jlmclean

I have an 86 Jeep Wagoneer with the straight 4.0 6 cyl engine, Renix electronic system, Auto Trans. It has a free run miss. While driving up hill under acceleration, it runs fine. Going downhill under deceleration, it runs fine. When you move the throttle between acceleration and deceleration, it will misfire, it’s a jerking uneven misfire and does the same thing between deceleration and acceleration and does the same jerking misfire when you’re on level road and just trying to hold an even speed. It also does it when taking off from a standstill if you take off in a normal matter. You can take off like you’re on a drag strip and it doesn’t miss. Another thing I’ve noticed lately is that when you let off the throttle and coasting to a stop, you can hear the engine surging up and down in RPM, no miss but just the surging. I’ve worked with the throttle position sensor some but it doesn’t seem to make any difference and all the plugs, wires , cap etc are in good condition. Any help is greatly appreciated.

highmileage

Go to Cruisers' tips in the info threads, or to Cruisers' page, he has alot of Renix tips there to start.

cruiser54

https://www.cherokeeforum.com/f51/cr...x-tips-153657/

jlmclean

Thanks for the replies. I had a typo, it’s an ‘88 instead ofan ‘86. Cruiser, I’m glad you replied to my post. You’re the reason I found theCherokee Forum. I have used the Jeep Forum some but found this one when someonehad posted a link to your tips. First, thanks for putting so many helpful and “GOOD”tips out there for Jeep owners, GREAT JOB. You covered some of the areas I’ve questionedfor some time. Let me give a few more details about my misfire. I replaced myoriginal engine with a low mileage engine out of a wreck. It had a brokenintake so I basically used all my Renix components on the replacement engine.From day one after the swap, It would have a random miss on take off for thefirst couple times you’d stop and take off in the mornings. Since I had most ofthe sensors, I’ve switched some of them, installed new injectors, I did cleanthe two ground wires but didn’t upgrade them, replaced the CPS with a MOPARreplacement, tested all the sensors (according to the test in the manuals) andnumerous other things but never got that little miss out of it. Occasionally, I’vegot it to the point it wouldn’t miss for a couple days but it has always cameback. I finally just gave up and drove it like that for the last couple years.Seemed like if you’d warm it up a few minutes before you’d leave out with it inthe mornings, it didn’t miss that bad or even at all. It has gotten worse overtime and is now getting to the point it aggravates you to drive it. I’m goingto do most of the tips you have posted and hopefully one of them will cure theproblem. My question is, if you were working on it, which one would you dofirst and in what order?

cruiser54

They're already prioritized for your convenience. 1 through 8. And 13.

Have you ever sprayed carb cleaner along your intake to head mating surface? If you used an HO intake/exhaust gakset instead of a REnix one, you can get a vacuum leak there.

WE will figure this out.

Check your CPS wire routing while you're poking around.

cruiser54

Here's a diagram of the CPS wire routing.