Shuttering under load

[focusedfreedom]

Hi all,

I have a '91 GMC Sierra 4x4 pickup. It's started behaving in a way and I can't figure it out. This is in 2-wheel drive, as I rarely use 4x4. I'm not convinced it's transmission rebuild time but I don't know (and hope not.) The truck shifts out fine up and down (automatic). But when I start on a small incline or larger, usually around 35 to 50 mph, the truck shutters pretty badly. To the point that you can feel it in the steering wheel.

I bought the truck from my father-in-law and have had it a few years. He seems to have had the same problem in the past but he can't recall what it was. He believes it's something to do with the engine itself and not the transmission. He's driving it recently and believes the transmission is fine. He suggested starting with a good engine tune-up. Although I think I could do it (tune up) I likely will see a professional that can also check it out.

Any suggestions on what it might be? I might could even post a video of how it's behaving. I don't know.

Thanks for your help.

-- Jeff

[75K30]

Welcome to the site;

Are you confident that the transmission mount or engine mounts are still in good shape?
A broken mount, or even a weak, or oil saturated mount will cause the engine / trans to bounce around.
Seems like your problem is found while the vehicle is under a load.
Sounds like a busted mount to me.

[bigcountry78]

I had the same problem with my 98 z71, w/ the 350 and the auto. Mine would do it when you were trying to accelerate up a hill, it could be empty or loaded, didn't matter. Mine would always trigger the check engine light. I had the codes read several times and it always said "random cylinder misfire". I thought it was my tranny, but it was still there after the rebuild. I tried the tune up thing a couple different times, with no luck. Could be a computer problem, I never could trace it down. I just learned to live with it. I think it was in the motor, but I couldn't afford to throw parts at it while it was still running great the other 99.5% or the time. Hope this helps you narrow it down. Good luck.

[leolkfrm]

when checking all above, try manually downshifting it when it happens see if it clears up, it may be lugging

[focusedfreedom]

Thanks all. You guys are fast. I'm glad to have found this forum. I hope to be able to contribute as well.

I never thought about the engine mounts. I'll check that out.

Occasionally the engine light will come on when it starts doing this. Turning off the truck and back on again the light goes out.

I'll let you know how it goes as I continue searching for the cause. Does anyone know if Express Oil change does a good job on doing tune-ups?

God bless the USA. We really need it.

-- Jeff

[87c10slammer]

honestly anywhere with express anything in there name isnta good place to go to... you are getting poor quality part and less then satisfactory service... i would get the parts yourself and do it yourself... all you need are basic hand tools for a tune up.. nothing fancy.. even if you need a special tool it will come in handy the next time its due for service

[bigcountry78]

Doing a tune up yourself will also help you familiarize yourself with your engine and the things around it. Plus it just feels good to be able to do something yourself and save some money. It makes me feel good anyway.

[75K30]

IS the truck actually missing? Does the engine act as if it is losing spark?
This could be a completely different set of circumstances. Senspr problem, ignition problem. Maybe something as simple as a bad ground for ECM.
You may even have a fuel pressure problem.
I was under the impression that the engine just bucked around under load, and now that we see it also has a Check Engine light, you should probably have it scanned to see what is happening

[focusedfreedom]

The unfortunate thing is that I can always cause the shuttering problem to appear but the check engine light has only come on once or twice.

It's not obvious that the truck is missing when idling or when in motion. But it could be something like that.

When I bought the truck from my father-in-law he had just had the engine overhauled. I've not had it tuned up since then. Some say that after an overhaul it's good to have a tune up within a few months, especially replacing the plugs.

I'm not opposed to doing the tune-up myself and would enjoy doing it. I'm just not sure if I would get everything changed out that I should. I'm thinking plugs, plug wires, fuel filter, air filter. What else is standard for a tune up? I generally use EOC for routine oil changes. Is there anything special I should do for the electronics for resetting after a tune-up?

We have Oreilly, Autozone, and Advance all around here in Huntsville. I favor Oreilly but am curious as to the best places to get quality parts for a tune-up, even if it's online.

Thank you again.

-- Jeff

[FaselZ71]

Well as far as you go changing plugs wires air filter fuel filter and change the oil and oil filter it's simple I don't know how much EOC charges for an oil change but to change your oil only costs like 20-30 bucks max! I'm a religious advance auto parts customer and you shouldn't have to reset any electronic device on your vehical after a tune up.