Idles rough with a knock...
 

For the longest time, my truck was idling a little on the rough side, with a little bit of a knock to it...

Went away for a couple days after changing the spark plugs...

It seems to idle at about 650 - 700 RPM... I'm not sure it still makes the funny noise when you bring up the RPMS any higher... The fan is kind of overpowering, lol.

I'm kinda lost, since it ran great for a couple days...

RE: Idles rough with a knock...
 

Hmmm...I wonder if you have a carbon build-up.
How did the plugs look..oil foulded?
Is the knock from the bottom or the top of the engine and is it constant, or just on acceleration or on decelleration?

RE: Idles rough with a knock...
 

I can only hear it on idle... From the drivers seat that's the only time you can hear it...

The plugs did have a fair amount of blackness on the flat round surface in the combustion chamber , however the electrode and where it arcs to weren't fouled in any way...

I'm not sure where the knock is coming from, I'm assuming from the middle of the engine and up, lol.

It stopped for a few days after I changed the plugs... Maybe she's just running a little rich for idle... I'll see if I can snag a soundclip of it or something...

RE: Idles rough with a knock...
 

Update:

The knock only happens when it drops to about 600 - 700 RPM and lower.... It does not happen any RPM higher than that...

It also seems to only happen when the engine is warmed up...

RE: Idles rough with a knock...
 

is it a loud knock or soft knock does it sound like a metal to metal knock and since its only at idle i wonder if its pinging and not knocking im thinking i may know what it is but not sure just a guess im wondering if its your lifters or valves chattering just a guess though someone may have something better

RE: Idles rough with a knock...
 

Well, it's not a loud noise overall... Could be pinging, I suppose, lol.

But like I said, it disappears soon as it gets back up to the normal 900RPM or so (which has to be done manually, once it's been warmed up enough, the RPM's drop).

I think it's the low RPM making it knock/ping and such...

RE: Idles rough with a knock...
 

k does it seem more like a mechanical type of fix or something that can be helped by using higher grade gas and maybe even a fuel system cleaner another thing you can try is lucas oil stabilizer it takes a while to put in but it makes a difference see if any of that might help i know one of the others on the forum may have a better solution im just adding options that don't cost alot. hope it helps

RE: Idles rough with a knock...
 

Well, we'll see what an oil change nets me... It's been about 5000 or so km, so it's about due... Hopefully that'll help...

Gonna be getting a new fuel filter and air filter, too...

RE: Idles rough with a knock...
 

cool yea when you do the oil if you decide to go with the lucas it replaces exactly one quart of oil so instead of 4.5 quarts you would just by 4 quarts and get one bottle of lucas put the lucas in first cause the oil you put in after will help it curcilate better and get in the system faster plus then you willhave a half a quart left of regular oil so another thing too is for the lucas they have two types one for regular oil and one for synthetic the black label is for synthetic and the other is for regular let us know when you change your oil if it helps it helped mine alot ran cooler and better after i did it.

RE: Idles rough with a knock...
 

As this seems to be an engine performance issue, I fail to see how an oil stabilizer will help... As a rule of thumb, I stay away from the "meracle in a bottle" type products that are in for the duration.

Anyway, Dennis, when was the last time you did an upper intake cleaning? It may be time for one. I know I'll be doing the smoke show the next time I do an oil change on my Rainier and that only has 28k miles on it. Go grab yourself a bottle of Seafoam and run it through the throttle body. Since you just replaced your plugs, you shouldn't have any problem with them. Do the seafoam right before you change your oil. Warm up the engine. Remove the intake duct work, unplug the MAF sensor. Dribble 2/3rds of a bottle down through the throttle body with the engine running and your hand on the throttle to keep it running. With the last 1/3rd of a bottle, pour it in and let the engine stall. If it doesn't stall, have someone there to shut off the engine a short bit after you pour the last in. Don't worry, you won't damage the engine. Let it sit for a good 1/2 hour then drive it like you stole it until the smoke stops coming out of the tail pipe. Change the oil and you're done.

See how that goes. It's been a long time since I have recommended this and come to think of it, with the carbon buildup problems that these engines have, this could be the cause for a lot of peoples problems!

RE: Idles rough with a knock...
 

yea the miracle in a bottle thing i stay away from but when the stuff works i push it to people to try for themselves and let me know if it worked for them or not.Your idea is perfect which i need to try on mine it has 121,000 on it now and i think it might need it to clean it out but question on the sea foam do you have to do an oil change after you use it?

RE: Idles rough with a knock...
 

So far as I know, it's never been done... I've owned the Blazer for about 13,000km (8000 miles)... I suppose it could be due for a top end clean after 62,000km's (38500 miles) lol.

I usually use GM Top Cleaner when I do that... I have yet to find Seafoam in my city... I'll keep an eye out for it, though...


And thegr81, you don't have to change the oil afterwards at all, It just makes more sense for me to do that afterwards, as the oil will flow nice and free after having the piss driven out of it, lol.

I when I did it on my old Z34, I smoked out the entire block when that sucker started back up, lol... It was much easier to do on the S10, though... a vertical pointing throttle body is so much nicer...

Actually, after figuring out the trick for the 3rd plug, if it kills the plugs, I'm not overly worried...

I guess even hard driven vehicles get carbon build up, lol

Thanks for the reminder about that! I'd completely forgotten about the top cleaner part...

RE: Idles rough with a knock...
 

not a problem just wanted to help anyway possible sometimes it helps to back another forum person's thoughts and recomondations up if you agree that helps the person taking the info and using it more than just one person's thoughts

RE: Idles rough with a knock...
 

GM Top Engine Clean is a great product, but it is quite a bit more expensive than Seafoam.

The reason for the oil change after a top engine clean is the possibility of the cleaner washing down past the rings. It is just safer to do a top engine clean right before you do an oil change to reduce the likely hood of problems with the oil.

RE: Idles rough with a knock...
 

cool i never done that before so i just wanted all the info thanks kyle appreciate it i will do it the next time i do a oil change in 2500 miles i just did one so im going to wait thanks again

RE: Idles rough with a knock...
 

The GM Top Clean usually costs me like $8... Seafoam must be dirt cheap!

RE: Idles rough with a knock...
 

ive never seen gm top cleaner but around here, a can of seafoam is about $6.50

RE: Idles rough with a knock...
 

Chances are, you'll only see it if you go to the dealership and ask for it...

Edit: For now, I've decided to stick with the stock air box, since I do a lot of mudding and such, I figure the CAI would get too fouled up to be that much of a benefit... So I'm getting an AEM DryFlow panel filter! yay me! lol

RE: Idles rough with a knock...
 

Yup, GM top engine clean is a dealer item. Last time I bought Seafoam it was $4.50 at the local Napa store.

RE: Idles rough with a knock...
 

Hmmmm... Maybe I'll swing by Napa... I think we have one somewhere in one of the industrial areas... Just gotta find it...

RE: Idles rough with a knock...
 

i really wanted the AEM cai. i dont know if you have seen it but they havea thing you can dowload off of their website, its the test results from an independent research group.they tested4 of theleading air filter companies and thedryflow outperformed all of them.however i got my K&N for about $70 less than the AEM... i might eventually try to get a dryflow filter on my K&N however the filter that i have is 5" long while the dryflow filter on the blazer cai is 9" long

RE: Idles rough with a knock...
 

DryFlow rocks... No oiling! lol

Not sure what the cleaning process is on the K&N, but the AEM just needs a couple bottles of cleaning stuff and a 5 gallon or so pail of water...

RE: Idles rough with a knock...
 

K&N's are the same deal. I wash and oil mine about once a year.

I just got my fuel system cleaned, and then I went out yesterday to "drive it like I stole it" and I think I mighta fudged my tranny [:o]

I'm crossing my fingers tho......I've never felt a tranny slip before, so I hope my truck was just trippin out. from 1st to 2nd a couple times it seemed like the rpm dropped right when it tryed to shift.

but dr.perry I was happy with what Mr.lube does in their cleaning service.

RE: Idles rough with a knock...
 

But but but but! It's fun smoking out the block!


edit:

Here's what it sounds like, at any rate... Click Here

RE: Idles rough with a knock...
 

Update:

Well, the seafoam didn't change anything... gonna try to do an oil change after work, or if I'm to tired, tomorrow afternoon when I wake up...

RE: Idles rough with a knock...
 

You've probably already checked this but it isn't your PCV valve clapping together is it? Mine did that once and I shook it a bit and it stopped.

RE: Idles rough with a knock...
 

It's not the PCV valve... The noise is too "deep" for that... and you can hear it clearest when you stick your head by the front wheels...

I'm definitely checking out my distributor and cap + rotor tomorrow... or maybe I should just replace them on principle... I'll probably do that, depending on prices... might take a couple days extra, lol.

Because if it's not that, then I just might have a coolant leak into the engine... :(

I'll also pull a plug and see what she looks like, and load up a pic here, and see what the experts have to say..


I'm really leaning towards distributor cap + rotor, because that's such an easy fix, and don't want to do any gaskets, lol...

But as I said in the first post... the problem was gone for a few days after I changed the plugs, would that make the dist. a more likely culprit?

RE: Idles rough with a knock...
 

i don't think plugs or rotor will help. It sounds like a lifter tapping, or something internal.

RE: Idles rough with a knock...
 

Side note... Did a random scan of the trouble codes... No SES light, but there was a low voltage MAF or whatever it is... P0102 or something like that... Hopefully it's a leftover from when I did the seafoam treatment, as I didn't clear the codes, lol...

RE: Idles rough with a knock...
 

any contamination or debris on the sensing elements of the MAF sensor will set a code P0102

RE: Idles rough with a knock...
 

I think it was just a hold over from running it without it plugged in for the seafoam treatment... as the SES light wasn't on...

I dumped in a bunch of injector cleaner, and it seems to run better/smoother... still a bit of a miss and a knock, but not quite as bad...

Hopefully the fuel filter finishes it off...

RE: Idles rough with a knock...
 

How much of a chance is there of fouling the plugs up when using seafoam? I just changed the plugs (ac delco $5.88 a piece) 10,000 miles ago, dont want to fudge them up

RE: Idles rough with a knock...
 

They might be good enough that they'll be unaffected...

If you still have your old plugs, you can always swap them in...


Since the problem has gotten a little bit better, with the injector cleaner, it's pretty much confirmed that it's a spark, or fuel issue...

It doesn't start missing until it hits low idle, once it does, it always misses, until it cools down again... Maybe I should get my battery/alternator tested, lol.

RE: Idles rough with a knock...
 

You shouldn't have any problems with your plugs. If you think that you may, then I would just remove them after you are done and make sure that none of them are fouled.

RE: Idles rough with a knock...
 

Well, I changed my radiator cap today, and topped up my coolant overflow tank...

The radiator was full, though, so I don't think I have to worry about a headgasket...

RE: Idles rough with a knock...
 

I suppose I should've updated this thread... My engine blew a connecting rod :D

Not bad, I suppose... Since it'd been making this noise for a good 15000km.