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    Mercedes Benz E240 V6 2001 - Catalytic convertor efficiency # Archived Message

    Posted by Dave Hill on June 17, 2007, 10:23 pm

    Here is an interesting case.

    A local Jag specialist presented me with a 2001 E240 Merc (V6 2.4) with a MIL on & codes for catalyst efficiency (both banks) logged.

    It has had a pair of cheap catalysts fitted (Euro Car Parts) within the last six months. It belongs to the guys Dad ??. Anyway he asked me to look at it & see if I could make any sense of it (god knows why?)

    Here is a capture of it after a couple of minutes of 2,500 RPM…… Whilst this capture was taken, the emissions were well inside MOT standards






    This next capture is after prolonged fast idle ......



    This capture is taken at idle, imediatley after the fast idle test.....




    After a few minutes of idling, I decided to scope the fast idle again. I was surprised to see that the downstream sensor was switching again (like in the first image). It appears that the short period of idling was enough to bring the catalyst out of it's "zone" of efficiency.

    I suggested that it might be possible to fool the PCM by snipping the rearward sensor wires. (4 wire Zirconia type) so that a “no switching” signal could indicate an efficient catalyst. Unfortunately this didn’t work, as it soon logged a circuit fault both rear sensors. I left the ball in his court.

    He returned the vehicle to me again to put the light out. This time he had fitted one of the downstream sensors, further downstream, behind the single remaining catalyst where the two front pipes join into one. He had extended the wires from both downstream sensors & joined them so that the PCM is seeing the same signal for both bank (rear) sensors.

    I cleared his codes & sent him away. He hasn’t had a problem since (early days yet).

    I did suggest that he contact ECP to explain his concerns, but he thought it doubtful of any success.

    In conclusion, it appears that the catalyst’s are capable of meeting their efficiency requirements as far as “tailpipe” standards are concerned, but when it comes to engine management strategy is concerned it is quite another matter.

    Cheers for now

    Dave (Hill)

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