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Old 06-19-2003, 09:14 AM
stevebfl stevebfl is offline
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Re: Diagnostic "CARB" module....any theories?

[QUOTE]Originally posted by mithra
a) I am wondering if the distance (or time) from the shop is actually the number of "drive cycles" that the DM module monitors. Is this possible?

No, a drive cycle is mainly determined by engine temp. There has to be a change of 40 degrees. So once hot, all the small trips or otherwise aren't counted till it cools 40 deg.

b) Does it sound possible that the diagnostic module could be generating an intermittent voltage or current that is throwing the engine management system into a tizzy instead of triggering the MIL light?

Its hard to say how much command comes from the DM to the LH. Much of the contact between them is just information and I haven't heard of the DM affecting performance, but it wouldn't surprise me.

c) Should the Diagnostic module trip the MIL light when the engine is misfiring, running so rich that the O2 sensor is sooty, and the exhaust looks like that of a Mack truck?

I doubt the DM monitors misfires on that early car. It only monitored some testing early on.

c) Does it sound reasonable that once the Diagnostic module is pulled, the values for the LH2SFI MAF sensor went to normal?

If it happened I can believe it. could be just a conincedence. If it hasn't happened again in 400 miles and then does happen I pity your poor tech. If those old onboard diagnostics don't catch it the only way is a bunch of substitution.

d) Is there a method to test the MAF sensor to determine if it is in spec or faulty?

MB says NO. There are many things you can test. You can see if there is NO load signal but quantifying a signal is not possible do to the dynamics. A 10% wrong signal would be bad, 20 % unacceptable to pre 95 cars and yet the spec is about 50% wide.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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