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All,
I’ve been struggling to find a gremlin hiding in my 97 Jeep Grand Cherokee for a while now but still no joy. It’s been intermittent (over almost a year period) and usually I’ve been able to get by with just pulling over and restarting. This past week it has been misbehaving a lot so I’ll focus on that. I’m no mechanic, but I’d like to be more educated. I’m pretty handy…just need your help on what to do!
General Symptoms:
Misfiring / bucking throughout driving range (city & highway speeds)
Intermittent episodes to just shut down completely (sometimes voilent, sometimes like I turned off key)
Loss of throttle control (stepping on peddle doesn’t do anything)Basics:
1997 Jeep Grand Cherokee 2WD 4.0 L 6 Cylinder Automatic
215k milesRecent Service:
Regular oil changes every 3k miles (just to state the obvious)
7/02/11 – Replaced ECU(jeep was cutting off on its own – dealer verified this was problem)
7/02/11 – In process of debugging, shop replaced distributor, ignition coil, cap, and rotor button
4/27/12 – Water pump replaced (garage was flooded with coolant every day…)
6/15/12 – Used Marvel Mystery Oil because a friend suggested it’d be a good way to clean out my engine…problem ensued (could be coincidence)
10/20/12 – Replaced rotor button, cap, spark plugs, ignition coil, and air filter
– Replaced ignition coil because it had thrown a code that called it out (only 1 coil on
this jeep)
11/03/12 – New battery (tested bad)
11/09/12 – Replaced crankshaft position sensor (Firestone read a code Autozone could not (so they say) and it called out CPS). Took it to Firestone for misfiring symptoms
3/06/13 – Replaced fuel pump myself because jeep was still misbehaving. Thought I had bad fuel pump / clogged filter (in this jeep it’s all 1 unit and had to drop the tank so my time was already invested – easier just to replace) – did not test fuel pressure (I know I should have or I’m just throwing money at it)
5/11/13 – Replaced wires (noticed one was touching engine block and had some melting on casing)This Past Week:
5/14/13 – Driving on highway (~70mph). Constant acceleration to maintain speed, feel that no longer have throttle control. Pump gas pedal about halfway through range, car backfires. Pump one more time and she accelerates like normal and is fine.
5/26/13 – Driving on highway (~70mph). Constant acceleration to maintain speed, feel that no longer have throttle control. Pump gas – nothing. Start putting on blinkers/looking to get over and I hear/feel the car downshift (this is a new experience when this happens)…almost as if I had manually downshifted to brake the car. Pump gas, nothing. Push pedal to the floor and she almost instantly starts accelerating. Rest of drive was uneventful.
5/21/13 – Morning commute. Backing out of my driveway, hit a bump as the garage is uneven with driveway and front tires impact driveway. Car cuts out. Starts right up, back up into street (another bump) and she cuts out again!). Starts right up, pull forward into driveway and pop hood – shake some wires, check battery connection …nothing loose. Reverse back over bumps no issue, go through speedbumps in neighborhood no issue. Get out on highway and she loses throttle control and so I start pulling over (pumping gas is not doing anything). She starts bucking/misfiring as I’m sitting at a stop on side of road so I throw it in neutral and she immediately recovers. Rest of drive goes OK.
Afternoon commute: Start up in parking lot and she is misfiring like crazy…try giving gas but it’s like she’s not getting it and just keeps sputtering. Eventually violently cuts out. Start up again, same symptoms. Start up 3rd time and she’s fine. Get going on city roads on way to highway. Pull up to first stoplight and as I brake, I feel her cut out. No bucking/problems just a silent death like I turned off key. Starts right back up at light no issue. Start merging onto highway and she starts bucking/misfiring so I have to pull over, this time the neutral trick does not work and she dies. Rinse adn repeat a few times and I finally get home.Sorry for the essay I just wanted to give a lot of detail. Any idea what it could be? Is it a throttle position sensor? Air idle control valve? I’m at a loss….
Thanks in advance!
Mike
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Replies
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Hey uh….’update’.
Jeep decided to give me some problems this morning, but now that I’ve become accustomed to the hesitation or failure of the car to acknowledge I’m giving throttle I just ‘coast it out’ and eventually she comes around (rather than pulling over completely). However, this morning she did manage to backfire as I attempted to recover and I think I blew a hole in my muffler :whistle: Is that possible? I noticed once I got off the highway that she sounds more like a ‘race car’ when accelerating haha. I checked while idling and it’s not coming from under the hood – I think it’s all tied to the exhaust. This thing is going to hell in a handbasket….
Hi all! An update and some questions are below.
After ‘resetting’ the PCM by unplugging the negative battery cable over night, my Jeep ran like a dream compared to what it had been. Still not perfect, but no more breakdowns on the side of the road. I also became more ‘prepared’ for lack of a better term and if I felt her start to give me trouble, I would let off the gas and just coast for a minute and she’d be fine. She did seem to backfire more often during these episodes and I did end up blowing a ‘hole’ in my muffler. Unfortunately for me, instead of a hole it actually caused the muffler to separate from the ‘end cap’ as I’ll call it. Basically you have your extruded oval shape that is ‘capped’ on either end where the exhaust pipe goes through. The ‘crimp’ that mounts the cap to the muffler body split open.
So, other than sounding like a race car, things were good. I was tired of my wife nagging and the look from co-workers so I decided to ‘repair’ the hole with muffler tape (from AutoZone). I followed the instructions and it worked OK (it’s an awkward shape). A few days later my Jeep starts giving me trouble again. Coincidence? I don’t know for certain, but it is odd so I thought I’d mention it. So now she is giving me trouble more frequently and backfires and boom – blows open the muffler tape. I decide to leave it off for a few days to see if she starts behaving again (don’t know why it would change things but I decide to give it a shot). Her behavior doesn’t improve so I ‘reset’ her overnight. Drive around for a few days and she gives me trouble even without anything over the muffler so I’m guessing it’s just her time of the month and it was a coincidence.
So I go to pull codes from the engine and it still states Primary Ignition Coil (even when I clear it). I look at the mode 6 data (see previous post) and now notice that my O2 sensor 1/1 Half Cycle Counter and Catalyst Slow O2 1/1 Response Counter are failing per Mode 6 diagnostics.
I pull out my scantool and start graphing live data of the O2 sensor while the car is idling. Most of the sensors appear ‘fine’ in the sense that they are jumping around which at least proves to me they aren’t shorted and are outputting something. Then I graph “O2S B1 S2 STF” (whatever that means) and it is FLATLINED at 99.2%.
So…now I have several questions.
I’ve heard cars have 2 O2 sensors (one before the CAT and one after), but I’ve only been able to locate the 1 that is after. Does this mean my O2 sensor is bad? If the sensor is bad, could it be causing all this misfiring/stalling of my Jeep? I asked the guy at AZ and he said it sounded to him like a problem with my CAT.
I’d like to reiterate my car is throwing a Primary Ignition Coil code. I’ve replaced and checked the coil several times and it is fine. When searching the web, all signs point to a bad PCM if the code is being thrown and the coil checks good. Am I dealing with two separate issues here or are they somehow intertwined? If so, what is the cause and which is the symptom?
Thanks for any and all help!
MikeAnyone have any thoughts on this?
I’ve seen Eric’s video on how to tell if the CAT is bad and plan on checking that when my IR thermometer comes in. However, could a bad PCM be causing unburnt fuel to be sent to the CAT and clog it up so it chokes out the car? I’m only getting that primary ignition coil code so I don’t know if the PCM is causing the CAT to fail or the CAT is causing the engine to choke and throwing a false code….
see if this helps the troubleshooting.
http://www.justanswer.com/jeep/3m3wt-1997-jeep-grand-cherokee-code-p0351-set.html
All,
I ended up ‘throwing in the towel’ and replacing the PCM with a reman’d Cardone PCM from Autozone last week. So far so good – no backfires, no stalling/hiccups etc. Shortly after replacing the PCM, my Jeep started to be slow to turn over. I went and bought a battery charger and the battery was at ~75% so I charged it to full but it still seemed sluggish to start. Well the next morning she wouldn’t start at all – just a single click. I went ahead and replaced the starter and now she’s back to working. I think the starter going bad was just coincidence (it looked like the original when I pulled it off and the Jeep has 220k miles on it). Just thought I’d mention it for full disclosure.
In part of my search, I contacted ‘Big Banana’ the manufacturers of my scan tool. They provided some useful docs regarding Mode 6 data and since the web is sparse with info, I thought I’d upload it for posterity for others looking for Mode 6 data. I’m keeping my fingers crossed the PCM swap did it but I’ll keep yall updated.
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