mid throttle jerking while up to speed

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1 week 1 day ago - 1 week 1 day ago #201868 by sixteenacrewood
mid throttle jerking while up to speed was created by sixteenacrewood
Hi Everyone
I did an earlier post on when to give up on this motor. Here are her stats again.

93 GMC C1500 5.7 L 415,000 miles original motor. I plan to replace the motor but I am hoping to wait until January when business slows down. Starts up just fine, good idle, decent power for the miles she's gone, runs at 75 mph on interstate no problem.

I'm not sure how to describe what my truck is doing, but here it goes.

while at or above 40 mph, while holding a constant speed, the engine jerks/ misfires/ vibrates? the dash will shake.

It goes away completely when I accelerate or let off the gas, it only does this when trying to hold a constant speed at 40-75 mph. On another forum it was described as "trailer hitching" but no solution was posted.
Advise was egr valve causing a vacuum leak at higher speeds, this did not make sense to me.

Another was a worn distributer gear or failing pickup coil in distributer. This seemed to make better sense and I am thinking about putting in a new distributer.

Any input would be helpful

The only bad and obvious problem the motor has is a coolant leak on top of the intake manifold, but no coolant in the oil. She is burning coolant, around 10-16 oz per 2-300 miles
Could the leaking or cracked intake be the cause?

I could probably let this go and not fix it, but if I can fix it with a new distributer at $130 it would be worth it.
I just don't like throwing parts at a problem.
I imagine the new parts on this engine would be swapped over to the replacement?

Thanks again
Steve
Last edit: 1 week 1 day ago by sixteenacrewood.

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1 week 6 hours ago - 1 week 6 hours ago #201886 by ToyotaKarl
Replied by ToyotaKarl on topic mid throttle jerking while up to speed
May look into the Trans fluid level and the TCC Solenoid/wiring.

Good luck

-Karl

Give a man a fish and he will eat for a day. Teach a man to fish and he will sit in a boat all day drinking beer.

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Last edit: 1 week 6 hours ago by ToyotaKarl.

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5 days 7 hours ago #201907 by sixteenacrewood
Replied by sixteenacrewood on topic mid throttle jerking while up to speed
Thanks Karl!
I haven't checked the trans fluid in about a month, UGG!

Two quarts low and a slow leak, I topped it up and ran it for about 15 miles to get home.
Checked fluid and it was black!

I'll check it daily and get a feel for how quickly it's leaking.

It's not slipping or shifting hard, just the same issue at mid throttle.

Is it worth having the leak fixed?

Or, start saving for a replacement/rebuild.

A local shop here quoted me

$1800 for a rebuild 1 yr warranty
or
$2350 factory remanufactured 3 yr warranty

Not sure what to do but hoping I can get a month more use out of her!

Any more advice on the transmission?

Thanks again
S

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5 days 6 hours ago #201908 by ToyotaKarl
Replied by ToyotaKarl on topic mid throttle jerking while up to speed
Based upon what you have said, I think this may be a transmission issue.

I think you may be having an issue with your TCC locking up for overdrive. It could be solenoid related, or something deeper. The fact that your transmission fluid is black is not a good sign.

As far as what to do next, that is difficult. The costs incurred on a 26 year old vehicle may outweigh the complete value.... The transmission repair, may not solve the issue...

As you may know, changing the transmission fluid and filter at this point in the transmissions lifetime (especially the mileage) could lead to slipping and poorer performance (all the grit material will be removed and there will be slipping on the steel and what is left on the friction disks...

Personally, if it had to last a month. I suppose I would just ride it out for a month then sell it off... 415k is quite some mileage.

Best of luck

-Karl

Give a man a fish and he will eat for a day. Teach a man to fish and he will sit in a boat all day drinking beer.

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5 days 5 hours ago #201911 by sixteenacrewood
Replied by sixteenacrewood on topic mid throttle jerking while up to speed
Thanks again Karl
I have some thinking to do.
I don't mind dropping repair money into this truck even though the cost will exceed the value.
I hate car payments

I imagine doing the math, compare repair cost to car payments is what I need to consider. If I could renew the motor and trans for around 4k, that's not much more than what I pay annually for my wife's Subaru. There is not much other than a paint job wrong her, my truck that is.

Sorry to ramble

Thanks again Karl!

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