check engine light comes on briefly,(10-15 min) goes off and sometimes just flashes and goes off again, i put chrome tips on tailpipes and after a short 8-10 mile easy driving trip they're covered in carbon , i cleaned TB , installed new AC delco Iridium plugs ( old ones looked perfect for 55k), cleaned cam postioning solenoid, ran over $75 worth of injector cleaner through the thing in the last month ( 3 bottles of Techron and many Lucas), cleaned air filter.cleaned MAF, the shop ran a report and i'm getting misfire codes on all 5 cylinders, but.... the thing runs like a sewing machine, no misses, no symptoms or power loss when the check engine light comes on, idles perfect!?? dealership says can't do anything until it misfires while on thier computer. what now??? its a 2009 3.7, did they have head issues?

 

forgot to mention, 4 inch lift, torsion keys 16x10 with 35s , dealership says its the weight of the rims and tires maybe. i said BS. also the light goes out if you punch it!

 

Have you looked for intake air leaks?

 

Did you take the TB completely off when you cleaned it so that you could clean both sides? We were getting multiple random misfires also. Cleaned it and they all went away.

 

yes! removed it and cleaned it like i used to clean my rifle in basic training! also re-cleaned MAF after installing K&N in case a little oil got sucked through intake tube. i'm pissed off! i have babied this truck since new always maintained it to a tee and can't win...and again like always the dealerships play frickin stupid! might be my last GM.

 

I'm leaning towards just replacing both cam sensors and crank shaft pos. sensor. can't hurt...

 

Amazing how many people will buy fuel additives expecting them to actually do something? If all it take to fix something was to pour in a bottle of your favorite brand of wallet lightener, there would be no mechanics.

A common source for P0300 in I5s is an intake leak. Check the two PCV hoses (one under the stock intake resonator to a port on the head [12MM], the other to the right going into the intake [8MM]), check the intake manifold itself for cracks and to see if the fasteners have come loose (I5s vibrate). This creates discrepancy between the MAP, MAF and temp = CEL.

You can also get an intermittent P0300 from an overlapping O2 sensor problem. You can check that by running the vehicle on a scanner and watch what the O2 sensor does as it reaches full temp and switches from open loop to closed loop. If the PCM sees that temp comes up too fast or slow, or if the O2 sensor is slow to respond, then you get a CEL.

It could be a bad cam position sensor, but if you pull the sensor, make sure to clean where the sensor mounts to the motor, dirty oil crud can hamper their accuracy.

Dirty fuel injectors would be at the bottom last spot on my list, unless you make a habit of running El Cheapo fuel?

GM vehicles have black tail pipe, they ALL run rich.

Did you change the plugs before or after the problem started?

 

would'nt any kind of air leak cause it to idle or run funny? this thing runs PERFECT! as for fuel, only the GM approved stations, got the list in my glove box.

 

If there is a leak that it is detecting it is very small and not big enough for you to notice, but it can detect even the slightest of leaks and pressure drops. The H3's computer system is very advanced and quite complex, sometimes almost to the point of annoying, but it is a great system overall. I agree with Doc.