Idling Rough Lately

To touch on what Roadie stated.....have you checked your motor mounts? You may have cleared up your misfires but I can say for sure....at 600 RPM's +- 25 RPM, mine feels like it's almost running on 5 cylinders. Didn't really notice it too much but in the last couple months the mounts really showed me thier mean face.

When I fire it up it's smooth as silk, once it settles under 700 RPM's then it really vibrates. Could very easily be mistaken for a rough idle which technically that's what it is.
 
gmcman said:
To touch on what Roadie stated.....have you checked your motor mounts? You may have cleared up your misfires but I can say for sure....at 600 RPM's +- 25 RPM, mine feels like it's almost running on 5 cylinders. Didn't really notice it too much but in the last couple months the mounts really showed me thier mean face.

When I fire it up it's smooth as silk, once it settles under 700 RPM's then it really vibrates. Could very easily be mistaken for a rough idle which technically that's what it is.
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The problem I have with the motor mount excuse is that I originally had what Roadie described as the telltale resonance. After doing the BG 44K, Techron and a number of engine flushes the engine smoothed right out. It took about a year after running all the cleaners through but it did eventually stop resonating at idle. My understanding is that the I6 are susceptible to resonance however designers took that into consideration by balancing the engine.

After reading a number of tech articles I came to the conclusion that resonance is something that it not inherent to the engine itself and therefore even engine mounts could not be blamed for this resonance. Therefore there is an unbalance situation within the engine. That's why i recommended a compression test. I would also recommend a fuel injector cleaning service(Winn's service) that is done with compressed air and connected directly to the fuel rail.

Newer mounts will perform better than old ones but in my estimation it's just masking the real problem. The engine itself needs to be looked into. My .02
 
Yeah there is definite misfiring, etc. The vibration/unsmooth idle isn't really that bad, and the motor mounts are an afterthought at this point. I have no idea how to perform a compression test, and even if I did, would have no idea how to fix whatever is wrong with it.
 
DenaliHD66 said:
Yeah there is definite misfiring, etc.
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Ok, so I am going to ask you this again. Why dont you get a scan tool?

Also, How do you know that you have a misfire for sure? If you aren't using a scan tool to look at the misfire count data then your just guessing.

This is all pretty much impossible to diagnose in a forum without any data to go on.I would say you need a diagnostic done asap. A misfire can harm the catalytic converter and eventually overheat engine parts if not taken care of.
 
DenaliHD66 said:
I have no idea how to perform a compression test, and even if I did, would have no idea how to fix whatever is wrong with it.
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I can respect that. The forum is not full of identical people with identical skill levels and top-level enthusiasm and ability for collecting tools, although many of us are that person. For over ten years, I traveled almost half the time (>125K miles a year) and my time home was precious, so I left my car with an independent mechanic during trips so they could work on it at their convenience. That car-maintenance strategy was perfect at that time, but it's not my preferred strategy now.

I owned many vehicles with OBDII ports before I bought my first code reader with the Envoy.

It's frustrating to see folks find the forum AFTER they've spent money unnecessarily, but I've come to learn that we can't save everybody all the time by giving out free advice, and we can't help every little old lady across the street, but it in general is a feel-good mission and let's keep that in mind.
 
CaptainXL said:
Ok, so I am going to ask you this again. Why dont you get a scan tool?

Also, How do you know that you have a misfire for sure? If you aren't using a scan tool to look at the misfire count data then your just guessing.

This is all pretty much impossible to diagnose in a forum without any data to go on.I would say you need a diagnostic done asap. A misfire can harm the catalytic converter and eventually overheat engine parts if not taken care of.
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Okay so refer back a few posts and I said I had it scanned and the details of the scan were posted regarding the misfires. I didn't get the codes exactly, but didn't think to report them back to here at the time. My mechanic saw the codes and knows it needs to be checked out.

After looking up how to perform a compression test, it seems really easy, but from that point, I would have no idea how to check or fix whatever would be wrong. If it tested fine, then what? I'm not going to spend money on a compression test kit right now if it wouldn't apply to me actually being able to fix the source of the problem. I'm on here to find out whether or not people have had similar experiences, or if they would have more ideas as to what might be causing this.

If a compression test turns out fine, then does that mean the valves and piston rings are fine? Does it mean it would be fuel injector instead? Would it mean it is the head gasket (doubtful, but still, I don't know.) I'm learning as I go, and don't have the means or time to set aside to learn the advanced diagnostics and repair on my own just yet. My GMT is a great starting point to learn, and I'm on here for advice. I appreciate all the help and thought everyone here has given me.
 
OK. I understand where you are coming from. But in all truth the fact of the matter is that in order to help you, you need to help yourself a bit. In order to do this I recommend you obtain a Haynes manual and read up on the first section regarding troubleshooting based on symptoms. There is a nicely concise section there. Secondly you can then read up on how to perform a compression test if your evidence leads you towards it.

There are many reasons why an engine might have a rough idle. Your going to get a lot of opinions here. The best thing to do is take a systematic approach. The first step would be to make sure all your preventative maintenance items have been done.

But to answer your question. Yes. Burnt exhaust valves are a problem that can cause a rough idle. So can worn piston rings or carbon buildup on valves, weak coils...etc. Fuel injectors are no so likely at fault. In order to check those a tech2 is needed to perform an injector balance test.
 
When I ran seafoam recently through the boost line, I noticed smoke coming out near the exhaust manifold. So that exhaust valve suggestion might be something. It runs like a top... it stutters and hunts for gears a little bit more, but the engine itself is not lacking any bit of power.
 
DenaliHD66 said:
When I ran seafoam recently through the boost line, I noticed smoke coming out near the exhaust manifold. So that exhaust valve suggestion might be something. It runs like a top... it stutters and hunts for gears a little bit more, but the engine itself is not lacking any bit of power.
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Stop it with the seafoam. For god sake who told you to use that crap. Never dump anything down the brake boost line. Your gonna kill the engine if you dont watch it.

You got an exhaust leak and either need a new exhaust manifold or gasket. This can cause all kinds of issues. Get this fixed first.

I recommend you take it in and get a thorough once over.
 
DenaliHD66 said:
Thinking about just removing the entire exhaust and just running headers out. :D
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You have 1 just 1 exhaust manifold. Not plural. Please get a Haynes manual and stop working on this truck. Lol. I wouldnt pay you to put a header on my truck.

Btw, you found the noise you originally inquired about. Its the exhaust manifold.
 
CaptainXL said:
You have 1 just 1 exhaust manifold. Not plural. Please get a Haynes manual and stop working on this truck. Lol. I wouldnt pay you to put a header on my truck.

Btw, you found the noise you originally inquired about. Its the exhaust manifold.
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Obviously was an expression. I'm well aware there is one exhaust manifold. Why would you pay me to put a header on your truck when you are perfectly capable of doing it yourself? Why should I stop working on my truck? Do you have valid evidence or a reason as to why I can no longer work on my truck? If not, I should just assume that your statement is an opinion, not a fact. What I do know is that you are a complete smartass, and you might know how to work on this specific truck more than I, but what I know in comparison to you is kind of like comparing the size of the sun to a single corn kernel. Thank you.

P.S. I'll drag race you with my truck any day. We are both running the same setup, so I'd be curious to hear all the excuses pouring out as I run circles around you with 8 hot chicks in the back, while towing my Fountain Powerboat.
 
Take a piece of paper and hold it against the tailpipe so that the force of the exhaust folds it over. Pinch the paper with your fingers and hold it against the bottom of the tailpipe and if there is a hanging exhaust valve the paper will get sucked back to the tailpipe and make a quick slap against the opening.

May not happen right away so give it a few seconds. If it's steady then I would go with a compression test. Pick one up from Autozone or Advanced and remove a spark plug then just screw it into the spark plug hole in the head. Be sure to pull the fuel pump fuse and let it run out of fuel before you test.

Crank the engine and watch the needle as it should peak out after about 4-5 compression strokes. Note the results and get back to us.

Before you do this can you post a vid of the misfire? Take a glass of water and place it on the intake so we can visually see what the frequency is. May not show much but worth a try. Can you hear spitting from the exhaust? Have you checked the motor mounts with a prybar? Not sure exactly how but it has been mentioned here somewhere.

I would also check the vacuum, this will at least show if there is a leak somewhere. Are you sure the vacuum hoses are all attached, especially the one under the intake baffle?
 
Misfires are confirmed, yes I can hear it in the exhaust. Taking it in on Monday, but so far it seems as though my exhaust manifold may need replaced, and possibly checking the exhaust valves.
 
CaptainXL said:
You can learn much more using a vacuum gauge then using a piece of paper over the exhaust.
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This is true.

Only reason I suggested it was I remember he didn't have a vacuum gauge and is a quick test for exhaust valves.
 
gmcman said:
This is true.

Only reason I suggested it was I remember he didn't have a vacuum gauge and is a quick test for exhaust valves.
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Got it. The reason I commented is because you said to use both. So I was kind of scratching my head.
 
Denail, how many seafoam treatments do you have on our current set of spark plugs? I was never a big fan of seafoam and when I used it I replaced the plugs afterwards. Newer iridium pugs may not suffer from seafoam treatments but that's not to say you may have a bad plug or so.
You very well may have dislodged a large piece of carbon and it could be trapped under a valve seat. I believe Advanced or Auto zone may rent a compression tester, worth a try.

I would get a tester only to capitalize on the plugs already removed labor-wise.

Check all the plugs

Perform a compression test as you go

Of all the treatments you have used, have you tried BG44K yet exclusively?? Doesn't always work and I will feel bad recommending it if it doesn't but it's formlated to dissolve the carbon quickly and works very well.

If you go to Autozone they sell a decent vacuum gauge, kinda cheap.. this will tell you if you have a valve hanging by watching the needle fluctuate rapidly.

The paper test I described will point to an exhaust valve exclusively...I highly recommend you trying this.

Best to try this yourself before you run it down to the mechanic and toss money at them....let us know.
 
Perform the paper test and lets see if the exhaust is hanging open.

I will be replacing my plugs tomorrow and will perform a compression test and post some pics.
 

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Can't exactly do the paper test anyway. My tip fell off at the hanger so how it comes out is uneven and jagged anyway.
 
Paper may not slap back with as much authority but should still be drawn backwards
 
Alrighty well exactly one week after I had the codes pulled, and then cleared, I took it back in today for a compression test and to check out a possible exhaust leak in the manifold. There were no misfires and it was running as smooth as a top. No leaks in exhaust.

Apparently running all those cleaners through proved to work just fine, along with clearing the codes. Soo I love my truck again, and they didn't charge me a dime.
 
Good to hear. One treatment yearly is good practice, cool it wasn't anything expensive. :thumbsup:
 
I usually had been Seafoaming it every oil change... about every 6-7k miles. I think I'll stick to the techron in the fuel tank before spraying into the intake again, and any other problems that occur I'll just have to put more work into actually cleaning the intake manifold.
 
gmcman said:
Good to hear. One treatment yearly is good practice, cool it wasn't anything expensive. :thumbsup:
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BG recommends the 44K every other oil change. So yearly sounds about right.

I would replace the fuel filter if it hasnt been done and check fuel pressure. Just a precaution. My guess is that thw valves are carboned pretty good. While using the 44K or Techron make sure to get it out on the highway and pass some cars. It doesnt hurt to blow out some carbon everyonce in awhile.

Make sure to use the Chevron Techron Concentrate Plus, not the regular fuel injector cleaner. Gumout Regane and a few others with PEA do the same. 44K is purported to have the strongest concentration of PEA according to their marketing info.
 
Hm so it was about 45 degrees out tonight... not very cold at all. I turn on the 'Voy, drive about a mile, so its not quite fully warmed up yet. I'm sitting at a red light, and I hear this knocking-like sound. I immediately thought of exhaust manifold. I don't know how else to describe the noise. I think its time to replace it.

I see Dorman makes a really cheap one, but reviews say the heat shield doesn't fit very well? Any other good quality OEM or aftermarket manifolds work well?
 
DenaliHD66 said:
Hm so it was about 45 degrees out tonight... not very cold at all. I turn on the 'Voy, drive about a mile, so its not quite fully warmed up yet. I'm sitting at a red light, and I hear this knocking-like sound. I immediately thought of exhaust manifold. I don't know how else to describe the noise. I think its time to replace it.

I see Dorman makes a really cheap one, but reviews say the heat shield doesn't fit very well? Any other good quality OEM or aftermarket manifolds work well?
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I got the one from 1aauto.com. its good. You absolutely sure the manifold is cracked? Sometimes the back couple bolts break off and the metal compression gasket starts to leak. Solution is to remove broken off bolts from head and replace gasket.
 
I think I'm just going to replace the manifold and cat along with sensors when the time comes. Might as well just put the whole exhaust in.
 
A bad exhaust manifold sounds more like a harly motorcycle when leaking then a knock. And you only really hear it during acceleration and when engine gets hot usually quiets down.
 
Fired it up tonight after leaving the bar, misfires returned. I replaced the ignition coil for #5 as it was the one misfiring before, but it didn't help. If #5 isn't the one misfiring this time, would cleaning the springs in my ignition coils help? 5/6 are originals with 110k miles on them. They aren't cheap either so I wanna know if its worth cleaning them?


But anyway, back to the drawing board. Gotta get it scanned and then we'll go from there.
 
This is something that I think should be done when replacing plugs.

The springs are just metal but lose tension over time and the silicone boots don't degrade. What I did was I took all the springs out of the boots, cleaned them and stretched them about 1/2 inch and put them back in with a little boot grease on both ends. This ensures good contact between coil and plug.
 
Denali, did you use the dielectric grease when you installed the plugs?
 
Die electric grease sounds like goes on the end of plug boot goes into maybe inside boot. Where metal meets metal creating an electrical connection keep moisture out and prevent corrosion same stuff you put on headlight connections I think
 
Correct.

I push the tube of grease into the boot and squeeze a large pea-sized amount so the glob sits against the spring-coil.
 
Oil was low, put in a quart and a half today. About 7-8k miles on this oil change. Was going to go 10k miles on my first batch of mobil 1 extended performance with filter.
 
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