|Topic Review (Newest First)|
|05-18-2016 12:56 AM|
|aogmitch||Have you pulled the valve cover and looked at what the valves are doing compared to the other cylinders?|
|05-17-2016 05:53 PM|
I feel your pain. It is like shooting in the dark. Anyway, the one thing I don't see you having tried is to check the voltage of the O2 sensors, especially bank one. The voltage should be fluctuating fairly rapidly within a range of .20 to .90 volts.
I never thought bad O2 sensors had much to do with misfires but it did on mine. Make sure the voltages of the Map and TPS sensors display similar values. Good luck.
|05-17-2016 05:25 PM|
Fortunately, the CEL only comes on once every couple months so I'm able to ignore it fairly easily. Maybe I'll try the crankshaft position sensor next...
|03-19-2016 08:46 PM|
Another update regarding the chronic P0301 misfire that I've been battling since last summer. The past couple weeks I started getting a rough idle again and finally today the CEL came on on my Jeep and it threw a P0301 cylinder 1 misfire again. I was anticipating this and was able to pick up a new IAC sensor on Amazon for $12.99. I installed it today. While the new part didn't seem to fit the electrical connector very well, I was able to get it on as far as I could. After installing the new IAC sensor, I'm not sure I've ever heard my Jeep idle this smoothly before but that could just be placebo effect. Perhaps it was always the IAC sensor that was bad and the cleanings only helped limp the old one all along.
Anyways, I'll keep monitoring and will continue to post updates here if any other work is required by me. If I do not post anything new, the IAC sensor resolved the issue.
|01-24-2016 12:42 PM|
Originally Posted by JasonATC View Post
I too have to pass smog this year and was getting desperate; glad I found this fix.
|12-03-2015 11:06 AM|
Updates over the past six weeks...
- I tried using an entire can of Berryman's Motor Tune Up through the brake booster line (it's basically a competing product to Sea Foam). No dice there, not nearly as much smoke as when I used Sea Foam so there must not have been much carbon buildup left.
- I began a regimen of trying to clean out any engine sludge from my crankcase (IMO most of these products are simply snake oil, just like fuel injector cleaners, but I went against my better judgement to try them anyway). Basically, my plan was to try a different additive to the crankcase with each oil change as a part of my 100k mile clean-up of the engine. This started when I used 1/2 of a can of Sea Foam in the crankcase a few thousand miles ago (the other half went through the brake booster line as mentioned in my original post). Step two of this regimen was to try out put a quart of Marvel Mystery Oil in the place of a quart of oil when changing the oil. I also bought an additional quart of MMO to start using in the gas tank per the bottle's recommendation (i.e. 4 ounces for every 10 gallons of gas). Step three of this regimen is going to be a quart of Rislone with the next oil change in a couple thousand more miles. I'll still perform step three once the Jeep is ready for its next oil change.
- Last week I pulled the throttle body and cleaned out the IAC sensor, IAC housing, intake butterfly valve and MAP sensor breather hose hole (reference: https://www.jeepforum.com/forum/f9/cl...mmies-1114849/). All of the sensors looked fairly good without major issues or too much carbon buildup (i.e. the photos in the above link looked far worse than mine) so, at the time, I didn't think taking everything apart was necessary and couldn't be accomplished simply by spraying throttle body cleaner into the throttle body. During the cleaning process I had to create a new gasket out of RTV for the IAC housing since the old one crumbled and fell apart. Since I performed this cleaning over a week ago, I stopped having issues with the rough idle and have yet to throw a the P0301 code again. This work coincided with starting to add 4 ounces of MMO to the gas tank for every 10 gallons of gas so I cannot definitively say whether the cleaning of the intake sensors or the MMO in the tank were the solutions. Regardless, things seem to be running better now. Because it's a Jeep though, I'm sure in a month or two this problem will come back - if so, I'll post again. If you don't hear from me - this is what fixed my rough idle/P0301 cylinder 1 misfire.
For more information, here is another great thread to give you ideas if you're chasing a misfire: https://www.jeepforum.com/forum/f310/...guide-2212697/
Keep Tahoe blue.
|10-28-2015 08:48 AM|
Originally Posted by Knuckelhead View Post
but yeah, I would guess highly unlikely as well. Just putting out the information seeing as OP has been very thorough in his troubleshooting.
|10-28-2015 02:13 AM|
|Knuckelhead||So far-fedged that its nonexistent on the TJ 4.0L engine because the serpentine belt only drives accessories that have nothing to do with the engine timing, cam and crankshaft positioning. The timing chain takes care of that...|
|10-28-2015 12:18 AM|
Originally Posted by 97wranglerD View Post
|10-27-2015 11:52 AM|
another thing to note... "Anything that affects the speed of the crankshaft can cause a misfire DTC."
Just copying from some other Jeep FSM
- Visually inspect the engine for any of the following conditions.
- Worn serpentine belt
- Binding Engine-Driven accessories: A/C Compressor, P/S Pump, Water pump.
- Misalignment of the Water pump, P/S Pump and A/C Compressor pulleys
- Corroded PCM power and ground circuits.
- Improper CKP, CMP, MAP, and TP Sensor mounting
- Poor connector/terminal to component connection. i.e., CKP sensor, Fuel Injector, Ign coil, etc.
- Vacuum leaks
- Restricted Air Induction system or Exhaust system.
I never would have thought the belt could be have enough grip to change the crankshaft speed lol
|10-27-2015 12:31 AM|
|MorganDan||I had the same problem. Started with changing the spark plugs. Then swapped out injector 1 with with injector 4 and 6. Codes still read p0301. Fixed the problem with buying a new coil rail.|
|10-27-2015 12:00 AM|
Originally Posted by JasonATC View Post
|10-26-2015 07:12 PM|
|JasonATC||Update: I had the exact same issue and fixed it by replacing the crankshaft position sensor. I hope this helps somebody.|
|10-25-2015 11:25 PM|
Originally Posted by 97wranglerD View Post
|10-25-2015 10:00 PM|
I'm having the exact same issues. 2002 4.0L. P0300 code Also had a P0301 and P0305 code previously that got reset and never came back. I'm running out of options.
I have replaced the spark plugs, coil rail, all 6 injectors, cleaned throttle body, replaced the IAC module, and the TPS... I feel like I am just throwing parts at it.
It ran well after replacing the injectors with the Five-O "4 hole" injectors. It was purring like a kitten. But a day later the code came back, this time just the P0300, but with the same rough idle.
The symptoms are just that it seems to have a rough idle and maybe a misfire. With the other two codes, the CEL was flashing and on the highway I couldn't go over 35. I pulled into a gas station (at 1am) and put seafoam into the oil and gas and let it idle for 30min. The flashing went away and I was able to drive home. That was the original problem. I have done all of this work since then.
The question is: what is my next step? I've heard about TJ valve spring issues causing a P0300, from JeepForum.com, but I'm no mechanic, I can change simple bolt on stuff like Plugs and injectors, but I don't wanna mess with internal engine repairs. I have an appointment at the Jeep dealership to get the CEL diagnosed, what should I tell them? I think I need to tell them about all of the stuff I replaced, but I also don't want to hint at valve springs if that isn't the issue. Can they isolate if the valve springs are weak with a compression test, or will that just point to needing all new valves? I want to avoid a $1,000 repair job if I can.
Any tips or recommendations on my next step would be appreciated, thanks in advance for the ideas.
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