Mitsubishi Montero Misfires

Tiny
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I have a 1997 Mitsubishi Montero LS V-6 with 160,798 miles. It has been misfiring and losing power under hard acceleration and on uphill grades. The check engine light comes on and if you pull over and put the gear shift into neutral, the engine runs flawlessly, without any skipping throughout the entire RPM range. My dealership checked the code and reported that a plug was misfiring and that the vehicle would need new plugs and wires, even though they had replaced them at 120,000 miles. My original plugs and wires lasted 120,000 miles! At any rate, I had them put new plugs and wires in and the vehicle continues to misfire and shake on longer or steeper uphill grades (under a moderate load). Again, after pulling over and letting the vehicle idle in neutral it seems to clear up and you're on your way again, until the next time. I am thinking it might be some kind of sensor, but I am not sure what is going on; I know I am not going to replace the plugs and wires again until I get an answer to this question. I appreciate your help on this. Thanks very much.
Saturday, November 24th, 2007 AT 8:33 PM

8 Replies

Tiny
BLACKOP555
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If you unplug the MAF does it still surge or struggle under loads up a hill? Does it clear it up or make it worse.
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Sunday, November 25th, 2007 AT 1:01 PM
Tiny
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I am not sure what an MAF is, but I can pass along to my mechanic and get back to you. Unless of course, this is something that I can do myself. Please advise, and thanks for your interest and time.
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Sunday, November 25th, 2007 AT 3:34 PM
Tiny
BLACKOP555
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MAF stands for Mass Air Flow sensor. It is located on the air hoses going to the throttle body from the air cleaner. You will see wires going into the hoses.
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Sunday, November 25th, 2007 AT 7:48 PM
Tiny
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Thanks for the information. I will look for this tomorrow and try to disconnect the MAF and see what happens. I suspect that if it clears up, I need a new MAF? And if not, there will be something else for us to consider. Hey, I really appreciate your time and interest on my behalf. If we get this situation corrected, I will most definitely make a donation and give you all the props for your diagnostic work. I sure wish you were my personal mechanic!
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Sunday, November 25th, 2007 AT 8:22 PM
Tiny
BLACKOP555
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No problem, thats what im here for. You can just clean the MAF also for a temp fix. If it gets worse then you may have to clean the MAF also.
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Sunday, November 25th, 2007 AT 8:33 PM
Tiny
BLACKOP555
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Just in case that is not the problem I would like to go deeper!

Is it possible that you can get me the code?

First well start with loss of spark, first examine the wire to the cylinder that is missfiring examine it completely to verify it is not cracked or cut. Then check the distributor cap, one stud may be covered with carbon causing insufficient spark to go to that spark plug. If that checks out take out the plug, and check the gap if it checks out good then we have just ruled out spark!

Next, thing that coudl be amiss would be a plugged fuel injector, check for voltage at it, and if possible use a probe to listen to it with the car running and see if it is buzzing. If that is all good, then you should clean it, this would be a good time to clean all of the injectors, but this will be a undertaking, not to hard. Involves taking off the intake manifold and pulling out the fuel rail and injectors.

Another thing could be loss of compression, due to a bad exhaust valve on the cylinder, perform a compression test to check this, if it is low and one adjacent to it is, it may be a badheadgasket especially if it is loosing coolant.

That code would be nice, because it may be a random missfire.
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Sunday, November 25th, 2007 AT 8:55 PM
Tiny
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The code on the service order is as stated:

found code PO3 03 needs plugs and wires customer advised also has an Evap code cleared code will start with a tuneup customer advised

Hope this helps and thanks again.
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Monday, November 26th, 2007 AT 5:27 AM
Tiny
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That tells me that Cylinder #3 is missfiring, you should check the spark plug for proper gapping. Also try taking that plug and wire and switching it wiht another cylinder and clear the code, if it shows back up on the same cylinder (#3) then it is not the plug or wire and is probably the dist cap or rotor or something intnal such as a bad fuel injector or burned exhaust valve. If the code reshows but shows on cylinder one then it is the wires or spark plug. And you should replace accordingly.
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Monday, November 26th, 2007 AT 6:26 PM

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