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The vacuum leak idea is just a shot but another forum I'm on has had people report leaks in the brake booster / hose as a cause of intermittent stumbling.
HTH
If they are loose - do NOT OVERTIGHTEN! The studs are especially prone to snapping off & they all get 23 ft/lbs., if I recall correctly. (At least on my 4.0L.) I have the torque values etc on my site on this page:
INTAKE ? EXHAUST MANIFOLD TORQUE VALUES & TIGHTENING SEQUENCE
This page is for the older RENIX XJ's but other than some head port changes & HO exhausts not having the EGR tubing it should (SHOULD) be the same for all year 4.0L's.
Next time it doesn't start up - lift the hood & unplug then replug the Crankshaft Position Sensor connector. (Back of head, driver side on US models, wire runs from harness to nearly hidden sensor on upper area of bell housing - diagram on my website.)
Failing Crank sensors are a very, very common issue & often are intermittent until they finally crap out entirely. Connector is probably oxidized & morning moisture is causing enough extra resistance to prevent signal pulse from reaching computer.
Give it a try & let us know how it goes.
I was hoping someone might be able to help. Hopefully, I can phrase my problem correctly....
I have a 2000 Cherokee Sport 4.0 auto. It has 98000 miles on it, I bought it new and kept up all the maintenance.
About two weeks ago, it started giving me problems with hot start after a really hot day driving with the A/C on. It started fine cold. When hot, I had to really give it gas to get it to start and not immediately stall out. After a few minutes, the idle leveled out and all was well.
A week later, the condition reversed. Hot starts were easy; one crank and good, no rough idle. Cold starts became troublesome, long crank, rev the engine until it levels out, all is well. Unfortunately, the cranks are wearing down the battery and the problem is one my local mechanic can't nail down. His only comment was the battery seemed drained-- 11 volts (no wonder with all the cranking). I plan on replacing it as it's four years old already and probably won't cut it for a New England winter, but I'm skeptical that it's the problem.
Any thoughts? TPS? CPS? Coolant sensor? Plugs are three months old, Champion truck. I have the Haynes manual and I was planning on checking voltage resistance on each sensor.
BTW, I checked the forum already and saw the bit about priming the fuel pump by switching it on and off twice. It seems to make no difference.
Any and all suggestions would be great.
Thanks in advance.
--John
TPS voltages check out across the sweep range? (A Digital volt meter might miss any dead spots -heck an analog might miss a dead spot too but an old school volt meter with a needle will catch a dead spot easier.)
Wait a minute - I just re-read your post... Let me double check my understanding:
Idles well while in Drive or Reverse... but does not rev up?
Revs up in Park or Neutral.... but will not idle?
Thank you.
As to the stutter when braking: check your brake booster vacuum hose. Also a possibility that the booster has an internal rupture though not common.
Idle air controller (idle stepper motor) located on throttle body could be sticking as well & is a common pest with idle issues. Easy enough to remove from throttle body & clean.
Also, when on long car trips on the highway, the "Trans Over Temp" light on the dash comes on. I checked the transmission fluid dipstick and there is plenty in there, and there is also plenty antifreeze.
Any advice?
the other prob dont have a clue
Have a 2000 4.0 L Cherokee Sport. Have been having a problem with rough idle as well. At first thought it may be a PCM memory issue. I found battery conections badly corroded so I replaced them and cleaned and tightened all grounds in engine compartment. Worked Good after I reset memory settings.
Problem cleared up for 2 weeks as we ran through a full tank of Premium gas and fuel inj. cleaner. Now we are getting to less than 1/4 tank and the problem returned today. Runs great above idle. Now suspecting fuel issue.
I have read the stepper motor issues and will give that a try. Was kinda wondering if I may have a filter/pressure regulator issue at idle. Am gonna try that as well when I get time.
Does anyone have any other ideas?
Above info does not apply to HO engines - RENIX (Closed cooling system) only.
I am in Atlanta and traveling to Pittsburgh tomorow for a short term job for great money. I would have to spend a couple hundred to rent a car. Please Help!
Tom
If you have a mechanic go to them and ask about the computer. It may be the fuel pump. Have them check. Our computer went. We bought a refurbished on the internet because a brand new one costs $800 with out installation. It only costs $300 for a used one but the catch is you need to send them your old computer back to them. It worked out great and the car runs fine. Hope this helps!
Lisa
tidester, host
SUVs and Smart Shopper
Anyone with hands on experience, please feel free to jump right in here!
tidester, host
SUVs and Smart Shopper
tidester, host
SUVs and Smart Shopper