Bad News

Off Road Red · November 11, 2003

I went out to fire up my old 85 today and as it was warming up it started to develop a misfire so i did the usual ignition system/sparkplug check and found cylynders 3&5 werent firing and had oil on the plugs. Sounds simple enough to diagnose as worn rings, but heres the catch, at times the motor runs perfect, then at times it well miss and sometimes it misses so bad the whole truck just shakes because its running so rough and on the highway it seems to run good. Does it still sound like the rings are shot? I just find weird that 2 cylynder side by side would go at the same time, anyone have any opinion on what could be wrong? I won't be able to do compression and vaccum tests till tomorrow. Any input is appreciated.

Wingnut · November 11, 2003

If it's intermittent, I would lean more towards electrical, or sensor issues, rather than loss of compression.

When you lose compression, it's probably going to run like crap all the time.

Off Road Red · November 11, 2003

There is still spark at the plugs though.

Wingnut · November 11, 2003

Doesn't mean that a sensor (i.e. O2/anit-knock/etc) isn't messing up, and farting around with your timing and/or fuel/air mix.

duffy · November 12, 2003

I had an old 350 do something similar to that and it ended up being a busted valve spring. I had 2 cylinders that were dead. When I tore it down found the bad spring. The cylinder with the bad spring was robbing the other cylinder of the air/fuel and killing it. When it is missing bad kill it and try a compression test. Just an idea to look at.