Diamonddice6

Interesting that a bad cat caused misfires in cylinders 3 and 4. Kinda makes sense I guess if excessive exhaust backpressure causes the misfires, what with our interesting firing order and exhaust config.

 

Since the firing order is 1-3-2-4, maybe when the pass side bank fires 1-3 in a shared exhaust runner, 1 has a little room for the exhaust pulse, but it builds up pressure against the clogged cat, then cyl 3 observes high backpressure and misfires. Then there's a rest before these fire again.

 

Likewise, then the driver side bank fires 2-4 into its shared exhaust runner. This time 2 fires ok but starts to build pressure against the clogged cat, then cyl 4 observes high backpressure and misfires.Then there's a rest before these fire again.

 

Not sure if that makes sense - just trying to work out why 3 and 4 would be victims of misfires with just one common cat being clogged. I guess if it got any worse, eventually all cylinders would misfire under load. Especially when the cat warms up.

That was my question too when the mechanic told me it is the catalytic converter....why not all clynders and just 3 and 4....no logic explanation however the catalytic converter was badly broken from inside....it has a big whole and rattling sound....so i had to replace if it is the cause or not.....but the funny thing ....the car passed the immition test couple months before this issue happened !

 

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That'll be awesome if it fixes your problem!

 

Which cat got changed? Did your mechanic say why it needed changed? That seems like an unusual diagnosis for a misfire.

The car is running normal till now, no misfire codes, the catalytic converter was badly broken and the small chips were moving to the part after which i am not sure what they call and block...that's why the car was running good in first minute till accumulation of gas in the blocked catalytic converter...which caysing a back misfire...that was the explanation by the mechanic.

He changed the first two with Walker from Napa for $499 and the oxygen sensor for $150...plus his labor fee.

 

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I took the car to the mechanic shop who suggested change the catalytic converter, after doing that... the car running normal with no missfire...i will drive the this week to make sure there's no more missfire.

 

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I swapped the wires, the car didn't turn on, I tried twice and read the codes, no change p0303 and p0304, discovered an oil leak under the car not sure from the where that oil is dripping but it is around the oil filter towerds tires...otherwise the engine bay from up iis clean....

Thank you, i did it in different way before by using ometer...i will try your instructions.if didnt work will go again from zero....i am tired of this car..

Again, i have misfire in cylender 3 and 4.....can some tell me how to check the ignition coil? I already did but probably didnt do in right way....the rpm goes down to 600 with check engine light on when car get warm otherwise it is smooth when first turn the engin on.

I added half can tò the throttle body directly, using a small size diameter tube which insert under the air hose and pour the seafoam slowly while some one keep the rpm on 1800, dont forget to unplug the MAF when seafoam, plug it back after having few miles on the car and seeing no smoke going out from muffler . Car is running perfect and codes till now!

Four days ago, I changed the spark plugs #3 and 4, seafoam the engine with a half can...the results are amazing...car runs smooth and stable...i reset the codes of misfire and didnt have them back since, however i used the car for only 7 miles, probably should drivr it for longer distance and see if the problem has solved.

Tomorrow will drain the fuel from the tank and replace it with a super grade, two days a go I added heet to the fuel and car runs well, the codes disappeared...strange.. I know...lets see what wil happened and will update you guys.

Thank you.

no I didnt clean them, usually I go with the codes that car throwing, i am so careful of not ruining something else, the spare parts are so expensive, do you yhink these sensors can cause misfire?

I have the same issue, it's been parked since March, it started when changed the spark plugs with Denso iridium, throwing codes p0303 and p0304, returned back to old spark plugs, recheck the gap, changed the spark plugs, new set of wires, change the ignition coil, clean the fuel injectors, check the pressure in fuel lines, change the throttle body, change the rear O2 sensor, finally I changed the MAF, forgot to mention that I changed the fuel filter too, we thought the cause was the fuel as the car was idling fine with fuel aditive till reached the point of nothing help...with all of that still have misfire on cylender 3 and 4, both didnt move...still didnt get the time to do a compression test...probably this week...I am thinking in draining the fuel tank and add a new fuel? if didnt help will take it to dealer...