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John G.
John G., Honda Technician
Category: Honda
Satisfied Customers: 2652
Experience:  Dealership tech since 1982. ASE and Honda Master Technician.
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, 2002 Honda Odyssey LX. Rough running & misfires. Codes p0300-p0306.

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Hi, 2002 Honda Odyssey LX. Rough running & misfires. Codes p0300-p0306. Car was running great then after a short stop problem started. Had codes checked at parts store.; Disconnected MAP sensor and had a slight difference in running. Could it be O2sensors? Checked visually for vacuum leaks.
Thanks, Bill
This could be a few different things. A few are common.
How many miles are on the van?
Do you know if the spark plugs have been replaced at some point?
Customer: replied 6 years ago.
189,000 plugs replaced 15k ago by dealer- I would have suspected them but with the problem happening so suddenly I suspect a sensor of some kind
Ok, since it is a multiple misfire its probably an EGR problem. The Egr valves can stick open and cause this. Diagnose by removing the valve and install a cardboard block off under it and bolt it back down. If the problem is then gone, you know the cause.
If thats not it, then it can be tight valves, a bad coil or coils.
Customer: replied 6 years ago.
Will check now

Ok, great. I will be around all day....

Customer: replied 6 years ago.
Ok John, Pulled off the EGR (a lot of carbon build op on round sensor on bottom) placed cardboard and replaced EGR - same result - Rough running. How about a bad O2 sensor. Also, quick question, what is the sensor(?) or valve at the top of the intake manifold just before the throttle valve. It seems to have a fuel line going into it then out into the throttle body.
No its not going to be ab O2 sensor, but you can prove this by just unplugging it. If it nuns better its bad.
That part on the throttle is a purge solenoid for evap. emissions system. cant cause a running issue.
Does the engine idle rough or when cruising?
Customer: replied 6 years ago.
Not bad at idle, very rough when driving
Ok, so there is no dead miss at idle that you can locate by disconnecting coils one by one?
Customer: replied 6 years ago.
It is possible that I could find a bad cylinder at idle by checking each coil. The thing that is throwing me off, is that the codes are saying I have 5 bad cylinders, so I was thinking it must be one item causing ALL 5 cylinders at once, instead of 1 or 2 individual cylinders acting independantly. How do I go about disconnecting each coil at the coil or at the spark plug?
Its not going to be necessary to do that. There is a problem causing multiple cylinder misfires. If its idling ok, don't bother with that check.
Has the car been refueled right before this started?
Has it ever been overheated?

Edited by John G on 5/24/2010 at 4:58 PM EST
Customer: replied 6 years ago.
No and No. However, the oil level was down about 1.5 qts
Customer: replied 6 years ago.
John, Just to clearify, the idle is a little off. You can tell there is a slight problem, but the studdering starts to be much more pronounced when you press on the gas
Ok, remove the large black plastic engine cover. You then need to remove a smaller cover over the front valve cover.
You will then be able to see the 3 coils in front and the 3 in back.
Disconnect them one at a time while its idling.
If there is no change when a coil is unplugged, that cylinder is not working right.
Them you can swap coils from a good to a bad cylinder and see if the mis moves with it.
If not, you will need to do a compression check next.
Customer: replied 6 years ago.
Ok John, I checked all of the coils it seems that the center cylinder has a bad coil as I swapped between the other front 2 cylinders. I unplugged the coils in the back row and as I did the engine struggled with each one that I unplugged. So, I am led to believe the those coils are working properly. Do you agree? Also, why did you say I may have to do a compression check? Is there a possibility of engine damage?
No engine damage is likely since you have found a bad coil.
Sometimes multiple misfire codes do set even if there is really only one malfunctioning cylinder. Sounds like you have found the problem.....
Customer: replied 6 years ago.
On my way to pick one up. Is Auto Zone/Auto Palace ok for parts?
Generally they are, I have not used a coil from there on a Honda but I'm sure its ok
Customer: replied 6 years ago.
John, I got a new coil - All is good!!! You're the best.
I am upping my payment to you (if I can figure out how.)
Excellent,,,,,I appreciate the extra. A bonus can be added after you click accept if you wish. Thanks and have a great week.
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