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1997 z-71 with 6.5 wont start

Discussion in 'GM Diesel & DuraMax' started by five.fold, Aug 8, 2011.

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  1. five.fold

    five.fold New Member

    I just bought a 1997 z-71 from a 'friend' with the 6.5, auto tranny. its been sitting in his drive for about 6 months because he could not get it to start. He changed the glow plugs & relay, fuel pump(rail mount) and relay, mounted new drive module on firewall, new fuel filter, air filter, new starter and batteries with no luck. I started working on it today, eliminating possibilities, bleeding system, etc. I tried to start it with silicone spray/starting fluid but no luck at all. shouldn't this thing at least fire off on the starting fluid, unless there is something mechanically wrong, like jumped timing or such. it does not free wheel when trying to start like it would if the timing chain were broke; truck has 190,000 miles, so I guess it could have slipped timing?? BTW, he just had a newly rebuilt tranny installed 4 miles before it quit, when it quit on him, he had parked in the drive that night , came out the next morning, wouldnt start and its been there since. Any ideas on what to look for next?
    UPDATE- loosened line from an injector, turned engine over several times, no fuel from injector line. BAD INJECTOR PUMP? :confused:
    Last edited: Aug 9, 2011
  2. Asphalt Animal

    Asphalt Animal New Member 100 Posts

    Being that you are not getting fuel from the IP, I would suggest that you check to see if the fuel shut-off solenoid is opening. This is the cylinder that extends straight up off the top of the IP. When you turn the key to ON, it should open to allow fuel to enter the IP. Some times you may actually hear it click as it opens, usually you'll have to place your hand on it and have someone turn the key to ON. You should feel it snap open.
    You can also pull it out of the pump and check it too. Just be sure to disconnect power from the lift pump or when you turn the key to ON, you'll get a lot fuel out of the pump.

    As far as using starting fluid on a 6.5L, don't do it! You'll likely damage the new glow plugs. Also, you'd be much better off not mounting the PMD/FSD on the firewall. It's likely to go bad there in short order. Mount it on a large heat sink and keep it where it has constant airflow. These things generate a lot of heat and have to be securely mounted on something that will allow the heat to dissipate from the module. Avoid using long harnesses too, they can also impair the signal from the module to the IP.
  3. five.fold

    five.fold New Member

    Have already checked the solenoid, pulled out of the IP, retracts when powered up. there is about 1/4 inch of play(up-down) in the end of the piston.Is this normal? Also, the module is mounted on a heat sink on the firewall next to the master cyl. Replaced the crank sensor today, one wire was broken, did not help, still no fuel to injectors. will move module to a better place tomorrow.
    also replaced oil sending unit today. what else is left except the injector pump and the ecm?
    Last edited: Aug 10, 2011
  4. Asphalt Animal

    Asphalt Animal New Member 100 Posts

    Sadly, unless you find a wiring issue, it is likely to be either ECM or pump; possibly both. I would check for see if any codes are stored in the PCM, this may be valuable in determining what might be the cause.
    Since you already found a broken CPS wire, there should be a code in there for it. Much of the grounds for engine sensors are made through the PCM and it is possible that there simply could just be an issue with connections there; check the connectors at the PCM and the engine harness at the firewall.

    You can also disconnect the optical sensor harness from the sensor and see if this allows it to start. In some cases, it the sensor has gone out, the PCM will rely solely on the crank sensor for input and control of fuel timing, confirming it has likely failed or there is an issue in its circuit.

    You're likely using an extension harness from the original PMD harness to the PMD, connect the PMD directly to the original harness and see if there is a difference; I have seen extension harnesses be bad, even if new.
  5. five.fold

    five.fold New Member

    which connector is for the optical sensor? no codes in the ecm, have checked all connections, will also try connecting pmd directly as you suggested.
    will get back to you in a little while after i try your suggestions.
  6. Asphalt Animal

    Asphalt Animal New Member 100 Posts

    Optical sensor is the black connector on the top of the IP. Be careful disconnecting it; you don't want to break the retaining clip.
  7. five.fold

    five.fold New Member

    plugged pmd directly to short harness on IP, also unplugged top plug(optical sensor?) on IP, no fuel yet to injectors, no start.
  8. Asphalt Animal

    Asphalt Animal New Member 100 Posts

    Unless there is some sort of electrical issue as a result of the transmission repair, ground became loose or something.... You can check to be sure you hadn't snapped a chain, but I doubt it; remove the oil filler tube and have someone crank it over and see.... Otherwise it's the pump or PCM that fried. If you haven't checked for codes, do so before ordering a pump.

    If you got fuel to the pump, and are getting nothing out, good PMD, and have done about everything else to try and bypass a failed sensor it's probably just that the pump is shot. They don't often just quite, but can.
  9. five.fold

    five.fold New Member

    Checked chain-its ok. one code I cant seem to find out about p-0251. Is there any way to test the pmd itself short of replacing it with a new/other working module?
  10. Asphalt Animal

    Asphalt Animal New Member 100 Posts

    P0251 is the code for the optical sensor, if I recall correctly, either high resolution circuit or cam reference. Looks like it needs a pump. One reason why I had you try to disconnect it, just to see if removing it would allow it to start; in some cases it will.

    Optical sensor is responsible for the injection timing. It's basically a disc with two sets of windows. As I mentioned, it's used for injection timing, it also measures fuel temperature. In theory, if this fails, the PCM will resort to the crankshaft position sensor to determine timing based off of a predetermined set of commands to allow the engine to run....basically back-up mode.

    Check fuel quality when changing the pump, be sure there is no water or any alternate fuels like waste veggie oil and such. These pumps so not like anything other than clean diesel fuel, and a drop of water in the fuel can also destroy the pump. If there is any sign of contamination, flush the complete system before running the truck with a new pump.

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