05 GC LOOSING FULE MILEAGE 55,000 with K&N air filter. What is the best spark plug to use. Any other suggestions app.

 

Get the van back to factory specs. Plugs and wires and air filter. Also ck you tire pressure too.

 

Good Start.
Also, turn off the air conditioner... The compressor is big enough to run a 10,000 BTU home A/C.
Also, Run the trouble code check.
Click the ignition ON-OFF-ON-OFF-ON-OFF without starting the starter. Read the codes and check it against the list on this website.

Good Luck,
Tom

 

will try to get codes, What is the best spark plug to use.

 

I am also about to change my plugs. 50,000 miles.
I know they say they last longer.
But, it made such a difference on my last 97 GC. I'll never wait that long again.
Champions have been very good for me.
Although I've had better results with their traditional plugs, I cannot find them. So I'll try the Champion platinum this time.

Looks like the working room will be better on this van, than my old GC.

On the trouble codes, Look for a possible O2 sensor code. My van ran great, But got lousy mileage because of a failing (not dead yet) O2 sensor.

Good Luck,
Tom