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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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i see several issues being a possibility.
a bad TPS throttle position sensor, a bad MAP Manifold air pressure sensor or MAF mass airflow sensor, some wiring issues…it sounds like too me its electrical beacuse if it was low fuel pressure or lack of spark it would be more consistent. i do not think it would be so intermittent… you have already replaced your PCM i see, replaced the crank sensor, i would suggest getting someone who can plug a scantool that reads live data and plug it in and drive… kind of narrow it down.
I don’t know of anyone with a scantool…most of my buddies have a little more dough and just take their cars to the shop. I’ve been hesitant to buy a scantool because it seems like there are several types and I don’t know which one I’ll need. Can you recommend one? My wife has a 2008 Honda CRV so I’d like it to work on her car too if it ever starts having problems.
i have a scantool myself… it cost me about $100, it reads live data as well as reading powertrain codes, you will probably want something similar for your diagnosis if you know how too read live data on a scan tool and see it as a investment, weather it will garontee it will pinpoint your issue i cannot tell you… it takes a little bit of practice too learn how to use them and read some of the data too as they often have a ton of abbreviations and you are looking for certian things when you read live data.
for example, if your throttle position sensor is faulty you may notice as you increase or decrease pressure on the accelerator pedal the data on your scan tool typically shows a percentage of throttle position, and if its faulty typically rather than slowly going up and down in percent as you apply or release the throttle it may be more erratic or un responsive… just as a example this is something a scan tool can pinpoint and help you say “that needs replaced and thats whats causing my issue.”
parts stores typically sell scan tools, stores like AutoZone or NAPA or Orellys, tell them you want a scan tool that reads live engine data and reads powertrain codes, or see what scan tool fits best into your price bracket if you are interested in getting a scan tool.
Thanks for the info – I’ll look into it. Isn’t it true that for a TPS you can also hook it up to a multimeter and measure voltage change coming out of it? Do you know if the MAP or MAF can be tested in a similar manner?
yes i forgot, you can test a throttle position sensor with a DVOM, a throttle position sensor works buy varrying current from a reference voltage typically of about 5 volts.
however it is best in my experience too measure its resistance by setting the DVOM too Ohms, if it is working correctly the resistance should go up and down steadily depending on throttle application. i cant remember if its more throttle more resistance or more throttle less resistance. however the resistance should very steadily the more or less you apply the throttle.
the hot wire type MAF sensor you will probably need more of a scan tool too see how its behaving, but the older reostat type that acts like a swinging door you may be able too test like a throttle position sensor
some MAF sensors are a old fashioned rheostat style which like a throttle position sensor have sort of a swinging door, the more air flow the more it opens, the less air flow the less it opens, but you may have a more of a hot wire MAF sensor which is more common in modern vehicles in fact some just get dirty and can be cleaned off with MAF sensor cleaner, spray it off liberally and let it dry, BUT DO NOT TOUCH THE LITTLE SENSORS! they are ultra sensitive and easily damaged, if your vehicle has a MAF sensor, some vehicles just use a MAP sensor, my Buick uses both!
a falty MAP sensor may have a busted diaphram and not hold a vacuum the old sensor on my car once liteally fell apart when i took it out, how they are tested may depend, this is best tested buy watching manifold air pressure live data on a scan tool…
however when these things typically fail you get some sort of code, typically…
Update:
Whatever is going bad/causing problems is getting worse. This thing used to be once a week…now it’s multiple times a day.
Drove it this morning to work. Commute is about 3 miles on city roads to the interstate, ~10 miles of interstate, then ~2 miles of city roads to work. Made it out of driveway OK but the transmission was she had problems shifting going through the neighbordhood. You could hear the engine pulling more air and failing to shift at the point it should have..but nothing earth-shattering. Not sure if that is a slipping tranmission but that’s what I call it. Car never stumbled though and I made it about 1.5 miles down the road (some stoplights in between). Was going about 35-40 mph and it started to act up..wish I could give more detail but it was hard for me to tell what was happening because the road was rough and I was trying to pull over safely. Pulled over, she cut out, and started right back up. Got back on the road and got on the highway. About 2 miles on the highway she lurched like I downshifted but it’s an automatic. The engine didn’t feel like it was slowing down when you downshift…but that’s what the lurch felt like. Tried pumping the throttle with no joy. Car wouldn’t rev or anything…just as if I never applied throttle. I can feel the feedback of the pedal tho if that makes sense (resistance on my foot). As I was applying break and pulling over, I felt her downshift again. This is new because normally when I come to a stop, it’s always smooth and not “jerky”. Pull over, she stalls out, I start her up and she cranks right up. Rest of drive to work uneventful. I’m monitoring the tach and other gauges (oil pressure, engine temp, battery) during all of this and everything is solid (granted I don’t watch tach instantaneously when downshift occurs–trying not to crash!)
This afternoon I start it up after it’s been sitting for ~10 hours at work. Starts up with a rough idle but after about 15 seconds just sitting in park she calms down. I noticed the oil pressure was about 25% higher than normal during this period. Get into drive and she makes it about 30 ft before cutting out. Starts right up, then dies shortly thereafter. Crank her up a 3rd time and pull into a parking space and just let her idle for a while. No rough idle but i let it hang for about 2 minutes before getting on down the road. Make it to the first stoplight and she cuts out. Crank it up, cuts out shortly. Rinse and repeat about 4 times (granted it’s taking her longer to turn over the more times she quits). Finally she starts but a small puff of smoke comes from under the hood and she makes a noise like a horse exhaling (bad description but all I could come up with). Try to crank it up another time because people behind me are getting impatient and she finally starts and I make it a little further. She dies one more time before finally making it the rest of the way home.
I’m starting to think that every time she fails the engine is “cold”. Granted the engine temp says she’s at normal but it’s relatively early in my commute ~5-10 minutes…so not sure if that still constitutes a cold engine or not. Also, now she’s struggling more with starting, staying alive, and at city speeds whereas this has normally been a highway intermittent issue. Does it sound like something in the transmission is going bad?
I ended up breaking down and getting a scan tool from Walmart tonight – gonna try to drive around a little and see if she acts up but I’m thinking she’ll probably be fine until the engine cools down…which means another fun morning commute.
Turns out the scan tool I got (even though it shows it on the packaging) cannot read live data. No check engine light but it did pull a code.
It pulled a P0351 Ignition Coil A Primary/Secondary circuit. The problem is…my car has been throwing this code for over 6 months. I replaced the standard BWD coil with a high performance Accel coil. I even measured the resistance on it per the Haynes manual and made sure it was good before installing it. Any idea why this code would keep getting thrown?
this really sounds like a possiblity of a few things. a bad wire and or connection or ground somewhere either causing the coil to lose power, or some other system that controls the coil, its a 97 so its new enough to have some funky electrical systems onboard to control fuel emmissions / economy. this could also send false readings to the computer causing the irregular downshifting and what not. or it could be a vacume leak issue on a system as some electrical systems are still coupled with vacume switches or systems in genral. does your jeep have a form of traction control by chance? not that its directly related, but I would be more worried that its now affecting other parts of the vehicle (transmission) that it was not previously. its also plausible that the ECM (computer) itself is beginning to fail, but those are usually expensive, and its something I would not try to cheat out on $$$$ by replaceing it with one out of a salvaged vehicle. the fact that you feel that its more of a problem when the engine is “cold” really to me points more to a sensor sending false readings, but again, that could be a system further down the line with a bad wire/connection/ground doing that as well… ahh the joys of gremlins.
Thanks for all the suggestions. Just an update:
I did some more research and it turns out the P0351 tends to indicate a bad PCM if it’s not the coil. I went to the local junk-yard but all the jeeps had already been raided. Decided to unplug the negative battery cable overnight and see what happens since that seems to work for some jeep users.
So far I’m ~6 trips with around 60 miles and no issues. Think my PCM is going/is bad just don’t want to pay the $200 AutoZone wants. Will update if I am able to scrape together enough to replace it and if that fixes the problem.
ECM, PCM, ya they have so many different abbreviations for deviations for the same thing. I’m glad a small note of it pointed you in a semi-correct direction for research. I failed to think about the possibility of resetting it. wow, 60+ miles with no issues must feel like a god-send from what you were experianceing. Please do keep us posted!
Update:
So now I’ve been about 300 miles since ‘resetting the PCM’ and things are better. Still not perfect but back to the old intermittent hesitation that I can live with. I did manage to get a scantool that reads live data and Mode 6. Unfortunately, I think the update rate is a little on the slow side with the live data so I’m not sure if I’ll be keeping this one either.
I was able to pull off some Mode-6 data, though. The good news is that it has registered some tests as failing…the bad news is I have no idea how to decipher it. I sent an email off to the company that manufactures the tool asking for help and they said they’ll try to provide some guidance but it’s been about a week with no further response. Any chance you folks would know what this means? Codes are pulled from a 1997 Jeep Grand Cherokee Laredo. 5 “mode 6” test IDs in total, 3 pass and 2 fail. I’ll upload them all just in case it helps you get a better understanding of what’s happening under the hood.
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