Check engine light flashing.

Sarviss3 · September 11, 2016

I have a 2002 sierra 2500 hd. The check engine light flashes around 40 to 50 mph. It's been doing its since I bought it four years ago. I know it means there is a misfire detected, but I don't feel any misfire. I tow a 32ft camper with no problem. I've changed the plugs and wires and it didn't make any difference. I just replaced the muffler yesterday to make sure there wasn't any blockage. I was wondering if there was something else that could be making the light come on.

waumo1 · September 11, 2016

Have read the stored codes?

Sarviss3 · September 11, 2016

I have and it says multiple cylinder misfire. You would think I would be able to feel that.

rdnkcpa · September 12, 2016

Blinking CEL bad. Most likely doing damage to your cats.

Check fuel pressure. Easy.

Check for vacuum leaks.

Compression check.

Go from there.

Have fun.

Colossus · September 12, 2016

Yup, blinking CEL means urgent attention required. steady CEL = get in when possible, something is wrong. It only does it between 40-50 MPH, does it do it all the time? Only when towing? Have you tried to have it diagnosed yet at a repair facility? Yes it could be a misfire, but it could be something else with a misfire being a symptom. Think of it like an O2 sensor. Just because the CEL light came on and the computer reads bank 1 blah blah blah doesn't mean you go out and throw in a new O2 sensor (unless you have 150,000 miles in which case the O2 sensor is likely going to be weak anyways so its due) the sensor is simply reading abnormal readings, but what are causing the readings? Thus the importance of having it properly diagnosed and not throwing parts at it. You've got a fine truck there. Can we see some photos of it too? (the truck, not the CEL light)

Cheers

Sarviss3 · September 12, 2016

Its been doing it for the last four years. It doesnt matter if I'm towing or not. The truck has 128,000 miles on it. I haven't took it to the shop yet. I know they say when it's blinking to have it checked asap because it will cause damage but after four years the truck runs the same.

waumo1 · September 12, 2016

Sounds like you have decided it really isn't a problem after 4 years so just continue on as is.

dcheeseman · September 12, 2016

Check the intake manifold gasket as those are known to leak with age and cause misfire.

Daniel

Sarviss3 · September 12, 2016

It's a problem. I never really drove it enough before and now it's my full time ride. I feel it might be the reason the gas milage is poor, only getting 9.3 per gallon. I'll check the intake gasket tomorrow after work.

Daryl LBZ · September 13, 2016

My 2006 did this. After I cleaned a few grounds, replaced the ground cable for the battery, and swapped out all my oxygen sensors it hasn't done it since.

Colossus · September 13, 2016

have you pulled the plugs to inspect them and checked the wires? Hopefully the plugs and wires have been replaced once or twice since the vehicle was new...

Sarviss3 · September 13, 2016

I've replaced the plugs twice since I had it. I just replaced them a month ago. It never makes a difference. How do you know if the oxygen sensors are bad.

waumo1 · September 13, 2016

If it has 128,000 miles on the original O2 sensors, they are probably shot. I had a 94' Buick 5.7L that had 90K and it starting taking fits of running rich. Once the experts gave up, I changed the O2 sensors and it was fine. I actually cut open the O2 sensors and could see where the platinum plating was mostly gone off the ceramic part of the sensor.