• Help Support Hardline Crawlers :

Jeep 4.0 running like poo

Beerj

Sonzabitches!
Joined
Dec 7, 2014
Messages
3,925
Location
Amish Country
I know some of y'all are/were jeep guys. I've got a 94' yj 4.0 that is running like it's missing across all rpms. Starts fine and idles fine (except for the miss). The jeep sat for quite some time but I made sure to start it every month or so. Back in August I went to move it to a friend's house and as soon as it started is when the problem began. No warning signs prior. Fast forward to a few weeks ago when I went to move it back home and the fuel pump was dead. Trailer'd it home, replaced the pump and we're right back to rough running. All cylinders have spark and all injectors ohm'd out ok. I'm leaning towards it being a sensor just due to the suddenness of the issue but I've never really had to deal with any running issues on a 4.0. Anyone have any ideas as to where to start? I'd rather not just throw a bunch of money at it replacing all of the sensors since I have a prospective buyer. But if anyone has any ideas what might be the most likely culprit, at least I'll be able to trouble shoot this by focusing on the best bet first. Thanks in advance.
 
Let it run a while if the battery has been disconnected. If that doesn't fix it drain and replace fuel. Ethonal fuel sucks.

Sent from my XT1635-01 using Tapatalk
 
You could also do a tune up including replacing the coil. That shouldn't cost too much or be too complicated, and could rule out several things at once.
 
I only pulled the #1 plug. In my testing, when I pulled the #1 plug wire it didn't change how it ran but shocked the **** outta me. The plug seemed fine, wasn't wet or fouled. I am, however, getting a 27 code. 27: Logic module fuel circuit internal problem or TBI injector does not respond properly to control signal. Could point to a bad injector but I was also unplugging some injectors while it was running to see if it made a difference.
 
I'm leaning towards injector right now. Pulled #1 wire, no change. Pulled #2 wire, bogged and recovered. Plugged wire 2 into #1 injector, no change. Plugged wire 1 into #2, recovers. So both wires help injector #2 but neither helps #1. Sound plausible?
 
Yep. Injector. Go ahead and stick the 4 port injectors in their if you feel like screwing with doing all of them.
 
I know the new injectors say they come with orings. Probably just where they go into the intake. Should be able to find some for the rail side. Dude buying the jeep ordered 6 new 4 port injectors so at least I'm not fronting the bill on that one. Thanks guys!
 
Fuel pumps are notorious for those symptoms as well. They are in the tank and rarely get replaced. You can clean injectors and pulse them very easy with brake clean and a battery. Its clear to see the spray pattern.
 
cbrjeeper said:
Fuel pumps are notorious for those symptoms as well. They are in the tank and rarely get replaced. You can clean injectors and pulse them very easy with brake clean and a battery. Its clear to see the spray pattern.
We had a fuel pump go bad on our juggy (98 xj 4.0) Similar symptoms. Before you do anything check the pressure at the rail with a fuel pressure gauge. They also have a check valve in the return side that can cause problems also.
 
I second the fuel pump. Ethonal fuel is rough on them when they sit. I've pulled pumps less than a year old that are rusted and clogged up.

Sent from my XT1635-01 using Tapatalk
 
Take a test light and push into each of the top of the plug boots on the distributor. It will run tougher on all the good cylinders and not change on the bad one. That will indicate your bad injector/s.
 
Lol. Guess I should update. Replaced all 6 injectors and she purrs like a kitten now. New owner is beside himself happy.
 

Latest posts

Top