Everytime I go over 70 MPH on the highway, the service engine light comes on. And when I slow back down, it turns off. Whats this mean? Ive checked for codes, but none shows up. So is my car fine then?

86 T/A, 305, Carburated.

Does the engine slightly sputter or miss while the light is on?

What do you mean by sputter and miss? My engine starts shaking really bad.

If you're engine shakes at this speed (or RPM) only, you're coil is probably on it's way out. It sounds like you have a weak spark.

Where is the coil located and what does it look like and how do I go about fixing it?

If you're running a HEI distributor, then you're coil is inside the cap (on top)..... but if it's external, you'll see an additional spark plug wire leading from the distributor cap to a small cylinder (coil)....

Get yourself a nice aftermaket 47,000 - 50,000 volt coil. Some quality spark plug wires.... and Bosch plugs. You'll not only eliminate the problem, but you'll feel a much stronger pull throught the RPM band.

no..........you won't

What??? How do you figure this? Whether you add a MSD box, Super coil, coil packs etc..., you're going to get a much more complete burn in the combustion chamber(s) (thus feeling a stronger band). How do you figure that you won't/can't???

Also, if you thought that I was implying that he'd lose either a second or a half of second in the 1/4 mile, then yes.... this indeed won't happen. But as far as the engine running stronger, and more complete in combustion, then I have to disagree with you.... it'll feel MUCH stronger throught the band!

A more stronger/complete burn in compression forces the piston down the bore harder.... thus giving you a stronger feel.

That would be a sputter or miss.

Actually, you probably ARE getting an error code. The '12' you get when you scan for error codes means the ECM is getting no distributor reference pulses. That is normal when the ignition is on and the engine isn't running (while scanning for codes) but can also be a stored error code for distributor reference pulses that are "lost" while the engine is running. It may or may not be stored along with a '42' or '43' error code.

I asked because you might be missing pulses at upper RPMs, which could accompany missing or sputtering (cutting out). Thsi is typical of a weak pickup coil, weak HEI switching module, cracked reluctor, or other primary ignition system component (possibly even a coil).

Your coil on your '86 is screwed to the top of the distributor cap, under a plastic cover.

I just started having this problem as well...

I just replaced my O2 sensor... (maybe 1000 miles ago)

it just started happening after I replaced all my plugs and wires..

I had bosch platinums in before, replaced them with the same
got 8mm wires instead of 7mm...

CE light comes on at 100-110 kph, and sometimes it hangs around but usually it goes out as soon as I'm back doing city driving...

engine code is 45