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Discussion Starter #1
I've thought I had a transmission issue developing. On the interstate, on Cruise, when in the mid-60's mph, at times of light engine load like going downhill or with a strong tailwind, I would feel a "grumbling". The engine wouldn't take throttle. I could kick off Cruise, let it slow down just slightly, and then it would be fine. It didn't do it every time downhill or whatever, only every now and then. It only did it when on Cruise Control. I thought it seemed like an issue with OD kicking in and out.

I changed out and slightly corroded distributor cap (white crud on the posts), rotor, plugs & wires (plugs looked OK), and it didn't do the next couple of times I was on the interstate, then it started again. It didn't do it every time before, so 2 or 3 times didn't mean anything.

Last week it started doing it down in the 40's on city streets, which is the vast majority of my driving. Engine vibration is obvious now, either because it is getting more severe or the lower speed doesn't mask it. It doesn't seem to do it until the engine is warm. It did it real bad today on the outbound trip, but only once slightly coming back. I can let off the gas and get back into it and it will be OK until the engine load lightens and it decides to do it. I scanned for codes and it had some for "Catalyst system outside efficiency threshold" or something like that, and I had seen those before. I think the fuel pressure regulator might be leaking, but I haven't felt like getting into the manifold to change it.

Anyway, does this "grumbling" engine roughness sound familiar to anyone? It's not a distinct miss, it's like it is cutting out half of the cylinders. It's a regular grumbling. Actually, it is a lot like a bad front wheel bearing, but a much larger vibration. I assume it is the ECU doing something because of data it is getting. Maybe throttle position sensor is the most likely culprit .
 

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‘01 Silverado 2500HD 8.1/Allison 5sp xcab long bed
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Start with checking your fuel pressure.
 
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Discussion Starter #3
Yeah, but it doesn't feel like it's starving of fuel. It's too strong of a shake. I said above that it feels like it is cutting out half the cylinders, but that isn't right. It feels like half the cylinders are firing 180 out. Or 150. It did it today coming home at 35 mph, the first time it has done it at such a low speed, I tried giving it throttle and quickly determined that was not a good idea. The shaking got real bad. Let off, eased back in it and it ran fine.

The fuel pump is not a year old, or much over it, and is a NAPA brand. I know they are not what they used to be, but it's not an el cheapo.

I'm thinking about firing a small shot from the parts cannon and changing the Throttle Position Sensor. I had a hard shifting issue one day several months ago and one of the suggestions on here was the TPS. It hasn't done it but that one day.
 

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‘01 Silverado 2500HD 8.1/Allison 5sp xcab long bed
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Even so, ruling out the fuel pump is just good diagnostic procedure.
 
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If your not throwing any codes, suspect something mechanical like broken motor mounts.
 

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Discussion Starter #6
It will accelerate hard with no issues. Going slightly downhill and running just barely in the throttle will often cause it. I know not to let my opinion blind me, but it seems way too much like it is something to do with engine operation. That one yesterday at 35 mph, when I gave it throttle instead of letting off, the engine shaking alarmed me it was so strong. But letting off and then giving it gas again, it went on like nothing happened. It's got to be something stupid.
 

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Usually, but not always, engine problems will turn on the Check Engine Light.
 

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2000 Silverado Z71 4x4 5.3L 460k+ miles w/ GM rebuilt motor and trans
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I would check your motor mounts and then your fuel pressure to eliminate the pump. I've had multiple NAPA pumps fail the moment I installed them because of low pressure out of the box.
 

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Discussion Starter #9
Today I drove ~5 miles to my workshop and may have got to 45 for 1-1/2 miles, then 25 and 30 the rest of it. It didn't have the rough running problem. But, it usually doesn't do it on the first trip of the day until I've gone 10 miles or so. I put on a new TPS and drove 7 or 8 miles in town and it didn't do it. I got on the interstate for 4-1/2 miles and it didn't do it, but I was against a pretty good headwind, so the engine didn't get into the "lightly loaded" state. It'll get more of a test this evening in a 20+ mile interstate drive.
 

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2000 Silverado Z71 4x4 5.3L 460k+ miles w/ GM rebuilt motor and trans
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Already been suggested Jacob, he dismissed my mechanical problem suggestion without looking at their condition.
I was reiterating the validity of this statement. Had it happen to a 97 Silverado we thought had a bent crank. Turned out to be bad mounts.
 

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2004 Chevy Tahoe 2WD 5.3 Flex
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I agree with motor mount check also.. I am a non mechanic that has lived these issues over past five years. I am just happy others listed it as a possibility. makes me feel like I have learned some good thought skills.. good luck..
 

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Yeah, but it doesn't feel like it's starving of fuel. It's too strong of a shake. I said above that it feels like it is cutting out half the cylinders, but that isn't right. It feels like half the cylinders are firing 180 out. Or 150. It did it today coming home at 35 mph, the first time it has done it at such a low speed, I tried giving it throttle and quickly determined that was not a good idea. The shaking got real bad. Let off, eased back in it and it ran fine.

The fuel pump is not a year old, or much over it, and is a NAPA brand. I know they are not what they used to be, but it's not an el cheapo.

I'm thinking about firing a small shot from the parts cannon and changing the Throttle Position Sensor. I had a hard shifting issue one day several months ago and one of the suggestions on here was the TPS. It hasn't done it but that one day.
My 2010 avy had problems similar to this but I had codes...but it was the thottle control motor. Had to change the thottle body itself.
 

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My 2010 avy had problems similar to this but I had codes...but it was the thottle control motor. Had to change the thottle body itself.
This is a common problem on your generation of trucks. It actually had a TSB and a free fix, along with a 10 year warrantee.
His is a '97 and yes he could have a problem with the throttle position sensor; but as you said, there should be codes.
 

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This is a common problem on your generation of trucks. It actually had a TSB and a free fix, along with a 10 year warrantee.
His is a '97 and yes he could have a problem with the throttle position sensor; but as you said, there should be codes.
I have a 96 tahoe also and these trucks are funny with the fuel pressure. It will run well enough to trust but will give you small signs that the fuel pump is about to go. Dirty thottle bodies are a pain in the butt too. They will have you chasing your tail
 

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2010 Silverado 1500 LTZ
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TW97C1500, since you're not throwing codes and though the other posts are good things to check, my 96 Sub had a similar issue. I changed many of the things discussed here...but the problem was the tranny. Do yourself a favor, go the a parts store and get a tube of Dr Tranny. Pour it down the transmission tube. See what happens. It won't hurt anything, but my money says your problem disappears. Good luck.
 
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