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Anything I should look for if I'm having misfires on different cylinders when I left off the throttle and it goes to coast down timing right before and sometimes during dfco. Basically a stock tune on an 08 le5 2.4 other than torque management and rev limiter changed. It reads 2-4 misfires on 2-3 cylinders. I can feel a very slight jerk to the car on occasion when coasting as well. But other wise the car runs fine.
I found a small vacuum leak from the throttle body mounting gasket. I've fixed that but still have the same issue going on and no other vacuum leaks. It's reading rich on stft and ltft. Ltft hovers around -5 to -7 but has gone up to -15 a few times. Stft stays mostly rich. While driving it will occasionally go to 0 then hit +25 before returning to rich trims on the stft. Maf and map are reading appropriately. I believe it's causing the misfires being logged normally on coastdown or light cruising after being on the throttle. I get 2 to 4 misfires mostly on cylinders 2 and 3 but sometimes 1 and 4 will also report small misfires. No dtc stored or set either. I've checked logs from 3 months ago and didn't find misfires or rich trims and nothing has been changed on the car since then. I'm leaning towards sticky injectors or bad o2 but wanted to see if anyone had a better guess
without posting the tune and log of this happening you probably wont get to much help on the issue besides guessing - it could be anything really - plugs,coils,bad fuel,injector getting stuck however during dfco mode the injectors aren't used so if it happens then probably not a injector issue - i have seen o2 sensors cause misfires so if there old might be worth replacing - you can try switching the plugs and coils to see if the main problem cylinders switch
I cleaned the maf and solved the fuel trim issues. However, it's still having the random misfires when coasting down before entering dfco. I can't really feel the misfires in the logs, other than the normal slight engine deceleration when it switches over to dfco. The o2 sensor still appears to go into open loop randomly when driving showing 0 on the trims then +25 for a few cells before switching back to closed loop. I pulled and regapped ac iridium spark plugs, less than 30k mi on them and no signs of issues. No misfires on acceleration or WOT. I've attached the current tune. I haven't set up hp to log, so I've been using torque pro to do logging.
Attachment 85733
the "lean" tip in issue coming out of dfco is pretty normal because the ecm is adding the fueling back in so as long as the trims don't stay +25% there really isnt much that can be done about that
as for the misfires - if they only count up to 4 and then reset back to 0 i wouldn't worry to much about it as long as your not getting any driveability issues
any mods done to the vehicle minus the plugs? how old are the plugs?
disable the cat test
my lsj would randomly go into open loop commanding a random high or low afr because i took out my rear 02 and the ecm was doing a sanity check but that was only half my problem. i put it back in.
i have a heavily modded lsj and my supposed misfires which i don't have but the ecm thinks i have because of my mods would also cause it so i disabled my misfire counts and all is well for the random open loop switching.
so if you do a few checks by swapping some parts around and there still isnt any change - try a different gas station (top tier only for me) to eliminate bad fuel as a problem and get some gm fuel system treatment (pour in tank) and see how it goes
if you want to for shits and giggles check compression just to verify that but if all leads no where id just ignore it or disable the counts but thats me.
all cars in my experience have been known to show some misfire blips from time to time but the important thing is that the counters don't continue to rise because thats when theres a problem
Thanks for the help! I disabled the cat test and also I raised the dfco entry blend time thinking it may give it more time to transition into dfco where the misifire was common. After a quick log it seems to have fixed the misfire on coastdown into dfco. I had one misfire recorded for only one cell, it was between wot shifts in pe, not actually on throttle. But overall better than the previous logs. The plugs have probably 30k on them and about a year or 2 old. They still look good, but I may just replace them. I'm not sure if moving plugs, coils, or injectors around will narrow this one down, the misfire jumps around cylinders and only misfires on one cylinder at a time. I may just let it go for now. Only reason I noticed it was because I decided to log it after feeling unusual jerking on a long coastdown a few days ago but now I know my fuel trims were also messed up also and may have been what caused it. Last time I logged it was probably 6-8 months ago and had 0 misfires in any of those logs though. I'll try some better fuel and possibly new plugs and see what happens.
Yeah if it was more pronounced on 1 cylinder rather than across the board I'd say do the swap but as it seems it's not so it would probably be a waste of time but I was just tossing that out there and yes the fuel trims/maf could of very well been the problem.