Random misfire codes

Stewart91 · Post by **Stewart91** » 08 Nov 2018, 00:26

Okay let’s start from the beginning

So Volvo broke down on the highway on the wife towed back to the house and pulled codes. Had misfire for number five. Found number five cracked and started to melt. Replace coil five and all 6 spark plugs.

Then the Volvo got a O2 sensor code for the upstream and it proceed to get the code for both banks. Replaced both sensors. Took for a test drive after replacement.

Now got codes for random misfire and for cylinders 4,5,6. When replacing O2 sensors had the key of and cleared codes after install. Also disconnected a solenoid when key was off but plugged back in before turning key on. Also these four codes are all just pending. Not sure if they will go away after driving some or they are here to stay.

Any thoughts or past experience would be greatly appreciated

Stewart91 · Post by **Stewart91** » 08 Nov 2018, 07:13

Vehicle is a 2011 Volvo XC90

Post by **SuperHerman** » 08 Nov 2018, 20:49

I got caught on this the other day and forgot that on the Volvo it takes 2 cycles for codes to appear if they are there. So the pending code just may be waiting to pop up after the next operation. One smart poster wrote down the exact parameters that constitute a driving cycle - my take away (abbreviated version) get the car up to temperature, hit 50mph for a bit and drive for 10-15 minutes. Repeat a few times. If the codes don't reappear then the problem should be solved.

I am a little confused on a number of items regarding what were the original codes, the interim codes and current codes. But, one cylinder misfiring could cause all the others to misfire. At this point, if all your coils look good, clear the codes and drive it like it is going to fail (stay close to home or where you will not be left stranded) and go through two start/stop cycles.

What did the spark plugs look like? Oil condition? Oil usage? Service history? Which engine? Current mileage? Any other information could be helpful.

Stewart91 · Post by **Stewart91** » 08 Nov 2018, 21:59

Original code was just a misfire for cylinder 5 which also blew the ignition fuse. Replace all 6 spark plugs all looked good. Then got codes for both upstream box sensors. Believe they were low efficency codes. The replaces both o2 sensors. Then got mud fire code for 6,5,and 4 and random misfire. Going to check them when I get home light finally came on.use about a quart of oil every 3 months runs full synthetic. Mileage around 135,000. Has the 3.2 straight 6

Stewart91 · Post by **Stewart91** » 08 Nov 2018, 22:28

Sorry auto correct both upstream o2 sensors

Stewart91 · Post by **Stewart91** » 08 Nov 2018, 23:28

Ok so the misfire codes went away and now have PO420 “Catalyst System Efficiency Below Threshold (Bank 1). and PO430 “Catalyst System Efficiency Below Threshold (Bank 2). codes

Post by **oragex** » 10 Nov 2018, 18:25

How are the spark plugs? Its the first thing to check whem a coil is failing

Stewart91 · Post by **Stewart91** » 11 Nov 2018, 00:03

Replaced all 6 spark plugs

Post by **pgill** » 21 Nov 2018, 18:32

Stewart

There is some evidence that a failed thermostat causes the coil to get too hot and then the coil fails

If you change your thermostat let us know if it was broken

Some links

http://www.volvoxc.com/forums/showthrea ... -2009-XC70

viewtopic.php?f=31&t=86205

http://www.freel2.com/forum/topic32245.html

Good luck

Paul
2008 LR2 3.2
2010 S80 3.2

Post by **oragex** » 22 Nov 2018, 00:02

As above, the 3.2 stat is known to cause overheating. We have no information on whether there was some engine overheating, but the melted coil is suspicious. If replacing, look inside the stat see if the plastic part is broken.

From there, a possible scenario. Engine has overheating for a while, took down one or more coils, the car kept driving, unburnt fuel went and damaged the catalytic converter (thus the codes for O2 and efficiency). The O2 may have actualy been fine. Smell a little at the exhaust for a rotten smell. At this point I would replace all other coils, heat may have weakened them.

The scenario can be similar even if the stat is good and there was no overheating. The failed coil may have caused the cat to go bad, if the car kept driving for a while with a misfire.