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  1. #26
    FEP Power Member gmatt's Avatar
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    Jul 2009
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    Chicago, south subs
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    2,136

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    A couple of the 'tees' were cracked on mine. So much is hidden in the wire looms.

  2. #27
    FEP Senior Member
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    Dec 2016
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    I had a few minutes to play around with this yesterday afternoon. I hooked up a fuel pressure gauge to see what was going on there. What I saw was different from what I expected to see, but maybe that is how Ford CFI cars are. Basically with the gauge hooked up I turned the key on and the pressure slowly crept up to about 10psi. I tried to start it and as I was cranking it the fuel pressure rose some more. It started up when it got to about 20psi. Eventually the pressure rose to a steady 35psi with the engine running. Granted I didn't have a perfect leak proof connection at the Schrader valve, but it wasn't like fuel was spraying everywhere either.

    I am more used to seeing the fuel pressure come right up to running pressure when the key is turned on. I ran it a few more times and the same thing happened. I did just let it sit with the KOEO just to see what would happen and I think it got up to 20psi before I ran out of patience and started the car. I know people like to see 40psi on these, but according to the FSM 35-45psi is the range it needs. I didn't feel like removing the cover of the fuel pressure regulator to try to increase it.

    Now to the interesting part. As the engine was running and I was looking things over pondering my next steps I started wiggling wiring harnesses to see if I could find any loose connections, broken wires, etc. Everything looked fine until I got to the extension wiring harness that plugs into the ICM. As you recall I moved my ICM over to the fender well to help it stay cooler. This move involved creating a jumper wiring harness that ran from the pins on the distributor that the ICM would normally plug into over to the relocated ICM. I also had to extend the harness that normally plugs into the end of the ICM as the stock harness was about 12" too short. The extension was completed using soldered and shrink wrapped joints. When I did this I noticed that the stock harness was shielded. I figured if the stock harness needed to be shielded then I should probably shield the extension as well. I used the same method that I used to construct the jumper harness which involved stripping a piece of copper wiring, stranding that around the wiring bundle, wrapping that in aluminum foil, and then wrapping that in tape. I overlapped the original shielding. I could not see where the shielding was grounded on the ICM connector side so I assumed it was grounded on the ECM end and did not ground the extension I created. Everything had been working fine.

    So I wiggled that extension harness and I could get the engine to stall. If I left the key on after it stalled I could hear relays clicking on and off as I wiggled the harness. I assumed it must have been one or more of my soldered joints so I started working my way back up the harness unwrapping the tape and foil shield. Every time I thought I got to a bad section of harness it would disappear after I removed the foil. I got back to one splice that seemed like it was THE one and again after i removed the foil it was fine. It would seem that somehow the shield I had constructed was interfering with the harness. I proceeded to remove the aluminum and left the copper for now. I need to retape the harness. Once I removed all of the foil the engine ran fine again. I think I may try to find some of the OEM shielding on a car in the junkyard. That seems like it would be the best approach. I don't want to leave it unshielded, but I also don't want to redo what I had on their either. The good news is the alternator and coil are on the other side of the engine, but the harness does cross over several plug wires.
    '89 XR-7 5 Speed
    '95 SC 5 Speed
    '91 Crown Vic P72 351W
    '97 Thunderbird
    '85 Ford LTD Squire

  3. #28
    FEP Super Member xctasy's Avatar
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    Jun 2012
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    Dunedin 9011, New Zealand, South Pacific
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    You've got inductance, and pure digital systems don't like it. A;ll wire crossovers have to be 90 degrees, and sepated. I ran the cables at Mondelēz Cadbury Candy plant in Dunedin. My boss was insistant that Inductance is worst with pure O and 1 data. In your case, the TFi ignItion system is partly digital, part voltage change. Ford did what they did to eliminate problems with RF.


    The remote ICM is a great idea, but the wire then creates another lash Radio interferance, just like an old Alpine Lash radio set.

    What you've done is found the problem. To sort it, you need to try some other kind on non ferric or silver insulation. Gray data cables are covered with silver coated candy layer inside. Data cables suffer the same issues.

    Experiment, and give yourself a pat on the back.

  4. #29
    FEP Senior Member
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    Dec 2016
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    Grand Rapids, MI
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    I'm going to try to liberate some of the OEM EFI/RFI shielding from a harness in a junkyard and wrap the harness extension in that. I'm a bit surprised that this issue didn't pop up until after 3-4 months of driving though.

    Anybody have any input/feedback on the fuel pressure readings/performance?
    '89 XR-7 5 Speed
    '95 SC 5 Speed
    '91 Crown Vic P72 351W
    '97 Thunderbird
    '85 Ford LTD Squire

  5. #30
    FEP Senior Member
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    Dec 2016
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    Grand Rapids, MI
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    Forgot to update this. I did not end up rewrapping that section of harness with any special shielding. I wrapped it with electrical tape and put it back in the harness loom. We drove it down to Kentucky a few weeks ago (around 750+ miles round trip) and it performed well. Well, as well as a 3.8CFI three speed car can do at highway speeds these days. I still get that mild panic when running on the highway with the A/C on and the compressor kicks on and you can feel the power drag down and for a split second it feels like it might have stalled. I'm going to let it be. As it is it will be going down for the winter soon anyway.
    '89 XR-7 5 Speed
    '95 SC 5 Speed
    '91 Crown Vic P72 351W
    '97 Thunderbird
    '85 Ford LTD Squire

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