Need help with my truck!

[SteveM]

Since I cant find an automotive tech forum as good as this tractor forum (suggestions appreciated) I will post here: my newest toy for the farm is an '88 GMC 6000 medium duty truck with a gas 366 V8 carb.

Problem: it starts hard; fires just enough to disengage the starter-takes about 2mins of false starts to finally catch and run fine. When shutting down, it 'diesels' moderately.

Solutions? I am thinking to replace plugs and plug wires - but does it possibly need timing adjustment? Runs great otherwise.

Thanks guys!

 

[looch]

I'm no mechanic, but it sounds like a timing issue. Maybe just a matter of giving the distributor a twist - hopefully not a worn out camshaft.

Replacing the plugs and wires is a good idea if that hasn't been done in awhile. Since this vehicle is new to you, I would recommend doing that and a bunch (a whack - indside joke) of other tune-up type things:

Change the oil and filter
Change the air filter
Change the gas filter
Clean the battery terminals
Lube the chassis (tie rod ends, ball joints if they have zerts, steering components, etc)
Lube the drive shaft U-joints (again if they have zerts)
Check all fluid levels - tranny (automatic?); coolant; brake; power steering; differential; windshield washer /w3tcompact/icons/wink.gif.

By taking care of these initial items, not only do you reduce troubleshooting time, but you may notice other things that need attention.

 

[jdrotert]

take the dist. cap off and wiggle the rotor to see if there's any play. If not, replace the cap, rotor, wires and plugs with new ones. Check timing and correct if it's off. If the rotor wiggles (rotates) with more than about 1/8" of play, replace the dist. gear. You must use one that is compatible with the cam gear. Dist. gears are made of cast iron, steel, bronze even nylon. make sure you get the right one or the cam gear will chew it up (or you'll ruin the cam gear). This problem definitly sounds like an ignition issue though.

john

 

[cowboydoc]

If it's carb those had alot of problems with the carbs. Probably needs adjusted or a new kit.

 

[Egon]

Assumming it runs fine once it's warmed up.
I'm guessing choke for the starting and carbon deposits for the dieseling.

Egon

 

[StoneHeartFarm]

It's an 88 and it has a carb? Most of GM's smaller engines switched to throttle bodies during the 80's, I'm not sure about the 366.

Does it start hard in cold weather, hot weather or all weather? Does it have a point type distributor or electronic ignition? Again, the smaller engines had pretty much all migrated to electronics by the late 80's. With electronics, all kinds of things can happen because a sensor goes out. A faulty temp sensor can make the system think it is 50 degrees out when its actually 20 below. Usually, there is also an anti-diesel sensor.

If it runs good otherwise, I would be cautious about changing the timing. I'd do the plugs and check all the vacuum lines first.

SHF

 

[rdln]

366s are small bore big blocks made by GM Tonawanda, the run on after shutting off ignition sounds like a carb gasket or adjustment, also make sure butterfly isn't stuck open when starting.

And when turning off let it sit and idle for a minute and then turn off.
my two cents

 

[kubmech]

I'll agree with the timing, also is the the idle set too high? May even want to try cleaning some of the carbon out of the cylinders. Remove the air cleaner, run it up to a fast idle(about 2000 RPM) and pour a stream of water through the carb for a few minutes and then give it a few good revs (ATF works better if you don't mind creating your own smoke screen) Could also use a tune-up, old plugs and wires can mess with the timing.

 

[gator]

When the truck hasn't been driven for a while, take the top of the air cleaner off, floor the gas pedal once and make sure your choke butterfly is closing. If it is, try pumping the gas pedal while trying to start it, if it starts quicker than normal, I would check the fuel pump.I had this problem on an 83 Chevy C-20 with 350 and 4bbl carb.My mechanical fuel pump had a pin hole in the diaphram and wouldn't hold pressure after sat for while(also had a gas smell in front of truck but no puddle).I agree with the others about timing and/or carbon build up for the dieseling, till you can figure it out, if its an auto trans shut the truck off in gear and it should shut right down.Check your spark to, pull a plug and hold the electrode on the head away from the cylinder you pulled it out of and crank it over.Spark should be bluish, if its yellow its probably a weak coil.I would rebuild the carb to and change distributor cap and rotor along with the plugs, then check and/or adjust timing.Hope this helps.