4.0 trouble

SPOA87YJ

SPOA87YJ

Well-Known Member
Joined
Oct 28, 2005
Location
Charlotte
Most of you know that I've been having alot of trouble out of my 4.0 since Fall Crawl. I'll save the story and get on with the tech.

I have installed NEW:

Rotor button
Dizzy cap
Air Filter
Fuel Filter
Plug Wires
Plugs (first set was bosch platinum they fouled out, so installed NGKs)

Now, I'm getting fuel at the rail, and it is cycling back to the tank as it should. I'm running an e2000 as I have been for about 2 years. Its working fine. I have spark, and a full tank of fuel.

The motor is a 92 4.0ho out of an xj that I swapped into my yj. It has been running like a top for the past 2 years, never had any trouble. I'm 99.999999% its my wiring. I kept the original harness from the xj and paid/worked with a guy who helped me strip it down to the essentials.

I ran it this way for around year and a half. No trouble. One day my stock gauges decided to quit working completely, lights would cut out etc. Stripped all that mess out, built new dash yada yada. I now have 5 gauges, some switches, and some other stuff. The rig is pretty much bare bones when it comes to wiring. I just can't figure out why it won't run.

Sometimes I'll walk out to the garage it will crank first try and run. Other times it won't crank for a whole week. If it does crank it will run for around 15 minutes then just quit. Other times it runs for 1 minute and will quit. It fired this afternoon so I drove it around the parking lot and then let it run for around 10 minutes in the garage, ran great. Then I backed it out for a second to move some stuff around and it cut off. Wouldn't crank back for around 2 hours. Then it just fired right up and I pulled it in.

Maybe its a sensor? Some people have mentioned CPS, and auto shutdown relay. I don't think its the CPS as it will fire and run fine at times but who knows? Also, I have no auto shut down relay as the guy I paid to wire it stripped everything out. I have the xj computer running the motor and none of the other stock stuff.

SO anyone got any ideas?
 
I know you say you have fuel, but have you checked the actual pressure? Especially when it won't run. e2000 pumps are hit and miss for reliability after being swapped into something.

Sure does sound like the typical cps problems too though. You can test it with a multimeter, but it's almost not worth worrying about. Especially since they are almost certain to die at somepoint shitty anyway.
 
I haven't put a gauge on the fuel yet. So I'm not sure exactly what pressure it has. It does spit out of the valve on the rail though.

You think it'd be worth my time to go ahead and install a new CPS anyways? I guess that way I could rule it out of the equation, and look at it as forced maintenance.
 
Sounds like the pick up coil is going bad, or the wiring going to it. The distributors on those are common for problems. The rebuilt replacment from autozone is like 55 bucks. I would start there. Then check out the cps. Does not sound like a cps to me though.
 
I didn't think so either, I feel like if it was it wouldn't want to run at all instead of being so intermittent.
 
The reason I bring it up is I replaced a crank sensor on a 92 a while ago for close to the same problem. It would decide whether it wanted to run or not and when. Cost him a starter as well. The CPS, shitty batt cables, and the NSS are going to be the cause of a sudden non-start on an xj 90% of the time...

Before buying anything, try cleaning the cps connector that sits over the intake manifold and see if anything changes.
 
Will do, thanks for the advice guys. I'm not ruling anything out bc I know nothing at this point. Just looking for some direction.
 
Crank sensor at the dealership we see more crank sensor problems then anything else. I usually keep a spare in my glove box because you just never know when it's going to die.
 
have you taken out a plug, put the wire back on the plug, and grounded the plug to check for spark? Make sure you have the plug grounded or you'll get a little jolt, while someone is cranking it. This will positively identify in what aspect the problem is Ignition/fuel, etc.

If I had to guess, id say bad ground somewhere on something, and CPS
 
i'd second/third/whatever the cps. my brother's wj was having intermittent problems cutting off, not starting, etc. would fire up sometimes and others it wouldn't start for a few hours.

if it's not starting like you say, check for spark from the coil. if you don't have it and the motor is turning i'd say replace the cps because that's what tells the coil to fire if i remember correctly.

if it's not that I have no other advice! :) let us know how it goes man
 
Changed the CPS and so far so good. Cranks every time. Tried it about 5 times and let it run for a few and it always cranked. So as far as I can tell that was the issue. The old sensor had a small amount of dirt on it, but nothing to crazy. Haven't got to drive it yet, but I plan to tomorrow.
 
Thanks Chad.

Turns out its not fixed however. Dunno what the problem is, drove it all the way across town then sitting at a light it just cut off. Wouldn't crank back same scenario. Got a ride home from a friend on the strap about an hour ago. I'm done with this for a while I'm just gonna let it rot in the garage. Maybe I'll figure it out one of these days :shaking:
 
pick up coil..
 
Check all chassis grounds,also coud be feul pump going bad.They will come and go,messed with my dodge for a month,finally changed feul pump, not missed a lick since.
 
Sounds like either bad ground or cps... had same prob with my zj replaced everything and cps was last thing! ran great till it blew.
 
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