Topic: Back fire when shifting

[jeeplover]

1998 TJ 2.5 Manual Trans.
When shifting from 2nd to 3rd gear, I get a back fire. Not reall loud, just enough to question if something is wrong. I have 52,000 miles on her and all maintenance is up to date.

This happens all the time, and only shifting from 2nd to 3rd.

[Jeffy]

So you're getting flames out the TB?  Or are you referring to 'afterfire'(often confused with backfire) which is when you get unburnt air/fuel into the exhaust and it ignites inside the exhaust. Afterfire isn't good since it tends to melt the cat.

It might be good to give us the RPM this happens at and the speed.  Does this happen exactly when shifting?  Can you get it to happen at the same RPM in another gear?  How about the same speed in a different gear?  Does it happen if you shift sooner or rev higher then shift?  What you're trying to do here is to see if it's just RPM or speed dependent.

[jeeplover]

No flames. So it would be afterfire. Happens around 3300-3500RPMs, and when shifting fast and getting on the gas. If I shift slow and go easy on the gas pedal it won't do it.
I have a brand new exhaust system, from the manifold to tailpipe, and new O2 sensors.

[YJmechanic]

get the specs on line for the tps and hook some jumpers and a voltmeter to the connector and monitor it.  i had mine go out and that is how it started and then it just got worse until it did it all the time.  should also turn the mil lamp on as it gets worse.  have a dealer or someone with a good scanner to check for stored codes and freeze frame data.