FiTech injection - RPM noise issues

Discussion in 'High Tech for Old Iron' started by LandYacht, Apr 25, 2017.

  1. LandYacht

    LandYacht Member

    I've got a Fitech GoEFI 4 600HP installed on a big block. I'm using an OE style coil and what looks like an OE type electronic distributor. I can't actually tell who made the distributor - it has part no. 1112027 on it.
    The Fitech is wired to the coil to read engine speed (the blue wire to the negative coil post for you Fitech guys out there).

    The Fitech is giving me an RPM noise error code (P0335). On throttle it runs like a dream. When warmed up at idle though (in park or drive) the RPMs bounce around constantly and the idle bogs down, pops up...i.e., runs like crap as it tries to compensate for the varying RPM signal. So far I've tried the following in sequence to cut out the noise:

    1) Taking the fitech harness apart, spreading out the wires and moving them as far from electrical noise sources as possible.
    2) Shielding the rpm signal wire (blue) in braided metal RF shielding from Electriduct with a ground.
    3) Shielding the adjacent white wire to the ignition in braided metal RF shielding with a ground.
    4) Adding a second braided metal RF shield over the entire wiring harness.
    5) Soldering a 10k Ohm resistor into the rpm signal wire (blue) about 10 inches from the Fitech ECU - apparently, this acts like a low pass filter when coupled with the capacitive qualities of the ECU itself (allegedly according to some of the Facebook fitech commentators).

    No luck so far.

    My next step is to try replacing the coil, and then if that doesn't work, replacing the distributor. I'm tempted to just skip ahead and get a reproduction HEI distributor from TA Performance to see if that solves the issue. With an HEI, the Fitech blue rpm signal wire will connect to the HEI's tach signal connection.

    I'm thinking out loud here, but have two specific questions for you Buick and Fitech guys:

    1) Any strong feelings about the TA HEI distributor versus an MSD or other manufacturer?
    The 455 in question is a mild build in my 72' LeSabre convertible - she's a torque cruiser land yacht. Mild cam, short tube headers, Edelbroke performer intake, and the FiTech.

    2) Any ideas about what else I might be missing in my troubleshooting so far?

    I suppose I could try to put my hands on a oscilloscope, figure out how to use it and try testing the RPM signal at the coil, along the blue wire...i.e. try to isolate where the noise is coming in. It's possible its coming from someplace else altogether into the ECU. The reminds me to check the grounding on the ECU with a meter too.
     
  2. bobc455

    bobc455 Well-Known Member

    On my FI (not FITech), I had to move away from an HEI distributor and move to an external coil, because of ignition noise to the RPM signal. I was not able to solve this by only re-routing or adding shielding.

    MSD (the Multiple Spark Discharge system, not necessarily the MSD distributor you are consdiering) will make this issue even worse (if in fact this is your problem).

    -Bob C.
     
  3. LandYacht

    LandYacht Member

  4. 70purplerag

    70purplerag Silver Level contributor

    Have you talked to the guys @ Fitech. It is hit and miss but they deal with issues from many installs. I had a hunting idle issue that I resolved by richening the idle mixture. I think 13.4 was the sweet spot.
     
  5. LandYacht

    LandYacht Member

    I did - the issue is the noise in the RpM signal, but they didn't have any brilliant ideas. Just going to have to isolate or filter it out.
     
  6. Bens99gtp

    Bens99gtp Well-Known Member

    Not familiar with your system first hand, but if you have shielded and grounded all the wires you say, could the issue be coming from the module inside the dist. That number you gave shows to be a regular points dist. When you say or style electronic, I'm assuming you mean there is some form of module in there not the points. It could be the operation of the module causing your noise. Some of those setup are done by mag pick, some are done by hall effect. You might find the manufacture of the conversion and make sure it's compatible.

    The other thing I can think of is your white wire, where does it hook too??

    It should be a clean switched source.....for temp set up since you can get the running issue at idle without having to drive it sounds, put that wire right to the battery.....see if it cleans up. If so you have your answer and you can simply pull the wire from the battery to shut it off when wired this way. It's possable you could be getting alternator noise of something like that back through the ststem.

    When I did a fast system on a mustang I had to add several extra ground wires to clean signals up. Might try to make sure you have a good clean ground from motor to battery, from firewall to motor, from frame as well.

    Is there any thing like aftermarket stereo or amp in your car? Sometimes those cause weird issues to
     
  7. LandYacht

    LandYacht Member


    Thanks, Ben. Appreciate the input and good suggestions.
    - I've also been checking grounds throughout the car - the ECU, the motor and firewall all checked out excellent.
    - I'm going to try running the white wire direct to the battery - I particularly like this. Right now its tied to the positive terminal on the coil and that is very suspect.
    - I've also been eyeing the module in the distributor with suspicion. Next I'll try swapping it for a known one to eliminate that variable.
     
  8. sailbrd

    sailbrd Well-Known Member

    I have done two Fitech's now and both run great. A few ideas. Run a ground wire from the TB to the body. White wire is sourced to a relay not to the key directly. Did this on both the cars I set up.
     
  9. ttotired

    ttotired Well-Known Member

    I don't have a TB injection on my car yet, but I have done a bit if work on them (I am an auto elec)
    It is very important to connect all the power and earth wiring directly to the battery. Obviously, the ignition wire (switched power) cant go direct, but
    it can be wired through a relay to the battery. Don't be cheap here, the battery supply to the relay should be done separately than the actual battery
    supply, not just piggybacked off it. Run the earth(ground, neg, whatever you want to call it) also to the battery and (if it don't have one) fit an earth wire from the
    module (side of the throttle body) to also go to the battery.
    The battery acts like a big capacitor and eliminates a lot of noise. You also get a lot of noise in the wiring due to voltage drop and varied load on any one given wire or circuit.
    The voltage on the headlight circuit will be different than that on the ignition circuit for example, so, if your battery supply point is on the headlight circuit @ 13.1 volts and your ignition supply voltage is at 13.4 volts, you already have a .3 volt noise.
    Just for those internet warriors out there, the volt levels, I pulled out of the sky, they are there as an example only, not what you might actually measure on your car :)
    So, Summery, all power and earth supplies to the battery, advise to rum the module harness away from all other wiring in the car if possible, and shielding the module harness can help.
    Mick
     
  10. TexasJohn55

    TexasJohn55 Well-Known Member

    Quote: "2) Any ideas about what else I might be missing in my troubleshooting so far?"
    Take the power wire off the alternator, test for results. Also unplug harness from alternator to take it all offline.
     
    Last edited: May 18, 2017

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