uncledave11

Random misfire codes for cyl. 2, 4, & 6

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After a tune up, R&R spark plugs, air filter, cleaned MAP sensor, coolant hose fix, PCV valve cleaned...everything went extremely well. While getting a very smooth running engine up to operating temp to check for any leaks (ran AC on full, then heater to make sure coolant levels were full and engine at normal temp) the engine went from smooth idle to surging slightly RPM up and down and running a bit rough. Check engine Light flashed so checked codes and found random misfire and a code for cylinders 2, 4 & 6. (front bank) Checked all vacuum connections, electrical & anything else I might Have disturbed during the tune up. I'm guessing there is something now going on that is affecting only the front cylinder bank but I'm not sure where to look as the back bank (1,3,& 5) seem to be fine (no codes anyway!) Any incite on what to run down first as I feel there has been a change in fuel mix due to a vacuum leak maybe to the front bank? Appreciate any response or suggestions on where to proceed next!  

 

Thx,

 

Dave

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Hi Marty:

I appreciate the response and yes it does sound like coil packs but.....since one of them I had to replace about 2 months ago is new, the misfire codes are all in the front bank (cyls. 2, 4, & 6) what's the reason for your conclusion? Coil packs are about $70 each, normal preventive maintenance for electronics is that if you have alike components in a group that perform the same functions you can expect additional failures to occur after the first incident. Yup, 19 years and one finally fails and I know the possibility of others to follow exists. but at the same time I'm trying to avoid "breaking the bank" while not being a cheapskate due to recent finances that we won't discuss here. I'm still looking for a more scientific explanation using the laws of cause and effect! what started with a vehicle that needed a good tune up and ran ok and all 6 cyl without any issues that suggested serious problems. Yes the plugs were quite worn and the air filter was dirty. The only codes I had was the one that gives owners a fit and cost large $ to eliminate is the "catalyst is below spec limits" Meaning your converter doesn't quite get as hot as it is supposed to and because of ECU parameters that can't be bypassed or changed you get a anti lock and trac off signal that has absolutely nothing to do with the emissions end of anything! But it will get (especially moms!) your attention when you feel unsafe in winter driving conditions. Your anti lock brakes of course still function but your traction control does not. But the Lexus dealer service dept will fix it even if they have to replace the entire anti lock brake control system and every other sensor related to emissions except the cat converter. Having bought this car in 2004 as a pre-certified car with a 3 yr bumper to bumper (20.000 miles at delivery) I saw every failure incident get parts thrown at it till you wondered how can they afford to operate that way? Ha, 14 yrs later, I know. So If you or any other members can come up with any other possibilities I'd be all ears an eternally grateful!

 

Thanks,

 

Dave

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did you replace the plenum gasket.  look at hose connections carefully.   I don't know how many miles yours has, but 02 sensors are considered maintenance items by some,  over 100-130K miles.  try resetting adaptives by touching the neg batt cable to the pos cable, with the dirty air filter, who knows?   seafoam in the tank might help the reported catalyst code, as well as 02 sensors

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it could be another ignition coil, they don't really go in bunches, but sometimes the engine Ecu can't really determine which cylinder it is exactly so it throws a random misfire code, with a generic code reader you won't get the full story on what DTC's that are actually stored in the ecu such as if there's actual freeze frame data on one of the cylinder misfire (which would be a smoking gun on which cylinder is actually misfiring) or if there's another Toyota/Lexus specific code to do with the O2 sensors. If it started just after you had work done it, the problem is most likely related to that. Disconnected injectors, ground wire not reattached to valve cover etc. There is one wire harness connector right under the battery that I think has all of the front bank's coil, or injector wires in it. I can't remember which... think it's a 6 pin grey connector right next to an identical 6 pin black connector, although I don't know why someone would've gone near those ones...

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