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  1. #1

    Default 1985 5.0 CFI Poor throttle response

    1985 Mustang GT 5.0 CFI AOD
    I recently fixed quite a few vacuum leaks, replaced the plugs, TPS, fuel filter, temp sensor, Cap/Rotor fighting a idle hunting issue.
    The good news is the idle is 85% better with just a slight miss.

    The bad news is the car still has very poor throttle response. In other words, the car either from a dead stop, if you floor it, it starts to go for a half sec, then falls on its face. Also when at speed say 35-45 MPH, if you mash the gas to get going, it doesn't take off, it almost bogs. The car will downshift and start to take off, but then it just sort of levels out and really doesn't accelerate. It almost seems like if you let off the throttle partially the acceleration actually responds better. It seems like its starving for fuel. Right now the car wont even spin the tires with the brake held down.

    I have checked the fuel pressure and its at 36-37 psi. The TPS was replaced and adjusted. I'm looking for ideas.
    Could the choke be coming on when you press the throttle hard? Is there something vacuum related that causing the injectors to shut down?
    I hate to keep shot gunning parts at this thing. Would bad injectors cause this issue? Funny part is on the highway at 70mph, the car runs awesome.

  2. #2
    FEP Super Member
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    There is no choke , so dont worry about that .
    What is the timing set to?
    clowns to the left of me , Jokers to the right

  3. #3

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    I believe it is standard at 10. I did check it and don't remember setting higher. At most it would be 12

  4. #4

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    Check the sealing integrity of the spacer and gaskets below the throttle body:




    Check for trouble codes. Explanations:
    http://vb.foureyedpride.com/showthre...lanations-from


    Test trouble code-indicated sensors/circuits:
    http://vb.foureyedpride.com/showthre...s-Testing-from



    Some tips in order to verify some basics, and to best dial in CFI:

    - With the investment of a little time, adjustable fuel pressure is possible. The regulators on these older CFI units are rugged AND are adjustable, but "anti-tamper", but the tampering for adjust-ability is real easy...
    There was what looked like a button in the top of this one. You carefully drill (off the car, and so no metal gets into the throttle body) about a 1/8" hole in the "button", thread in a small screw and it comes out, because the tip of the screw goes down into the hex of an Allen bolt (which you will later use to adjust fuel pressure with your gauge connected to the fuel rail) and presses it up and out, or you grab the small screw head and pull that "button" out like you're pulling a tooth, lol







    - Also with just a little time, elongate the screw mount holes in the TPS sensor so that it can be rotated and adjustable. Adjust it to 0.98 at idle with the key on/engine off, open the throttle slowly and see that the voltage number increases gradually and smoothly with no "drop outs", and see that it ends up somewhere less than 5-volts at wide open throttle.

    - Even if you never get a MAP sensor trouble code, periodically, or when there seems to be a stupid running issue, verify it's output signal voltages, but even better, it's frequency output signals. They can be WAY out to lunch, causing all sorts of running issues. Seen below behind the engine coolant overflow tank:




    Good luck with it
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  5. #5

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    As well as those tips, is your egr functioning correctly? Pcv?

    First step is codes though.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  6. #6

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    Yep, no choke on this. It is fuel injected. I suspect the fuel injectors are the original OEM units (could have missed it in a reply) and although I TOTALLY agree with not throwing parts at something, any 33 year old fuel injector is likely well beyond functional. It does sound contrary to proper troubleshooting practice but if you don't know how old they are, I would put a new fuel pump and filter and injectors in this. Compared to anything built in the last 10 years, this is a crazy cheap project and even if it does not resolve your issue, it still needed to be done. To me after 33 years, it's like changing the oil filter. NO, changing the oil filter will not fix this issue but if the filter is 33 years old I am doing it anyway. Yes, that's an exaggeration but I hope you get my point. Running down the road at 70, you can get enough fuel through the tip of a ball point pen to make a car run but if you mash the throttle wide open, that's a different story.

  7. #7

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    Codes first though. That costs 34 dollars for the reader and will be used frequently enough that it is worth it.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  8. #8
    FEP Power Member 4-barrel Mike's Avatar
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    Quote Originally Posted by emerygt350 View Post
    Codes first though. That costs 34 dollars for the reader and will be used frequently enough that it is worth it.
    Less: https://www.amazon.com/Innova-3145-F...70_&dpSrc=srch

    Mike

  9. #9

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    Thanks guys....got some work to do.

  10. #10
    FEP Senior Member Matt J's Avatar
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    Once you do the codes, which will point you probably in confusing different directions because you probably have more than one thing wrong (been there, done that) keep looking for vacuum leaks. If a few of the hoses were leaking, they probably mostly all are leaking or close to it. There are also a lot of vacuum controlled devices under the hood that have rubber bladders in them (choke heater, dashpot, cruise control module in the driver fender well, etc). They can all leak, and in my case, they did. Look for anything that has a hose plugged into it and make sure it's not leaking. Some things you'll need to pull off to see inside. If the idle is better but still a little rough, you probably still have some vacuum leaks, and you're not going to get anything fixed right until those are all completely worked out. This setup is difficult at first to figure out, but once everything is working it actually works very well and is quite dependable.

    Oh, and I assume you already tried this, but if you haven't run a little fuel injector cleaner into it too. Even if you're going to replace your injectors at some point, it can't hurt in the meantime. I thought I heard that replacements were hard to find, but I might be wrong about that. Mine worked fine, in any case.

    Good luck!

  11. #11

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    Is there any sane way to get at the cruise module? Mine is off by 5 and creeps so I suspect a leak...
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  12. #12
    FEP Super Member
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    Pull the inner fender liner .
    clowns to the left of me , Jokers to the right

  13. #13

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    Quote Originally Posted by ashley roachclip View Post
    Pull the inner fender liner .
    I looked at that and decided it wasn't sane. Is that easy to do?
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  14. #14

    Default

    Not real easy, no. More frustrating than hard. Look here at post #248 and you can see the rubber protective "bag" over the CC unit and also the next post shows the vacuum line routing if that helps any. You can see I removed the fender and the liner is still in place. It might honestly be faster. You can tell though that one has to go to get to this module because the unit is right on top of the fender liner.

    http://vb.foureyedpride.com/showthre...oration/page10
    Last edited by homer302; 07-27-2018 at 07:54 PM.

  15. #15

    Default

    Yeah, I think I will just pass on that.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  16. #16
    FEP Senior Member Matt J's Avatar
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    Check the dashpot, I think when you turn on the AC it turns on to crack the throttle up a bit when idling. If it has a leak, that could be the source of your problem, and it's easy to get at and replace if needed.

  17. #17

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    No, the votm is working fine, the problem is the cruise is off by 5 mph... But I don't want to hijack this thread...
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  18. #18

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    I'm not familiar with the 85 CFI system. Does it use an O2 sensor? An old O2 sensor that is reading slowly can can cause the problems described in the original post.

  19. #19

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    Yes...it has a single O2 sensor. Which brings up a good question......the car has Kooks full aftermarket exhaust (factory headers). It only has an O2 cell on one side if the system. Could this be causing odd readings? (lean/rich)

  20. #20

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    Mine only has the one as well, that shouldn't cause this kind of thing even if the two banks are way off.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    K&N filter in a stock dual snorkel, GT40 heads, Edelbrock 3721 intake, MSD 8456 Dist., MSD 8227 coil
    Comp cams XE254H, hypereutectic pistons
    Hooker Super Comp Shorty Equal Length Headers, catted BBK H-pipe, full custom duals
    Maximum Motorsports caster/camber plates and strut tower brace, 3.73 rear, dura grip (both Yukon)
    Ford Performance Springs, Firehawk A/S 225/55r16 on LMR TRX r390 wheels (street)
    Federal 595 rs-rr 245/40r17 and 255/40r17 on OE cobra r wheels (race)
    AOD rebuilt with a 6 clutch direct drum, Koline steels stacked with 8 clutches, Kevlar band, superior shift kit, new torque converter. --Everything else stock and fully functional.

  21. #21

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    Quote Originally Posted by Hawkeye View Post
    Yes...it has a single O2 sensor. Which brings up a good question......the car has Kooks full aftermarket exhaust (factory headers). It only has an O2 cell on one side if the system. Could this be causing odd readings? (lean/rich)
    If your car has factory headers, then the O2 sensor location should be fine. On an engine with long tube headers, the exhaust gases can cool too much before reaching the O2 sensor. This can cause the O2 sensor to send back incorrect data to the ECM.

    Do you know if the O2 sensor on you car has been replaced? As O2 sensors age the rate at which they read oxygen in the exhaust stream begins to degrade. They send signals back to the ECM much more slowly. This can cause air/fuel ratio problems and poor drive-ability. I don't want to say that this is causing the problem on your car, but it is a possibility. I think they are a little expensive but under a c-note.

    I was surprised to hear that your 5.0 CFI car has factory headers. It is my understanding that most of the production for 85 5.0 CFI cars had cast iron exhaust manifolds. Your car must have been produced late in the 85 model year. Also, one O2 sensor on a V8 car was normal for early OBD1 systems.

  22. #22
    FEP Super Member xctasy's Avatar
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    The later 85 CFi 's have a different ECM EEICIV batch code, with different control to the earlier 84-1/2 CFi's. The 02 sensor earth is in the ECM.

  23. #23

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    Mine has factory headers, if I recall correctly, they used both factory cast Iron manifolds and tubular headers depending when they were manufactured in 85.

  24. #24
    FEP Power Member 4-barrel Mike's Avatar
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    My 4/85 Capri has tubular headers.

    Mike

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