Here's the background: Yesterday, got in my Blazer and drove about 5 miles on an errand, shut it off, came back out and it started fine and drove home (mix of highway and surface streets). Pulled up to my mail box and it suddenly had a very heavy miss. Would barely idle. Up to now, no driveability issues. Very sudden that it quit running right. Blazer would barely pull itself the two blocks home. I had been meaning to put a fuel filter on it, so I did, and it didn't help. But, when I blew it out, the gas was black. What does that suggest? It is missing on cylinders 1,2, and 6. Anything that these three have in common that I could check? I don't know if it turned on the SES light, my air pump is dead, and I've just been driving with the SES light on. I don't have a scan tool, but I'll have to be getting one soon. Anything obvious in these symptoms?

 

Black gas coming out of the filter is normal, it means the filter did its job and collected all the dirt and gunk before it can get to your injectors. As for the sudden misfires, thats kind of hard to determine without knowing if the wires, cap, plugs and rotor are in good working order. When was the last time your Blazer had a tune up? How many miles do you have on the fuel injectors?

 

The cap and rotor look bad, so they are getting replaced. The tip of the rotor is eroded and black and there is some slight soot on the plastic around the center contact. The cap has slight erosion on the terminals, but there are three brown spots on the conductor that goes from the #1 contact to the #1 plug wire attachment. You can see the spots from the underside of the cap only. I don't know if this is just innocent dis-coloration or an arcing problem. The plugs look normal and have less than 5000 miles on them. I don't know how old the injectors are, but I bought this with 145xxx miles on it and it has 153xxx now. I've never done anything to the injectors. Any chance a bad ignition module would fire only three cylinders?

 

Yeah a bad distributor cap and rotor can cause this type of problem. Change them and see how it runs. If the wires are old or look dry rotted, I'd change those too.

 

i would do a basic tune up plugs, wires, cap, rotor and dont use cheap stuff AC delco only

 

Turns out that the connections to the computer were loose. The top one was the culprit. I got them both tightened up and it runs perfectly.