Alert from CNET Staff

 Attention forum users:  We want you to try out the new CNET forums platform! Click here to read the details. Thanks!

Car Tech forum: JEEP... SENSORS and PCMs FIXES FOUND

by: Cat5 Cane March 19, 2009 7:43 AM PDT

Like this

0 people like this thread

Staff pick


by Cat5 Cane - 3/19/09 7:43 AM


Strange... check your sensors
by Cat5 Cane - 2/16/09 6:47 AM In reply to: Very strange. by tintinuae
Yours sounds like it is more of an electrical/transmission (sensor) failure, then an engine failure (but the coil and plugs or injectors could come into play)... throw in a heavy dose of Lucas gas treatment to clean injectors.

I'm not a mechanic but have been here, it seems forever...

First Check diagnostics codes before disconnecting battery... then disconnect the PCM plugs (remember the order), clean the tips with CRC electronic cleaner, let set for 2 hours, then reattach the PCM plugs, then the battery... thinking it should erase the codes and car might work properly for a short time until the computer resets to the information from the sensors, if bad... it will go back to screwing up after one hour to a weeks time.

two sensors come into play... Camshaft position sensor and the crankshaft position sensor. I went on line to auto zone directory...

Crankshaft Position Sensor Operation:
A magnetic or hall effect sensor that provides the computer with the engine speed and crankshaft position so proper injector sequence and ignition spark can be determined. It allows the ECC or PCM (engine control computer) to change injector openings as the engine RPM changes. It also signals the coil packs to fire the spark plugs.

Camshaft Position Sensor Operation:
A magnetic or hall effect sensor. It sends a signal to the computer relaying information about shaft speed, position and acceleration or deceleration. This information determines when the fuel/air mixture needs to be ignited and how much mixture is needed for the engine.

Go to site and read How to... Inspect, test and service... Lots of good info

JMO... Sensors are critical keys to running right and to buy Jeep sensor parts... not auto zone imitations.

Just an after thought. If still not fixed...By the way... also check/replace transmission filter and check Trans oil level

After you fix it... come back to tell everyone your answer to the fix... Be complete for the next guy...

That's all I got... good luck!!!

Billy's Misfire
by askyward - 2/28/09 4:11 AM In reply to: 1997 jeep g/c 4.0 spudder and stall issues by BillyTheJeep94/97
I feel your pain. Most of the replies to your post seem to be giving you great advice. I would echo one comment about the camshaft sensor, it cleared up some of my problems when I was getting misfire codes. I think you said you got a new distb, and most come with a new Cam sensor included in the distb. In fact the cost of the cam sensor is just a few bucks less than an entire new distributer at Autozone.
You mentioned that the problems surface after the car warms up. That reminded me of when I replaced my two O2 sensors that screw into the exhaust system. I had read in my repair manual that the PCM disregards those sensors until they reach operating temp and then make timing and mixture adjustments. I doubt that these sensors are the villain in your Jeep, but I just wanted to pass along that I got an instant 3 mpg increase!!
Its amazing how smart these PCMs are. How they learn to vary their outputs based on sensor inputs.(Just teasing Mr MCCain just a little bit)

For me, replacing my PCM with a truly rebuilt PCM was the turning point. I now have my reliable ZJ back once again, and this forum has been a great source of advice and direction. Good Luck!!
Mine's Fixed
by D E H - 3/18/09 4:11 PM
In reply to: Now try this by tintinuae
I have not read all the posts on here, but this was my experience.

For what it's worth to anyone, my 98 Cherokee 4.0L was sputtering, bucking (and stalled twice) in the mornings when the engine was cool and on occasion when it was warmed up it would do the same thing on a turn or from a dead stop, but always occurred under a light load (or about 25-40% throttle). I hooked up my scanner one morning for a cold start and recorded the O2 sensors (both) in relation to the throttle positioning sensor and mass air flow sensor. Less than a minute into the drive the bucking/ popping/ sputtering occurred under load. Luckily I looked over to my scanner and saw the O2 sensors were changing from open loop to closed loop (preprogrammed values- to reading the heated O2 sensors input) at that moment. I had attempted to repair this problem by the usual in the posts Ive read (cleaning PCM connectors, replacing the crank sensor etc...) to no avail. When I saw the erratic O2 sensor reading and saw that it happened when the heated O2 came online I decided it was time to replace the O2 and the heated O2 sensors. Let me preface the outcome with saying that this was one of the most frustrating diagnosis that I have had recently and the fact that the check eng. light NEVER CAME ON ONCE to give me some kind of help, nor was I able to pull any history codes from the PCM.

It's been about 5 or 6 months and I have not had one drivability issue with the Jeep. It drives soooo much smoother, holds it's rpm's longer when shifting providing a much smoother shift and it feels almost new (98,000mi. on the odometer)

Again, take this information as direction, not a sure fix. It might not hurt to print it and give it to a mechanic who has a graphing scanner and some patience.

Mine's Fixed Too. Does Recall E22 ring a bell?
by askyward - 3/18/09 11:43 PM
In reply to: Mine's Fixed by D E H
I changed my PCM and O2 sensors about the same time. Since then my trusty Jeep runs great. My previous posts stated what a remarkable improvement new O2 sensor made, and what an easy install.

But it reminds me of my original frustrations over a year ago. This all started after the dealer re-flashed the PCM with RECALL ITEM E22.

E22 triggers a "check engine light" when the CATALYTIC Converter fails. What sensors feed this PCM Reprogram??? The O2 sensors!!

The EPA mandated the E22 because jeepers were driving around polluting the world with faulty CATs but didnt know it. Jeep paid for a new CAT and reflashed the PCM per EPA orders. I'll bet they should a replaced the O2 sensors as part of the recall.

Maybe someday a pissed off Jeep owner/lawyer will figure this all out and prove that Jeep should use some of its bailout/stimulus $$$ to reimburse everyone in this forum.

Im sure I am just tired and paranoid, but I'll always wonder about the rocket scientists that drafted E22.


Bad... O2 sensor and or wiring
by Cat5 Cane - 3/16/09 4:37 AM
Probably most of us have started out doing the scanner diagnostics thing and then start out by running down the check list, replacing the plugs, The distributer cap, The wires, relays and fuses, 02 sensor, Fuel filter, fuel pump... part after part... Ahhhh did that... Check, next... till ya get down to the PCM/ECM. But wait a minute... is it the PCM or did YOU or Your Mechanic replace the parts with after market parts from Auto Zone or Discount Auto or the junk yard (Could be the same thing or maybe it works, but do you want to take the chance).

When it comes down to RELAYS, SENSORS and PCM's... don't cut corners. Jeeps (Think...NASA Rockets) built the engines with electric and air loads that are critically dependent, with little room for error to read the right loads. If the PCM get bad info, it reacts accordingly and adjusts other components to compensate... Buy Factory RELAYS, SENSORS and PCM's. If replacing 02 sensors... then replace both... Per my factory trained mechanic (now retired) who owned and operated his own shop for 25 years... That's the best advice he could give anybody.

His words for Jeep... Grand Junks, as once they start breaking down, they're junk!!! Owners and Mechanics try everything before they came to him and when they did, you start all over on the list, looking for non Jeep parts first... Jeep was no fool when they designed the engines.

Soooo, when it comes down to RELAYS, SENSORS and PCM's... don't cut corners.
1997 jeep grand Cherokee 4.0 and the stalling issues
by BillyTheJeep94/97 - 2/20/09 11:38 AM In reply to: Strange... check your sensors by Cat5 Cane
my wifes 97 gc has been stalling these last 2 months, Ive replaced the fuel pump, crank sensor,coil,battery,pcm,plugs,wires,distributar,pick up,cap,rotor,idle control sensor. it would run a day or so great, then start sputtering, then eventually at a loss here now, ive sunk over 2k into it, with the same results, and it seems from the posts ive read,many people have experinced the same thing, I did check the pcm to see if it was seated right, it has a plastic case, with the screws placed in a plasted clip type thing to the fire wall. sometimes the check engine light comes on, then go off, the reading it would give is multible misfire,even after i replaced the entire distributar cap,and conponants,with new plugs and wires..can someone please give me any suggestions that i havent tried that may work, when it does run right, it runs great..
PCM ?? to Billy the Jeep
by askyward - 2/20/09 12:03 PM In reply to: 1997 jeep grand cherokee 4.0 and the stalling issues by BillyTheJeep94/97
Hey Billy, Looks like you have done everything. I would ask yourself about the PCM. You listed the PCM as something you replaced. Well actually this is a really big deal... just what exactly did you replace it with??? Please read the posts about buying a PCM. You need to have bought a completely rebuilt PCM... not a refurbished PCM. I hate the words rebuilt and refurbished, they are so similar, but SOOOO different. If you replaced it with a refurbished one, your problems will likely remain no matter how much $$$ you throw at it. Again... please read the posts about Buying a PCM. **** Luck, Dave
1997 jeep grand Cherokee 4.0 and the stalling issues
by caj1996 - 2/20/09 4:56 PM In reply to: 1997 jeep grand cherokee 4.0 and the stalling issues by BillyTheJeep94/97
Did you replace the Idle Air Control Valve "Sensor". They cost about $35.00 at Autozone and takes about 20 minutes to change. You will need a Torx 20 socket to do this.
Did you remove the air intake hose and clean the throttle body. This should be done when you replace the Idle Air Control Valve "Sensor".
They sell a cleaner that will clean this area called Throttle Body Cleaner. Be careful with it and wear safety glasses. When you start the Jeep after using the cleaner it may be a little hard to start and run rough for a couple of minutes until the cleaner burns off.

It sounds like you have done all the rest. If you replace the CPM, buy a remanufactured one. Don't by a refurbished. I included a company in Florida that has them.

I found them by typing in the search line, 1997 Jeep PCM by ACR. "Allcomputerresources"

This a different company than the ACE company.

A company in Florida named ACR sells them for about $289.00 with a life time warranty.
Good luck.

Forum Icon Legend

  • UnreadUnread
  • ReadRead
  • Locked threadLocked thread
  • ModeratorModerator
  • CNET StaffCNET Staff
  • Samsung StaffSamsung Staff
  • Norton Authorized Support TeamNorton Authorized Support Team
  • AVG StaffAVG Staff
  • avast! Staffavast! Staff
  • Webroot Support TeamWebroot Support Team
  • Acer Customer Experience TeamAcer Customer Experience Team
  • Windows Outreach TeamWindows Outreach Team
  • DISH staffDISH staff
  • Dell StaffDell Staff
  • Intel StaffIntel Staff
  • QuestionQuestion
  • Resolved questionResolved question
  • General discussionGeneral discussion
  • TipTip
  • Alert or warningAlert or warning
  • PraisePraise
  • RantRant

You are e-mailing the following post: Post Subject

Your e-mail address is used only to let the recipient know who sent the e-mail and in case of transmission error. Neither your address nor the recipient's address will be used for any other purpose.

Sorry, there was a problem emailing this post. Please try again.

Submit Email Cancel

Thank you. Sent email to


Thank you. Sent email to


You are reporting the following post: Post Subject

If you believe this post is offensive or violates the CNET Forums' Usage policies, you can report it below (this will not automatically remove the post). Once reported, our moderators will be notified and the post will be reviewed.

Offensive: Sexually explicit or offensive language

Spam: Advertisements or commercial links

Disruptive posting: Flaming or offending other users

Illegal activities: Promote cracked software, or other illegal content

Sorry, there was a problem submitting your post. Please try again.

Submit Report Cancel

Your message has been submitted and will be reviewed by our staff. Thank you for helping us maintain CNET's great community.


Your message has been submitted and will be reviewed by our staff. Thank you for helping us maintain CNET's great community.


You are posting a reply to: Post Subject

The posting of advertisements, profanity, or personal attacks is prohibited. Please refer to the CNET Forums policies for details. All submitted content is subject to CBS Interactive Site Terms of Use.

You are currently tracking this discussion. Click here to manage your tracked discussions.

If you're asking for technical help, please be sure to include all your system info, including operating system, model number, and any other specifics related to the problem. Also please exercise your best judgment when posting in the forums--revealing personal information such as your e-mail address, telephone number, and address is not recommended.

Sorry, there was a problem submitting your post. Please try again.

Sorry, there was a problem generating the preview. Please try again.

Duplicate posts are not allowed in the forums. Please edit your post and submit again.

Submit Reply Preview Cancel

Thank you, , your post has been submitted and will appear on our site shortly.