Won’t shift down, detonation.

This has happened twice in the last month now.

Shortly after starting on a short commute, my 2017 802A with 10k miles accelerated to city traffic speed (30mph) normally with no problems, but then when I go to accelerate slightly, the truck won’t shift down and the engine will detonate. I can’t simply try to accelerate more without causing much worse banging/detonation from the engine.

Both times, I have manually shifted down a few gears and it smartens up and then the truck runs normally when placed back in auto. It seems like the transmission is sticking in top gears when lugging around town. Today it happened and I noticed the transmission was in 9th, and didn’t want to shift down. It gave one small bang which I assume is detonation when I tried to apply more pedal.

It has happened when very cold, and also today, soon after leaving a warm garage.

Usually the truck runs and shifts perfectly.
There are no diagnostic lights when or after this occurs.

Wondering if any of you have experienced this. Thoughts or ideas appreciated before I take it to the dealer, thanks.

Part out

dude1782 said:

Part out

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Will do, thanks.

I've noticed that mine doesn't downshift very aggressively, so when I want it to do so, I give the throttle a decent stab, then immediately back off... this gives me a downshift without big throttle opening... just enough to merge or do whatever I want to do.

This is in Normal mode... I haven't driven it in Sport mode enough to know what it does in regard to downshifts.

dude1782 said:

Part out

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kirch:
To produce excrements in an accidental manner, esp. to ****/shit your pants

hefer:
A negative word towards a female. Usually meaning that she is fat and ugly, rude and ******.

Pretty much spot on!

I think it must be wind resistance from the huge factory antenna. Throw a stubby on there and it should start shifting right.

No, actually detonation normally makes a pinging or metallic popping sound and only goes BANG when you ventilate a block. I think you are probably backfiring. Maybe take it to an expert. Detonation, if that’s what it is, is very tough on a motor.

ThugHunter said:

kirch:
To produce excrements in an accidental manner, esp. to ****/shit your pants

hefer:
A negative word towards a female. Usually meaning that she is fat and ugly, rude and ******.

Pretty much spot on!

Click to expand...

Now let's get this thread back on track

bailer said:

This has happened twice in the last month now.

Shortly after starting on a short commute, my 2017 802A with 10k miles accelerated to city traffic speed (30mph) normally with no problems, but then when I go to accelerate slightly, the truck won’t shift down and the engine will detonate. I can’t simply try to accelerate more without causing much worse banging/detonation from the engine.

Both times, I have manually shifted down a few gears and it smartens up and then the truck runs normally when placed back in auto. It seems like the transmission is sticking in top gears when lugging around town. Today it happened and I noticed the transmission was in 9th, and didn’t want to shift down. It gave one small bang which I assume is detonation when I tried to apply more pedal.

It has happened when very cold, and also today, soon after leaving a warm garage.

Usually the truck runs and shifts perfectly.
There are no diagnostic lights when or after this occurs.

Wondering if any of you have experienced this. Thoughts or ideas appreciated before I take it to the dealer, thanks.

Click to expand...

The detonation is a problem, and you need to get to a dealer. I can lug the $hit out of Lucille and not a hint of detonation in coldest of cold or hottest of heat.

As to the transmission; The shifting logic in normal mode is straight up economy, force to the highest gear attainable. By just over 40mph, I can have Lucille in 10th gear. Rpms are just over 1k. This causes a couple issues with drivability. First, if you floor it from 10th at 40, it takes about 1.5 seconds to downshift and accelerate. Literally, you’re 2 seconds until the truck is actually going faster. 2nd, if you don’t floor it, the programming in normal mode is literally to “disbelieve” anything but WFO throttle. if you give it say, 25% throttle, the programming is like “No, really what you meant was 5%, so that’s what we’re going to give you and, we’re not downshifting, you’re getting boost and you’ll like it. If you don’t like it, buy something with fewer gears”. In normal mode, the truck will try desperately not to downshift.

You should go straight to the dealer if you’re hearing detonation, regardless of what grade fuel you have in the truck.

once they fix that, the transmission shifting you have a few options.

1) Drive harder. Life is short.
The truck will adapt to your more aggressive throttling after a few moments. If you baby the truck for a long period, you have to cane her to get the truck to respond better in normal.
2) Use Sport mode. The truck will not linger in high gears using sport mode.
3) get a pedal commander. Used, they’re way too expensive new. PC doesn’t add any power, but fools the computer into thinking you have a much more aggressive right foot. It makes normal mode tolerable. You can still have the 1.5 second shifts from 10th to 3rd or 4th, but it doesn’t hold on to top gear, bitterly clinging to EPA numbers.
4) get a tune with a shift algorithm.

Ironwood said:

I think it must be wind resistance from the huge factory antenna. Throw a stubby on there and it should start shifting right.

No, actually detonation normally makes a pinging or metallic popping sound and only goes BANG when you ventilate a block. I think you are probably backfiring. Maybe take it to an expert. Detonation, if that’s what it is, is very tough on a motor.

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Yup, I believe you are correct, it would be backfiring. It is too loud for detonation and more of a bang.

I let the pedal off both times, thinking wtf is happening. The first time I tried back on the pedal but it banged some more.

Shifting down and getting the rpms up gets it running perfect.

I played around with it some more later today and it is running perfect and downshifting properly. It really seems like my transmission isn’t wanting to downshift the couple times it’s happened.

I am running premium. The truck always has shifted up and down smoothly and predictably other than these two times.

Thanks everybody for the input. I will let you know what I find out but I suspect it will be one of these, no codes, can’t replicate type of visits.

dude1782 said:

Now let's get this thread back on track

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I bet you clicked on some of those links too.