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Discussion Starter · #1 · (Edited)
95 YJ 4.0L 5 Spd.

let's start the list

replaced already:
TP sensor
O2 sensor
crank position sensor
idle air controller
map sensor
plugs, wire, cap, rotor
coil & 2 wires going to coil from ecm
timing good
excellent fuel pressure, compression & spark readings
fuel pump
fuel filter
no fault codes

so it takes quite a few extra cranks to get it started, idles rough, and most of the time backfires like a 12 gauge is going off. leads me to believe i'm not igniting the fuel efficiently. eventually will hold idle, however will bog down intermittently. haven't taken it on a long trip in awhile, no more then 5 minutes, but it used to randomly shut off. the only thing i can think of is the electrical signal to the coil is insufficient or messed up, leading me again to beleive it may be the ECM. I'm hoping that's not it and someone has had something like this and gimmie a direction to look at next.
 

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Did it just start to do this or did you swap a new motor in or did you do anything to the motor like upgrades or a cam swap........?
 

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Discussion Starter · #5 ·
everything is original-spec. no swap or upgrades. just decided to start doing this one day. we did find that we could get it to cut out by fiddling with the wires going into the coil, but as i said i've replaced those and since then have tried to mess with them again, and I get no negative response. no error codes either.
 

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Always good to make sure you have a good ground to the engine block.

Maybe bad computer, have you tried that?


Or try adjusting the timing some more. If you have excessive miles on it the timing chain could be streched and need adjusting for that.
 

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have you chaecked tha cat? if its overfueling (leaking injector, etc) then the excess unburnt fuel can get into the cat, ignite there, and appears as a backfire
 

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Check your fuel regulator, am sure thats it

Hey..Mine was doing the SAME thing !! few extra cranks.. then the backfires..Oh yeah.. Thought the timing was off..thought alot of different things like you really. It turned out it was the fuel regulator. Gas was getting thru it. going right to the cylinders causing the backfire. and also causing the hard start.. Check that.. Am sure thats the problem.. Easy to check and fix too. Start it up pull that little hose off the end of regulator. If gas is getting thru it. Then theres your problem.. about 70 bucks and five minutes to change it, and your rollin'..
 

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Discussion Starter · #9 ·
Forgot to add grounds in there, I went thru and cleaned all the grounds and tightened them all up.

I haven't replaced the ECM, trying to stay away from that since it's the most expensive.

No cat on this jeep, just a replacement pipe where it used to be.
 

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sim sim balla bim
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Did you have the distributor out at all? The only way the timing could be off is if it was maybe one tooth off as it is not ajustable. All the wires correct?
 

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Forgot to add grounds in there, I went thru and cleaned all the grounds and tightened them all up.

I haven't replaced the ECM, trying to stay away from that since it's the most expensive.

No cat on this jeep, just a replacement pipe where it used to be.
Did you clean the grounds to the ECM, too? Often its grounded through the case where its bolted to the body. Remove it, sand between them.
 

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Discussion Starter · #12 · (Edited)
new information:

no blow by at the fuel regulator
removed ECM, cleaned it, no ground hidden behind it

incase I didn't clarify in earlier posts, the main issue is prolonged cranking to start, then accelerator needing to be applied gently for it to grab idle, then it holds idle. when i started it this morning, no backfiring, just about 30-40 cranks for it to start. Also, say I get it to start and it let it run for 5 minutes or more. it'll start up just fine the rest of the day. but if i let it sit overnight or what i assume would be let it sit until it cools down completely, that's when the prolonged starting takes place

Did you have the distributor out at all? The only way the timing could be off is if it was maybe one tooth off as it is not ajustable. All the wires correct?
I've never taken the distributor out and all wires are correct. when we did the major portion of the diagnosis when it wouldn't start at all (or so we thought) when we were checking for spark the damn thing fired up on 5 cylinders. go figure.

I really appreciate everyones help, you guys are top notch.
 

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HURL SCOUTS
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i know you said you had good fuel pressure, when is the last time you changed the fuel filter or checked the screen on the sender in the tank?
 

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i have a 95yj 2.5l 5 speed. mine did the same thing so me and my dad did all the stuff you did fuelpump, fuel filter to much to say but it turned out to be the main cumputer i think its called ecm. good luck.
 

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ummmm.....check your exhaust system i had a chevy pickup do similar....it was a stupid flap of rusted metal in the pipe that actually blocked the flow intermitentally into the muffler. i know its way out there but its a possibility.

could also be your ecm is all wacked out
 

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Discussion Starter · #18 ·
ummmm.....check your exhaust system i had a chevy pickup do similar....it was a stupid flap of rusted metal in the pipe that actually blocked the flow intermitentally into the muffler. i know its way out there but its a possibility.

could also be your ecm is all wacked out
exhuast just went thru last week, finally welded up all the gaps but thanks for the help
 

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cheese
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Cam sensor in distributor? Had to replace the distributor in my '93 because the wire harness had no pins left. Hate to ask but... How old is the fuel?
 

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Dirty fuel injectors?


Have you tried the carb cleaner into the intake as mentioned above? If it starts right up with that then you are not getting fuel.

Or tried pulling the plugs to see if they are wet? If they are wet you are getting too much fuel or not enough spark if any.


That would rule out fuel issues.


Then check spark to each plug.
 
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