Intermittent SES / fuel trim codes

[upallnight]

Originally Posted by RocketyMan

"A rule of thumb on a MAF's air flow rate at 500 rpm is 1 gram per second per liter of engine displacement."

This rule of thumb only works for an engine that has relatively no load on it, e.g. no A/C on and no heavy electrics (like cooling fan). So since you have a 3.0L engine, that means at 1000 rpms, you should be seeing about 6 g/s of air being reported by the MAF. This is the easiest to do with just the throttle. Then you can check it by then rev'ing slowly to 1500 rpms, 2000 rpms and record what readings you are getting. This should follow a linear fashion, so you can also interpolate data if you are running at say 700 rpms or something in between.

Obviously there will be pumping losses and and friction involved, so more likely than not the mass flow rate is going to be slightly higher.

Make sense?

Only to a Rocket Scientist. So why not just answer his question about which MAF is reporting the correct airflow? The old Siemens or the new VDO?

So just from your explanation, the new VDO is not correct since a BMW M54 idles around 700 rpm so 7.8 g/s is Waaaaay too much.

[RocketyMan]

At first glance, that would def seem too much. But I never really experimented with the flowrate of the AC compressor on, fan, blower, etc. when the engine is under any load.

Doing some maths, the 7.28g/s would suggest idling at about 1200 rpms, but I didn't see anywhere in the OP that he reported the idle speed with that flow rate as it could've been reported on a cold engine with startup...I dunno. I guess I'd have to assume the idle was at 750 rpms re-reading that post.

The 4.48g/s suggest idle of around 750 rpms. That seems perfect, but a good self check would be to take it to several rpm points like 1500, 2000, etc, and determine if the reporting follows a linear fashion.