Hey guys, got an odd one here.

Car was driving great yesterday, no issues. Then at a red light, the CES light came on, then went off. Did it again when pulling away from the light, came on, then went off. Car drove fine after that the rest of the day.

This morning, ready to goto work, turn the key and crank, crank, crank sputter - POP!, crank, crank, crank, sputter - POP - keep repeating.

Well, I think codes! BUt there's no codes… so I had a new coil anyway, put that on - no change.

crank, crank, crank, sputter - POP

it's an 05 MCS with 94,000. Please share your thoughts on where to look next.

Thanks in advance!

 

Can put a video of the noise up on youtube?

 

was the popping coming from the engine compartment, or the exhaust?

 

Pop is definitely from the exhaust.
Since I've been trying to get it going, the pop has stopped…

I feel the fuel relay clicking. Lifting the seat I can hear the pump priming. But still nothing. I'd have thought if it were fuel related, there would be a code stored some but am I wrong there?

 

bad spark plug(s)/wire(s) causing a misfire?

running the proper fuel?

if the light came on, there should ne a stored code.

 

I thought that too about the light - figured - HEY! engine light = code, but plugged in scanner and no codes were in the system.

I'm waiting for a flatbed to take it to my mechanic. Damn shame that work gets in the way of servicing, but hopefully it's nothing serious.

 

Well, right now it's looking like the problem is the back O2 sensor. Never knew it could shut down an engine, but here you go. They disconnected it, and it's running like a champ.

Hopefully this is all it is. They're doing a little more diagnostic to make sure there nothing else.

Remember, check your O2 sensors

 

sounds very strange to me.

the pre cat sensor is the important one. post cat isnt really necessary (other than keeping the cel off). i doubt it would be the cause of your problem... unless its some how electrically shorting something else out.

the readings it sends to the ecu shouldnt affect the drivability as its main function is to monitor compliance with epa laws. thats my.understanding anyway. i know it has other functions, but the pre cat sensor is the one that adjusts the afr.

im curious to hear more about this.

 

I don't quite get it either. But it's running like a champ now.

He did say it seemed to be shorting. So maybe that's it. Who knows. I trust these guys more than any dealer mechanic when it comes to understanding the car and putting it together.