Hey guys. I'm experiencing a rough idle and lean conditions, so I started by first pulling all my plugs for a visual inspection. I then moved on to the cap and rotor on the distributor. The first thing I noticed when I lifted the cap off of the distributor body was a light gray build up of some kind covering the entire brass contact for the spark plug #6. The other seven contacts were fine, just number six had this light gray residue build up on it.

Anyone have any ideas what may be causing this? Is this a precursory symptom of somekind?


--1993 F150, 302, 2WD, 1/2-ton, 87K miles

 

Anybody got any ideas about why there's a gray residue build up on the brass contact?

 

I believe it is probably oxidation and can be cleaned up with some fine sandpaper or steel wool and then coated with a little bit of dielectric grease, as shoud the rest of the contacts

 

If you still have the original wires and cap/rotor, maybe it is time for a new cap and rotor. I would change those first, they are very cheap. My original wires on two Fords lasted 139,000, and 122,000 miles. The 122,000 mile wires were fine, I just felt like changing them, during a major engine repair.

I wouldn't worry too much about that fine powdery buildup on 6, probably a small glitch.

Visually inspect the coil anode, make sure that it isn't being eaten away, a poor connection or corrosion leads to arcing which eats the coil output terminal up.
Inspect all the terminals(inside the rubber boots) on your wires. If you are seeing too much corrosion, either rusty-colored or all caked up with whitish corrosion(galvanic) then maybe new wires will help. You mentioned running lean, I don't think a faulty high voltage system would cause that, but bad wires, cap or rotor can surely cause a rough idle and will probably also be felt at cruising speed as momentary hesistations.

 

Thanks guys for your thoughts and suggestions. I may very well look into a new wire set, cap, and rotor.

The base timing is where it should be--10 degrees BTDC. I checked for any codes the other day with a code reader (OBD I) that I purchased at Wal-Mart for $33. I received an 11-10-41 (C) during the KOEO test mode. The 'C' represents the mode I was in during the system test which stands for 'Continuous Memory'. A Code 41 means the Oxygen sensor, located in the exhaust manifold, voltage is out of range and running lean. I'm not sure where to proceed next. Any thoughts?

 

Chane the O2 sensor, this may help with how the truck is running
Tom

 

When you replace the O2 sensor, you will probably handle most of the idle issues due to mixture. It would be a good ideat to clean your Idle Air Controller with carb cleaner as it may have some buildup in the ports. See what this get you and let us know.

 

Hi guys.

On Saturday, I bought a new Bosch O2 sensor (4-pin connector harness that was 6-inches long) from Napa for $50 as well as a new cap and rotor (NAPA-Echlin brand).

I replaced the O2 sensor, cap, and rotor. For the cap and rotor, I lightly coated the contacts with silicone dielectric grease. I've never coated the contacts with dielectic grease before. I'm kind of curious as to how the brass contacts on the cap are doing with the grease applied, so I'm going to check on them after work today.

As for the Idle Air Controller (IAC), I checked the reference voltage and it was within range. I then removed the IAC from the throttle body and was very surprised by how much carbon was on the brass rod. I cleaned as much off as best I could with carb cleaner, then dried the component with compressed air. I definitely thought cleaning the IAC would cure the rough idle.

The new parts has greatly improved performance and fuel economy since installation on Saturday. But with these new components and a clean IAC, they haven't cured the rough idle (while in Park or at a stoplight in Drive). I think it may be time to troubleshoot the fuel-exhaust system next. Sigh...

Thanks for the very helpful tips guys.

 

Don't laugh or think I'm pushing snake oil. Try a can of Seafoam, 1/3 or so in the vacuum system above the intake and the remaining amount in your gas tank. The stuff's amazing. You might find that it will smoke like the dickens at first and run cobby, but it will clear up and just might do the trick, for $5.25 or so. Worth a shot. It worked for me very well.