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2006 VZ Exec - Tranny thump after exhaust quitened.

bigdaddycool

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I'll be breif:

I have a 2006 VZ Exec, Pacemaker Headers, 150Cell Hi-Flows. I've changed my exhaust a million times but here's my issue and I'm after opinions.

1. From my hi-flows it runs 2" stock lines. I recently had a 2.5" twin xforce system put on but it was way loud due to my ultra flow cats....... so I took it to my exhaust shop and asked em what I could do to quiten it without touching the xforce setup. They then put in 2 glass packed resonators straight after the cats. Since then I've had a MAJOR tranny issue. It thumps, hesitates etc.........

It got slightly better but ..... I ended up pulling the xforce off, putting my old system back on as I could directly bolt it back on. My current setup runs 2" into a central muffler after the center joint, which then goes out a 2.75" to a rear resonator with a 2.5" out.

The thump remains and shifting is bad. I've got VCM Suite and I've been trying to tune the torque out a bit and up the shift pressure to elevate this problem. I've improved it but it's still sh*thouse.

How here's the thing. My thoughts are the two front resonators are creating too much back pressure causing the tranny to go haywire for some reason however........ I have got more torque now and dont loose any uptop.......... nor is my engine getting hotter. Which to me says it's ok.

Obviously the answer lies in getting the two resonators that were added "removed" and then it'll be fine again.

My question is.......... is my exhaust in general too restrictive as it has 3 resonators in total (2 front, 1 rear) and a central straight thru muffler.

The car sounds good, quiet but has a nice level note all the way thru the rev range. I was hoping to keep my new resonators, without them my rear resonator sounds like a tinny b*tch.

Would removing the rear resonator and just having a straight thru pipe help or? ........ I was thinking of unbolting the rear resonator temporarily and going for a drive to see if removing that small restriction helps. But of course it comes back to if it makes the exhaust loud again.

99% of all exhausts out there for the alloytechs like mine dont work on mine due to my cats being a lil more flowy then most peoples hi-flows.

1. Are the two front cats the cause of my problem?
2. Will removing the rear resonator help as the front help with keeping low down torque.
3. Are maybe the o2 sensors telling something weird to the ecu bout the setup causing the tranny thump? as the resonators pretty much sit directly behind the cat at the joint where the rear o2's are also sitting on the rear of the hi-flows.

A. Tuning the thump out? idea's..... the currently setup, can I lower torque longer to help it shift (stock 0.5) tried 0.4........ shifts a bit quicker. Adding shift pressure actually makes it worse.

HELP. IDEA'S.
 

84dez

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um i had a similar problem when i changed from my stock to xforce back to standard xu6 system and i found that my exhaust didnt clear a part near my rear diff and all i had to do was get a bracket made up to clear that rear housing, maybe check all of ur mounts and then see if u have any clearance issues, if anything maybe a gearbox oil change is needed
 

bigdaddycool

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Nah just had my tranny change done like 2 weeks ago. This only happened once the two front resonators were put on just behind the cats. I bolted on my old exhaust on over the weekend which never had an issue......... the clearance is fine. However the resonators do sit near my transmission ........ but no it happens all the time, even when the car is cold. It's just hard to imagine back pressure being the culprite. I know if I pull them off it'll fix it but.......... I'd just be nice to know WTF ....... I doubt it's back pressure, maybe it's messing with the rear o2's ......
 

84dez

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yeah clearance could be good when the car is turned off but when u move along it would hit i had the same issue cleared when off but once the car got moving it would hit when slowing down, and gear changes just make sure on all ur clearance and maybe check on how much movement u have in the exhaust
 

bigdaddycool

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had that checked already, as when i bolted my old exhaust on the front resonators behind my cats were hitting two bolts on a bracket near the tranny. had that fixed pronto (same day) ........ they pretty much bent the exhausts away (bit of welding done). I was considering getting them to just put the straight pipes back in at that point..... but I held off til I read up a bit more on this.
 

84dez

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ok hmm only other thing i can think of is maybe a engine mount could have gone soft due to the excess torque which might not cause the exhaust to move but cause the motor and gearbox to move causing it to bump something, not sure never had a engine mount go in my comos but had one gone in my evo powered lancer and it cause a fair bit of trouble,
 

bigdaddycool

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i'll have to check but it's unlikely cause i just had ultratune go over it for me, told them to find everything that needs doing. that was when i had my tranmission serviced few weeks back. they replaced my front strut bushes with aftermarkets as they'd gone and i took it back to get a wheel alignment and balance cause they screwd it up doing the bushes etc. but yeh i'm stumped
 

84dez

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yeah very wierd maybe take it to and exhaust shop or maybe a different mechanic and see what they say
 

bigdaddycool

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ok after some diagnosing i have some results.......

Those two front resonators are messing with something that results in the ecu reporting a "invalid torque signal" to the TCU...... now the tcu was set to shift at "Maximum Pressure" in the invalid torque signal from which I have now disabled.

It seems that has fixed my delima, all I have to do now is smooth out a few minor high-rpm shift points and it should be ok.

But for anyone here who knows about exhaust back pressure or tuning, do you think the car is ok to stay how it is or should I just have those resonators removed anyway? ..... maybe put in some smaller hotdog pipe resonators.
 
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impulsesv6

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A quick Alloytec
turning off options inst fixing your issue, your treating the symptoms,

the twin 2.5 is way too big for a NA alloytec, yes it sounds good, but its not ideal for low down torque.

i have a modified exhaust of an SS for sale,



pm me for more info if ya want
 
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