Hesitation going fast

[beachinblazer]

I've got an 86 K5 with 305 in it. It recently has begun to hesitate badly at higher RPMs. I rebuilt the distributor, so everything is new there. The timing is set 8 BTDC and with the vacuum applied its runs great. The only problem is whenever it sees higher RPMs (not sure when exactly) it misses and hesitates badly. Also, in 3rd (700r4 tranny) going about 45mph into the wind is about the most it can do without missing. Anyone know what might be the problem?

 

[Thunder]

How long has it been sence the fuel filter has been replaced. It may be clogged and starving your engine for fuel at higher RPMs.
Are you FI or Carbed?

 

[bklynlifted]

CARB OR FUEL INJECTION EITHER WAY IT SOUNDS LIKE A FUEL RESTRICTION PROBLEM. CHECK YOUR FUEL DELIVERY SYSTEM. DOES THIS HAPPEN ONLY UNDER A LOAD OR WHEN STANDING STILL AND REVING IT UP. PS FILL OUT YOUR VEHICLE PROFILE FOR A MORE ACCURATE RESPONSE . GOOD LUCK

 

[beachinblazer]

i've already checked the fuel filter. you think a fuel pump is good for almost 170,000 miles? if not then thats probably my problem. It really only happens under load (going up hill or into the wind)

 

[Thunder]

Yeah it could be the pump. The symptoms sound like it. After 170K miles it's probabally getting weak.

 

[k5ntexas]

yeah its the pump. the same thing happened to me a few weeks ago. replaced it and it ran much better. i also had a crimp in my fuel line right where it goes into my fuel filter into the carb. it was a bad crimp. but the fuel pump was a gonner cuss we put a clear inline fuel filter and we had not much gas. so just replace the fuel pump and most likely that will be it. hope this helps. later.

jacob

 

[MudNurI]

Im suprised nobody mentioned this--

a cracked spark plug will cause the same problems. our 89 was running horribly- but only when you got after it, almost puking..etc.. brought it in- they changed the fuel filter, no better, brought it back, they changed the plugs- said one was cracked, no better- brought it back- they had cracked a different one, they replaced it and to this day- running like a charm, with over 400K miles on it, driven every day...check the little stuff- before you go replacing the pump...

Brandy

 

[Can Can]

And a bad wire can cause the same thing, too. I wouldn't rule out an ignition problem.