Service engine light on?

OLDMAN66

MEMBER
2003 CHEVROLET TRAILBLAZER
6 CYL
4WD
AUTOMATIC
169,000 MILES

A while back my service engine soon light came on flashing when I came to a stop it was idling rough. I drove to my local mechanic, and he ran a diagnosis, and it said cylinder six misfiring. I don't know when it has been tuned up last, so I had them change plugs and the coil on six. It seemed to work okay for a while then it acted up again. It can go several days without it acting up running well but then I can't get five miles down the road before service light comes on. Then there are times it comes on runs rough but then it goes off and runs okay. My mechanic is baffled.

1 Reply

AL514

MECHANIC
4,692 POSTS

Hello, there can be a number of things happening, but if the ignition system was already replaced, that leaves a fuel injector acting up. Or a compression issue such as a sticking intake or exhaust valve. The check engine light is flashing because the misfire is bad enough to damage the Catalytic Converter. And when the issue is happening it really shouldn't be that difficult to figure out, if he has a scan tool, looking at some live data during the misfire can give direction. If it's a Fuel Injector sticking semi open or closed, doing a fuel injector balance test will help determine if that's the issue. Or doing a compression test during the fault. A fuel Injector issue can come and go with temperature, so can a compression issue. If the fuel injector is sticking closed and there is a lack of fuel causing the misfire, this will cause the ignition coil to fail prematurely if left like this. It will overwork the coil with a lack of fuel in the cylinder.

Here are some guides to help understand testing these two issues. But know, this misfire will eventually cause other components to fail if not repaired correctly. Maybe take the vehicle to a different shop for diagnostics.

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

https://www.2carpros.com/articles/how-to-test-engine-compression

https://www.2carpros.com/articles/the-reasons-for-low-compression