misfire on #3 cyl. question

[Outlaw178]

I 'm getting a code that reads a misfire on number 3 cyl. I have noticed that the light comes on every time I reach around 70 mph when at easy ride or under heavy pedal. and comes on when every time when I step on it pretty hard.

Here's the question:

I know this is either a plug. wire , cap , or rotor or maybe a fuel injector.

I changed the plug already....(good god who ever come up with how they ran the brake lines needs to be shot!) I'm going to change wires/cap/rotor If I can find a good set of 8 or 9 mm wires . But how do I check to see if the fuel injector is going bad or not?

Truck is an 03 extreme 4.3. with 40000 all stock except the K&N

[Sparky2263]

40k is a bit early for needing ignition components but not unheard of. If it was mine or a customer of mine, I'd go ahead and do a full tune, plugs, wires, cap and rotor. With carbon tracking being the problem it is with todays high amp ignition systems, you can actually miss the problem and transfer it to the new part.

It just doesn't pay to "one at a time" replace secondary ignition components.

[Outlaw178]

I agree wit ya Sparky but I had a couple of plugs sitting in the shop all ready so I went ahead and changed it. I have been looking to upgrade as well as replace the components when I do the tune up. All I have found is the accell tune kit and I think it comes with std. 7mm wires. I'm wanting a custom set not a universal set of good 8mm or better.

I've been looking to upgrade the coil but everywhere I look they say they don;t have one for the 4.3.

going to surf Summit and see what they got.

But my question still remains, How do you check and rule out injector?

I was thinking you get a different code for injectors but I can't remember.

[Sparky2263]

The high end scan tools can actuate the injectors. With that and a fuel pressure gauge a diagnosis is possible. There are other ways, with a wiring diagram, an injector actuator and a gauge, but that's beyond the scope of 99% of the guys out there.

Bottom line, the computer only knows it's misfiring, not if it's ignition, fuel, compression, etc.