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Tuning

Discussion in 'FAST Support Forum' started by J.K., May 31, 2017.

  1. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Interference can affect any wiring.

    On my '81 pickup, I routed the TBI harness though the air gap on the Victor style intake - to the front of the engine. The ECU sits on the inner fender panel of the '81. The way I routed it, it really doesn't get near any other wiring. I even routed the sparkplug wiring under the headers against the block.

    On my '85 TA, the TBI harness runs across the sparkplug wiring on the passenger side of the intake at a 90 degree angle - separated by an inch or so. The harness is in the distributor area, but distanced from the distributor. I don't run any primary harness wiring near or under the distributor - with the exception of the two wires connecting the distributor magnetic pickup assembly. I plan to change this one day as the sparkplug wiring will look a lot neater running under the Victor intake runners and out the sides, and then over the valve covers to the sparkplugs. This will even further distance the TBI harness from the secondary wiring - still away from the distributor and give a neater look there.

    Of course, all engines don't have rear mounted distributors. But for those that do, the harness should route forward or across the side of the engine. You already know how your OEM Camaro harness was affected by your distributor - and how difficult it was to find. Any primary wiring near a distributor or an ignition box/box wiring is bad news.

    Short answer - I don't route any ECU harness wiring against, under, above, or around the distributor. I keep it all as far as possible away from the distributor. My MSD plug wires are 40 Ohm per inch spiral wound, but I still prefer all harness wiring as far as possible from any secondary wiring.
     
    Last edited: Jul 25, 2017
  2. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    Yes I haven't forgotten that hair pulling journey moving wires around to eliminate those pesky gremlins. It's not an easy task trying to keep things functional and tidy also.

    I think I'll visit the throttle body harness. It may not be an issue, but then again it might. My plug wires run around the back and outsides of the valve covers. The throttle body harness passes the distributor by about 3 inches, then crossing the 1,3,5,7 plug wires at a 90 degree angle. From that point on it doesn't pass anymore wiring along the way to the ecu.
     
  3. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    That could help you. My TBI harness on the TA is as far forward of the distributor as the rear of the intake allows - and crosses over #s 2,4,6,8 plug wires to the front of the air conditioner box where it is secured with nylon ties. My ECU harness comes through the firewall below and to the middle of the box. My actual power and fuse wiring comes out the factory computer side port near the door and back of the fender. Those wires then travel up over the inner wheel well cover to the front of the battery and elsewhere. It all looks GM factory in neat looms.

    I would have liked to run my plug wires on the TA like you did, but my tall fabricated valve covers won't allow it. I even had to modify the windshield wiper housing to clear the one on the drivers side. The heater hoses are also in the way on the passenger side.
     
    Last edited: Jul 25, 2017
  4. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    So last night I moved the throttle body harness further away, as much as I could anyway. Warmed it up and drove around some. Let it idle and observed the actual and target AFR. The actual was doing better in maintaining the target. Before it would tend to hang on the rich side several points. Now it was fluctuating + and - of the target. Also it seemed to drive so much better, absolutely no hick ups, dead spots between shifts. I also then turned accel fuel all the way to -8. After a couple seconds it was on the lean side of the target several points and trying to work it's way down to target. This swing tells me there must be still some interference pulsing the injectors.

    One thing I researched last night but haven't tried yet, I have my msd wires from the box (mainly coil orange and black wires, tach wire, switched ignition wire, and the points wire which is connected to the FAST wiring). Since the FAST system uses the points wire to trigger the mad, is there a potential something in the other wires in this loom I described that could be sending a false signal down the points wire somehow? I'm sure I removed the orange and black coil wires from this loom in the past with no noticeable difference. That still would have left the tach, switched 12 volt, and points wire together though.
     
  5. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Another likely problem would be the main power wires to the MSD - especially if you don't have the ground wire connected to the engine. The MSD filter is also an easy install. You just remove some insulation from the main power wires and connect them to the MSD filter capacitor. The wires don't need cutting or any terminals made up - just a loop around each terminal and tightening the terminal nuts.

    Twist the wires going to the coil from the MSD. This will help prevent the possibility of them affecting the tach wire or others.
     
    Last edited: Jul 27, 2017
  6. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    I may try that filter also. I have the msd grounded to the frame close to the drivers side engine mount. I thought it was sufficient as there is a ground strap on the opposite side frame to engine block. Plus a heavy ground cable from block to battery.

    Also I already have the two coil wires twisted, but I suppose them being in the same loom as the tach and points wire could still be an issue. The tach wire from the msd is only feeding my factory tach as if memory serves me correct with the FAST wire hooked up to msd points wire...no other tach wire is used to the ecu. I can't see how my factory tach wire could hinder the ecu since the aren't part of eachother. Still leaves the twisted coil wires in the same loom as the points trigger wire. I could see that a possible opportunity for noise.
     
    Last edited: Jul 27, 2017
  7. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    The engine is a better ground for the MSD, with less chance of resistance or interference intrusion. You just don't want the MSD ground wire connected directly to the actual negative battery terminal.
     
  8. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    I want to separate my fast power supply from sharing the same battery terminal with my other devices, is there enough filtering in a car battery with both side and top terminals to effectively reduce potential noise from other devices if I hook up the FAST to the top post and have any other devices hooked to the side terminal along with my main power supply? The fast wire would have the top post dedicated to itself. Or would it be more beneficial to hook up those other devices down by the starter.
    I have my fan power feed and msd box sharing the top post with the fast wire now. The fan feed from what I understand is a noisy wire due to uncoupling of the relays.
     
  9. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Probably not. If you connected the FAST ECU power and ground directly to the battery posts, the battery will filter it. If you connect a wire of some length to the battery post to create a connection point away from the posts for other +12V connections, that can help prevent interference to the FAST ECU. This is why the starter +12V and ground cables can be directly connected to the same posts as the ECU - they don't make an "unbroken" connection that is likely to induce interference.

    Use the engine block as the direct ground for your MSD. You can connect the MSD +12V wire to the same post as the ECU +12V. This will stop interference in most cases. If it doesn't, add the MSD capacitor to the MSD CD box power wires. If you still have interference, it is coming from somewhere other than from the main power wiring.

    The same applies to the fan feeds.
     
  10. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    Would I also be better off relocating my fan grounds to the block as per the msd ground? My fan grounds are currently located on the radiator support.
     
  11. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Yes, along with any fan controller grounds.
     
    Last edited: Jul 30, 2017
  12. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    While we're on the topic of fans, something just occurred to me that I hadn't thought of before. I'm using both the fan wires to run both my fans (each through their own relay). The fast fan wires are only triggering the ground for the relay coils. Most people recommend placing a diode across the coil to gently release the energy that gets fed backwards during the deenergizing phase. Is ecu's fan control wire protected internally already or would it be wise to install the diode at the relay anyway.
     
  13. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    The ECU fan grounds are unprotected. As long as the relay is wired and working correctly, there is no need for a diode.
     
  14. J.K.

    J.K. Member

    Joined:
    Aug 7, 2016
    Any idea why the fan wires come from fast with fuses wired into them? Typically you don't see fuses inline of a ground wire, which is what the fan wires are essentially. My first hunch is they intended for the fuses to act as a current suppressing diode. I'm also no electronic whiz, just seems odd there's inline fuses on a ground wire.
     
  15. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    The fuses suppress nothing other than they blow to protect circuits. So long as the fuse completes the circuit - the relays and wiring are protected. I fused the power wires of my dual fans so there would be less chance of a wiring short getting my relays and relay wiring. I've seen improperly wired fans take out relays and their wiring in the past - when a fan motor went south.
     

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