Truck runs rough, help!

[1987 GMC Jimmy]

Lol wtf u mean "opinion"?

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[Johnathan25]

Did somebody put the wrong fuel in? Maybe theres something in the tank? I almost wonder if something happened to the carb. Could you have missed a vaccum leak? Try the old spray bottle of soapy water. Check the fuel filter. Double check firing order and such.

I know it's all no brainer stuff, but what harm can double checking do. Also, how old is the engine? Could it be wounded? Did it get put under heavy load or get revved out? Did someone maybe borrow it right before the problem start?

No the right fuel has always been put in, the carb is perfectly fine as it’s brand new and I’ve checked numerous time to make sure it’s all good, there are absolutely no vacuum leaks at all anywhere and the fuel filter is clean. I’ve also checked the firing order multiple times. The engine is as old as the truck with 135,000 miles on it and pretty well maintained. It has not been put under a heavy load or anything since I’ve owned it and I’m the only one that drives it.

 

[idahovette]

Could be timing chain-plastic gear???

 

[Termite_Delight]

Could be timing chain-plastic gear???

I had a 1985 GMC van with a 305, the plastic timing gear disintegrated and left little pieces in the oil pan.

 

[Johnathan25]

Update: battery cable was kinda corroded but changing it didn’t fix the problem, and the timing gear isn’t bad.

 

[Rusty Nail]

Do the symptoms change with operating temperature?
Verify grounds at/near intake manifold and cylinder heads and don't make me say pick-up coil !

 

[bucket]

Do the symptoms change with operating temperature?
Verify grounds at/near intake manifold and cylinder heads and don't make me say pick-up coil !

The distributor was one of the things that were replaced. Even if it was a used unit, I wouldn't suspect the pickup coil. Every time I've had or seen one fail, the symptoms were different, or they just plain wouldn't run at all.

 

[Johnathan25]

Ok so the grounds are good, actually every wire is good, I went ahead and checked them all. And as for how it does with temperature, it does this no matter if it’s warmed up or not, it might be slightly worse when warm but not by much.

 

[Rusty Nail]

Sounds good.
Did you check for codes at all like ever?
You know about the grounding of the ALDL right?

 

[WFO]

Sounds good.
Did you check for codes at all like ever?
You know about the grounding of the ALDL right?

Codes on an 85?

 

[Johnathan25]

This truck does not have an ALDL connector

 

[roboto65]

My first post how about that. Have you checked the compression? What transmission do you have ,does it have vacuum to it have you checked the vacuum there if applicable. Maybe you picked up some bad fuel maybe water.

 

[Johnathan25]

My first post how about that. Have you checked the compression? What transmission do you have ,does it have vacuum to it have you checked the vacuum there if applicable. Maybe you picked up some bad fuel maybe water.

Compression is good. It has a th350 trans, and vacuum I’ve checked the vacuum and it is fine. I’ve also tried getting gas from somewhere else and made no difference.

 

[Bigalturk1]

Just a couple of ideas...
You mentioned no smog, but if the converter is still on... It may be partially clogged.
Also:
Could be faulty power brake check valve (If equipped)
Could be Vacuum line disconnected from Transmission Modulator (If equipped)
Could be rounded-off (Worn) cam lobe
Could be loose or jumped timing chain
>>With engine cold turn the crankshaft (Using a 5/8 socket) back and forth to see if there is excessive play)<<
Good luck!

 

[Bean]

Hello everyone. I have a 1985 Chevy c10 that’s been running pretty rough here recently and I cannot for the life of me figure out why. When you try to crank it up you have to hold it for awhile before it fires up, and then as soon as it fires up it acts like it struggles to stay cranked, every now and again it won’t even crank and you have to wait awhile and then it will. Once it’s warmed up it idles pretty rough and jumps around, and when in gear it does it even more. Turning the air on makes it jump around way worse to the point where it almost wants to shut off. It doesn’t jump around while going up the road, but when you start off from a stop or slow down and start to pick up speed again it really feels like the engine is struggling to keep up and won’t pick up speed very quick, almost like it’s lost it’s power. Occasionally it’ll bog down so bad from a stop that it’ll almost stall out.

Here’s some info on my truck:
-the engine is completely stock minus a Holley carb that was added not too long ago and the emission stuff gone.
-just replaced spark plugs, wires, distributor cap, coil, and rotor.
-just replaced valve cover gaskets
-nothing else has been modified or tampered with.

If anyone has any idea on what could be wrong I’d really appreciate it!

Sounds like the timing is off or the carb isn't tuned properly!