2012 Tahoe 5.3 with Misfire on 4 ...

[Ivanhoe]

Hello,

I have turned to this forum for ideas as I’m losing patience with my Tahoe. I have a 2012 5.3 Tahoe with 225,000kms. It has rough idle, the stabiltrack and traction side orders and misfire on cylinder 4. A friend mechanic has pulled the head to check the AFM lifters and cam - all seem fine. Plugs changed, coils and leads all ok. I believe injectors were checked as well. Looking for ideas of where to check next ? Code reader gave up p0300 random multiple misfire then p0304 cylinder 4 misfire.
New engine/ dealer repair price is beyond my means .
Any ideas ?
Thanks

 

[wjburken]

How did they check the coils? Did they swap them and get the problem to move or did they stay?

Might be your coil harness.

 

[Ivanhoe]

How did they check the coils? Did they swap them and get the problem to move or did they stay?

Might be your coil harness.

Not sure as I was away working at the time. The mechanic is usually very thorough and very experienced, the work was done for a favour so I didn’t want to question his work too much. I changed the coils and cables myself as well and no change. I cleaned MAF sensor and after attaching battery again the faults cleared for about 10 minutes then returned

 

[iamdub]

The problem could be in the VLOM, which wouldn't be visible. Clear the codes and drive with it in manual mode in gear 4. This will keep AFM from engaging. If all is well, shift into "D" and see if the misfires come back as soon as it tries to go into V4 mode.

 

[Ivanhoe]

I have a range afm disabler on it now to prevent the afm kicking in

 

[BG1988]

I have a range afm disabler on it now to prevent the afm kicking in

did you make sure it has enough oil low oil can cause misfire as well

 

[malvizar]

When I had this issue with my 07 Tahoe, it was a collapsed lifter due to oil starvation. I had to get an AFM delete kit and that revised valve cover for oil consumption. Runs on all 8 cylinders now at all times like it should’ve to begin with. Runs great now. Good luck

 

[iamdub]

I have a range afm disabler on it now to prevent the afm kicking in

Well, shit. Your problems may be more serious. No ticking or anything when it's misfiring? Maybe it is injector or spark after all.

 

[wjburken]

I really think it’s worth while to check the harness going to the coils.

 

[wsteele]

The multiple misfire code might be telling you something about a general condition that exhibits itself most often in number 4 due to tolerance stacking and/or maybe two separate issues.

Does your mechanic friend (or you) have access to a scan tool where he/you might look at misfire counts, watch the numbers in real time, check O2 sensors, fuel trim, etc?

Although a long shot given the inspections that have already been performed, I probably would do a quick and dirty compression check on 4 as well.

 

[Ivanhoe]

The multiple misfire code might be telling you something about a general condition that exhibits itself most often in number 4 due to tolerance stacking and/or maybe two separate issues.


Does your mechanic friend (or you) have access to a scan tool where he/you might look at misfire counts, watch the numbers in real time, check O2 sensors, fuel trim, etc
Although a long shot given the inspections that have already been performed, I probably would do a quick and dirty compression check on 4 as well.

I have borrowed a code reader and will see if it does that

 

[Geotrash]

I have borrowed a code reader and will see if it does that

The Tech2 scanner would be a huge help in this. Not sure if the Diablo or any of the others can monitor the parameters you'd need to watch to see what's going on. If you've already ruled out the obvious (fuel injector, coil, plug and plug wire), the next most likely would seem to be the harness - either wiring or connectors, or a mechanical fault (VLOM, AFM lifter sticking, etc).

 

[wsteele]

On the compression check, there is a GM service bulletin dated sometime in 2017 that covers P0300-308 codes.

It is related to carbon buildup in the intake ports, causing leaks around the valve seats and misfires. The culprit according to the service bulletin is “bad gas” or at least not using a “Top Tier” gas, which have industry standard minimum detergent additives.

Kind of a generic, check your ports and valves, kind of bulletin.

One of the diagnostics, other than looking down into the exposed ports (intake manifold off), or removing the head and valves and individually inspecting the valves, is to run a compression check on a cold engine. It says if the condition is present, the cylinders will show low or no compression.

Probably worth a shot, testing number 4 on a cold engine should be a breeze (the easy side to work on).

 

[Ivanhoe]

Thank you for all the helpful advice so far.

I cleaned the MAF sensor today while i was looking at other things ( im sure it was checked previously but you never know) , reattached battery afterwards and CEL light was off and no problems and truck ran better ( not perfect but noticeably better) I did a quick drive ( 2 miles ) and no lights and truck seemed ok. Got back home thinking I was a genius and switched off, let it sit for 10 minutes and when i set off again the CEL and previous symptoms were back. Could it be a MAF issue ? would it cause a misfire to just one cylinder ?

 

[wsteele]

Thank you for all the helpful advice so far.

I cleaned the MAF sensor today while i was looking at other things ( im sure it was checked previously but you never know) , reattached battery afterwards and CEL light was off and no problems and truck ran better ( not perfect but noticeably better) I did a quick drive ( 2 miles ) and no lights and truck seemed ok. Got back home thinking I was a genius and switched off, let it sit for 10 minutes and when i set off again the CEL and previous symptoms were back. Could it be a MAF issue ? would it cause a misfire to just one cylinder ?

I would think it unlikely a bad MAF would cause a single cylinder misfire. Frankly, for a rough idle and random or single cylinder misfires, the MAF wouldn’t be the first thing I looked at. Hard starting, hesitation, stumble or quitting, maybe one of the first, but rough idle and a cylinder 4 misfire, MAF wouldn’t be the first place I would look.

Did you have any luck with the scan tool? Getting a feel for what cylinders have misfires (only #4, many random with #4 worst, mostly random, is it one bank, etc.), may help a lot in narrowing things down.

You can buy ODBII readers (like $20 US) that can give you a lot of real time data on misfires, fuel trim (helps with isolating O2 issues in closed loop, cylinder leaks, etc.), etc. pretty cheaply (like a Bluetooth or WiFi dongle that your smart phone can talk to), might tell you a lot.

 

[Ivanhoe]

Scanner only shows #4 misfire p0304

 

[wsteele]

Scanner only shows #4 misfire p0304

View attachment 268493 View attachment 268494

Other than the P0304, it doesn't seem to offer any insight into the other misfires (P0300), whether it is bank specific, etc?

Looking at the very brief description on one of the retail sites for that scanner, it says something about reporting O2 sensor status. It would be good to know if the upstream O2 sensor on Bank 2 (the bank you know for sure you have a misfire on) was functioning properly. Maybe correlating what it is saying with any fuel trim reaction, might tell you if you have a bad O2 sensor on that side?

Back on the compression stuff. When your friend pulled the head on bank 2, did he do any kind of seal test on the valves?

 

[Ivanhoe]

Other than the P0304, it doesn't seem to offer any insight into the other misfires (P0300), whether it is bank specific, etc?

Looking at the very brief description on one of the retail sites for that scanner, it says something about reporting O2 sensor status. It would be good to know if the upstream O2 sensor on Bank 2 (the bank you know for sure you have a misfire on) was functioning properly. Maybe correlating what it is saying with any fuel trim reaction, might tell you if you have a bad O2 sensor on that side?

Back on the compression stuff. When your friend pulled the head on bank 2, did he do any kind of seal test on the valves?

not sure as he’s away working at the minute, but he is very thorough and doesn’t like it when he can’t find what it it

 

[wsteele]

not sure as he’s away working at the minute, but he is very thorough and doesn’t like it when he can’t find what it it

If he does it for a living, he likely took a good look at the valves. Pretty hard for a mechanic to pull a head and not recommend freshening the heads, unless they look pretty darn good.

I think I would still try that cold engine compression test.

There really isn’t all that much to it, fuel, spark and compression. Oh, and of course, everything happening at the right time, with the right mix.

 

[Leevon]

You mentioned you changed the coils, plugs and wires. I have seen carbon tracking on a coil boot cause issues. I doubt it, since #4 is typically the first AFM cylinder to cause problems...but worth a free check.