PCM 555 does not even resemble anything closely to MEFI 1 thru 3.. And MEFI 3 only displays 17 fault codes and how many does PCM 555 display ? how about over 236 . , here is the jist,

MEFI 3 code 44 = can not detect knock activity - MEFI 1 did not have this fault code period, MEFI 2 did have code 44 but the info for MEFI 2 is below

MEFI 2 it was only used on 2 apps and for 1998 ONLY. Very rare to see a REAL MEFI 2.

MEFI 2 was used for 1998 350 MAG and 7.4 MPI L29 only. it had only 14 fault codes period

PCM 555 / ECM 555 code 44 = EST 1 shorted circuit. And for anyone wants to know what EST is = Electronic Spark timing. Keep in mind as well neither PCM 555 and ECM 555 use a distributor.

Next info PCM 555 does not even use the same knock sensor(s) as MEFI - Merc apps. plus you have knock 1 bank and knock 2 bank for the 555.

if you have both knock codes constantly - then you possible have way more issues than knock sensors. Wonder what testing was done on the bad PCM 555

That's close but is the other way around. Was not part of MEFI 1 but was for MEFI 2 and higher

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