2002 V70 T5M Engine Issue, Mystery... Help.

J5T · Post by **J5T** » 26 Apr 2010, 21:11

My kid has a 2002 V70 T5M. She just got the vehicle a short time ago and it need some repairs that I did for her. After 183xxx miles I had to replace the lower control arms, end links, timing belt and accessories, cam seals front and rear, spark plugs, air filter, VVT gasket, clutch, plate, clutch slave, changed all the fluids, and no thanks to the people at Belle Tire for cracking the oil and claiming that they did not do it, I had to change the oil pan. All of this was just for some back ground but I was driving the V70 today to get some gas and pull out on the main road kind of fast. By the time I got to the gas station (1/2 mile) the engine was running rough and died. I managed to get it started and get gas. On the back home it was rough at idle and was lacking power. Then it seem to have lost a cylinder. At this point the check engine light came on. I get the V70 home, plug the code reader, get misfire in cyl 5 and cyl 2. I pull the plugs and it looks as if something hit the electrodes of #2 and #5 plugs and closed up the gaps. I looked the best I could to see if the piston had any witness marks and there were none that I could see. I am not sure on these engines if it is even possible that the piston could hit the electrode. I regapped the plugs and put a shop vac to each cylinder in case something was in it. Put the plugs back in and it seems to be working fine again for now. Anyone have any insight as to what the issue could be? Danke.

jda2000 · Post by **jda2000** » 27 Apr 2010, 07:56

failing spark plug coils? Next time you get a misfiring code, swap the offending coil to a different cylinder and see if the misfire changes accordingly.

J5T · Post by **J5T** » 27 Apr 2010, 19:52

It is not the coils that cause the spark plug gap to close. It has to be something physical that is moving the electrode. I have never seen this in the 38 years I have been turning wrench.

Post by **JDS60R** » 27 Apr 2010, 20:07

Fellow wrench here.

That's a good one. I have seen it a few times and sometimes it remains a mystery. I usually don't see it in 2 cylinders at once though. Nothing common about it with your motor. You should not expect to see this again if the intake is clean and well maintained.
To physically close the gap it had to be as tall as the piston to plug gap as well as the spark plug gap.

With no witness marks on the piston and no damage to the spark plug itself I would guess a few flakes of intake track carbon.
Let us know if you see damage on the spark plug electrode.

If you cleaned the TB or anything else it could have set carbon something loose.

Its obviously gone or you would hear it rattling around. In these motors we sometimes get a small fragment of metal from the midline of the cylinder wall right before the engine fails from overheating. These fragments are not heard as they are too small and I have never seen one do any more damage than a misfire (crosses the plug gap).

The only metal large enough to do it is a valve or piston fragment. If it idles poorly or a leakdown test shows poor results in those cylinders you may want to pull the head - but I doubt you find that.

Given what you said above I assume a piston showing no signs of detonation. With all of that in mind I would bet on loose carbon and forget it. Run a compression or leakdown test and if all is well then just move on.

J5T · Post by **J5T** » 29 Apr 2010, 20:40

Did not hear anything as far as noise. Car runs fine now even at idle. Cannot tell that anything is wrong. Thanks for the insight on the carbon. Never heard that carbon could bend electrodes. I did not do any cleaning of the TB or intake. I guess I will have to check out the intake if I can get the car back from the kid. I will keep an eye out on it to see if I have any more problems. Thanks again.

skeeter123 · Post by **skeeter123** » 30 Apr 2010, 09:22

I have heard of a problem on Nissans where the tiny screws that hold the throttle butterfly valves in place can fall out, and go thru the engine/combustion chamber, sometimes cause damage, sometimes not. Just a thought.....

J5T · Post by **J5T** » 30 Apr 2010, 15:31

Thanks skeeter123, I will check the TB screws when I get the V70 back to have a look at it. It has the ETM so I have not seen what one of these looks like but it does not hurt to have a look.