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COMM ERROR ! Issues

Discussion in 'FAST Support Forum' started by AaronMiller, Mar 10, 2017.

  1. AaronMiller

    AaronMiller New Member

    Joined:
    Mar 10, 2017
    I am getting COMM ERROR's on my handheld now and then. I have checked the connection between the handheld and ecu. I am not using the extension cord between the handheld and ECU as they are right next to one another, mounted in the glove box. Here are the facts on my situation..

    -new build, ~10 miles on testing and tuning
    -when the COMM ERROR comes up on the screen, the car continues to run as it should, it has never acted up, shutdown, etc.
    -when the COMM ERROR comes up, the handheld resets itself, sometimes will go to HOME screen until I select Live Data or Advance, etc. then it will either enter those screens or go back to COMM ERROR.
    -it has never gone from the Live Data screen (which I mostly have on) to COMM ERROR or gone to COMM ERROR during operation, it is always when I try to enter the Live Data or Advance screen from the Home screen.
    -when I REALLY want to access the advance screen and am getting the COMM ERROR, I just continue letting the ECU reset itself and eventually, when I choose the screen I want (usually Live Data) the screen will come up showing everything operating. It has never gone from this screen to a COMM ERROR. I have tried wiggling plugs, pulling at wiring, etc. The best I can get from the tech line is that there must be a connection issue. I am not convinced this is really a connection issue as the tech line has told me, but I would be happy to find where it is!

    [​IMG]

    Here is how I have it wired:
    -Positive wire to positive of battery in the trunk, Negative to negative side of battery. I had to extend wire length by a few feet (maybe 2-3) and did so by using next size up wire, soldered to the provided power and ground wire. The power and ground wire are run under the passenger side door sill all the way back to the trunk. There are no other wires run along with these wires.
    -RPM input signal is from MSD 6AL Box, which also powers Autometer 5" Tach.
    -MSD 6AL mounted under driver's side fender, powered by positive and negative wires run directly to the battery under the driver's side door sill all the way back to the battery.
    -ECU and handheld mounted in the glove box.
    -Fan outputs wired to ground on BeCool provided relays, relays powered by 12+ power distribution block. These work fine so far, the only problem I have noticed is one time when I went to check fan on/off values, there was a 110* split between the two. For example, it would say FAN ON: 201 FAN OFF: 091. I thought this was strange, so I shut it down, turned the key back on and got another COMM ERROR which seemed to bring these values back to a more reasonable split (I don't remember what the difference was).

    [​IMG]

    -FAST is NOT controlling timing for me.

    [​IMG]

    Any other questions anyone would have I would be happy to answer. So far I am happy with the system but the COMM ERROR's are getting annoying, especially when I want to show off how well the system works to other gear heads.. "hey check out the live screen" COMM ERROR!! :)
     
  2. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Handheld rebooting is is not an isolated issue. Check that none the ECU wires are running near radio or speaker wiring or other component power wiring. Be sure all engine and chassis grounds are good under the hood and to the body. Keep all ECU wiring away from the distributor area and secondary wiring as much as possible.

    The MSD 6AL is likely a problem. Ground it to the engine. Connect the positive wire to positive at the starter. Be sure the ECU pink 12V ignition "on" wire is getting continuous +12 with the key on and during starting.

    If this doesn't help, add a MSD filter capacitor. If the problem still exists, try adding a non-electrolytic 82 Pico Farad (50 volt or better) capacitor. The Pico Farad capacitor should be installed with one leg to a good ground and the other leg installed to the ECU pink 12V ignition "on" wire.
     
  3. AaronMiller

    AaronMiller New Member

    Joined:
    Mar 10, 2017
    Thank you for your reply. Just wanted to share an updated..

    I have no radio or speaker wiring (stock 67 AM radio, 1 speaker). I am running a ground from the battery (in trunk) to the engine block via 0 gauge wire and then a braided 2 gauge grounding strap from the bellhousing to the body of the car.

    I have tried grounding the MSD box to the body and moving the power wire from the battery with the same results. The pink wire is getting power in on/crank/run. I will check later today to see what other wires are connected to this "on" feed and supply designated power to the switched ECU pink +12 wire.

    I have been reading quite a bit about this issue and found alot of talk about isolating distributor wires. My distributor has 2 wires running from the MSD box to the distributor, these wires are routed under the driver's side fender, under the dash, through a bulkhead in the firewall and under the engine to the distributor. Is there a type of sleeving I should put over these wires (other than braided tech flex) to help isolate noise or is this not an issue? Through the bulkhead is the only area where the EZ Harness and MSD 2-wires come into contact, then run side-by-side for about 3 inches.

    [​IMG]

    I am assuming the MSD 8830 cap only isolates noise from the MSD power wires and not the distributor signal, but I am definitely willing to give it a try.

    I have located the capacitor you are referring to (82pf, 50V+) and will have it later today so I can change one thing at a time. I will report back with my findings.
     
  4. Denis

    Denis Member

    Joined:
    Dec 2, 2009
    Location:
    Mendocino County, Northern Calif
    AA is right by suggesting the use of the MSD capacitor to solve your problem. With a trunk mounted battery you will have noise from the MSD on your entire 12V system. It was so bad in my car that it destroyed a GM ECU. Additionally, you should install an additional ground to the body at the battery, keeping it as short as possible. The problem with the trunk mounted battery is the impedance of the long cables. With DC the impedance is no big deal but when it comes to noise the long cables act like a big resistor and the higher the frequency the worse it gets.
     
  5. AaronMiller

    AaronMiller New Member

    Joined:
    Mar 10, 2017
    Thanks Dennis, I will add an extra ground there as well. I will do one thing at a time and check on the COMM issue as I go, I would really like to isolate the problem to help others in the future!
     
  6. AaronMiller

    AaronMiller New Member

    Joined:
    Mar 10, 2017
    Just wanted to share an update.. I added the MSD 8830 capacitor filter, no change. I added the 82 pf capacitor between the pink 12v on wire and good ground, no change. I also added a ground to the ECU, talked to FAST support on this and they said it needed to be grounded (then he backtracked) so I grounded it anyway, no change. Next step will be to add an additional ground from the body to the battery (not optimistic on this but will try). I guess the good news is that it works some of the time and I don't seem to be losing any parameters or settings, still an annoying issue.
     
  7. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    You were previously losing user settings before, so the 82 Pico Farad capacitor solution is working to now prevent that. I came up with that fix when my com user settings were getting badly scrambled in my '85 TA. You're have multiple interference issues that may have been corrected, but it also looks like there may still be a problem with the ECU ignition power connection. The capacitor only removes frequency spikes there. Try using a direct connection from the battery to the ECU pink ignition wire to see if the com errors stop. If they do, you have an ignition switch problem or a problem with ignition power to the switch. The ECU ignition power wire also supplies power for the voltage reading in the handheld (which looks fine), but there could be a problem causing very short power interruptions. This won't affect the MSD, but will immediately affect the ECU.

    Also, be sure the TBI to ECU main harness is away from the distributor and not parallel to any sparkplug wires or other power wiring. Remember to check for error codes before turning the ignition off.
     
  8. A A

    A A Well-Known Member

    Joined:
    Jun 22, 2014
    Just spotted something in your mounting picture - be sure nothing is pressing against the ECU main connector when that door is closed, or pulling at the connector with the door open. Also be sure the connector bolt is just lightly tightened.
     
  9. shelbydogg

    shelbydogg Member

    Joined:
    Jul 19, 2010
    I know yours is fairly new but all of that movement of the glove box door opening and closing will eventually weaken the wires. Stranded copper wires are for movement but you know what happens when you continually move a wire back and forth, it will break. Your main ECU is mounted on the door too?
     
  10. Dr.Corvette

    Dr.Corvette New Member

    Joined:
    Aug 28, 2013
    I had the same problem with the touchscreen. Most of the time I would start the car and get the comm error. Car would run fine. Sometimes the would takes as many as 7 restarts of the screen to get it to start functioning.
    Other times it worked the 1st time. Went through all the check connections crap . Never found a problem. Also mine would fail just by tuning the key on and not starting the engine. So it is not an electrical interference problem.
    Then I had the opportunity to try another screen. This one worked every time. Called FAST told them I tried another screen and it had no problems. Sent mine back to them and got another. Never had this problem again.
     

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