MEMCALS DO GO BAD! I took my '94 chevy g20 van 305 to a chevy dealer after replacing every possible sensor and even the timing chain with 2" of slack in it and still got MAP code 33 and oxy sensor code 45 after 5 seconds of very rough hunting idle upon start up SES light would come on and it would go into limp mode and idle better but gobbled up fuel and blew heavy black smoke and foulded the new plugs quickly. The chevy dealer told me it needed a new ecm. I told him he was wrong, he replced it anyway and it still did the same thing. He told me there was nothing he could do because all of his sophisticated diagnosis equipment told him the ecm was bad and charged $80 diagnosis. The key thing was that he then lent me the chevy manual that described how the engine starts on the distibutor module and immediately at 400 rpm switches timing duty over to memcal.

I took the van back home, diconnected the wire that forces the engine to run on distributor module only and noticed the idle smoothed out somewhat. I then went to a junkyard and picked up a used 1994 ecm from a Yukon with a 350 for $50. I Pulled the memcal and put it in my 305's ecm. After letting the ecm go throuh idle learn procerss it now runs perfectly and idles like a dream with no service engine soon light!

There must not be much difference between a 350 prom and a 305 prom.

I'm no genius but nowhere on the internet or through any mechanic could I find out that YES INDEED MEMCALS DO GO BAD! In fact I was told by at least 6 mechanics and parts counter guys that they had never heard of a bad Memcal. GO FIGURE!