Does your 6.2 misfire at idle ?

[diesel4me]

Just curious if anyone else has noticed their 6.2 doesn't idle all that smoothly,especially in drive sitting at a red light..like one cylinder fails to fire randomly..

Mine has always done that to some degree,but this summer when I was using some additive like Power Service "kleener",I noticed it did seem to idle much smoother,not perfect,but smoother than it was..once you give it some throttle past idle,it smooths out and you can't notice any misfiring while driving...now that its getting cold again,I notice it "coming back" again..

Is it "normal" or just a result of high mileage ,maybe dirty injectors ,or a valve not sealing 100% ?..it gets 16+ mpg as usual,has decent power and doesn't seem to have any oil consumption issues..wondering if a cylinder is getting too low on compression to fire at idle..

 

[yellowK20]

Just curious if anyone else has noticed their 6.2 doesn't idle all that smoothly,especially in drive sitting at a red light..like one cylinder fails to fire randomly..

Mine has always done that to some degree,but this summer when I was using some additive like Power Service "kleener",I noticed it did seem to idle much smoother,not perfect,but smoother than it was..once you give it some throttle past idle,it smooths out and you can't notice any misfiring while driving...now that its getting cold again,I notice it "coming back" again..

Is it "normal" or just a result of high mileage ,maybe dirty injectors ,or a valve not sealing 100% ?..it gets 16+ mpg as usual,has decent power and doesn't seem to have any oil consumption issues..wondering if a cylinder is getting too low on compression to fire at idle..

Sounds like it’s time for a set injectors , the service interval on those is 100k

If you know someone with a injector test stand it is possible to reshim the spring to get the correct popping pressure. That’s pretty much all they do with reman injectors .

Pump could be suspect as well , but typically if your not having other issues like hot restart etc the pump is usually fine.

Do some searching anset of injectors isn’t terrible, about the cost of a quality tuneup on a small block

 

[diesel4me]

The engine is not original to the truck,from what I was told it was a salvage yard used one with about 80K on it --I've put maybe 15,000 on it in the past 16 years..it sat a lot in the past,I had other vehicles and used it mostly to take trash to the dump,and plow my driveway..only the past 6 years has it been my daily driver--and I don't go far with it..

The fuel filter on it was new when I got it and I was lax about replacing it,figuring the low amount of miles I put on it yearly and the size of it wouldn't require it to be changed (wrong ! )--this resulted in it plugging up one summer day 15 miles away,and a $100 tow was required to drag it back home..
I cut it open and it was nasty inside--can was rusty,and had about 3" of sludgy muck in the bottom..learned my lesson not to wait so long..

I have since replaced the filter twice,(first one I doubt was dirty,only had a few thousand miles on it--the electric fuel pump it had that was added near the fuel tank had died and led me to think the filter may have plugged up,but it was no different with the new filter..So I kept the first filter as a "spare"..
Replacing the electric pump cured the issues it was having..engine still has a mechanical lift pump too,and it is still hooked up..never tested it to see if its pressure is good or not though..doesn't look original,may have been replaced before I got the truck..
I assume its working OK..

The fuel tank was replaced about 5 years ago with a clean used one from a gas powered truck,the sending unit some was nice & clean,so its not like the tank is delivering crappy fuel or restricting the flow any..I ran copper tubing from the tank to the firewall filter,and used only short rubber sections to join it at each end..however ,the fuel lines from the lift pump to injector pump are rubber and I've never messed with them..probably should replace them just because they are so old..but the engine never acts starved for fuel,even on long uphill wide open pulls..

I'm avoiding messing with the injectors because of rusty injector lines that will likely not survive being removed..though I have a good condition spare set from a CA member here and another set on a parts 6.2 that snapped the crank (that are about as rusty as the existing ones),I'd rather not start disabling the truck now,when I need it most to plow..

The engine starts with 1/2 a turn when hot,so the IP should be fine..
It's getting the pig to fire up when its below 30*F that is a pain..
Since it has always run this way more or less,I hope to be able to put off doing any repairs till winter is over..

Meanwhile I'll keep using the additive--I got 6 bottles of Stanedyne fuel treatment recently ,have yet to add any--previously I used the Power Service & Howes Lubricator ,and some Solder-Seal Fuel Oil Conditioner,which seemed to make the biggest improvement..unfortunately that stuff hasn't been made in years,I should have bought the whole case of it I saw at the flea market instead of only 2 bottles of it..guy was getting $1 each for it..was dumb not to buy all 12 bottles....

I changed the oil last week to 15W-40,and thought about adding some Marvel Mystery Oil to the fuel and crankcase--it thins the oil some,which wont hurt,but last time I added some to the fuel during the winter it seemed to start harder..the flash point on it is higher than most motor oils..was going to get 5W-40,but I couldn't justify using full synthetic in it for nearly $50 when I already had the 15W-40,and I'm leery of switching to full synthetic in an old engine that may not like it much..I'd rather put the $50 towards new batteries instead..

 

[campfire]

Since it has always run this way more or less,I hope to be able to put off doing any repairs till winter is over..

That is why I didn't feel like answering the question this time. If you've already decided to put off the engine's general maintenance, having more advice won't be helpful.

Yes, I've had rough idling before. Yes, I think injectors are overdue. Especially if fuel treatments are making a difference, your injectors are likely suspects.

It's not a loss of compression, or the cylinder would be dead/struggling at all engine loads, not just at idle.

With a mechanical lift pump, it's possible for a small pinhole leak to cause stalling at idle without causing problems at higher engine speeds. This is because the mechanical pump is able to move more fuel at higher speeds, which doesn't always match the amount of fuel needed by the engine. If it's moving excess fuel, the bubbles tend to go back to the tank via the return line. If it's not, the engine starves out. A little bit of air at WOT is less noticeable than the same amount of air at idle. Put a piece of clear tubing on the IP return line and watch for bubbles. You shouldn't see any substantial ones if the system is working properly.

 

[diesel4me]

Well,Saturday morning I started it up cold ,let it warm up a few minutes,and the usual white smoke it makes for about 30 seconds subsided slower than usual,and one cylinder wasn't firing consistently--after the 3 mile ride to the gas station ,sitting in line waiting to get to the diesel pump,it still felt like only 7 cylinders were firing,like one wasn't firing at all now!..not "coming and going",but not making any power..kind of like a stuck valve or over pumped up lifter type of skip a gas engine has..

After I put in about 1/2 a quart of Power Service cleaner,and filled the tank,on the way home I noticed a large improvement,it was now firing on all 8 with only a slight missed beat once in a while (like it always has since I got it decades ago)...I drove it ten miles later in the afternoon and it ran much better than it had been..

This was the first time in quite a while that I let the tank get below half full,I put 180 miles on it since the last fill up in November--usually I fill it weekly due to the fact the fuel gauge doesn't work,sending unit is junk...

I'm wondering if I got "summer diesel" at the last fill up back then--it wasn't until the weather got colder that the lopey idle came about..Saturday was unusually warm too at 50+ degrees though..

I will put a clear hose on the return line and see if any bubbles are there--I suspect some will be ,the IP I think has a weepy seal at the throttle shaft and that too may be the culprit..the engine pulls strong past idle on all 8,so it could be dirty or worn injectors I suppose,but I'm not in a position to go messing with them now..

The mechanical lift pump has been on it since I got the truck in 2003--it appeared to be a new replacement then,and I've always had an electric fuel pump near the tank ,which has been replaced in the past year--not sure if the mechanical one has any issues,but its not leaking externally or filling the crankcase with diesel,so I assume its OK..

Reason I asked about the misfiring at idle or lopey idle,was because I've heard and seen several other 6.2's act the same way,and it might be considered "normal"...also the IP timing marks are aligned dead on,this engine may have enough slop in the timing chain to throw off the timing or make it erratic and idle lousy too,maybe advancing the timing a bit might help..but for now the additive seems to be helping a lot..