Check Engine Light at 40-45mph

I am having some trouble with a truck I just bought. It is a 1993 K2500 with a 350. I found that the spark plug wires were the wrong ones and that the timing was way too far advanced. I currently have it set to 4 degrees btdc. Now when driving somewhere between 40 and 45 mph and when the engine is at operating temperature the check engine light comes on. When I turn the truck off and restart it the light is off. I have tried to scan the codes but it always comes up clear. Also the truck runs great lots of power no hesitations. What could be the problem?

I am having some trouble with a truck I just bought. It is a 1993 K2500 with a 350. I found that the spark plug wires were the wrong ones and that the timing was way too far advanced. I currently have it set to 4 degrees btdc. Now when driving somewhere between 40 and 45 mph and when the engine is at operating temperature the check engine light comes on. When I turn the truck off and restart it the light is off. I have tried to scan the codes but it always comes up clear. Also the truck runs great lots of power no hesitations. What could be the problem?

Is it a steady check engine light or a flashing check engine light.

Code scanners only show present codes.
If light is not back on after a restart the code has clearer on restart.
Check for codes before after light has come on and before you turn off engine.
Or get a engine capable scanner that will read out history codes.

If you can get code no post back code no.

I thought stock timing on this motor was 0 degrees BTDC? But advancing it by 4 degrees shouldn't cause any issues if it doesn't ping.

It is a steady check engine light. There are also no knocks or pings. I can try bringing the timing back to 0 to see if that makes any difference. I have a 94 Sierra that is set up the same way and it is not experiencing any issues like this.

Hmmm, what does the lable on the fan shroud say for timing spec? And you are disconnecting the tan/black wire to put in in base timing before setting it?

It is a steady check engine light. There are also no knocks or pings. I can try bringing the timing back to 0 to see if that makes any difference. I have a 94 Sierra that is set up the same way and it is not experiencing any issues like this.

When the light comes on check for codes before you turn engine off.
Post back code no.