Misfire under load (P0300)

[bikerbill7]

I recently replaced the plugs after I got my '99 GP GT (3.8L) back from my kids after they used it for the past 4 years at school. It had just hit 100K miles. The center electrode was pretty worn. I don't remember the gap, but it was pretty large. Anyway, the car now has new plugs and it starts fine. But when trying to give it 3/4 throttle to get out in front of the pack, or when trying to pass on the highway, the engine would start to miss and even backfire into the intake manifold.

 

Thankfully, someone had already posted here about the same problem and how removing the spark plug heat shields solved his “missing†problem. So, I just tried doing the same... and the #1 plug wire broke inside the boot. I can see the metal part still on the spark plug. Considering the time in the evening, I wasn’t going to run out to get a new wire. I was able to spread the wire clamp and pull the broken part out, and cut the insulator off the broken tip of the remaining wire, folding the inner wire over and re-clamping the clamp.

 

After removing the dog-bone bolts (engine side) - don't forget to have the car in something other than PARK so you can tilt the motor forward, and then use one of the dog-bone bolts in the left dog-bone to hold the motor forward - so you can give yourself more room to get at those back bank plugs. I removed the spark plug heat shields and took the car out for a spin. The “missing†was gone!! I hope this helps out someone else!

 

[sl3196]

I've never had to rotate my engine to do the rear plugs heh. I took out the brackets for lifting the motor and tons of room.

[BIGBULS]

Oh my GOD!

 

WEIRD!

 

You had to do plug WIRES as well as plugs............

 

 

 

 

 

 

Um......

 

Like, Derrrrrr.

 

I can pretty much guarantee any time you do the 100K tune-up you WILL be doing wires along with plugs and a PCV valve.

 

 

 

Oh, and if you DON'T put the heatshields BACK on, you will be doing the wires AGAIN.

 

Just so you know