Bob D
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- Dec 22, 2019
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Huge gap on that plug, had same issues with the double platinum’s, changed to plain NGK $2 each…problem solved on my yukon
2012 Suburban Misfire #5 drama
- Thread starter Keiterburb
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- #misfire
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Keiterburb
Member
I was able to find the crankcase relearn in the innova 5610 today completed and drive 20 minutes no change. Also, valves would open and close seen in borescope. Unfortunately it doesn’t turn enough for good view of their seated position
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Keiterburb
Member
All new plugs were installed and gap checked as stated in initial post
Quite the head scratcher.
I'm still pretty sure it's a lifter.... keep in mind that during the compression test where you just crank it over a couple times, that isn't really an example of the compression you have at idle. Too many other variables at play. At idle, the lifters have oil pressure, and you may have a lifter only acting up every 10th or 20th rotation of the camshaft. The only way you'd see that on a compression test is by manually pressurizing the system through the port on the driver side of the block up front, and doing 20 or 30 compression tests...... But what if the lifter only acts up once it's heated up to a certain temperature? You'll never accomplish that cranking it over with the key.
That's why at this point I would pull the heads, and not just replace the lifters, but do a full AFM delete for future reliability and peace of mind. One reason for this is you can eliminate any mechanical reason if the problem still persists. The second reason is, on these vehicles it is just plain simple preventative maintenance.
On a side note, you can easily verify and visualize the spark plugs steadily firing very inexpensively in the old school way. If you don't have an old timing light laying around, get yourself a cheap harbor freight one. Connect the two clamps to the battery for power, but the other clamp around the spark plug wire to number five and start the engine. You don't need to point the timing light at any marker like on an old small block Chevy.... Just watch the light pulses and you'll see a regular pattern. And you'll definitely see if it's not firing periodically. For the fuel injector, with a needle probe into the back side of the plug, you can watch for the voltage signal also on a regular basis. You rule both those things out, time to start pulling the head bolts. Note, if it's missing a spark periodically put a brand new plug in and test again. If it's still missing periodically, it's upstream in the wiring possibly all the way to the ECM itself. If you're missing a fuel injector signal periodically, that will definitely be upstream all the way to the ECM. If the ECM is not sending the correct signal consistently for spark or the injector, then you have to question the ECM itself, or the signal that it's receiving from the crank and camshaft position sensors. (which I find unlikely, because then typically you'd have a random misfire and not just on one cylinder. I'm betting you find a consistent spark, and a consistent fuel injector voltage cycle.)
That's my old school technique, before I bought all my electronic toys to plug in, to determine I've got a check ball and a lifter acting flaky ;-)
I'm still pretty sure it's a lifter.... keep in mind that during the compression test where you just crank it over a couple times, that isn't really an example of the compression you have at idle. Too many other variables at play. At idle, the lifters have oil pressure, and you may have a lifter only acting up every 10th or 20th rotation of the camshaft. The only way you'd see that on a compression test is by manually pressurizing the system through the port on the driver side of the block up front, and doing 20 or 30 compression tests...... But what if the lifter only acts up once it's heated up to a certain temperature? You'll never accomplish that cranking it over with the key.
That's why at this point I would pull the heads, and not just replace the lifters, but do a full AFM delete for future reliability and peace of mind. One reason for this is you can eliminate any mechanical reason if the problem still persists. The second reason is, on these vehicles it is just plain simple preventative maintenance.
On a side note, you can easily verify and visualize the spark plugs steadily firing very inexpensively in the old school way. If you don't have an old timing light laying around, get yourself a cheap harbor freight one. Connect the two clamps to the battery for power, but the other clamp around the spark plug wire to number five and start the engine. You don't need to point the timing light at any marker like on an old small block Chevy.... Just watch the light pulses and you'll see a regular pattern. And you'll definitely see if it's not firing periodically. For the fuel injector, with a needle probe into the back side of the plug, you can watch for the voltage signal also on a regular basis. You rule both those things out, time to start pulling the head bolts. Note, if it's missing a spark periodically put a brand new plug in and test again. If it's still missing periodically, it's upstream in the wiring possibly all the way to the ECM itself. If you're missing a fuel injector signal periodically, that will definitely be upstream all the way to the ECM. If the ECM is not sending the correct signal consistently for spark or the injector, then you have to question the ECM itself, or the signal that it's receiving from the crank and camshaft position sensors. (which I find unlikely, because then typically you'd have a random misfire and not just on one cylinder. I'm betting you find a consistent spark, and a consistent fuel injector voltage cycle.)
That's my old school technique, before I bought all my electronic toys to plug in, to determine I've got a check ball and a lifter acting flaky ;-)
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Keiterburb
Member
Thanks for breaking down your testing methods and recommendations as well as why compression test may give false hope.
I feel it’s definitely heading in the direction of bad lifter. My main concern with full AFM delete and cam swap would be knowing the remaining engine life warrants the cost? I don’t live close to a machine shop so I would need to find one if I ever went full rebuild, closest city 1.5 hour one way drive. Engine is at 197K+ and I guess if every cylinder leak down test is at 4% like #5 was then the rings and bore are still holding up good??
It's not unusual to find it at that mileage to still see the original hone marks in the cylinders. I wouldn't worry about the bottom end. You will see somewhere on the front camshaft bearing, pretty normal. If you Google that you'll see examples that at first glance might make you cringe..... Yeah that's pretty common to just slide a new camshaft in and get another hundred thousand plus miles out of it. The consensus seems to be don't worry about the cam bearings unless you have extremely low oil pressure or upon inspection with the scope if you have a cam bearing that's walked out of the bore or missing pieces. Remember, these engines about AFM routinely exceed 300,000 miles as long as they get regular oil changes. One of my co-workers has an L92, which is the 6.2 without AFM, but has the variable valve timing.... He's up around 360,000 miles and still running strong.
I just realized I read that wrong. it's removing 10% from bank one and 9% from bank 2 as well.
so 2 things I don't know if have been asked. will your scanner read alcoholic content? it should be 0-5% or so, if it's up in the 40+ on non e85. that can cause issues and what does you maf read in g/s at idle warm ac off? it should roughly match the exhaust cc.
Good examples of what could cause random misfires on multiple cylinders..... I just don't see those items only affecting cylinder number five? But then again, I think we've all seen some very bizarre symptoms that often can't exactly be explained.
well knock counter isn't active while missing, and the one plug seems a bit carboned up.
so yeah, this one has me stumped. Just trying to think of the basic stuff missed. something is making the whole engine run rich.
so you replaced injectors. any details on those? other than a oem injector of the same part number, there's a bunch of injector data about dead times and voltage in the tune. even thou they arw the same lbhr rating they can be completely different flow rates without the correct data. of course this doesn't explain the 1 cyl but I could explain the fuel trims.
