Hi everybody,i am new on this forum,but not to jeeps.My 99 xj 4.0 has started to loose power,backfire through the inlet manifold,and cutting out.Ihave replaced the TPS and cleaned the throttle body,but it has had no effect. I have replaced the plugs and all HT leads.Any thoughts or help would be great.Thanks in advance,Ally.

 

if there is no vacumleak, then i would test the upstream o2 sensor and the map sensor. it sounds like to lean mixture.

good luck

 

Replaced o2 sensor,alot better,but still a bit lumpy.Where is the map sensor?

 

what do you meen with lumpy, im from denmark and my english isnt that good.

the map sensor is at the throttlebody at the outmost position. to the right when you stand in front of the jeep.

but hold that a second. and try test if your tps is correctly adjustet.

 

ups i forgot. pop the dist. cap and look at the rotor and the cap. there should be no build up on the terminals

 

When i say lumpy,its as if its idling unevenly,but when you put the hammer down it clears.Tps was fitted by the dealer so should be fine,new bosch o2 sensor fitted,although runs ALOT better,still feels as if its going to cut out.Im at a loss as to what to do now other than have the dealer do a diagnostic on it.Any advice greatly appreciated.

 

If it backfires you might wanna check the timing on the distributor or it could possibly be valve timing but highly unlikely and very expensive to fix.

 

Dont think its timing as it starts first time,every time.Just noticed that it does this when engine is warming up between 90 and 100 degrees,once its been cleared and run for a few miles problem dosent appear until you switch off then re start....