driveabilty problem
 

well the blazer i just bought drives really well on the surface streets , but when i get it on the freeway it starts to miss all over the place at a bout 45 to 50 mph i checked the firing order and put in a new cap and rotor it has been converted to hei and from what i could tell the po put in a new wire from the dizzy to the ignition unfused could my problem be the vaccum advance ? ignition module ? any ideas would be great thanks..... tom

Re: driveabilty problem
 

First thing to check would probably be the fuel filter also a good idea to check the total advance and make sure it's not above around 38 degrees at 3000 rpm. If you don't have access to a dial back to zero timing light just unhook the vacuum advance and cap the port on the carb and drive it to see if it's better. Also look it over for vacuum leaks. If it doesn't change check the valve adjustment and make sure it doesn't have any tight valves. I had a problem with a 454 doing something similar and it was due to two valves being tight...not tight enough to be a problem at low rpm but seemingly tight enough to cause cylinders to drop at about 2800-3000 rpm range. It's hard to diagnose a problem via pc but these are things I would check first along with anything I might have missed suggested by other members. Hope you get it figured out.

Re: driveabilty problem
 

I only would add one more thing check your charging system.

Re: driveabilty problem
 

Good advise so far.

I'd be suspect of the plug wires themselves as well.
How do the plugs look?

If their not new, I'd go right through and replace both the spark plugs and the spark plug wires if it were me. Just my .02.

Re: driveabilty problem
 

man old truck fanatic was rite it was one of those in 5 dollar clear in line filters plugged solid thanks alot for all of the in put .

Re: driveabilty problem
 

Glad you got it fixed :metal:

Re: driveabilty problem
 

me too the thing screams now life is much better now