2018 5.3 miss with no CEL

Superman_006 · July 23, 2019

I have an 2018 crew cab ltz plus with the 5.3/8spd I have about 5k miles on it so far. In the 1st few hundred miles I noticed the engine stumble a few times (no CEL). Took to the dealer who said all the new trucks mis when you don’t warm them up and they flashed the ECU with an update.

I took the truck to the beach twice (sea level) both times I went there the truck missed so bad for the first 10+ miles the tires would chirp as I would take off (no CEL) I tired prem gas and mid gas. On my way home it missed for over 40 miles on the interstate (not the transmission shutter) still No check engine light). Occasionally when I start it ... it will keep dipping to ~200rpms for a sew seconds/ vibrating then reving up.

I took it back to the dealer at like 8:45am and told them it does it every morning when the engine is cold or sits for 4-5 hours and my foot is barley on the gas it will miss so bad the tires will chirp for the first few mins.

They called me about 2pm and said it’s all good and I can come pick it up and that the truck isn’t missing and think it’s the transmission. They said I need some special transmission fluid that hasn’t been shipped out yet. I asked about it missing in park, they were adamant that if it was missing the CEL would be on.

I pick up my truck and noticed that my 50mpg adv is now 7mpg, so I pull my smart driver and can see a trip with the driver score of 0 that started at 9:06am along with a 9:06 heavy acceleration ... 9 more heavy accelerations with 14 heavy de-accelerations in a 12 mile trip around town. This is more driving alerts than I have cause in 5k.

I have a GoPro and want to video the missing. I tried to put in the the engine compartment and drive this evening but it’s pitch dark., I put it on the windshield but all you can hear is wind. When it misses you can literally hear the engine pause for a second then suck in air like a deep breath.

I havent heard of anyone anyone else having problems of the CEL not coming on with it missing. Any suggestions?

CamGTP · July 23, 2019

I'm not really sure what to say without watching a scanner.

If I was the tech working on it I too would be trying to re-create the misfire and doing full throttle pulls is part of the gig to make the engine act up. I'm sure he's watching misfire counters on each cylinder to see what he can try to find.

I think them having the truck over night would have been better because you say the issue is there when it's cold cold. If they went out and drove it 20 minutes after you dropped it off, they won't see that issue.

Superman_006 · July 23, 2019

I kinda see what you are saying when looking for a constant miss but I think when someone says “only does this- at light acceleration when cold” and you jump in when it’s hot and go straight to WOT and slamming on the brakes ... makes about as much sense as driving 100mph to find a vibration at 20mph to me.

batman900 · July 23, 2019

Mine has a miss when cold for the first 5-10 miles also, at 13k miles I guess I've just accepted it. Different gas etc no difference, tried the range to disable 4 cyl and still no difference. Just is what it is I guess, it's very noticeable and annoying but without a CEL or any damage the dealer won't help.

Superman_006 · July 24, 2019

Strange how everyone else is getting a CEL without feeling it missing over the injectors. Mine is falling on its face the first few miles and no CEL like GM has programmed it ignore misfires for the first 20 something mins? I’m still trying different places for my GoPro, I tried the headlight this morning but all you can hear is wind after 2-3 mph.

blaib · July 24, 2019

I also have a 2018 LT 5.3 6 Speed with about 1800 miles. Since day one of picking it up new it has missed when cold for the first 3-5 minute's of driving. I am also a tech and own a auto repair shop. I have monitored it several times and it appears as though all of the cylinders miss and count up. Took it to my buddy at GM dealer and he said it had two bad injectors. He replaced them and the damn thing still misses exactly the same as before. It behaves exactly as OP described definite misfire on light acceleration.

Hope they figure this one out because it is driving me crazy!