Glow Plug heater question

Discussion in '1982-Present GM Diesel' started by Hossbaby50, Aug 20, 2002.

  1. Hossbaby50

    Hossbaby50 3/4 ton status

    Sep 1, 2001
    Likes Received:
    Peoria, AZ
    A buddy of mine is just bought a 83 K5 with 6.2. The PO did a crap job on the wiring. The glow plug preheater is on a toggle switch and crapped out the other day after he had to drop the starter (to fix the crap wiring on the starter). So now his truck won't start.

    Question time:

    Where is the GP preheater, and how is it wired?
    What else could have failed and cause a problem?
    Is there any way to start the truck without preheating GP's?

    On a side note, how exactly do you time on of these 6.2's?
    What is the procedure?
    Is it the same as a gas motor?
    What should the timing be set to?
    Is the distributor in the same spot as a gasser? (as you can tell I don't know jack about the 6.2's)

  2. arveetek

    arveetek 1/2 ton status

    Mar 1, 2002
    Likes Received:
    Granby, MIssouri, USA
    Well, you got several questions here to go over.....

    First of all, the glow plug controller on the the 82-84 models are junk. They're also expensive to replace. What a lot of guys do is wire up a momenary switch on the dash, like the PO did. This is not so bad, but you have to be careful not to glow for too long or you'll burn the plugs up. The best alternative is to convert the glow system over to the 85-93 glow controller. Information on how to do this can be obtained from (the best resource on the net for GM diesels).

    The glow controller is located on the rear of the driver's side head, on the intake side, pointing up. It screws into the water jacket of the head. It has a bunch of wires sticking out of the top of it.

    I suggest you get Hayne's diesel engine repair manual. It covers all the basics, plus the glow plug systems.

    Unfortunately, the 6.2L needs the glow plugs in order to start when the engine is cold. A diesel is a compression-ignition engine, meaning that the heat of the compression ignites the fuel. When the 6.2L is cold, there's not enough heat generated when cranking the motor to iginite the fuel. The glow plugs heat up and aid in iginiting the fuel at first.

    To time the diesel engine, you have to have a special timing tool. There is no distributor, no spark plug wires to clamp the probe onto. Most diesel timing lights have a probe that screws into a glow plug hole. Some nicer models have a probe that clamps onto an injection line.

    The 6.2L uses a distributor-style fuel injection pump. It's mounted right in the middle of the valley of the engine. You can see it right in front of the air cleaner. It has eight injection lines running out the backside and going to each injector. This pump delivers and times the fuel injection. To adjust the timing, you have to rotate the pump itself. There are three mounting nuts you have to loosen, and then you rotate the pump towards the driver's side to advance the timing, and towards the left to retard the timing. It's best to have someone with a diesel timing light to adjust the timing.

    In the back of the engine where the distributor would be on a gasser, there is a vacuum pump. Since a diesel has no throttle valves, it produces no vacuum. The vacuum pump is just used for accessories, such as the A/C vents, cruise control, etc.

    Hope this helps.


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