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vibe/noise at startup

thooogy

NAXJA Forum User
Location
LONG ISLAND, NY
When I start the engine it kicks a bit as it starts - almost like a backfire, but lately I realize it comes from under the floor (transfer case?) and I can feel it as much as hear it. It's just a single jolt then idles fine. If I restart engine soon after it doesn't do it - just when it's been sitting (and not every time).

I only noticed it after I installed new exhaust (Dynomax catback & Magnaflow cat) but I wonder if this is the old You-Need-An-SYE-Thing. I have some other symptoms (front end shimmy at 50-55 mph) but I've never heard of this one. Any ideas or tips on troubleshooting? Thanks

'99 XJ, NP 231, AX-15, 3" lift
 
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i doubt a You-Need-An-SYE-Thing is neexded at start up.

i would recheck the exhaust work you did. check the clearance of cat convertor and crossmember and all hangers. at start up, the engine can shift a bit(also check motor mounts) and twist the exhaust causing the pipe between the cat convertor and muffler to come in contact with crossmember.
 
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