Close



Results 1 to 17 of 17
  1. #1

    Default 85 GT TBI Rough Idle and hesitation during acceleration

    As the title says, I have a 1985 GT Convertible, all stock except for Pypes full length exhaust. I just bought the car.
    I have an issue where at idle, especially while in gear (its and auto) the rpm surge from 400-500 to 900-1000. It almost act like it missing.
    Also, when driving, the car always feels like it can't find the right RPM to accelerate smoothly. You step on the gas and it hesitates until it downshifts or finds a higher RPM that it like to get going. Even during acceleration you can feel its just not smooth. Other times it idles and pulls fine. I am not Fuel injection schooled at all, as all my previous cars were carburated.

    Any thoughts on what to look for? Keeping in mind I know nothing about the TBI that this car apparently has.

  2. #2

    Default

    I've been through this for the past 5 months, but my 85 is carbureted. I found a bunch of vacuum leaks and replaced the EGR valve and now it's running great. Also another possibilty is distributor. You need to hook a vacuum gauge up to the manifold and see what it's doing. Good luck.

  3. #3
    FEP Super Member erratic50's Avatar
    Join Date
    Dec 2016
    Location
    Nebraska
    Posts
    4,575

    Default

    Throttle body can get gummed up and cause problems too.

  4. #4

    Default

    Thanks guys, i will start with these ideas and let you know. I probably should have thought of the vacuum leaks, but being FI I wasn't sure where to start.

  5. #5
    FEP Senior Member Matt J's Avatar
    Join Date
    Jul 2012
    Location
    Georgia
    Posts
    620

    Default

    This type of fuel injection isn't that far away from a carb that your experience can't still help you. It's basically a carb with two injectors in it. It is 1980s computer tech, though, so it's not controlled like a modern injection system. All the computer inputs and sensors are analog and many of them are run off of vacuum lines. one little leak, and the whole thing runs bad. And trust me, just about EVERYTHING under the hood has a vacuum line running into it, including the cruise control module (if you have it) which is conveniently located in the driver's side fender behind the skirt. Mine had a bad leak. There are sensors (throttle position, EGR, stuff like that) which can contribute as well, some of them have rubber bladders in them which can also leak (like the choke pull-off or dashpot). You'll need to start at the top and work your way through all of it.

    Despite that, don't forget the basics that you already know. How long has the car sat before you bought it? Is the fuel bad? Does it stink when you run it? Mine had 5 year old gas in it when I bought it, it stunk until I got it worked out of there. How old is the fuel filter, plugs, wires, air filter? If the car has sat for a while or doesn't look like it's been well cared after, consider a simple tune up and replace the filters to start. Run some injector cleaner into it. Also, the computer that controls this system "learns" how to run with use, if it hasn't had a battery in it for a while it might take a little adjustment, though it shouldn't make the car run rough.

    I think you'll find that with a tune up and checking around for leaks you'll probably get it under control pretty quickly. The computer has the ability to tell you what's going on as well, you can run test codes out of it, which is very handy!

    Good luck!

  6. #6
    FEP Super Member xctasy's Avatar
    Join Date
    Jun 2012
    Location
    Dunedin 9011, New Zealand, South Pacific
    Posts
    3,961

    Default

    The CFI EECIV has limited KAM (Keep Alive Memory), despite what has been siad about Throttle Body Injection systems NOT havng it.



    They do.


    Ask Walking Tall about how difficult it can be to sort through the whole system. 3.8 V6 CFI isn't exactly the same as the HO 5.0 system, which has an additional TFI ignition control used instead of the idle stepper motor. The choke pulldown is also used in a unique way in the CFI's. Bigger injectors require good flow rates, and its always good to have them checked. The fuel pressure can be adjusted, but its not normally out of spec. The two stage LO---> Hi pressure pump system is designed to allow run down to the last ounce of gas in your 15.6 gallon tank, but often the fuel supply has aged component issues.


    Ford has some TSB items with respect to the kind of gasket your CFI used..on the 3.8's there was a service replacement, and many have missed the up grade. It pays to checkit for leaks using the "Unlit" Propane Lighter/Torch method of bleeding Butane into the gaskets sourounding the CFI unit. Since Butane/Propane is 100 octonae or nearto, it causes the engine to pickup revs if there is a leak.

    A hand pump to produce the 20 to 25" Hg vac reading required to set the choke pulloff.

    Others, its just aged internal components like capacitors or(most likely) Matt J 's vac leaks.

    The work done in FEP forums debugging the operation of this system has been significant.


    Reading the codes from the self test is a good idea. But it requires a lot of additional discussion and detective work to turn what we call today Dealer Trouble Codes (DTC's) into an action plan to tune your CFI. Its not brain dead or stupid, just missing some of the later real time data logging abilites you get from Car Code or other OBDII systems on post 1996 Fords.

    1985 DTC's can be pulled real time by some of the the older Rotundra Baord systems, but that stuff is missing on the modern 60 dollar code readers.

    So pull the codes.

    Do the propane leak check.

    Get the hand vac pump

    And read the info.


    Then your action plan is fuel deliver system cleaning and clearing, and , without breaking Sh!+, doing a resonably through check of the LO--->HI pump, its fuel delivery pressure and just making sure the car hasn't had a continued diet of Av Gas or leaded fuel to clogg the catalysts.


    Well I tend to relink every darned thing, because most of it is pure gold.

    Hawkeye
    I've PM'd you the best of eight ( links that will help you.

    Matt J features in many of them

  7. #7

    Default

    Thanks so much! I have a lot of ideas now and a good starting point.

  8. #8

    Default

    Please don't ask me, I'm still trying to block it all, lol

    Running the test procedures to see if there are any trouble codes first is your best bet. The hope is that any found resultant codes from those tests will tell you if any of the sensors (or the wiring to/from them) are shorting out or open, not grounding, or the sensor itself is out of range and needing replacement. The ECT (Engine Coolant Temperature) sensor is particularly dictatorial in how these run, the MAP (Manifold Absolute Pressure) sensor and it's vacuum lines and connections, and ditto with the TPS (Throttle Position Sensor), etc...

    Making one of these work as best it can (which I'm afraid to say isn't much but mediocre in my opinion of what good function is) involves diving deep into the integrity of all vacuum lines and wires and connections, and the function of all the components and sensors in the system. If you can find and pick up the Probst book, "How to Understand, Service and Modify - Ford Fuel Injection & Electronic Engine Control", it'll become your new best friend, as to each of the sensors' and components' inner workings and proper resistance and voltage ranges etc... Good luck with it.
    Last edited by Walking-Tall; 03-11-2017 at 03:57 PM.
    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/

  9. #9
    FEP Super Member xctasy's Avatar
    Join Date
    Jun 2012
    Location
    Dunedin 9011, New Zealand, South Pacific
    Posts
    3,961

    Default

    Quote Originally Posted by Walking-Tall View Post
    Please don't ask me, I'm still trying to block it all, lol

    Yep, good work Mike.


    If I pay postage, will you send me your old gear?

  10. #10

    Default

    Quote Originally Posted by xctasy View Post
    Yep, good work Mike.


    If I pay postage, will you send me your old gear?
    I'd ask for you to define gear, my friend. I butchered/scavenged some from the harness and the vacuum lines, and I'm forced to try to at least recoup some of the $100 (for sale locally) hard pill to swallow the new MAP sensor cost me. Lemme know what you're looking to get, as I assume you're looking to look at the puzzle pieces and map things out or figure out the what and why of the lackluster function, and I can find out what the boxed up stuff's postage would be.

    FWIW, based on how the car acted while still stifled with the CFI, there's a few situations where too much ignition advance was added, and more situations where not enough ignition advance was added, as well as an across-the-board abundance of far more fuel added all over the place than necessary.
    Last edited by Walking-Tall; 03-20-2017 at 03:43 PM.
    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/

  11. #11

    Default

    SO, quick update.....
    I checked for vacuum leaks with propane and found two significant ones. There was a sensor down near the drivers side fender that had a bunch of double vaccum line sensors in a row and this particular one was completely disconnected. The second one was on the air cleaner "warm up" diaphram that heats the air through the tubes that come up from headers. (not sure what these are actually called)
    I reconnected the sensor at the fender and disconnected and hooked the entire air cleaner and all its vacuum lines to a good vacuum source.
    No change in idle or hesitation.
    I changed the air filter, and checked fuel pressure that the TPS.

    Fuel pressure was reading 35 at idle with engine on. I wasn't able to get a good reading with key on engine off. ( read like 17 or something, it didn't feel like a good reading on the meter)
    I figured 35 at idle was good.

    TPS was reading 1.05 Engine off key on, idle. I adjusted it to .96V.

    Another tidbit was I had my battery disconnected for a while to reset the computer.

    So my problem is very intermittent now. Meaning....
    My car will idle and drive fantastic, and then it will start the rough idle again and upon pulling (throttling) the car misses badly. Then it starts to run good again.
    I put a bottle of injector cleaner in it and want to drive it some more to see what happens.
    Thoughts?

  12. #12

    Default

    Oh one more thing. I noticed with the car running and the idle starts to run rough, I can see with the air cleaner removed, the injectors sort of "spit" as the engine runs rough. Not sure if this is an injector issue or the voltage to the injector causing it to do this? What controls the injectors that could cause this "spit"?

  13. #13
    FEP Senior Member Matt J's Avatar
    Join Date
    Jul 2012
    Location
    Georgia
    Posts
    620

    Default

    It's good you found those leaks, trust me there are probably more, you'll be chasing them for a while, and remember it's not just hoses that can leak, there are other components those hoses connect to which also have rubber internals that can leak too. Those sensors at the driver's fender are most likely the solenoids that control the engine operation with those vacuum lines (like I said, 80s tech). Works well when it works, but it's going to take you a while to learn your car and figure out what's what. I never had the courage to stick my head over the top of the throttle body while the car was running, so I can't tell you how it should look, but I'd guess when it's running rough it would be shaking and not drawing the fuel consistently which probably doesn't help much either. It's safe to say, though, that it shouldn't be spitting fuel out like that. If the injectors are dirty it might take a little time for the injector cleaner to help fix that. I suspect your rough idle isn't from that, it might still be from some remaining air leaks. Also, keep in mind that the car has been tinkered with by lots of folks over the years, so you can't assume that anything under the hood is set to "spec". You can get a repair manual which can help with that.

    I bought a code reader that plugs into the computer for about 30 bucks on Amazon. You can use a test light, but I like the code reader better, it stores the results and can also clear the computer of its old codes. This will help you tremendously to figure out where something is out of range, which means a faulty sensor, or other problems. These are the things that control the idle and other stuff that makes it run right. There are lots of good folks on this board that can help, don't give up on it. Once you get it nailed, it works great!

  14. #14
    FEP Power Member
    Join Date
    Nov 2007
    Location
    San Mateo, CA
    Posts
    2,271

    Default

    Don't forget the check or replace the throttle position sensor. The check valve up by the firewall can be a source of vacuum leaks if things under the dash have issues.
    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,
    03 Mach 1 7900 miles, 74 Mustang II, 69 Mustang, 67 Mustang, 07 GT500,
    14 Mustang CS/GT, 15 F150 FTX Tuscany, 16 F250 Crewcab, 67 Tbird 47K miles

  15. #15
    FEP Senior Member Matt J's Avatar
    Join Date
    Jul 2012
    Location
    Georgia
    Posts
    620

    Default

    I meant to add that when the problem is intermittent, while it's more frustrating, it's actually a good sign. It means that when something warms up or when one of those solenoids click on or off, something changes, and that thing is what is probably needing to be replaced or leaking vacuum. If the computer and everything is stock, look up the threads on how to use a test light to read the OBD codes from the computer. It will actually tell you what's wrong. You'll probably end up needing to replace the TPS, choke heater, dashpot, all those things on top of the throttle body that control the idle and performance when hard on the throttle. I definitely wouldn't do that without reading the computer codes first, and if you're going to keep it stock I highly recommend the code reader. You want to be able to tell when you change something if it makes a code go away, or a new one pop up. Just use the Yahoo machine to look up Ford OBD code reader, and you'll see a bunch. I think you might even find one at your local parts store if you're in a hurry.

    If you're like me, you'll probably be chasing down a problem that, once fixed, shows the next problem that you weren't aware the thing had. Back in the day, when all this computer stuff was new and not what most folks and mechanics were used to, they figured out ways to unplug this or that, cut that hose and turn up the idle screws, and it would seem to "fix" the problem. You're going to probably have to go back in there and reconnect a few things (keeping in mind that sometimes they were disconnected because they weren't working and the part should have been replaced), then once they're reconnected and/or fixed/replaced you'll need to fix that problem that was there in 1993 that never got fixed right back then.

    I want to tell you that it's part of the fun, but it is frustrating from time to time. Look for any posts from JACOOK, he's been extremely helpful to me as he knows more about these systems than anyone!

  16. #16

    Default

    Thanks guys! I am going to have to figure out where you plug in this code reader, and I actually like tests lights so I may try that route first.

    Quote Originally Posted by Matt J View Post
    I meant to add that when the problem is intermittent, while it's more frustrating, it's actually a good sign. It means that when something warms up or when one of those solenoids click on or off, something changes, and that thing is what is probably needing to be replaced or leaking vacuum. If the computer and everything is stock, look up the threads on how to use a test light to read the OBD codes from the computer. It will actually tell you what's wrong. You'll probably end up needing to replace the TPS, choke heater, dashpot, all those things on top of the throttle body that control the idle and performance when hard on the throttle. I definitely wouldn't do that without reading the computer codes first, and if you're going to keep it stock I highly recommend the code reader. You want to be able to tell when you change something if it makes a code go away, or a new one pop up. Just use the Yahoo machine to look up Ford OBD code reader, and you'll see a bunch. I think you might even find one at your local parts store if you're in a hurry.

    If you're like me, you'll probably be chasing down a problem that, once fixed, shows the next problem that you weren't aware the thing had. Back in the day, when all this computer stuff was new and not what most folks and mechanics were used to, they figured out ways to unplug this or that, cut that hose and turn up the idle screws, and it would seem to "fix" the problem. You're going to probably have to go back in there and reconnect a few things (keeping in mind that sometimes they were disconnected because they weren't working and the part should have been replaced), then once they're reconnected and/or fixed/replaced you'll need to fix that problem that was there in 1993 that never got fixed right back then.

    I want to tell you that it's part of the fun, but it is frustrating from time to time. Look for any posts from JACOOK, he's been extremely helpful to me as he knows more about these systems than anyone!

  17. #17
    FEP Senior Member Matt J's Avatar
    Join Date
    Jul 2012
    Location
    Georgia
    Posts
    620

    Default

    There are leads up near the brake booster at the top of the firewall that just hang there. Those are the connection for the code reader. Plenty of threads on that and how to use it. One of the best parts of keeping the TBI system in tact is that you can use the computer to help diagnose problems!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •