Hey Everyone,

I have an 81' F 150, 4x4, 351w, EEC III, 7200 Variable Venturi carb, K&N filter, MSD ignition, with 150K+ miles on the engine.

My problem is .......excessive pinging at lower elevations.

I live in California (this will be important later) at an altitude of about 2500 feet and have noticed that my truck will start pinging (freeway speeds about 2500rpm) when I drive it near sea level elevations.

It doesn't ping while cruising, it only does it when I ask her for just a little more--such as passing or pulling a hill or pulling a small trailer.
The pinging gets so bad I have to "feather" the gas pedal to quiet it down. Full throttle is not an option.

Oddly enough, as soon as I drive back up to about 1500 feet the pinging stops and try as I might, I can' get it to ping--not even by puttin' my foot all the way in it.

Since I live in the "Peoples Republic of California" and CAN NOT change the carburetor and/or the EECIII (timing is computer controlled and not adjustable) for emmissions reasons, does it sound like adjusting the jets on the WONDERFUL MOTORCRAFT 7200 VARIABLE VENTURI carb to get a little "leaner" mixture might resolve this ??

Anyone ever deal with this ??

Any and all suggestions will be GREATLY appreciated !!!

The clattering of "valve metal" is worse than fingernails on a chalkboard.


Bob

 

You would actually would want to richen your mixture when you go down to sealevel. There is less and less air when you go up.

Another problem is probably your K&N. Brings in more air than it needs too.

The other thing you might check is your MAP sensor. It might be out of whack enough to think the atmospheric pressure is higher / lower than it really is.

 

Make sure your egr is working. The engine will have a tendency to ping if it's not working. If you can see the egr, with the engine fully warm, rev the engine a little, and you should see the egr move a little bit.

 

Hey guy's .......

Problem solved !!!!!!

I took a trip to Autozone saturday to purchase an o2 sensor, air filter, and a MAP sensor.

To my surprise, the MAP sensor retailed for $ 220.00.
I kinda' balked at that price and the counter clerk suggested going to a "U-Pull It" yard and pick up a used one for a song and a dance.
To make a long story short.....I purchased an o2 sensor, the "special" socket for removing/installing it, and a new air filter.

I changed the o2 sensor (appeared to be the origional from 81' and boy was it a bear to get out), installed the new (non K&N) air filter and trimmed about 1/2" of the vaccuum line @ the MAP sensor (the vaccuum line slipped on and off it WAY too easy).

Today I took a trip "down to the valley" and almost all of the pinging was gone.
While I was down there, I decided to pick up some "octane booster" to see if I could get rid of ALL of the pinging.

Guess what ????
IT WORKED !!!!!!!!
I tried everything to get it to ping and nada !!!!!!
Ye Haw !!!!

Anyhow, for the archives........
I think the combination of replacing the (possibly bad) o2 sensor, making sure the vaccuum line going to the MAP sensor wasn't leaking, and replacing the K&N air filter all contributed to solving my pinging problem.

Since the EEC III has NO code readouts it seems to be a "repair by symptom" system and at that, my Haynes manual didn't have much in it as far as the EEC III goes.

EEC III owners BEWARE !!!!!!

Thanks a million for the responses guys......
You certianly helped me in my time of need.....

Happy wrenchin' to all of you !!!

Bob

p.s. The post about changing the headlight switch to get brighter instrument panel lights worked for me too. I did that a few weeks ago !!!