I have borrowed a code reader and will see if it does that
2012 Tahoe 5.3 with Misfire on 4 ...
- Thread starter Ivanhoe
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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).
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).
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).
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 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.
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
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
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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.
