(Sorry if this has already appeared. I originally sent it 8/31/05, but it has not appeared on my news server yet.)
A friend's 1997 Astro with a 4.3 liter engine has 245,000 miles on it. Recently, it started to miss. When I ran the scanner for codes, I got P0305 (misfire cylinder 5), P0175 (System too rich, bank 2), and P0172 (System too rich, bank 1).
With my limited knowledge, I suggested he do a complete tune-up: replace spark plugs (platinum), spark plug wires, rotor, distributor cap, fuel filter, air filter, pcv valve and run some Chevron Techron Fuel System Cleaner through it.
My friend said the cab company we drive for had done a complete tune-up some 25-30,000 miles ago so would replace the #5 spark plug and wire and use the Chevron Techron. We changed the spark plug, but could not find the correct single spark plug wire, so re-used the original one. The number five cylinder started to fire, but the number four cylinder stopped firing (P0304) The Chevron Techron did not correct the other problem. I suggested that he at least replace the distributor cap and the number 4 plug. He has done so, along with the 2 & 6 plugs and wires. He will replace the plugs and wires on the other side this week end.
When he replaced the distributor cap, he said a piece of metal fell out of one of the holes the wires go in, and when he replaced the #4 plug, the insulator was cracked. But against all my expectations, #4 cylinder is still missing. I ran the P0304 code, erased it, and it came right back.
I wanted to exhaust the cheaper things that I know how to do before suggesting anything expensive. My next thought is that the fuel injector for #4 cylinder is malfunctioning.
I suggested that he go to a garage that I have tried just for them to diagnose the problem and we could do the work if it was within our knowledge and abilities.
I personally have not ridden in it, but my buddy says it only misses at idle and smooths out as soon as he gives it any gas. I think it still misses at fast idle, but smooths out when he drives it.
Thanks in advance to anyone who has any suggestions.