Random stumble/ missfire
 

Hi my 305 just started getting a missfire randomly any thoughts

Re: Random stumble/ missfire
 

Lots of thoughts. Too many to list. Can you describe misfire? Stumble? Not sure if it's a fuel stumble or ignition "misfire". When noticed? how often? backfire? Idling rough? only under load/acceleration/hills? Don't know your abilities or experience with motors. First thing is determine gas or electric. There are deeper issues also, valve timing et al. Please confess to anything recently done to motor or gas tank. Anything. Daily driver? Weekend driver? Been sitting long time?
You may be able to isolate a particular cylinder by pulling each plug wire off one at a time. If one does not change motor, that is the one that is missing....or check each plug to see that it is firing properly. Or without removing anything, you can use an inductive timing light on each plug wire to watch the light and see if it pulses at a constant rhythm or matches the misfire.

Re: Random stumble/ missfire
 

Just started running rough out of nowhere? Or doing it worse and now noticing it? Many factors at play here. Could you be more specific?

If it's a pop once in awhile it could be a lazy valve.

Az ken
 

Ken,

Thanks for all the advice a few days back. It WAS the gas cap!! Running great now. Please stay in touch.

Bob
rsrose@gmail.com

Re: Random stumble/ missfire
 

Turns out it was points or condenser I changed both she runs like a champ again

Re: Random stumble/ missfire
 

Cool! Always a good feeling when it's just something simple. For the future, Petronix makes an HEI kit for these dizzys. I have one and it makes it run that much smoother. Or you can go the USA route and get the one from HEIDIZZY on Ebay. Direct hei swap. $325 for it though. haha But a dern good setup. :ok:

Re: Random stumble/ missfire
 

TJ's right, you can get easier starts with an HEI setup, but you should know the rest though - in the event of SHTF situation your truck will be as worthless as all the other modern vehicles. You can probably swap back and get 'er running again in that situation if you keep the parts on a shelf, but you may not have time to pull out the wrenches if you're close to a big city.

Re: Random stumble/ missfire
 

In the situation like that most chances an HEI will just get a burned out module, like myself I carry a spare module and it's easier than replacing a set of points:teehee:

Re: Random stumble/ missfire
 

I've had the pertronix for 6 years and no problems yet...course...I said something now. :lolsmack2:

Re: Random stumble/ missfire
 

Pretty neat you have been a GMC owner since u was 11 years old - seeing that you had Pertonix for 6 years - most 17 year old kids wouldn't know what a distributor with points or HEI was at that age. Keep on truckin' :ok: