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Engine cuts off for a second???

AJsArmor

NAXJA Forum User
Location
Iowa
Fixed the cooling issues I was having in my 89, works perfectly...but now another problem reared it's ugly head. Driving it down the road and BAM- from the rearend...first thought is something is very wrong with the powertrax locker back there. A little longer down the road it does it again and so on and so on all the way home, maybe getting a little bit worse as I go. I watched the tach and saw the rpm's drop right off when it happens, so the rearend thing is just a result of the engine flipping on and off quick.

Here's the skinny....89XJ, 4.0, AW4..blah blah... It did something similar to this awhile ago and it was the EGR solenoid, haven't checked it yet. What else could cause this? I had the CPS go bad last year, so it's not that old and it's never failed to start since replacing that. O2 sensor was replaced last year as well. Other than the engine cutting off it runs just fine. Can sit there and let it idle and it will never cut off, just going down the road...doesn't matter if it's under load or flat surface. I'm heading out now to check that stinking EGR solenoid, but any other causes of this???
 
My guess would have been CPS, but you said it was just replaced in the past year...hmmm...those were the same symptoms I had when mine went out - RPMs on the tach would just drop to zero, like the whole vehicle was shut off...then all the sudden it would kick back on....
 
renix xjs have a whole pile of places that can cause spooky stuff like this. neither of my 89's have the dreaded c101 connector but they can cause this and other things. there are several relays that can get corroded inside and fail and cause this type of behavior. bad grounds can do this too.

all that having been said the first place i would check is the connector on that year old cps. if it's scungy and corroded it definitely can do that. the randomness and recurrence of the problem would seem to indicate some thing in the critical circuits for ignition has a bad connection. if you don't have it already i strongly recommend the renix manual from the factory. it is commonly available on the web in a scanned pdf format. pm me if google doesn't turn it right up.
 
EGR solenoid is fine. I eliminated the CPS connector and just soldered it. If it were acting up, wouldn't it outright just kill the engine at idle since the rpm's are so low? While I was going through a few connectors I let it idle for a good 30 minutes, reached temp and ran fine. Guess it's time to grab some contact cleaner and go crazy.
 
Check to make sure that the CPS harness hasn't burned through on the exhaust manifold - I've had that happen, and the symptoms are as you describe. It will rest against the tube and short out - the vibration from the engine cutting out will shake the wiring loose.

Also, check (and clean!) the ground from the cylidner head to the firewall - it's the primary chassis ground, and it's known as the "RENIX Killer."

That's what comes to mind first.
 
AJsArmor said:
Fixed the cooling issues I was having in my 89, works perfectly...but now another problem reared it's ugly head. Driving it down the road and BAM- from the rearend...first thought is something is very wrong with the powertrax locker back there. A little longer down the road it does it again and so on and so on all the way home, maybe getting a little bit worse as I go. I watched the tach and saw the rpm's drop right off when it happens, so the rearend thing is just a result of the engine flipping on and off quick.

Here's the skinny....89XJ, 4.0, AW4..blah blah... It did something similar to this awhile ago and it was the EGR solenoid, haven't checked it yet. What else could cause this? I had the CPS go bad last year, so it's not that old and it's never failed to start since replacing that. O2 sensor was replaced last year as well. Other than the engine cutting off it runs just fine. Can sit there and let it idle and it will never cut off, just going down the road...doesn't matter if it's under load or flat surface. I'm heading out now to check that stinking EGR solenoid, but any other causes of this???

My 87 does this. Theres a wiring harness that runs from the driverside down near the bottom of the radiator, around the the passenger side and then spiders out from there. That harness catches part of the front clip and tends to wear through one of the wires there cutting my engine out. I've rerouted it twice, wrapped it in rubber and plastic, eventually it wears through again. Once it managed to catch fire. Now I finally have it routed in a fashion that its not happening, but its something you should check before it does what mine did ;)

wires.jpg
 
That's a nasty mess, I'll have to check mine and see if there's any signs of wear. But I think I got it fixed! New coil, cap and rotor and it's running good again. Ahhh...back to driving an XJ.
 
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