1997 k1500 Chevrolet Suburban shaking/shuddering/jerking at highway speeds

[Fredje]

Had just ordered all new ignition components and out of curiosity checked the contacts on the "Gold Standard" UMP blue cap... mother *******... the gap at the rotor to cylinder is several mm.

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I also ordered that one. Is it bad that the gap is several mm’s? I dunno how much the gap is with the GM parts?

 

[Fredje]

This is a cheap design feature that was used to fire fouled plugs. I also am putting on a new coil and ICM, so we will see how long their shortened lifespan will be lol.

The ICM I did not order, is this part prone to failure?

 

[SAR K2500 Burb]

The ICM I did not order, is this part prone to failure?

I've seen some last forever with a properly maintained ignition system, and in the same breath, I've replaced 4 in as many months due to not inspecting a new billet distributor that came fully assembled in my GBody.

They only *slightly* tightened the coil's case ground under the HEI cover. My fault for being lazy

I also ordered that one. Is it bad that the gap is several mm’s? I dunno how much the gap is with the GM parts?

I'm going to send it because I love testing anything against previous knowledge, but I also distinctly remember a time where if the rotor and cap weren't on perfectly due to a .05ish gap, either the cap or rotor would Crack from physical contact.

There's also the electrical theory of using a big gap there to force the coil to push more amps to bridge higher gaps, which in turn had no problem firing off a fouled plug with just sheer current.

The way my head works, I see the company using physics to initially "wow" a customer at their awesome product, with zero regard for taxes down the line.

It would also explain why the crab caps are blowing through the plastic at 3? Where it bends around the coil...it's literally less effort to find a ground.

 

[Fredje]

I've seen some last forever with a properly maintained ignition system, and in the same breath, I've replaced 4 in as many months due to not inspecting a new billet distributor that came fully assembled in my GBody.

Is there a procedure for checking if the ICM is good or bad?
I have found this:
https://www.gmt400.com/threads/any-way-to-test-the-ignition-control-module.21180/post-595716

 

[Fredje]

Well today I exchanged my recently installed (6000km's) distributor cap with a used but still good one a mechanic in my area had laying around. Meanwhile we changed the plugs and voila, no more jerking. So I am pretty happy we have solved this mystery. Who would have thought a newly installed dizzy cap could give me such a headache...
A lot of lessons learned but especially the one to never ever exclude one thing or another even if the part has been renewed recently. It is a pitty that I, almost a year ago now, thought it had something to do with the transmission. I jumped to conclusions, and my TM guy said he suspected the TCC. And we did find a lot of issues in the transmission like burnt 3-4 clutch plates and other anomalies. So luckily that was money well spent.
Now I will have a lot of spares lying around I could use in further episodes. I'll change out the dizzy cap again when I receive my new ones but all the rest will go into my useful spare parts package.
I would like to thank all of you for being this helpful, I extremely appreciate this as al this helpfulness is more something friends do instead of strangers merely communicating over the internet.
Makes me love my USA made car even more. Wonderful!

 

[1998_K1500_Sub]

A lot of lessons learned but especially the one to never ever exclude one thing or another even if the part has been renewed recently.

^^^ Agreed. Too often a problem is introduced by some recent change, even if that change was supposed to be "an improvement".

"What did you f___ with last?" is usually a good debugging question.

I hate to see someone making "improvements" by installing a bunch of "new" parts; every change is a potential latent problem.

I'm glad to hear you got it sorted-out.

 

[toolmakerson]

What you're experiencing is very likely to be the TCC slipping, however I'd confirm with a bidirectional scan tool...Plug it in, take for a test drive with live transmission and torque converter data displayed on the screen...Things you will be looking at are TCC slip speed and TCC Duty Cycle...When duty cycle is at or near max, slip speed should be 5RPM or less...If you observe slip speeds well in excess of that, esp during the shuddering episodes, then your TCC is slipping...Then the question becomes, why is it slipping...Causes usually include TCC regulator valve in the valve body (usually P1870 sets/stores, if so), leak in the TCC apply circuit either at the worm tracks between the spacer plate, valve body and case (unlikely), o-ring on the end of the input shaft (possible) or TC simply worn and failing due to old age (possible).

Let us know what the scan tool indicates and we can go from there.

funny thing Nick, i started bookmarking your posts when i come across them. but i think i'll skip that, too many, i can always just search based on your id if/when i need to.

 

[Fredje]

Strange thing is the scan tool didn’t register any misfires either…
Another strange thing, maybe pointing to a high voltage (ignition) issue: my radio had this annoying tick about the frequency of one of the spark plugs ignition. Now that’s completely gone too…
My plugs were highly due for replacement, all of them… a bit oily too…

 

[H2814D]

I had a similar issue many years ago with my truck. <<<That one. It would run fine when in Drive, but when I put it in Over Drive it would hesitate and buck a little bit. If I took it out of OD, I didn't have the problem. I was sure it was my transmission too and was dreading the repair. At some point, I came across someone who mentioned replacing the cap and wires. I did that. The problem went away. I may have even mentioned this somewhere in one of my earlier posts here. I can't remember now. Glad it worked for you though.

 

[1998_K1500_Sub]

... no more jerking...

When you log the RPM, are the values smoother then before?

This is from earlier:

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