6.2 diesel questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

78customdeluxe · 04-03-2003, 10:05 PM

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 · 04-04-2003, 11:50 AM

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 · 04-05-2003, 12:49 AM

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 · 04-05-2003, 01:11 AM

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

04-03-2003, 10:05 PM	#1
78customdeluxe Registered User Join Date: Dec 2002 Location: Upper Sandusky Ohio Posts: 72	6.2 diesel questions 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 __________________ 88 Crewcab Dually 5.9 Cummins, 5306 Eaton 6-speed, converted 4x4 w/52's up front, 90 front clip(parting out) 1986 ElCamino (needs motor) 1970 C30(future service truck for my ag-equipment repair business) 1970 CST10(parting out and partial donor for the '70 C30) 2000 GMC 1500 ext cab sb, z71, 5.3 loaded auto

04-04-2003, 11:50 AM	#2
RockHQ ROCKET POWER! Join Date: Feb 2003 Location: Finland, Europe Posts: 509	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 __________________ What did i do last nite? I had a wonderful time, That's what they tell me What did i do last nite? 1979 C-10 shortfleet: Olds 350, Th400, 12 bolt Current project: 1969 Olds 455 W-30, needing a rebuild

04-05-2003, 12:49 AM	#3
arveetek Ultimate Diesel Dude Join Date: Oct 2002 Location: Southwest Missouri Posts: 328	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. __________________ Project truck: '81 C/20 converted to 6.2L TURBO DIESEL bored .040", gear drive, 6.5L injectors/pump, custom pistons, custom 4" exhaust, 700R4, 4.10's Daily Driver: '95 K1500 Tahoe, 6.5L TURBO DIESEL, NP241, 4L80E, 3.42's

04-05-2003, 01:11 AM	#4
Prerunner1982 Registered User Join Date: Oct 2002 Location: Edmond, OK Posts: 5,904	i was waiting for Casey to hit on this thread... __________________ Jon 1982 Chevy Silverado 350/th350.... RETIRED 1993 Jeep XJ 2 door(Cherokee) 4wd 4.0ltr/AX-15 (5spd)/NP231 .... Oklahoma Roll Call



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