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Thread: Commander 950 Not Priming

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  1. #1

    Default Commander 950 Not Priming

    Hello. I have a Holley Commander 950 installed in a '69 Mustang. I installed the system 7 years ago, and it has run without any major issues. In the past few months, the system will not prime the fuel pump with key on. I have the ECU set to prime for 4.9 seconds. Again, this has always worked.

    In troubleshooting, I've tested the relays (both the system supplied as well as a relay I installed at the fuel pump).
    In probing the wires going into the ECU directly:
    I have 12 volts at the red wire.
    I have 12 volts at the red/white wire when the key is on.
    I do not have any voltage at the green/black striped wire during key on, when the system does not prime.
    When the system does prime, I'm getting 12 volts on the green/black stripe wire.

    The problem is intermittent and I cannot seem to reliably make it prime. It seems to work for awhile and then quit. Of course, it quits when I'm parked away from my home.

    If I'm getting 12 volts at the green wire when it works and not when it doesn't, does that give any clues? I've checked & cleaned ground wire and looked for any other obvious issues without success.

    The only other clue I can provide is, I don't seem to be able to get the laptop connected to the ECU when the system isn't priming. I'm able to connect them when the system primes & starts.

    I'd appreciate any help troubleshooting this, as I can't drive the car with the risk it will leave me stranded unable to start during intermittent issue. Thanks in advance.

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
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    21,807

    Default

    Quote Originally Posted by jeffawarner View Post
    I do not have any voltage at the green/black striped wire during key on, when the system does not prime.
    When the system does prime, I'm getting 12 volts on the green/black stripe wire.
    The problem is intermittent and I cannot seem to reliably make it prime. It seems to work for awhile and then quit.
    I would start by performing a continuity & wiggle test on the main harness. Also, check the ECU connector & its terminals for a bad connection. Check the system relay terminals for corrosion too.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  3. #3

    Default

    Thanks Danny, I appreciate the response. I've checked the ECU connector & terminals, and the system relay terminals as well. I have wiggled wires across the harness and it didn't seem to change the conditions. It is odd because it's so unpredictable. I will do the continuity test on the main harness. Two follow-up questions:
    1) On the continuity test, for the system to prime, are there specific conditions I should look for (wires that may be more suspect that are required for the system to prime)? I'm trying to target my search.
    2) Is there any way to test the ECU? I'm just looking for a way to rule out that the ECU is failing. Thanks again! Jeff

  4. #4
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    21,807

    Default

    Quote Originally Posted by jeffawarner View Post
    1) On the continuity test, for the system to prime, are there specific conditions I should look for (wires that may be more suspect that are required for the system to prime)?
    Red/white +12V switched wire (ECU A6 pin), and green/black fuel pump relay trigger wire (ECU A2 pin). Of course, the main battery power (fused) & ground must be good too.
    http://documents.holley.com/techlibrary_r10149-7.pdf (Holley Commander 950 Pro EFI Manual - Figure 86, Page 111)

    2) Is there any way to test the ECU? I'm just looking for a way to rule out that the ECU is failing.
    I don't know if Holley still tests C950 ECUs. If everything checks out (wiring & relay), you probably have a defective ECU.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: Dominator MPFI & DIS, A/C, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/X-pipe/shorty headers, 100HP progressive dry direct-port NOS, 160A 3G alternator, Optima Red battery, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  5. #5

    Default

    I'm pretty sure I had one flashed & tested about 3 years ago. I had bought a spare off eBay. If it turns out you need an ECU, I have two. I upgraded to the HP EFI ECU.

  6. #6

    Default

    Thanks guys. I appreciate the help. I'm still having no luck. I will call Holley on Monday and see what the options are. I'll come back to you if it turns out it's a bad ECU. By the way, I haven't dug into the HP EFI. Is the HP EFI worthwhile for me to consider instead of fixing/replacing the C950? I'm running TBI on my Ford FE engine. I'm interested in how easy the upgrade is and what the benefits are for TBI. Thanks again!
    Last edited by jeffawarner; 11-26-2016 at 10:53 AM.

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