If your mechanic doesn't know how to diagnose this, ask him to call a tech support line. The charge is $50, but they'll walk him through the fix step by step.
If it is producing a misfire code it is not a defective check engine light. We really need to know what code(s) are produced.
I would next be looking at a sticking EGR valve letting too much exhaust as into the intake at times. Misfire codes are calculated - the ECU does not know if the engine has actually misfired but it sees the crank taking longer from one cylinder firing to the next and assumes it was not generating power.
The check engine light coming on intermittently is usually a sign of a loose or corroded connection between a wiring harness and sensor,a open or short in the ignition or fuel injector circuit,a loose spark plug wire on cap or spark plug,or a sensor that hasn't gone out yet but has an intermittent fault.If the truck is running fine I wouldn't worry about it.I'm assuming you disconnected the neg battery cable or used a scanner to clear any codes out after you had those repairs done.If not,disconnect the neg battery cable and see if the light will extinquish.Anytime the check engine light comes on and sensors or components are replaced,failing to clear codes after repairs will cause the correction factor for the old component to be applied to the new component.A misfire code can also be due to a faulty injector,injector harness connecter,exhaust leak,or vacuum leak.Let engine idle,spray carb cleaner around every gasket,vacuum hose,and vacuum operated component.
With indicator light going on and off, that's an intermittent problem. Did you replace plug wires, coil wire, or coil? When you just replace all the parts you don't know what parts are really bad. Also, I've learned that a new part can be faulty. You also don't know what parts are still good.
The check engine light is controlled by computer and it is gathering info from the sensors. You need to know what trouble code is activated, and start checking that circuit.
See main dealer. They an interrogate systems and see if it's faulty sensor etc.
Runs like a charm...Do you have any codes other then ...and i assume, p0300...odd stuff I've seen brake booster,you may not notice misfire when braking to a stop... this was forgivable, but
plug wire internally broken, only breaking down under heavy load...fuel pressure low on WOT road test found bad filter one and faulty new aftermarket pump...
These are simple checks most technicians do before and after the parts replacements you've had...comebacks don't pay the bills...
you may not have paid cash but you bartered something for it. You shouldn't need a dealership drivablity tech to properly diagnose this..
So I've got an issue going on with my 2002 Chevy S10. Check Engine light is coming on and off randomly. It shows that a misfire is occurring. Problem is, I took it to my mechanic. I was fortunate and had my spark plugs, distributor cap, fuel injection cleansing, fuel pump, timing belts, a few hoses replaced and everything else that could effect this problem from happening at no cost to me. Bartered for my services. He's completely stumped as to what could be wrong especially since it does not have any evidence showing a misfire. Truck is running like a charm. I feel nor hear any misfire. He believes it could just be a faulty check engine light. What could I do to fix this?
