else stock and fully functional.

  16. #16

    Default

    Go to AutoZone and buy a code reader for 28 dollars instead. Saves money and time.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    Hooker Super Comp Shorty Equal Length Headers
    GT40 heads, Edelbrock 3721, K&N filter in stock dual snorkel,
    Comp cams XE254H, hypereutectic pistons, catted BBK H-pipe, full custom duals.
    3.73 rear. CS5 225/60/15 on 10 holes (street) Federal 595 rs-rr 225/45/15 on 10 holes (race)
    Everything else stock and fully functional.

  17. #17
    FEP Senior Member Matt J's Avatar
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    When I first got mine it had been sitting for a long time, and it needed a lot to get it running well. The good news it that it's actually pretty simple and you can get pretty much anything you need from your local NAPA. The bad news it that it's EARLY computer tech, which means electronically controlled but in conjunction with a lot of analog and vacuum parts. I'll nearly guarantee that your problems are mostly vacuum related. A small leak anywhere will make it run poorly, or idle poorly, or both. The fact that it's intermittent probably means that it's a leak in something that isn't always ported to vacuum, so it only happens when that unit is "on", thus leaking. The dashpot and the "choke heater" on the opposite side of the CFI have vacuum bladders in them, they both degrade and can leak. If you have cruise control, mine leaked badly and caused a lot of problems. It's located behind the inner fender on the driver's side, and is a pain to get to. If your cruise is working, then it's probably not an issue. If it isn't, then plug the vacuum hose that runs to it. You'll want to replace most or all of your vacuum hoses, they get old and crack. Most of your sensors will probably be not too great either, I replaced my TPS and a few other things. They're not expensive and easy to replace. A code reader is a huge plus, and about 30 bucks, and will help determine if your sensors are working in range. Keep in mind when you read it that if it says there's a problem with something, it might not mean you need to replace a part...it could be as simple as something else is making that part read wrong. But it all starts with vacuum. I promise you'll find cracked hoses and connectors. It doesn't take much to make the whole thing run poorly.

    Also keep in mind that over the years lots of well-intentioned mechanics who had no need of these new fangled electronic controls and vacuum lines used to cut things off and plug them all the time. In other words, you might fix one thing and make it work worse because someone had deliberately broken it 25 years ago. You'll probably spend some time chasing multiple issues that cause different problems in seemingly unrelated areas.

    The good news, and take some heart here, is that once you get things right, it runs very well, starts and idles well, and is pretty much maintenance free after that. It's just going to take some time to get things right.

  18. #18

    Default

    What he said.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    Hooker Super Comp Shorty Equal Length Headers
    GT40 heads, Edelbrock 3721, K&N filter in stock dual snorkel,
    Comp cams XE254H, hypereutectic pistons, catted BBK H-pipe, full custom duals.
    3.73 rear. CS5 225/60/15 on 10 holes (street) Federal 595 rs-rr 225/45/15 on 10 holes (race)
    Everything else stock and fully functional.

  19. #19

    Default

    Thank you for the comment. I was getting ready to give up. Will keep trying.

  20. #20
    FEP Senior Member Matt J's Avatar
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    Just make sure you only pull one line off at a time when replacing them...also, you can unplug things while it's running and see if it changes the idle at all, and put your finger over the line to see if it has any vacuum on it. If it doesn't, this isn't necessarily a problem as not everything has vacuum running to it all the time, but most things do. If you have air conditioning, the dashpot will also activate to crack open the throttle a little to kick up the idle. If you have your ac off but the defroster on, i think that kicks on the ac as well. But either way, it does have a bladder in it that holds vacuum, as does the choke heater. If you have a vacuum pump you can test them by hand. I pulled mine off and could see the bladder was deteriorated so I replaced it. I'm not a fan of just replacing everything as this stuff can be costly, but if those parts are original to the car they've been in use for 30 years.

    You can test a lot of the parts with a voltmeter. Remember that the computer relies on vacuum and analog readings from the sensors to tell it what it needs to do. So you replaced your TPS, but you can put it on a tester and watch as the voltage increases or decreases as you move the throttle. If it jumps around, that's going to cause problems. Mine needed to be replaced too. You can find lots of good posts in here, like mentioned before, those users are super helpful and helped me figure stuff out.

  21. #21

    Default

    You can borrow a vacuum pump at most auto stores. Very useful for quickly removing parts from your potential problem list.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    Hooker Super Comp Shorty Equal Length Headers
    GT40 heads, Edelbrock 3721, K&N filter in stock dual snorkel,
    Comp cams XE254H, hypereutectic pistons, catted BBK H-pipe, full custom duals.
    3.73 rear. CS5 225/60/15 on 10 holes (street) Federal 595 rs-rr 225/45/15 on 10 holes (race)
    Everything else stock and fully functional.

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