Topic: popping and backfiring on deceleration YJ with tbi 2.5

[Backroads]

Its been in the garage more than on the road so I dont know how long its been going on...

When I'm decelerating in gear I get a popping/backfiring at the throttle body (at least thats where it sounds like its coming from) If I was to take a guess its the idle control (the box the throttle plate lays on when the throttle is closed) I tried adjusting it out for more idle but didn't make a difference. My idle right now is right around 1K rpms when warmed up. When cold its a bit lower, but I dont have the hot air tube going to the airbox.

Is theres something I need to be adjusting here? Or is something bad? Thanks!

[Torch_Ind]

only thing I can think of off the top of my head would be to check the throttle position sensor it may not be going back far enough to cut the fuel on decelerate. aka thinks that your holding the fuel slightly open so keeps the fueling.

[FourbangerYJ]

I thought that backfiring thru the TB was a timing issue?  Not that I know much about engines. 

[chardrc]

the reason the idle position didn't change is probably because the idle control box will adjust in and out to get the idle rpm it wants. Ive found that when my jeep isn't used a lot it tends to idle close to 1000 rpm where if i use it steadily for a while i get an idle near 800 rpm. i don't run the hot air tube either (mine deteriorated to pieces and got sucked into the air cleaner) but haven't had any ill effects form its removal. I would probably start by testing the tps like Torch_Ind suggested. but could also be a timing issue...

[Backroads]

Come to think of it, when I first swapped this motor in, I dont remember it doing that....Then had all the vacuum and gas (if you guys remember me) issues and I did change out the TPS while trouble shooting. I actually tossed the original muddy colored TPS in my YJ spare parts box! Maybe I'll try swapping it out, heck it might just need adjusted if I remember right the bolt holes on the sides are slotted right? I'll have to find the correct way to set it.

[Backroads]

I thought that backfiring thru the TB was a timing issue?  Not that I know much about engines. 

I know what your referring to, and maybe I'm mistakingly describing it becuase I did exactly that when I first set the timing. It was way off and it would backfire through the TB, but it wouldnt even start, just snap crackle and pop...

This is runs fine, it just has a popping sound when decelerating in gear...but doesnt do it if I let off throttle and put it in neutral and coast.

[Torch_Ind]

Come to think of it, when I first swapped this motor in, I dont remember it doing that....Then had all the vacuum and gas (if you guys remember me) issues and I did change out the TPS while trouble shooting. I actually tossed the original muddy colored TPS in my YJ spare parts box! Maybe I'll try swapping it out, heck it might just need adjusted if I remember right the bolt holes on the sides are slotted right? I'll have to find the correct way to set it.

+1 on the adjust the tps as starter point. there should be a spec as to what the feed back should be at when throttle closed.

[Backroads]

So Ive been messing with this on and off and I can not get this thing to run right.

It seems like its got a dead spot when accellerating where it kind of sputters. Especially if I hold the throttle constant at that spot, but above and below that in speed and on the throttle it will accelerate fine.

Also still pops and backfires when decelerating. If I decelerate in gear enough to really slow down it will give a good backfire through the exhaust.

what am I doing wrong here?! it didnt always run like this and everything I changed aside from the entire gas tank, I've tried putting back to stock and its still the same issues

[Torch_Ind]

considering you have a dead spot in your throttle did you try a tps sensor?

[Backroads]

Not a new one no.

after I posted that I went back out and swapped to another TPS I have, and now that dead spot on acceleration has stopped...but still pops and backfires when decelerating. It only really does it if the RPMS get up pretty high, if I gradually slow down using the brakes before I downshift its not as bad, but still does it.

So I'm pretty sure the dead spot was because of the other TPS.

But how do I probe the TPS to test it? I popped the little cover on the back of the sensor plug but there is no way to get the multimeter probes in there to contact anything.

My manual says to put the positive on the center wire and negative on the black (ground) but neither of my other 2 wires are black lol.

[Dylan]

Check for an exhaust leak.

[sharpxmen]

i might as well take a shot at it too
1 - too  much fuel (injector leaking could be one of the reasons, but that would make it run rich at idle also)
2 - some ignition problem (if fuel does not burn completely would cause backfiring)
3 - a bad valve or maybe cam related (incomplete fuel burn as before).

[Torch_Ind]

i might as well take a shot at it too
1 - too  much fuel (injector leaking could be one of the reasons, but that would make it run rich at idle also)
2 - some ignition problem (if fuel does not burn completely would cause backfiring)
3 - a bad valve or maybe cam related (incomplete fuel burn as before).

+1 on #3 that was also beginning symptoms of my jeep when my cam lob worn off on the exhaust side wasn't letting exhaust gasses out causing it to rumble throw the intake

[Backroads]

Well that #3 option would fit the rest of the new year so far!!

SO I think im just gonna drive it til it goes kaboom then look for something else haha

[Backroads]

This thing is driving me freaking crazy.

SO I changed out to a different TPS (spare I had) also the IAS or whatever it is that controls your idle speed, right at the throttle lever on the TB. After that it actually ran pretty descent. It would still get a little pop and backfire if I downshifted at a high rpm and let the engine whine down....But all the sputtering and crap stopped.

Fast forward to yesterday. Took it to the carwash to spray off all the salt and accumulation because for the first time in a long time I drove it a week or so with no problems!!!

Washed it off, tried to avoid the engine area as much as possible. Finished up drove home fine, woohoo everything is good!

So I poked around, checked my belts and oil yada yada, didnt really mess with anything electrical. Fired it up to park it back in the driveway and its sputtering and popping and wont idle.

had no choice but to drive to work today and it was backfiring loudly now, popping under deceleration, runs ok if I'm heavy into the throttle, but doesnt like easing up to speed. Is it the damn TPS? But how nothing got wet! As hidden as that freakin this is under the TB I cant imagine water got to it.

What do you guys think? I cant afford to go out and buy a bunch of new sensors for trial and error.

also, seemed like I burned up most all of a tank of gas on my way to work. I cant verify because my gauge sucks...but I ran 100 miles or so on the last partial fill, this time I went about 45-50 and it was back at my predicted 'empty' spot lol? hat gives?!?!?!?!?!!!!!