Misfire On Cylinders 5 & 6 - 1999 Es 300

[Beer Dave]

This is a follow up to an earlier question I had. Here's the background:

Had the CEL (flashing) & Trac off lights come on with multiple codes for O2 sensors and random cylinder misfiring.

I replaced the O2 sensors and reset the trouble codes, thinking possibly a bad signal from the sensors were causing the misfire (now I think it was probably just the opposite). Yesterday the CEL only came on flashing again and the code showed only cylinder 6 misfiring. I had a post yesterday asking the orientation of the cylinders as I guessed it was either a bad coil or plug.

Started the car this morning and the flashing CEL and the Trac off light came back on. Trouble codes now showing misfiring on cylinders 5 & 6. By the way, it is misfiring at idle and all speeds. Car has 95K miles and original plugs and wires.

As there is a separate coil for each cylinder, I am guessing that it is not the plugs or the coils?? (although the plugs are due) Reviewing the forums I have seen some suggestions that the cylinder head water temperature sensor may cause misfire problems, however it wasn't clear if there were separate sensors for each pair of cylinders or not? To be honest, I am not even sure what the or those sensors look like or where they are located. I have been fortunate not to have any problems with the car until recently so I just learning my way around this engine.

Can anyone let me know if I am on the right track or suggest another possible problem. If I am on the right track I would appreciate some info on the temp sensors.

[jragosta]

This is a follow up to an earlier question I had.  Here's the background:

Had the CEL (flashing) & Trac off lights come on with multiple codes for O2 sensors and random cylinder misfiring.

I replaced the O2 sensors and reset the trouble codes, thinking possibly a bad signal from the sensors were causing the misfire (now I think it was probably just the opposite).  Yesterday the CEL only came on flashing again and the code showed only cylinder 6 misfiring.  I had a post yesterday asking the orientation of the cylinders as I guessed it was either a bad coil or plug.

Started the car this morning and the flashing CEL and the Trac off light came back on.  Trouble codes now showing misfiring on cylinders 5 & 6.  By the way, it is misfiring at idle and all speeds.  Car has 95K miles and original plugs and wires.

As there is a separate coil for each cylinder, I am guessing that it is not the plugs or the coils?? (although the plugs are due)  Reviewing the forums I have seen some suggestions that the cylinder head water temperature sensor may cause misfire problems, however it wasn't clear if there were separate sensors for each pair of cylinders or not?  To be honest, I am not even sure what the or those sensors look like or where they are located.  I have been fortunate not to have any problems with the car until recently so I just learning my way around this engine.

Can anyone let me know if I am on the right track or suggest another possible problem.  If I am on the right track I would appreciate some info on the temp sensors.

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Well, since you're due for plugs and wires, anyway, that's where I'd start.

[mehullica]

Swap coils #5 and #6 with others and see if the misfire moves to another cylinder. Have seen many of these coils fail.

[blake918]

Dave, definantly change your plugs and wires. I had this problem to the "t" last year although it was on my LS, and cylinders 2,4,6,8 were mis firing. Come to find out I filled up the spark plugs with water the weekend before while cleaning in the engine bay. New plugs and wires did the trick, and the car ran like a top after that.

I wouldn't drive your car until you get new plugs and coils in there since the blinking check engine light denotes an over heating catalytic converter...my car had the blinking light too.

[Beer Dave]

Mehullica,

I don't know why I didn't think of that before. I just swapped #2 and #6 coils, reset the ECU and ran until the code came back. Now #2 is misfiring. #5 came on a little later after I reset from the O2 sensor change, but hasn't come back after my quick drive around the neighborhood.

What are the chances two separate coils go out at the same time?? Anyway, I will swap #5 out tomorrow and see if I see anything else.

Thanks for the feedback. I will report back my results tomorrow.

Dave

[Beer Dave]

Dave, definantly change your plugs and wires. I had this problem to the "t" last year although it was on my LS, and cylinders 2,4,6,8 were mis firing. Come to find out I filled up the spark plugs with water the weekend before while cleaning in the engine bay.  New plugs and wires did the trick, and the car ran like a top after that.

I wouldn't drive your car until you get new plugs and coils in there since the blinking check engine light denotes an over heating catalytic converter...my car  had the blinking light too.

←

Blake,

Thanks for the feedback, new plugs and wires are definitely on the agenda. I had to drive the car to work last couple of days and will need to drive to the parts store. I certainly don't want to have to replace the cat converter. Any idea how much driving with CEL flashing can cause significant damage to the cat converter?

Dave

[blake918]

Dave, I'm not sure how long it will take before it causes damage. I was just shocked to see a flashing cel in my car when I was having the problems....I didn't know that the light would do that! My guess is that your car probably isn't as bad as mine was if you are still driving it. I had to park mine while I waited for Park Place to ship the parts; she would hardly run-I had to leave it in second gear just to make it home, and the exhaust smelled like something dead!lol I hardly made out of the neighborhood when the light started to flash. I got scared and immediately turned around. I checked the service manual immediately when I got home, and it said the cat was getting hot. It didn't go in to any specifics.

[SKperformance]

The rear plugs should have wires form the coil packs

while the front ones are still coils mounted directly ontop of the plugs still

[Beer Dave]

Update:

Replaced bad coil that was misfiring on #6 and problem solved. When I relocated the coil from cylinder #5 to another cylinder to test I didn't get any more misfires from that coil. All I can think is that with #6 being just opposite of #5 it was causing random misfires not related to the coil??

Anyway, thanks to all for the feedback I appreciate it. Only $90 for the new coil, which is a heck of a lot cheaper than if I had taken it to the dealer.

SK - just an FYI, mine has a separate coil on each plug. They must have changed them on the earlier or later models.