1984 GMC C7000 366

[frank@signsfors]

I have a truck that has been sitting since 2010. It is not running. It turns over, It was not getting gas, I replaced the fuel pump and now am feeding it from a gas can. It is now getting gas

I don't think it was getting spark, I replaced the distributor cap, rotor and coil. still nothing. there are 4 wires into the distributor cap, a red, yellow and two plugs. I guess red is 12 volts, yellow is grounded through the ignition switch???

The plugs are Autolite 144s, they are carbon coated

I had it running today for about 30-40 seconds, then nothing

What could be holding it back? Maybe a fuse? fouled plugs? bad carb?

 

[Junkyard]

If memory serves none of the wires that plug into the cap are grounds, you'll have two wires on the row farthest out from cap, one is 12 volts and the other is an output to a tach. The row closer in goes to the module. I assume that age truck has HEI ignition with the coil in cap. Assuming you have 12 volts with key in run position as well as when it's in start position that narrows spark down to coil or module. Both can be tested and replaced cheap enough if need be.

Any backfire or hints of wanting to run? Still have the factory quadra-junk carb? If you feed it gas through the top of the carb will it run? Fuel and fire is what it takes to run. If you crank it over with a plug wire off will it arc? HEI is pretty stout so don't let it bite you!

If the plugs are crap that ain't gonna help matters. At least brush them clean and make sure they're gapped close to right, maybe plug one in while cranking and see if it arcs clean or acts fouled. Beyond fuel and fire we move on to compression which with most gas motors it won't take much to run or at least try.

If that carb sat full of old fuel it may be in need of a rebuild. If it turns out to be the issue and is a quadrajet I'd consider a replacement such as an Edelbrock. Easy to tune and it'll get better mileage. If that matters lol.

Double check you've got 12 volts to dist in run and crank position. Make sure everything is plugged in cap, sometimes the terminals come out of clip and appear to be connected but aren't. Sometimes the modules burn out or get ate up with corrosion and cease to function. I'd lean towards a fuel issue just because gas these days sucks and turns to chit in no time.

Report back and we will figure it out.

Junkyard

 

[bvfdfire]

I've had to get many of those older Chevies running in the past, believe it or not, a lot of the time an oil change will help with compression. Lifters in those 366's are notorious for refusing to pump up after they have sat for long periods. Many of the medium duties also had Holley base plate governed carbs instead of quadrajunks. They will leak fuel past the power valve and through the venturis which will thin the fuel even further causing such low viscosity that again, lifters wont pump up. Lastly, AC plugs are excellent plugs but they dont stand setting up for long periods of time. The internal resistors in each plug decay to the point that they simply cant push enough voltage through them. Hope this helps.

 

[Junkyard]

Good points, I haven't messed with a gas motor in quite a few years other than race motors and they don't see abuse related to neglect they see it from my right foot!

Makes perfect sense oil dilution wise and now that you mention it I recall seeing some Holley carbs on them. You may have hit the nail on the head.

 

[frank@signsfors]

I pulled a plug and tried to buy 8 new ones. My parts stores did not have them, but i think I know a place that does. I will do a compression test as I pull each. Had problems with the distributor electric plug connectors (I am an older guy) up on top of the truck reaching in and to the back of the engine is awkward. Also the wires are short, but I think I can get a multimeter on that from the top (remove 2 screws from a cover. and probe it)

The Carb is an antique. What size Edelbrock? Got one on a 390 Caddy Convt, I think it is a 600, I don't want anything too big - it ain't a race car.

 

[Junkyard]

600 would work fine. May need an adapter depending on what the manifold is. Squarebore to spreadbore or vice versa I don't recall which is which. Yes getting to a GM dist is a pain especially in something taller like an old 2 ton, darn air cleaner stud likes to perforate your chest! You can buy new pigtails for the wiring which may help clean that up.

Junkyard

 

[918OkieCat]

I pulled a plug and tried to buy 8 new ones. My parts stores did not have them, but i think I know a place that does. I will do a compression test as I pull each. Had problems with the distributor electric plug connectors (I am an older guy) up on top of the truck reaching in and to the back of the engine is awkward. Also the wires are short, but I think I can get a multimeter on that from the top (remove 2 screws from a cover. and probe it)

The Carb is an antique. What size Edelbrock? Got one on a 390 Caddy Convt, I think it is a 600, I don't want anything too big - it ain't a race car.

I have an 82 C70 with a 366. I replaced the worn out Holley with a 1405 manual choke 600 cfm Edelbrock. Easy replacement, works great. All I had to do was adjust the mixture screws a little.

 

[Junkyard]

The old Carter/Edelbrock style carb is hard to beat for tuning and efficiency for their cost. No power valve issues and they don't have dinky front barrels and monster back barrels like a quadrajet to suck fuel like crazy when you're into all 4. And who isn't?!?!?

 

[nowing75]

After working on this new stuff I say bring back the carburetor. No wires or stupid sensors.

 

[nowing75]

I have an old chevy 6500 366 gas with a crane that I use to unload machines when I shop on eBay for $700. It sits for a couple years but put a battery in it and it fires up.