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Misfire and code scanner

Tiny
CASMIHOK
  • MEMBER
  • 2005 JEEP LIBERTY
  • 3.7L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 161,000 MILES
Hello hope you're having a good day.

I have been putting my vehicle to work this year, traveling 12 hours one way back and forth from my GMA. It has treated me well, luckily I made it back here a few weeks ago and I give it a lot of rest when I am here and I drive my late grandfather's old Buick. Anyway, I take it for a drive once or twice a week and I was driving it the other day on a straight away around 60 mph, and it started aggressively jerking. Check engine started flashing and I slowed down, turned around and got home ASAP. I haven't driven it since. On that drive, it continued to jerk, especially around 2,000 RPM's. I took it really easy on the way back, not pushing much more than 50. At some stop signs it would jerk badly when I first hit the gas regardless how soft I hit it. I am assuming it's a misfire, I had a misfire fixed a year ago not long after I got the truck, I don't remember what cylinder it was on and I don't have the receipt anymore. I am not in contact with that mechanic anymore.

Will this scanner work for my truck, it's affordable and I don't want to drive the jeep down to O'Reilly in case those few miles do more expensive damage.

https://www.amazon.com/TOPDON-Diagnostic-Portable-Automotive-Scanner/dp/B07DQG2LG4/ref=sr_1_3?crid=119XTOI5WRXQE&keywords=car+code+scanner&m=ATVPDKIKX0DER&qid=1572371082&refinements=p_85%3A2470955011%2Cp_6%3AATVPDKIKX0DER&rnid=331541011&rps=1&s=automotive&sprefix=car+code+scanner%2Caps%2C173&sr=1-3

My brother told me maybe its spark plugs, coils, etc. But I have also read a few things like possible valve intakes problems, or clogged catalytic converter. What do y'all think? I appreciate the help, this website it a life saver for a kid without a trust fund! Haha, thank you. Let me know if you need any more information.
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Tuesday, October 29th, 2019 AT 10:53 AM

14 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,597 POSTS
Hello again. The 3.7 has a few known issues. They need spark plug changes every 35K with copper core plugs or they start acting up. They also like to burn out ignition coils if the plugs are not changed regularly. Both of those will cause misfires. Don't use the fancy plugs in that engine, I've seen that cause misfires in them unless you can be sure the plugs use a copper core to pass the spark to the electrodes, last I knew there was only one brand that did that and they stopped making the correct number. The worst item is that they drop valves.

That scan tool might work, never tried one. I have an Autel AL329 that stays in the car just in case I might need it. It seems to work OK on many vehicles. I grabbed it in a walmart while out one day. It is update-able online for free.

You could track down the misfire without a code reader. You just unplug the coils one at a time and listen for the engine to change, when you find one that doesn't change the sound of the engine you found the misfire. If the plugs haven't been changed in 35-40K I would start with those anyway. Then I would trace the coils.
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Tuesday, October 29th, 2019 AT 3:38 PM
Tiny
CASMIHOK
  • MEMBER
  • 204 POSTS
Thank you, so Im going to get all new spark plugs. How can I tell if I need new ignition coils?
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Wednesday, October 30th, 2019 AT 9:43 AM
Tiny
CASMIHOK
  • MEMBER
  • 204 POSTS
My apologies, I am editing this whole response because I was able to reach all the spark plugs, but, I notice a change in sound with all 6. So I am left very confused, all 6 caused a change in sound. What now? Am I left to have a code read? I don't know what else to do. Thanks Steve.
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Wednesday, October 30th, 2019 AT 11:24 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,597 POSTS
I would read the codes and see what you have and go from there. Is the light still on and flashing while the engine is running? It is possible that you have a coil(s) that are breaking down when they warm up. The codes would at least give you an idea of where to look.
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Wednesday, October 30th, 2019 AT 12:59 PM
Tiny
CASMIHOK
  • MEMBER
  • 204 POSTS
Hey Steve, thank you so much for the response again. So I disconnected all the spark plugs with it running and I heard a change in every one. I took it down to Advanced, I honestly didn't notice it flashing. I am not positive and I should have taken note but I think it is just consistency on now. But the codes that read were as follows:
P0339 Crankshaft Position Sensor A Circuit Intermittent Stored
P2305 Ignition Coil B Secondary Circuit Confirmed
P0837 Four Wheel Drive Switch Circuit Range / Performance Stored

What do you make of that? I asked him if it expresses what ignition coil could be causing it, the guy didn't really provide me with much info other than the codes. Which is fine, he's just an auto parts employee and I appreciate his information. What do you make of it? Thanks Steve, hope you're having a good day
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Wednesday, October 30th, 2019 AT 1:03 PM
Tiny
CASMIHOK
  • MEMBER
  • 204 POSTS
Just gathering information online, I am thinking replace spark plugs for sure. "B" means cylinder 2 if these other forums are correct (correct me if I am wrong), should I just replace cylinder 2 spark plug? I figure I might as well do all 6 since it has been some time and many thousands of miles since my last change. Replace all 6 spark plugs, and cylinder 2 ignition coil? Does P2305 guarantee that cylinder 2 ignition coil is no good? Thanks for helping.
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Wednesday, October 30th, 2019 AT 1:12 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,597 POSTS
Both of the first codes can cause the issues you are having. The P0339 crankshaft sensor signal dropping out would cause the timing to change and cause misfires and loss of power. Because that is a stored code it isn't one that is current, but it is likely an intermittent issue and could be as simple as a bad ground or wire that is failing.
P2305 on the other hand is a current code. It is showing an issue with the control side of the coils. That could mean a failing coil or that the Powertrain Control Module itself is faulty. As it isn't showing a current or stored misfire code for one cylinder it is may be the PCM failing under heat. What I would likely do is change all the plugs. Then play musical coils. Move the coil for cylinder 2 to another cylinder. Then erase the codes and run the engine to see if the codes come back.
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Wednesday, October 30th, 2019 AT 1:49 PM
Tiny
CASMIHOK
  • MEMBER
  • 204 POSTS
Awesome, thank you. I will start with the plugs. I've read good things about these:

https://shop.advanceautoparts.com/p/ngk-v-power-spark-plug-6987/18090252-P
Do you recommend these? They seem to have good reviews and copper material as well.

Do they need anti-seize? Thank you
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Wednesday, October 30th, 2019 AT 1:56 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,597 POSTS
I've used various plugs, the NGK 6987 you list are the OEM plugs. I've used those and Denso 3169 both with no issues in the 3.7s I've owned. Be careful changing them, it's easy to crack the porcelain. They don't need anti-sieze as a general rule as the NGK plugs have a coating already.
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Wednesday, October 30th, 2019 AT 4:51 PM
Tiny
CASMIHOK
  • MEMBER
  • 204 POSTS
Does the porcelain crack if you over tighten? Just have to be careful in that sense, correct? Thank you
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Wednesday, October 30th, 2019 AT 4:57 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,597 POSTS
They crack if you get the socket in on an angle, the plugs don't set perfectly straight in the head. I like to use a flex plug socket and not push down on it as it turns.
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Wednesday, October 30th, 2019 AT 5:07 PM
Tiny
CASMIHOK
  • MEMBER
  • 204 POSTS
Very good to know, thank you very much! I'll get the plugs tomorrow.
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Wednesday, October 30th, 2019 AT 5:18 PM
Tiny
CASMIHOK
  • MEMBER
  • 204 POSTS
Steve, should I replace crankshaft sensor while Im at it? Or could the spark plugs be causing the sensor to mess up? Or does P0339 guarantee I have a bad crankshaft sensor? I can get it $23.99, I could pick it up with the spark plugs tomorrow. Let me know what you think. Thank you
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Thursday, October 31st, 2019 AT 8:20 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,597 POSTS
That is your choice. I would look over the wiring and the sensors connection real well. Being it is a stored code it could be a wire that rubbed through or a bad connector or a failing sensor.
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Thursday, October 31st, 2019 AT 9:35 PM

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