Topic: popping and backfiring on deceleration YJ with tbi 2.5

[Jeffy]

Is it triggering the CEL?  have any stored codes?

[Backroads]

I didnt think the older yjs had the CEL? Its a 1990. If it does how do I check that? I dont have any engine lights or service lights on. It just randomly went back to running like crap.

It would be more explainable if it did it right after the wash, and something got wet. But I literally took the long way home and played around and it was running the same as it was before the wash. I added about 1/2qt of oil, but i dont see how that would change a thing!

[Jeffy]

Doh, my mistake!  You're right, it's pre-OBDI.

[Backroads]

So unless my TPS somehow got ruined what else could it be? CPS? Or 02 sensor?

I read in the manual about checking these things for voltage, but how do I get to the wires without shaving some of the coating off to expose the wire to tap into?

It just really doesnt make any sense anymore! Its does it immediately after starting it, so I almost think its not a sensor. I thought I also read that if a sensor was bad it wouldnt really cause any problem until it was warmed up.

So could it be something with the fuel tank? or pressure?

[Jeffy]

So unless my TPS somehow got ruined what else could it be? CPS? Or 02 sensor?

I read in the manual about checking these things for voltage, but how do I get to the wires without shaving some of the coating off to expose the wire to tap into?

It just really doesnt make any sense anymore! Its does it immediately after starting it, so I almost think its not a sensor. I thought I also read that if a sensor was bad it wouldnt really cause any problem until it was warmed up.

So could it be something with the fuel tank? or pressure?

The computer?

To tap into wires you can use a VOM with a probe at the backside of the connectors.  Or you could push a pin through the wires although I don't really like doing that.

[chardrc]

id triple check the tps and then move onto trying to check the cps. and if all else fails make sure you have good connections to the battery and the big collection of wires at the firewall between the motor and the battery. weird things can happen if your not getting good connections. although that would be less likely than tps or cps id think. but easy to check anyways. i would digg into the books abit for you but school is killing me right now. 

[Backroads]

I appreciate the input. So I messed with the TPS (2) I have, they both result in the same thing, BUT if I manually push the little lever it does make it idle up and down slightly. I'm thinking its not that...

But I did pull the cover off the throttle body and compared to when I looked at it before it looks like its REALLY getting a lot of fuel dumped in it. I can literally see it all but pooling up on top of the butterfly at warmed up idle. Would the CPS cause that? That would have been the only thing that really could have gotten soaked when washing the thing the other day.

I'm just thinking if its fuel related, it doesnt seem likely that its gonna run great one day, and then flooded and like crap the next. I guess I could have a clogged return line, but I just put in the tank and new lines and filter etc.

So should I try a cps? Is that even something that causes these kind of symptoms?

also my whole exhaust sucks, could it be an exhaust issue? From when it was doing this a week or so ago, I havent touched the exhaust and it went from not running good, to running good, back to not. crappy exhaust stayed the same.

[sharpxmen]

I appreciate the input. So I messed with the TPS (2) I have, they both result in the same thing, BUT if I manually push the little lever it does make it idle up and down slightly. I'm thinking its not that...

But I did pull the cover off the throttle body and compared to when I looked at it before it looks like its REALLY getting a lot of fuel dumped in it. I can literally see it all but pooling up on top of the butterfly at warmed up idle. Would the CPS cause that? That would have been the only thing that really could have gotten soaked when washing the thing the other day.

I'm just thinking if its fuel related, it doesnt seem likely that its gonna run great one day, and then flooded and like crap the next. I guess I could have a clogged return line, but I just put in the tank and new lines and filter etc.

So should I try a cps? Is that even something that causes these kind of symptoms?

also my whole exhaust sucks, could it be an exhaust issue? From when it was doing this a week or so ago, I havent touched the exhaust and it went from not running good, to running good, back to not. crappy exhaust stayed the same.

cps would have nothing to do with the extra fuel (if that's the problem) - for that check the MAP sensor that is actually hooked up properly and that the output is correct (something like 0.6v at idle, 4.6v at wot, not exactly that but somewhere around those values, if you have >1v at idle that could be your problem for example). also, what's your fuel pressure and is your injector leaking any fuel when the engine is not running?

[Backroads]

Ill have to check and see if its leaking. not taht I was aware of.

I guess its possible the MAP got wet when I opened the hood and had some drippage, its right there ready to get dripped on...

I dont have any kind of gauge to test fuel pressure. Whats a cheap something to buy for that? I went and asked about it before at a local store and it was astronomical!

[Backroads]

injector is not leaking. The top of the butterfly is dry now thats its been sitting for an hour or so. I did pull the vacuum hose for the MAP sensor earlier and it actually wanted to stall when I did that. I duno if that means its working properly or not. Going to attempt to test it later.

jeffy; the problem with my voltmeter is the prongs are too big and there are rubber grommets at the back of all the sensor plugs, theres no real way to get in there to contact any metal without breaking it apart...Thats what I was looking for tricks on how to do..

[sharpxmen]

injector is not leaking. The top of the butterfly is dry now thats its been sitting for an hour or so. I did pull the vacuum hose for the MAP sensor earlier and it actually wanted to stall when I did that. I duno if that means its working properly or not. Going to attempt to test it later.

jeffy; the problem with my voltmeter is the prongs are too big and there are rubber grommets at the back of all the sensor plugs, theres no real way to get in there to contact any metal without breaking it apart...Thats what I was looking for tricks on how to do..

if it was about to stall when you pulled the vac line off the MAP would indicate that it works so start with the fuel pressure. I had my return plugged and my pressure was going nuts.

how's your O2 sensor?

[Backroads]

o2 is old and ugly. just like the rest of my exhaust haha

[sharpxmen]

o2 is old and ugly. just like the rest of my exhaust haha

just something to consider though

[Backroads]

just something to consider though

you got it!!!!!


Well sorta...I did however figure it out. After trying EVERYTHING I could short of replacing the whole damn engine.

So last friday I checked my belts, which included reaching under the intake/exhaust mani to loose up the pivot bolt for the power steering. WELL I must have tweaked the manifolds enough to cause a leak. Here I found the bolts to the firewall side of the engine that hold the intake/exhaust mani on were just a bit loose. So it was 1 leaking exhaust causing all the popping and backfiring. 2 it was leaning itself out with a vacuum leak on the intake mani, causing it to overfuel which explains it eating up a tank of gas as well as all the backfiring!

So I snugged those bolts up and its purrs like a kitten.

Damn simple crap gets me every time!

Thanks a million for all the help guys!

[Torch_Ind]

you got it!!!!!


Well sorta...I did however figure it out. After trying EVERYTHING I could short of replacing the whole damn engine.

So last friday I checked my belts, which included reaching under the intake/exhaust mani to loose up the pivot bolt for the power steering. WELL I must have tweaked the manifolds enough to cause a leak. Here I found the bolts to the firewall side of the engine that hold the intake/exhaust mani on were just a bit loose. So it was 1 leaking exhaust causing all the popping and backfiring. 2 it was leaning itself out with a vacuum leak on the intake mani, causing it to overfuel which explains it eating up a tank of gas as well as all the backfiring!

So I snugged those bolts up and its purrs like a kitten.

Damn simple crap gets me every time!

Thanks a million for all the help guys!

  awesome these small things really put egg on your face but there cheep fix to!!! lol just glad you found your problem thats all that matters in the end!!