2001 Yukon 5.3 - Sounds like a miss, only at idle.

[bill9000]

Hi all, I'm trying to squeeze this winter out of my wife's old 2001 Yukon 5.3 - it's tired... it has 152,000 miles and it barely ran/had no power, I've been trying to get it to be usable for her short commute this winter.

After putting new Iridium spark plugs and wires, it seems to run significantly better than before. It can at least go down the road. However, it seems to idle a low (490/500) and has a sporadic miss (or so it sounds like) but only at idle, runs fine under power - it has a Flowmaster exhaust, so I can hear it pretty well and it sounds like an off beat miss, with no real pattern.

Today, I removed and cleaned the throttle body and MAF (throttle body was HORRIFIC dirty) - put all back together... same exact problem. Paying a little more attention, I notice that there's a click sound near the coil packs on the passenger side that clicks each time the engine sounds like it's missing.

Any thoughts on what to maybe do here?

My thoughts are in the direction of maybe a bad spark plug wire even though its a new set? or perhaps replacing the coil packs? Anything else I could be looking at here?

I really do feel like the click that goes along in sync with the miss is probably a very good clue. I can upload a video if it's really necessary, but I feel like the click likely means something!

thanks in advance for any help!

That throttle body was dirty!

 

[iamdub]

This thing should just be around it's middle age with only 152,000 miles.

Did the miss/click exist before and after the new set of wires? If not, as a quick and easy test you should first make sure all the boots are fully clicked into place. If no change, you could swap the four wires from the left bank with those on the right bank and see of the sound follows. Make sure the coil packs are all plugged in, you could left-right swap those as well if you wanted. Just unbolt the whole coil bracket from the valve/rocker cover and swap all four at the same time.

If the ignition checks out ok, I'd test the fuel pressure. These things are known to have noisy injectors. Your symptoms are synonymous with a weak fuel supply in pressure and/or volume. Maybe the fuel pressure is barely adequate and one injector is slamming closed a little harder than the others, making the sound?

 

[bill9000]

interesting ok. The car did sit for like a year, it has a new fuel pump because that died a bit ago... I was thinking along the lines of clogged fuel filter, but it doesn't seem to be starved for gas under power. Problem only exist at idle.

 

[lkrasner]

I'd dump a can or 2 of seafoam in the tank (real strong, close to an empty tank if you can) and go hammer on it to give the injectors a good cleaning. There are better methods than this, but if it is some injectors not squirting well this should help enough to notice. That throttle body looked disgusting...

Any chance you damaged a plug putting them in? I dropped one once, and even though it looked fine, It was arcing enough to cause similar issues after putting it it. Had to pull every damn one after forgetting where I put the bad one before i found it. If you're lucky you might be able to see it arc at night. The arc did make this kind of clicking noise.

A vacuum leak can cause weird idle, though it would usually be higher. Check your fuel trims on a scanner, they should be right around 0. if one side is significantly different, you have a leak somewhere. Check all the lines, and even more likely, intake gasket. This gave me a headache for a while. was never able to find exactly where the leak was, but I replaced it and it ran much better.

 

[bill9000]

Thanks,

I dont hammer on this engine, ever. Especially not with the miles it has... But the path you are suggesting of maybe a bad plug or something could be possible... I didn't drop any but maybe I just received a bad one... hard to say! I checked it in the dark last night, no visible arc anywhere.

The fuel trim, I was just watching a video about that, I think the guy was using a Snap On Solus - I'm looking into those, seems like it may be useful to have.

 

[lkrasner]

Thanks,

I dont hammer on this engine, ever. Especially not with the miles it has... But the path you are suggesting of maybe a bad plug or something could be possible... I didn't drop any but maybe I just received a bad one... hard to say! I checked it in the dark last night, no visible arc anywhere.

The fuel trim, I was just watching a video about that, I think the guy was using a Snap On Solus - I'm looking into those, seems like it may be useful to have.

Say what you will, but I have 350K on my engine, and I honestly believe it is good to run them hard occasionally. This is based mostly on experience and not science, but my feeling is it is necessary to burn off crap. The engine was built to handle abuse. I'm not saying drive crazy all the time, but a few minutes of hard acceleration with some cleaner in the fuel isn't going to blow it up.

I use a cheap bluetooth scanner and Torque on android and it works great for 90% of what I need to do. sure, a nice snapon unit would be great, but this does the trick and at less than $20 it's totally worth it.

 

[bill9000]

my view on the "run it hard" thing used to be carb's needing to be cleared out and not fouling spark plugs from over fueling as most people run bigger carbs than what the engine really needs.

with an fuel injected engine, I can't see any reason why revving it hard would change anything other than put unnecessary stress on things that are already old.
(I don't mean to be rude for sure!!! - I'm just debating why I don't agree on that particular point) - And of course, if someone has some evidence, a technical reason I'm definitely willing to listen.)

sounds interesting on the phone bluetooth thing, I hadn't considered that!

 

[Doubeleive]

in addition to the remedies mentioned above, I would also either run several bottles of injector cleaner thru it for the foreseeable future or take it to a good shop for a fuel injection cleaning, from the looks of the TB this truck probably has not had a lot of common maintenance, you can pick up a set of "herko" coil packs off of ebay or amazon pretty reasonable if any are questionable I would just change the whole set. you also might want to consider a new maf it can have a lot of affect on the entire system including the transmission shifting. I would say the maf is probably getting near end life at 160k (just my opinion) The mileage you are at for the motor is nothing it's still a baby, however at 160k if it hasn't been maintained your going to be looking at wheel hubs and suspension parts also in the near future probably it's just one of those mileage points where a little TLC is needed.

 

[lkrasner]

my view on the "run it hard" thing used to be carb's needing to be cleared out and not fouling spark plugs from over fueling as most people run bigger carbs than what the engine really needs.

with an fuel injected engine, I can't see any reason why revving it hard would change anything other than put unnecessary stress on things that are already old.
(I don't mean to be rude for sure!!! - I'm just debating why I don't agree on that particular point) - And of course, if someone has some evidence, a technical reason I'm definitely willing to listen.)

sounds interesting on the phone bluetooth thing, I hadn't considered that!

I'm not fighting either, I've gotten into this debate with people before (similarly, the debate of leave the old engine alone, it's crap build up is probably keeping it running how it wants to vs clean it out as best possible). I too would love to see some actual research into the matter and haven't been able to find much reliable.

My thinking with fuel injection is that injectors pushing more fuel are going to push more cleaner through, and work harder to blow out any crap making them not spray nicely. Now, maybe this means running it ******* highly concentrated cleaner will do the same thing as running a smaller amount through light use for a longer period of time as many people suggest. Just as you could obviously remove them and do a proper cleaning over a shorter period of time with concentrated cleaner. I'm not always a believer in magic liquid cleaner, but fuel systems do get dirty, and I really think consistent maintenance with some cleaners works wonders. Judging by that throttle body, your truck clearly hadn't been maintained the best, so it has some catching up to do.

Definitely check out the BT scanners. Unfortunately most don't work with iPhone due to Apple hardware description, but I believe there are some compatible now. I've had good luck with my cheap knockoff one (search amazon, there are lots of choices). The BT is a bit glitchy, and it definitely is cheaply made, but hasn't failed me yet. The amount of data it can read surpasses many handheld scanners, but lags behind the best ones for sure. There is a set of extended codes for Chevy that you can download to give you a lot more too. For example, I do not have a trans. temp gauge, but GM installs the sensor in all the trans regardless. I can read this with the Torque app, which is very nice to have when off road or towing. Some people go as far as to install an android device in dash to supplement gauges. In my mind, the speed at which data is read with the protocol these trucks use is too slow for this to work well, but it is really cool with newer CAN bus vehicles that can really read everything in real time, and a hell of a lot cheaper than dedicated units.

 

[bill9000]

very nice thank you! that sounds like its worth checking out, I use android anyway, I have a new note9.

I'll check into that!