random misfire

[tweety2300]

Are you talking about the air intake sensor that goes before the maf?

Yes, I think it's in the stock air box stock I don't remember as I have an Sri

Cr3 if your referring to me my 323 has a chipped ecu, so it still relies on the stock sensors

 

[CR3 Motorsports]

Sorry that was to JDM.

 

[JDMazdaFamilia]

So replacing my exhaust bolts helped a bit but now I've gotten a ton of other problems and its sad for me to say but my car is my only transportation and lately days have been kicking my ass and I have no time to work on my car. So first of all I was driving the car 40 miles to get to school, car drove perfect until less than a mile away from school. I was coming up to a stop light, threw it in neutral and the car went to low idle and tuned off. Turned the car back on and then it started making a nasty knock once in awhile like a rock was being tossed in the combustion chamber. Pulled the dipstick oil seemed to be fine. Had to carry on through the day and later on the knock sound went away but then got a cyl #4 misfire. Pulled out #4 plug and it was shut all the way with no gap. Looked inside the cyl with a snap on scope/camera, all I found in there was a big puddle of oil on the piston. Regapped the plug and it ran fine. Next day double checked the piston it was dry with no signs of damage. But then oddly it started idling choppy and at high rpm. Now I'm getting codes for: idle air control, cyl #4 misfire AGAIN, pre cat warmup effeciency, still getting random misfires, and on top of that it leaks a s*** ton of oil now. All these problems came out of no where and I'm pulling my hair out! I'm afraid for my msp. I checked my tps for the idle issue and the voltage its getting is within spec. There's oil all over my bay but I think its coming from a cam seal, I pulled out the cam position sensor and it had oil on it

 

[tweety2300]

If its knocking dont drive it, that knock will become a bang and then you have metal and oil scattered on the road. Do a compression test and see if the compression is good and go from there, there should never be a puddle of oil on the piston. It may have jumped time and what you're hearing is either detonation or a valve hitting the piston, and I know what happens when those come down too far at 9500 rpms on a scooter, it's not very pretty I'd hat to see it happen in a car. Although that's not likely if its only one piston having issues

Install shield just a thought for you, since it is colder there is more air being drawn into the motor which obviously means more fuel. Do you think it could be a bad connection on the coil packs and them not having enough power to produce a big enough spark? I know they use a waste spark system but I'm not real familiar with it.

 

[Installshield 2]

^^^i should've replied after i did the work...The underside of one coil pack had completely cracked through from heat cycling...i could see that the grounding was completely ruined...it was most likely arching onto the head cover instead of down the boot to the plug...and the plate they sit on was completely warped and distorted. So i'm guessing it was them being dead in multiple ways (the connection barely held onto them too...was very loose, but nice and tight on the new coils?)...

car has run perfect ever since i changed them...I didn't inspect them closely when i changed the plugs, would've saved a few days for waiting for new parts...but for now, i'm sure that was my only problem.

Oh and wasted spark is simply the coil design. The coils get a signal to ignite a plug, but they only do it to both cylinders at the same time...not just one...so one cylinder is nearing TDC of the compression stroke...but the other is nearing tdc of the exhaust stroke...the 'wasted' comes from sparking the exhaust stroke, thats all...but its much simpler and cheaper way to manufacture coils this way.

 

[JDMazdaFamilia]

Tweety- I had no choice man. The knocking went away after 2 days. What I think happened is a small foreign object got into the combustion chamber, made the knock and closed the spark plug shut. As far as the oil on the piston I have no idea why that got in there. Anyway I think I got very lucky that the ugly knocking stopped, there is no damage done to the piston, all the other cylinders look fine and compression is good. Today I found one of my oil problems, my valve cover gasket ripped right over the cam gear. Still need to see if its still leaking oil. Stumped as to what else to look at for my idle issue. Tps and vacuum are all good

 

[tweety2300]

Could be leaking around the spark plug.