92 chevy falls on it face...

RGMartin

Well-known Member
92 C-70, throttle body injected 366.

It runs fair for 10 minutes(5 miles or so of hard running). I dump at the elevator and head back for another load... On the way back it stumbles within the first 1/4 mile, "Blah, Blah", then recovers, it will repeat this a few times over the course of a few minutes. It always seems to happen between 2-3000 rpms while accelerating. It hasn't stalled yet, but is enough to make you think you will be walking home.

Any thoughts before I start throwing parts at it? I was thinking a distributor and coil...maybe heat related.
 
Does your 366 have a govenor on it? The company I drove for had some semi tractors with 366s in them and they acted like that when the govenor was going bad.
 
It is fuel injected, so everything is electronic as best I can tell. No governor, mechanical or otherwise.
 
Check the fuel pressure. Sounds like you may have a pump
heading south or a fuel restriction. Does it stumble if you
slowly push the fuel pedal? If it doesn"t I"m on the right
track.
 
I'll rig up a gauge if I can find a port.

It actually seems to do it more when I am gentle with it, unloaded, slowing for a bend, or rough road. When I drive it like I stole it(loaded, uphill etc), not so much, but I tend to keep in the 3-4000 rpm range when loaded.
 
When was the last time it had a good tune up? We went thru this with a carb version of this truck. Pulling our hair out and changed the plugs,wires,fuel filter. It made a little difference but found the dist cap was toast,causing erratic spark.
 
That is why I was thinking distributor... It had plugs a year and 2000 miles ago...

A real tune up??? Not since I have had it.

Wires are 4 different colors, cap looks tired, the stamped frame around the coil is coming apart.

I was looking at prices, looks like I can buy a new complete distributor, coil, and set of wires for $125. Nice thing about Chevy gassers, parts are cheap.
 
Going at it from another direction.
At the elevator do you use the truck mounted hoist or do they lift the whole front end? If you let them lift the front end, does it stumble only after dumping? Once it recovers, does it run okay until the next dumping session? What type gas tank & how much gas in it?
More than likely not your problem, but there is the slight chance that while the front end is lifted, somehow an air bubble gets in the gas line, & it takes a few minutes to work its way through.
Just for grins & giggles, after dumping the next load, pull out of the way & let it sit about 10 minutes running around 1000 rpm & see what happens.
Willie
 
Interesting theory, but I use the truck's hoist. I don't know how big the tanks is, sits under the drivers door. I put $200 of premium in it, and it didn't fill it last time.

I just ordered a complete set of ignition parts, Dist, Coil, wires... $98 delivered.

If anyone needs them, Amazon has Autolite wire sets for big block Chevy for $4.26. Seems ridiculously cheap.
 
Worked on a lot of GMC rental trucks back then with
the 366 engines. First thing I always did was spin
on a new fuel filter and go from there. I do recall
there were a few years of the 366 having a recall on
the distributor and we change a lot of them out.
Other than tune ups they were good trucks.
 
I think you need fuel with a higher vapor pressure. You are essentially getting vapor lock because you just got your engine warmed up good wheeling into town, then sit using no or little fuel and there is all that heat boiling the fuel close to the engine. See if you can find a non-ethanol premium, or an additive to increase the vapor point. Or aviation gas. Joe
 
I wouldnt be surprised if you have a faulty coil. Your tune up should eliminate that issue. Clean the throttle body while your at it. All you have to do is get throttle body cleaner and spray it all in there with the plate open.
 
(quoted from post at 17:51:01 10/16/13) 92 C-70, throttle body injected 366.

It [b:aeac6d116d]runs fair for 10 minutes[/b:aeac6d116d](5 miles or so of hard running). I dump at the elevator and head back for another load... On the way back it stumbles within the first 1/4 mile, "Blah, Blah", then recovers, it will repeat this a few times over the course of a few minutes. It always seems to happen between 2-3000 rpms while accelerating. It hasn't stalled yet, but is enough to make you think you will be walking home.

Any thoughts before I start throwing parts at it? I was thinking a distributor and coil...maybe heat related.

This sounds like a coil to me. Fuel issues on fuel injection are usually immediate problems.
 
gm TBI systems can be a real headache. The big block intake manifold has same bolt patern as 4 barrel carb. just a suggestion.
 
I know whereof I speak.
My brother had a similar age TBI Buick, spent many hundreds of dollars on all of the cures others have postulated; coils, fuel injectors, pump, filters, spark plugs and wires. The various shops were always ready to take his money and attach some other useless new part.
On his way to work each day he would drive about 6 miles and make a stop at a relative's house, then continue on to work. Frequently he dealt with hard starting and sputtering upon restart. I was there one day when he experienced the problem. We found a gas station that sold a higher octane low ethanol summer blend of gasoline. End of problems. Joe
 
I've changed a ton of distributor caps and rotors in the last 15
years, on those engines. Burnt plug wires are about second on
the list. They need to have the factory steel heat shields over
the plug boots.
The distributor recall was about the little vents in the bottom of
the housing plugging up. If the top bearing is worn bad it will
have erratic spark, but all the time. I've changed more
distributors than coils, and more fuel pumps than distributors.
Spark plugs usually last about 30,000 miles.
I thought that GM had governors on all those engines, it's the
cylinder sticking out the left side of the throttle body.
After you do your ignition tune up, if you still have the problem,
I would change the fuel pump.
 

Timmit, you are on the money! The HEI distributor was still used on these, they are notorious for burning up the center of the ignition rotor.
By the way, there is no fuel pressure test port for the TBI, must rig it inline.
 
I got everything changed out yesterday. The whole inside of the distributor was a mix of rust, corroded aluminum, and filth. Coil frame was badly rusted and falling apart. Wires came apart when pulling off the plugs...

I couldn't get my timing light to pickup the marks on the pulley so I set it by ear.

It sounds better, the test will come today.
 
(quoted from post at 16:37:27 10/16/13) That is why I was thinking distributor... It had plugs a year and 2000 miles ago...

A real tune up??? Not since I have had it.

Wires are 4 different colors, cap looks tired, the stamped frame around the coil is coming apart.

I was looking at prices, looks like I can buy a new complete distributor, coil, and set of wires for $125. Nice thing about Chevy gassers, parts are cheap.

did all that with my '91 excep for the coil and no more trubble could move the distributer shaft about 30-40 thoundsth bushing was shot . truck had 165 thousand mi. on it
 

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