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4.7L Random Misfires when Hot outside

8K views 13 replies 5 participants last post by  Big Blue 
#1 ·
Hello,

I have a 2007 4.7L Limited. My problem is that when it gets hot outside I start to get random misfires. Last year it would only do it when it was above 85 degrees. This year it is starting when its 70 degrees out. If I'm on the freeway its ok unless its really hot out above 95 degrees. But if I'm in start and stop traffic it will misfire till I drive about 5 mins then it goes away.
The only faults that i get are the P0420, P0430, and the P0300 random misfire. Before i spent $1,000 on new catalytic converters i wanted to check around. Other forums say that this is a common issue with this engine but no one says what the fix is. My gas tank also makes a loud "POP" sound a few mins after i turn the jeep off. I don't know if there is a pressure issue causing problems delivering fuel, or if the catys are to hot causing issues with the 02 sensors, or what.
 
#5 ·
Ok, so I have a 2007 Jeep Commander. About 4 years ago I had this problem. I spent over $4000 on chasing the problem. I changed the coils, fuel injectors, spark plugs, complete wiring harness (also because it was partly chewed by rats, but that is another issue too!). The error codes that came up were 300 codes, misfire coil #8 and/or #9. My mechanic and I were at a loss and just scratching our heads. Then all of a sudden things seemed to get better and i only had some minor problems. then, about 3 weeks ago the misfiring came back- at the same tome the weather started to heat up. I stopped using E85 and switched to unleaded. I read that the E85 gas burns hotter and maybe the heat is affecting some sensor in the engine and can be causing the misfire. So far (knock on wood) the issue hasn't happened again, even with the hot days we have had lately and while using air conditioning.
 
#8 ·
Keep us posted @BLEE8282, I'd like to know how this progresses.

I'd suggest having a diagnostics run and have them check that the mass-air/intake air temp sensor ,is reading the proper air temperature. Had a similar issue on my previous vehicle, an 08 GC and it wound up being a bad air intake temp sensor.
 
#9 ·
Will do. Im trying to get the PCM replaced. It was replaced two years ago. It actually started doing the same thing the 1st summer after the PCM was replaced i had it replaced late fall. I just parked it for the summer. This year it started doing the same thing a little earlier when it's 74 degrees out. So i figured i would get to the bottom of it. The PCM has a lifetime warranty so i figured i would start there since its free. The company has just been giving me the runaround on replacing the PCM. After two weeks of getting the runaround I reported them to the BBB.
Thx for the suggestion. I will buy the air temp sensor just to rule it out. Ive changed just about all the other sensors anyways.
 
#10 ·
Will do. Im trying to get the PCM replaced. It was replaced two years ago. It actually started doing the same thing the 1st summer after the PCM was replaced i had it replaced late fall. I just parked it for the summer. This year it started doing the same thing a little earlier when it's 74 degrees out. So i figured i would get to the bottom of it. The PCM has a lifetime warranty so i figured i would start there since its free. The company has just been giving me the runaround on replacing the PCM. After two weeks of getting the runaround I reported them to the BBB.
Thx for the suggestion. I will buy the air temp sensor just to rule it out. Ive changed just about all the other sensors anyways.
Great, let me know if anything changes after you swap it out.
 
#11 ·
Its not really fair to report them for not wanting to let you have a free part just to try out. If you had a mechanics diagnostic report that showed the PCM is faulty, i would then hold the PCM company responsible, but i doubt they would give as much "runaround" if you could show some objective evidence of failure.
In addition to the air temp sensor, the coolant/engine temp sensor can cause those issues as well. Often it doesnt throw a code for the sensor itself , because internal resistance within acceptable range just makes the computer think its a different engine temp than actual. Ive seen this problem with a few cars ive owned through the years, and if your look looking for cheap parts to try and dont feel like paying for a full diagnostic scan, its not a bad option.
 
#12 ·
Thank you for your input. I am going with the PCM because it is doing exactly the same thing as last time. The random missfires when its hot outside, the jeep shutting off. I had a compression test done and everything was good. The coil packs and plugs were changed last year as well. I went thru my records yesterday and last summer i replaced the air temp sensor and it did not help.
 
#13 ·
Well after having to file a complaint with the BBB I finally received my PCM. About 6 mins to install. And the Commander is working great again. No more random misfires and its been over 95 degrees out!!!!!!!
 
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