So I waa having some issues with stuttering under heavy load. So I replaced the serp belt and plugs. Also fixed a slight boost leak in the boots and after a year I switched out the vacuum line for the map sensor (attached image).

After fixing boost leak, map sensor line, and new plugs I was hitting peak boost (19lbs). However, after replacing serp belt I now can only get 16lbs of boost.

Not sure how this is possible. Anyone know why I would be getting less boost after putting on a new belt (napa 060532)?

 

Maybe you bypass valve is not closing all the way....
That's...a....er...interesting fix....sure its OK?

 

Hmm, I thought the pre facelifts had that issue. Mine is 05. Maybe I screwed something up when i took off the throttle body?

 

Even the facelifts have bypass issues, mine had a. Similar issue.

 

My throttle only opens to 88% according to the torque app knock test...going to try resetting the ecu tonight

 

Only change was MINI stated using a slightly stiffer spring...not as stiff as DT, but mechanicaly they are the same...
Change the throttle body? If you did adaptations must be reset.

 

I didnt change it, but I had to take off to replace the vacuum line though.

 

I think it could be a bad bpv. Just bought a dtbpv from a local buddy so we'll see if it helps.

 

So I installed the dt bpv and it only accentuated the stuttering issue. Except it feels more like a timing retard between 2700 and 3200 rpm. Also, I threw some codes after the intial startup. Have been having issues with misfiring this last week randomly on the highway.

Would a bad chain tensioner make the ecu retard timing between those rpm?

Im not sure if this is just one problem or multiple issues at this point :/

 

19psi boost? What's done to your motor to make hat much boost? Isn't a stock MCS around 8-10psi? What gauge are you using to read your boost? Electronic, or mechanical?

 

17% pulley reduction should make 19psi peak in cold weather.

 

That sounds awfully high for a 17% pulley. Are you using one of those electronic gauges that reads off of a MAP sensor?

My JCW makes 15psi of boost (autometer mechanical boost gauge) with a 17% pulley on it. To tell you the truth...I've never even heard of anyone making 19psi of boost with just a 17% pulley.

 

Yes it's the torque app that uses the map to calculate boost. Regardless, it has usually reached 19lbs according to the torque app and now it barely creeps to 18lbs.

17 to 18 lbs is normal on a 17% reduction. 15 psi is normal for a 15% reduction. 15 sounds low for a 17% reduction.

 

Could battery voltage be affecting the reading on your app that reads the boost? Just an idea...

 

The battery was replaced a month or two ago. My buddy reads the same psi from his scangauge. Same mods as me.

 

+1
Sounds about right...maybe 2 psi higher than expected...but likely well within the accuracy of the guage...they can be pretty bad...

Remember, a "jcw" will show LESS BOOST WITH THE SAME PULLEY...this is due to porting...
My gut says you T-MAP is bad.....but just a guess.
How sure are you that cold side map sensor repair you did is leakfree? That picture you have makes me wonder.....