6.2 diesel questions

[78customdeluxe]

i found a 84 gmc 6.2 in pretty good shape for 1000 bucks. its a 3/4 ton regular cab. it runs good and drives good but what i was told the glow plug "exciter" was bad. does he mean glow plug relay possibly? what kind of milage would you expect from this with a 4 speed manual tranny? thanks

[RockHQ]

Have you test driven the truck yourself?
I've never heard anyone use the term "exciter", so i'm guessing here.

Since it's a 1984 model, he could be talking about the glow plug electro-thermal controller, which controls the glow plug relay "on" time. The controller is essentially a series of bi-metal switches that are heated when on. The switches provide correct pre- and after-glow time by disconnecting the glow plug relay after they get hot enough.
I won't get into more detail about it because i would need wiring diagrams to make any sense. The controller switches can fail so that the plugs don't have pre-glow at all, or they are on for too long, or they won't have any after-glow. Glow plugs must not overheat because they will fail internally, or worse the tip can break off and drop in the pre-combustion chamber or even on top of the piston.

Now my second guess is that HPCA might not be working. HPCA stands for Housing Pressure Cold Advance. At cold start-up
a switch feeds +12 volts to the fast idle solenoid and the HPCA solenoid on the injection pump. HPCA solenoid decreases the injection pump internal pressure which advances injection timing by around 3-5 degrees, and the fast idle solenoid increases idle RPM, both help increase combustion chamber temperature. The switch is "on" at engine temperature below 125F, off above that. The same switch should also prevent glow plug operation again at temperature over 125F.

To test the glow system and HPCA, the engine must not be run for about 1 hour, and the ignition switch can't be in the "run" position. Turn the key to "Run", and see if the glow plug light comes on, it should stay on for about 8-10 seconds. Start the engine after the light goes off, after that the light should briefly cycle on and off 3-4 times and stay off. Idle RPM should go down to normal in about 5-10 minutes, depending on the weather.


Well, that's all i can think off now. You can PM me if you've got any questions.

-Axle

[arveetek]

Mileage depends on gearing, which most likely would be 4.10's on a 3/4 ton diesel. I'd say around 15-17 mpg. I get 18.5 + with my 3/4 ton, but I have overdrive.

[Prerunner1982]

i was waiting for Casey to hit on this thread...