crossfire injection

[John Moran]

I would like to know how to adjust the fuel mixture in my 82 C3. I recently replaced the spark plugs and noticed the plugs seemed to be damp with gas. I am assuming the mixture is too rich but not having any experience with the crossfire, computer controlled fuel distribution, I have no idea where to begin. Give me a good old carburator any day!

Your advise would be greatly appreciated.

Thank you,
Captain Jack

[William C.]

Re: crossfire injection

The mixture is self adjusting, if you have a service manual, it will tell you how to put the computer in a "read out" mode that will verify computer function as well as read out any trouble codes for you to follow up on (the meaning of the codes is also in the service manual. In essence, the mixture is controlled by a signal from the O2 sensor in the exhaust. damp plugs do not indicate anything unless they are damp when pulled immediately after a period of normal operation including a complete warmup. The older C-4 systems take a longer time to go into "closed loop" mode than the newer sustems. How is the fuel economy on a long trip? If the check engine light comes on at bulb check, and goes off after starting, and the mileage is in the low 20 mpg range on a 100 mile trip on an interstate, you are ok. Also, plugs will last 50,000 miles or more under normal conditions with that system.

[Terry M.]

Re: crossfire injection

Bill gives good advice. These computer-controlled systems are self-evaluating, and a shotgun approach to repair is often needlessly costly and unproductive.

That said, one might consider that O2 sensors do wear out (become sluggish over time) and any exhaust leak on the engine side of the O2 will cause rich operation -- the leak allows introduction of oxygen into the exhaust stream causing the O2 sensor to think the engine is running lean so it drives the injectors to put in more fuel resulting in rich operation.

If your normal mode of operation is a brief engine run in the garage the engine never warms up and never goes into closed loop -- thus the system is always running rich.