engine misses 4000 rpm
 

I just got an 86 GXL that runs great until around
4000 rpm, and then the engine misses quite badly.
I realize that this is a very vague question, but thought I'd give it a shot. Plugs, fuel filter,.....??

it could be fuel filter or a bad ignition component. it could be bad timing. if you just got it ... give it a full tune-up (including wires), then if the problem persists, post again and let us know.

4000 rpm lag
 

I've read numerous articles about the ground problem in the "boost sensor" being related to this problem.
Anybody here try this fix?

It seems like an easy task and one that could do no harm.

Sounds like u r experiencing the common 3800 rpm hesitation. Do a search. Good luck.

if its a 6 port see if they are frozen
would have the similar effect of a really retarded ignition