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Old 06-18-2003, 09:31 AM
mithra mithra is offline
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Join Date: Apr 2002
Location: a space in time
Posts: 132
Nope, not O2 sensors.....

Tech took car for ride, brought it in "hot", hooked up diagnostics which pointed to the LH2SFI side of things. The tech then switched the connectors side to side for the O2 sensors, change in values. The tech then pulled the O2 sensors and physically switched the sensors side to side. You could see that the O2 sensor from the driver's side was black and sooty. After the switch, the diagnostics still indicated values that were way out of wack for the LH2SFI side. The tech then disconnected the MAF for the LH2SFI side and the readings dropped to the values that they should when the MAF is disconnected. Reconnect the MAF and the readings go way out of wack again (all this happpening at idle).

Here's where the fun starts........ We retrieve the old MAF from the trunk and connect it to the circuit "BUT" the MAF is NOT installed in the intake plumbing.... the diagnostic values are perfect. So, out comes the new replacement MAF and in goes the old MAF and the values go thru the roof.(at idle) We remove the old MAF and replace the new MAF (which showed proper values when not in the intake plumbing) and the values are back thru the roof again.

The whole time this process was underway(about 4 hours), the tech was on the phone with MB technical support going step by step with the diagnostics in conjunction with a pinout box verifying actual values and comparing them on both engine banks.

Values were checked and verified correct for throttle actuators, idle and WOT switches and on and on (I can't remember them all). Values at connections for the MAF's were checked and verified.

At some point late in the process, MB tech support suggested pulling the diagnostic module ( check engine light, no codes). After the diagnostic module was pulled from the box, and the engine restarted, all the values immediately went to spec, and the car idled normally. All the values for the LH2SFI were where they should be.

With the diagnostic module out of the loop, we haven't been able (so far) to get the car to go to the intermittent extreme rich mixture that has been plaguing me. The next few days should tell wether or not this is the root of the problem.

This particular module has a sticker on it that says "CARB", the tech indicates that I can drive the car without it until we verify that this module is causing the heartache.

If I have understood the information from JimF's auto page properly, does this module trigger the air injection system on startup? ( No.....I reread JimF's pages...this triggers the diagnostics)

I guess I'm trying to figure out how a "diagnostic module" could affect the engine's performance. (If, this is the root of the problem)

93 sl600
93 600sel

A mercedes is an inanimate object and therefore must respond to logic and reason.

Last edited by mithra; 06-19-2003 at 07:39 AM.
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