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  1. #1

    Default 86 3.8 CFI running rich/stalls at idle

    Okay so here's the rundown.

    Years ago a user by the name of "86lx" did an IRS swap on his 86 4-eye and had issues with starting it after the swap was done.

    This is the same car.

    The 3.8 starts, only I have to hold the throttle wide open to get it to light up, after that it'll run rich up until 3500 rpm, after that it's practically flawless. That is up until you lift off the gas, then it'll stall out immediately. We recently switched out the old injectors/filter for brand new ones. As far as I can tell, there shouldn't be anything pinched or kinked as the car has been sitting in a garage for a decade. Did all the normal fluid changes, after that we noticed that gas was leaking from the top of one of the injectors until the battery was disconnected. After that, we cleaned and rebuilt the TB and the leak was gone.

    After sifting through threads for awhile I'm starting to rule out the fuel pressure regulator and timing, that doesn't mean that they're not the problem yet, I'll be going through it again soon enough so I can identify the sole issue. I would appreciate any advice anyone could offer. Thanks.

  2. #2
    FEP Super Member xctasy's Avatar
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    The fuel tank and return lines,and the way the electric fuel pump changed on 1986's menas you have to check proper fuel delivery. First, its a fuel pressure matter, but you have to go back to the in take electric pump. Cut outs do to poor wiring are sadly typical of the system. Its nicely designed, but old wires cause a lot of problems. It wasn't that flash in 1986, less so now. So you have a whole bunch of little things to check.

    Jeff Cooks 1 standard drink Shot glass with mineral terpentine and then flush and clean and dry the electrical connections that feed back to the ECM connections and anything related to the TAB/TAD. The O2 sensor is heated, so you just need to check that its in okay shape. All the hard wire connectors tend to oxidise out. Use the clip removal tool, and don't worry if you break the connectors, but don't be harsh with them. Each one in the 1986 Ford EVTM book is listed in a diagramtic picture, but the numbers are not always exactly right. You should check each one.

    Then pull the codes. The Idle Air Control needs to be operating properly.


    Beware. Igintion components are no longer OEM Ford Motorcraft Spec unless you get them from Ford. Lots of problems happen when a Speed Density computer doesn't get a clean signal from the TFi ignition. The TPS signal sometimes isn't clean through the sweep from 0.9 to peak voltage. The intake manifold 2-bbl CFi gasket was subject of a TSB upgrade, so make sure its still in good shape. A propane torch unlit can allow you to find leaks.

    The EGR has a different kind of sensor,and Walking Tall noted that it can generate odd voltages. It needs a clean signal to work. MAP sensors are commonly out of range too.


    Tamper proof fuel regulator is adjustable when the Poly Ethyeline bung is removed, and you check it with a proper rated fuel gauge. 38 to 42 psi is possiable, and idle varies massively when its not within the sweet spot.


    If your AOD setting is not correct, the idle can be influenced. Best way to do that is by Fuel perssure gauge, so set AOD idle and in gear pressure to spec, with the correct adjustment, and then reset fuel pressure.

    Basically, a non polling sensor giving dirty data to the ECM can send CFI off line, so it hunts around keeping everything running. Ford had gotten all of these system dugged by 1986.

    Code reading should be a good step.

    EGR ports are commonly ridled with crud, so expect that the codes relating to EGR might be out.

    Walking Tall has them listed.


    Keep cheking an asking. Your not alone.

    CFi has some negatives, but its operation is just going trough the VECI diamgram and Electrical Vaccum Trouble shooting Manual, and then foring a Prognisis, applying a Remedy, and then Curing the problem.

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