Unusual sensor problem
Thread Starter
CF Veteran
Joined: Jan 2009
Posts: 1,964
Likes: 6
From: Baltimore, Maryland
Year: 1994 1993
Model: Cherokee
Engine: 4.0
Well, I put a big layer of JB Weld on the exhuast crack. I don't know if it just needed to cure overnight but after several hours I drove to the gas station. Needless to say I had smoke pouring out from under the hood. The JB weld stuff turned black and the crack reappeared.
Thread Starter
CF Veteran
Joined: Jan 2009
Posts: 1,964
Likes: 6
From: Baltimore, Maryland
Year: 1994 1993
Model: Cherokee
Engine: 4.0
First off thanks for all the helpful advice I`ve gotten on this. Especially those wise enough to suggest a groud problem.
I'm sure I`ll jinx myself by saying this but I think after more than 2 years dealing with this problem I have stumbled upon the cause of all this ...Recently I had come to the conclusion that it had to be some sort of common ground problem after looking over the wiring diagram and noting that all the sensors seem to use the same blue/black ground wires and that at various points they combine into one wire...So a few days I ago I figured I`d start tracing every single one of those ground wires from end to end...I started with the ones coming off the O2 sensor, CTS, TPS etc as they are all right in the front and on top and easy to get to...I'm sure everyone is aware that all those wires run thru that long 1" or so square black plastic housing which runs between the fuel rail and the valve cover.
Anyway I started undoing all the plastic wire loom and electrical tape and finally took the top off that long black plastic housing and I noticed that at the rear end of it closest to the fire wall the blue/black wires from all those front sensors (Maybe 4-5 total) went into some sort of fat hard heat shrink looking thing where I suppose in some way they are combined into one wire since from that thing on back only one blue/black wire continues into the wiring harness along the firewall...I poked and pulled at that thing a bit as I pondered how they combined all the wires into one inside and figured I`d make that my first point to take apart this weekend and check.
Now here it is 3 days later and the check engine light has not popped on yet!...There were certain things that made it come on daily without fail and I have gone out of my way to make sure I do all those things far more than normal and I can`t make it come on at all..I cleared out the codes from the computer last night after work and then went out for 2 hours driving and parking and backing up etc and even though anyone of 20 things I did should have caused that check engine light to appear as it has for 2+ years it never came on and the Jeeps ran perfectly...I suppose just pulling and messing with that wire connection somehow caused something which wasnt touching to touch or something that wasnt suppose to be touching to untouch...I'll wait untill Friday when I am off and if it still hasn`t came back on I`ll either take that thing apart and re attach and joing the wires inside or just cut it out and splice in another junction from a newer junkyard Jeep.
Keep your fingers crossed!
I'm sure I`ll jinx myself by saying this but I think after more than 2 years dealing with this problem I have stumbled upon the cause of all this ...Recently I had come to the conclusion that it had to be some sort of common ground problem after looking over the wiring diagram and noting that all the sensors seem to use the same blue/black ground wires and that at various points they combine into one wire...So a few days I ago I figured I`d start tracing every single one of those ground wires from end to end...I started with the ones coming off the O2 sensor, CTS, TPS etc as they are all right in the front and on top and easy to get to...I'm sure everyone is aware that all those wires run thru that long 1" or so square black plastic housing which runs between the fuel rail and the valve cover.
Anyway I started undoing all the plastic wire loom and electrical tape and finally took the top off that long black plastic housing and I noticed that at the rear end of it closest to the fire wall the blue/black wires from all those front sensors (Maybe 4-5 total) went into some sort of fat hard heat shrink looking thing where I suppose in some way they are combined into one wire since from that thing on back only one blue/black wire continues into the wiring harness along the firewall...I poked and pulled at that thing a bit as I pondered how they combined all the wires into one inside and figured I`d make that my first point to take apart this weekend and check.
Now here it is 3 days later and the check engine light has not popped on yet!...There were certain things that made it come on daily without fail and I have gone out of my way to make sure I do all those things far more than normal and I can`t make it come on at all..I cleared out the codes from the computer last night after work and then went out for 2 hours driving and parking and backing up etc and even though anyone of 20 things I did should have caused that check engine light to appear as it has for 2+ years it never came on and the Jeeps ran perfectly...I suppose just pulling and messing with that wire connection somehow caused something which wasnt touching to touch or something that wasnt suppose to be touching to untouch...I'll wait untill Friday when I am off and if it still hasn`t came back on I`ll either take that thing apart and re attach and joing the wires inside or just cut it out and splice in another junction from a newer junkyard Jeep.
Keep your fingers crossed!
Last edited by Programbo; Aug 6, 2009 at 06:08 AM. Reason: More info
Member
Joined: May 2011
Posts: 199
Likes: 0
From: lewiston,maine
Year: 1999
Model: Cherokee
Engine: 4.0 straight 6
I cut the connectirs off and hardwwired my crank shaft sensor n theres no puttin or hesitation while drivingg and check engine light is no longer on
Senior Member
Joined: Jun 2009
Posts: 553
Likes: 1
From: West Texas
Year: 1991
Model: Cherokee
Engine: 4.0 L

Mr. Programbo..........
more than likely what happened to you is something like this.....
when your motor mount bolts broke, and your engine "toppled" within the engine compartment, you "mashed" or "grated" some of the wiring harness contents, grounds, sensor attachment wires etc etc. (FYI...when the production line assembles cars/trucks/jeeps there is only so much length the wiring harness is allowed when its built, its engineered that way for a reason. ) ergo, engine falls, wires stretch.
and by you going through and checking each one over time, you may have inadvertently stumbled on one of those connections, grounds, whatever that became stressed during that period...then by connecting, unconnecting, toying, fidgeting, browsing, cursing, belching, what-have-you, you may have properly re-seated the culprit (ground pin in a connector for instance).
so I wish you well, and glad you seemed to have nailed it.
one thing though, you were lucky the distributor held, you'd a had a LOT more problems had that not caught the motor!
cheers!
cpnwrench
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