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1999 Suburban
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Discussion Starter · #1 ·
Hey, folks!
Our Burb runs great 99% of the time because I rarely get the RPMs over 2k. However, when the RPMs hang around 3k for a few seconds, the engine feels like it loses all timing, and shakes like crazy for a few seconds... Then it smooths back out. This sequence will happen whether I continue to hold the RPM high or let off the gas.

In other words, I can get up to 3k for a few seconds, let off the gas, and then it will shake like the timing is out for a few seconds, then smooth out.

The check engine light will flash and then stay on.

The only codes I have seen refer to misfire: "random misfire" or "misfire on Cyl#(different ones)"

I replaced the cap and rotor because I read about the problems with the crab cap crossing arcs. That didn't fix it... UNLESS the cap went bad again already.

I have seen guys talk about the spider and distributor gear being worn, but I haven't checked those yet.

I have also seen a few forum posts (here and elsewhere) describing similar situations, with no replies at all...

Any thoughts? Thanks in advance!
 

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That sounds like a spark problem until you say it continues after you lift the right foot.
If it was a spark problem, you would see/feel it under load, as soon as you remove the load (lifting foot off gas) it should smooth out.

What engine, a 350?
 

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Discussion Starter · #3 ·
That sounds like a spark problem until you say it continues after you lift the right foot.
If it was a spark problem, you would see/feel it under load, as soon as you remove the load (lifting foot off gas) it should smooth out.

What engine, a 350?
Yep.. 5.7
 

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Try kicking it into neutral to see what happens.
 

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I wasn't thinking of a trans problem, just trying to remove the load off the engine and to get it back to idle.
When you this happens, have you watched the tach to see where the RPMs are when it stops?
 

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1999 Suburban
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Discussion Starter · #7 ·
I wasn't thinking of a trans problem, just trying to remove the load off the engine and to get it back to idle.
When you this happens, have you watched the tach to see where the RPMs are when it stops?
It’s never been consistent from what I can tell. It will do it regardless of what I do with the throttle...whether I let off or even if I try to keep the rpms up.
 

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have you tested the tps? a bad tps can show up like a transmission problem. it is a mechanical failure of an electrical part. it sends incorrect data that the computer believes. they are easily tested on these trucks with an obd2 scanner. on my cheap innova when I go to live data and click on the tps it goes to a graph. you dont really need the truck running but it the ignition needs to be in the run position, this will drain a battery but if it's a good battery there should be no problem. so the graph should rise nice and smooth as you press the gas peddle. it should not jump, fall or dissapear if it does anything other than rise nice and smoothly the tps is faulty.

Al
 

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Discussion Starter · #9 ·
have you tested the tps? a bad tps can show up like a transmission problem. it is a mechanical failure of an electrical part. it sends incorrect data that the computer believes. they are easily tested on these trucks with an obd2 scanner. on my cheap innova when I go to live data and click on the tps it goes to a graph. you dont really need the truck running but it the ignition needs to be in the run position, this will drain a battery but if it's a good battery there should be no problem. so the graph should rise nice and smooth as you press the gas peddle. it should not jump, fall or dissapear if it does anything other than rise nice and smoothly the tps is faulty.

Al
Yesterday I unplugged the tps with the engine running and revved it up. It hesitated and stumbled, etc.
My thought was that that meant the tps is working. But maybe not?

what about crank or cam sensor? Would either of those make it do this?
 

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Discussion Starter · #10 ·
I just realized that I should mention that the only time it acts up is when I’m pulling my camper, because that’s the only time I ever get the rpm to 3k

didn’t know if pulling a heavy load matters...
 

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Spark plugs and/or broken or worn plug wires I bet.
I'll bet your right, Yep did you change the plugs?
If you did, some brands don't play well with Chev engines, what did you buy?
 

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unplugging the tps gives the computer no information to work on. that's why it died. a scanner is the easiest way to test it but it can also be tested with a multimeter.

the computer needs to know how far open the throttle plate is, it also needs to know how fast the vehicle is moving through the VSS... vehicle speed sensor. without this information or with incorrect information it just wont work.

Al
 

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Discussion Starter · #14 ·
unplugging the tps gives the computer no information to work on. that's why it died. a scanner is the easiest way to test it but it can also be tested with a multimeter.

the computer needs to know how far open the throttle plate is, it also needs to know how fast the vehicle is moving through the VSS... vehicle speed sensor. without this information or with incorrect information it just wont work.

Al
That makes sense. Without owning a scanner, I figured if I unplugged the tps and nothing changed then maybe the tps was bad. Just took a shot in the dark.
 

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Discussion Starter · #15 ·
I'll bet your right, Yep did you change the plugs?
If you did, some brands don't play well with Chev engines, what did you buy?
Napa (Belden) wires and Autolite plugs were put on at 100k. It’s at 180k, so I will be changing them soon anyway.
what brands play well?
 

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Sounds like the same problem I had when towing. Also sounded like a blown exhaust manifold gasket under load.
Turned out to be my #1 (you have 8 of them) ignition spark module & $350 later for RnR and a happier mechanic.and me
 

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2012 Silverado 2WD, LT, LMG engine, All stock. 84,000 miles. A Florida truck, zero rust.
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It could be the TPS and not very expensive to replace. Have you tried it in a low gear say at 3000 rpm in third or fourth gear. At 180,000 miles it's possible the timing chain has stretched and it's flopping around at higher rpms.
 
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