V12 ECU's Reporting 'Not Ready' - PeachParts Mercedes-Benz Forum

MB-Dude · #10 11-12-2007, 04:39 PM

Local MB dealership does not sell vacuum tubing by the foot; I had to order it (!) pre-cut in about 5 foot lengths. It’s MB p/n 000.158.14.35 Price is fairly reasonable at US$3.60 per 5 foot section. Oh well, they only had one piece in stock. Ordered 10 pieces since I will be changing all the vacuum tubing on both my SL’s. The first attached pic shows one of the 5 (yes, five!) vacuum repairs I found on the 96 SL600… after taking ALL the plastic engine covers off! It’s amazing what one finds buried under all that fancy covering. Thus, my 94 SL500 is probably just as bad.

While waiting for the vacuum tubing, I went ahead and poked around the vacuum fittings. Lo and behold, I found a loose one – the vacuum connection to the master brake assembly. See second attached pic. This fitting was very loose and does connect to Bank 2. I was encouraged. But after tightening the nut and taking a quick warm-the-engine jaunt, I once again was staring at 0 volt output of the Bank 2 Sensor 1 O2 Sensor. Swapping the MAF’s between banks also made no change.

However, I did make an interesting observation. If I created a vacuum leak (at the vacuum repair in pic #1), I witnessed an immediate decrease in output voltage of Bank 1 Sensor 1 O2 Sensor. Remember, this is the bank that is operating correctly. Within 10 seconds of initiating the leak, the computer compensated for the leak and rebalanced fuel (presumably) so that normal O2 Sensor operation resulted. Reconnecting the vacuum line caused the O2 Sensor to output high, but only momentarily; the return to normal operation was a much faster response. In both cases, I witnessed the post-cat sensor following, though not as radically, the pre-cat sensor.

What this means is that small vacuum leaks – say, the size of small vacuum tubing – will not adversely affect this engine; the computer can compensate. In order for the computer to not compensate, the leak would have to be massive and, thus audible.

As a test, I revisited a previous post of mine…
http://www.peachparts.com/shopforum/showthread.php?t=195934
…and disconnected the vacuum line. Even with this fairly large, albeit metered, leak, the computer compensated fairly well. You could watch the O2 Sensor as the valve open/closed, but the computer maintained control.

Conclusion: While I definitely need to replace some vacuum tubing, I do not believe a vacuum leak is causing the problem.

So I’m back to square one. I’ll continue to poke around for vacuum leaks and will replace the tubing. However, I believe this problem is, unfortunately, electronic. Finally, myarmar asked if I could print out the ME-SFI data. Attached is a data snapshot. ProScan (the OBDII scanner I use) captures the data over and over, so the file is a series of successive snapshots. This is good for comparing oscillating or varying data. The file is really a .csv file, but to upload it, I had to rename it a .txt. Simply change the .txt to .csv and MS-Excel will read it correctly formatted. If further shots are needed, but only of a few variables, I can easily set that up.

QUESTION: Is there any harm in swapping the ECU’s between Bank 1 & Bank 2?

Not sure if there is any special information or bank-specific stuff that could cause a problem. Again guys, any and all ideas are welcome.

Cheers,
Jeff