# manual eco tranny "clunk" slowing down



## 70AARCUDA (Nov 14, 2010)

...sounds like the engine computer (ECM) "pulling" off the "boost" pressure which makes the engine react like a diesel "air-braking" down a steep mountain incline.


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## unitednations161 (Mar 13, 2011)

70AARCUDA said:


> ...sounds like the engine computer (ECM) "pulling" off the "boost" pressure which makes the engine react like a diesel "air-braking" down a steep mountain incline.



So is it normal? it doesnt slow down the car down anymore it just goes clunk lol kinda of like if you were to be in first gear and pushed the gas fast then let up and pushed it again, like the drive train has slack or the tranny. But im not pushing the gas at all, im braking. In 3rd/4th gear does it in 5th and 6th too but its really faint.


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## 70AARCUDA (Nov 14, 2010)

...if the car doesn't "slow" then it's likely NOT what I mentioned.


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## erlindbl (Apr 12, 2011)

I have a manual eco and have not noticed that.....


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## unitednations161 (Mar 13, 2011)

well drove another one, did the exact same thing. They said it was just the engine taking over from the coast. thats great to know.


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## GSDB (Apr 5, 2011)

I have noticed the same thing you have and I think it may be related to the deceleration fuel shutoff feature (DFCO). But I have not conculsive proof except that it seems to happen at about 1200-1500 rpm while coasting to a stop for me. My question is, why would it clunk if it is just turning the fuel injectors back on?

I think I will start my own DFCO thread...


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## Cruzemeister (Mar 22, 2011)

I'm not a tech by any means, but just wondering why the automatic 6's wouldn't do it too? (on slowdown)


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## 70AARCUDA (Nov 14, 2010)

Cruzemeister said:


> I'm not a tech by any means, but just wondering why the automatic 6's wouldn't do it too? (on slowdown)


...yes, it happens on our LTZ to differing degrees: _less_ noticable when driving very gingerly (for fuel economy), but _more_ noticable when driving more aggressively (for get-up & go).


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## Cruzemeister (Mar 22, 2011)

70AARCUDA said:


> ...yes, it happens on our LTZ to differing degrees: _less_ noticable when driving very gingerly (for fuel economy), but _more_ noticable when driving more aggressively (for get-up & go).


Interesting.... I haven't noticed it under any type driving.... even the firmer downshifts are barely there now that my LS auto has 1500mi on it....


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## cruzeman (Mar 13, 2011)

i have just started noticing this as well... if i coast in gear i all of a sudden feel a quick boost of power sorta.....strange but im sure its just the cars attitude!!


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## 70AARCUDA (Nov 14, 2010)

...that _"...sudden feel a quick boost of power..."_ is almost certainly the 6-speed *automatic* transmission downshifting to a lower gear, which results in the engine speed suddenly going much faster.

...with 6-speeds, the new tranny does MORE down/up--and SOONER--shifting than the older 3- and 4-speed transmissions that we're so familiar with.


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## cruzeman (Mar 13, 2011)

i have a manual eco though!!!


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## 70AARCUDA (Nov 14, 2010)

...oops, but it _still_ sounds like ECM pulling boost is what you're feeling.


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