4.0 YJ Missing

[xJ33Px]

My buddy just bought a 1993 Wrangler 4.0 5spd. He replaced the Plugs, wires, cap, and rotor and its still missing. It sputters from idle all the way through the RPMs. I took off the throttle body and cleaned it all up and cleaned the IAT. Hes throwing a code for IAT. It was pretty gunked up and I cleaned it all up for the most part. All the plugs are clean but two. Two were a little black. He also has ALOT of blowby coming into the airbox and into the throttle body. Any idea? I thought maybe a cracked injector for the whole missing and random black plugs.

[WillyNilly]

did he get the firing order right? double check the distributer is on in the rite position.... then check spark

[xJ33Px]

I checked the wires they are all in the right position. All the plugs are getting spark I checked that too.

[spunebil]

it could be a flat cam lobe

bad rocker arm

burnt valve

worn pushrod


they all could be problem besides the obvious electrical and injection ones

[xJ33Px]

For right now we are thinking the positive thoughts, that its something small!!! Haha

[WillyNilly]

way to send out the fear spune! just cause you got sent to jail today doesnt mean you can be mean!

[Guest]

If it is blowing back into the air box it would have some thing to do with an intake valve. Spune (aka Mr. Criminal) may be on the right track with his dire prognostications.

[xJ33Px]

So if I just find a good head it would probably be easier and cheaper than rebuilding the stock one.

[Guest]

My suggestion would be to check the compression on each cylinder first to be sure that's what the problem is. If there are one or two cylinders with bad valves they will show up as being low on compression.

If that turns out to be the case you then have the choice of doing a valve job on that head or as you suggest, buying a different one.

I'd hate to see you buy a different head without being sure of the diagnosis first.

[xJ33Px]

Oh I would for sure do a compression test first haha. I have a comp. tester here at the house so thats the plan tomorrow. Its throwing a code for Intake Air Temp and I cleaned it all up but it had so much gunk built up I think its just trashed. Buying a new one tomorrow and trying it out. That could make it run rich/lean but it shouldn't cause a miss. Oh well replacing bad parts along the way anyways. Never a bad thing.

[Guest]

If it is blowing compression back through an intake valve that could very well be affecting the intake temperature sensor.

[xJ33Px]

Yea the whole throttle body is covered in oil, inside and the tube wasn't real tight so it was blowing on the outside of the throttle body too. It's a good amount of oil thats for sure.