S&S header install and weird transmission shifting [Archive] - GrandAmGT.com Forum

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chris_gt_74
03-15-2012, 09:58 AM
Okay to start out the weird shifting was not present prior to installing the headers. So here's the deal, I installed my headers the other day and understandably I did get the P0420 code but nothing else. I have checked all of my vacuum lines and connections I may have came in contact with while installing the headers and have nothing out of place. The headers I got also came with the downpipe w/cat. The car has a noticeble increase in power but I seems to be having issues with the transmission line pressure I guess. The car acts like it does not want to shift or kind of like drags out before it does shift especially if I get on it. I might also ad that I still have the stock catback. Which means there is no gradual transition to the smaller diameter pipe. I believe the downpipe is 2.5" but could be mistaken and iirc stock it 2.25". But I'm not sure if that would even cause my symptoms or not. Can someone out there help me out here. Oh and it does not have a tune and the only other breathing mod is a cold air intake at the moment.

G.I.Ceo
03-15-2012, 02:14 PM
Check you MAP sensor harness on you UIM. I had a issue very similar to that when I installed my S&S headers. It ended up being a wire on the harness that was shorting causing my tranny to shift hard.