What ammeter do you use for mA measurement on 16v Motronic DPR?

[arne2]

Working with a 9A 2.0 16v swapped into a Mk1 Caddy. Trying to read and set the DPR. I know that spec is 2.5 mA ± 2.5 mA, and I see references that these engines like DPR at around 2.0 mA.

I've got a 0-200 mA scale on my ancient but trusty Craftsman digital meter, and built a quick and dirty adapter harness to connect it in as shown in the Bentley. No reading at all on the meter. Not sure if I'm doing it wrong (I don't think so), or if my meter isn't up to the task. What kinds of meters do folks typically use? Any tips?

[Butcher]

I use a Fluke and never really had an issue. I do know that it's fairly simple to make a tool and even simpler to hook up a meter to the tool.

Usually what happens with a ma meter is that the fuse blows because you hooked it up wrong. The leads may be wrong on the meter. It only takes a second to blow the fuse inside the meter.

[arne2]

That's a good thought. I don't know that I have ever used the ammeter ranges, but will check the fuse today. Thanks!

[arne2]

Sure enough, the fuse is bad. I'm on my way to get a replacement.

@Butcher - To make sure I don't reverse the polarity and blow it again, which of these should be the positive lead on the meter? At the DPR terminal, or at the harness connector?

[arne2]

Got the fuse replaced, and figured out the polarity of connection, and the meter worked!

Sort of...

Give's me a reading of 2.3-2.5 mA at idle - no matter what I do the the adjuster, the numbers don't change much. Rev it up and they drop into the mid-1s briefly, but always between 2.3-2.5 at idle, even if I crank the screw way out of whack one way or the other.

Any ideas?

[Butcher]

I have no VW training. Mercedes is where I got mine.

With a Mercedes, you hook up the tool and turn the key on, it will have a certain mA reading. If you did not, then you got problems so you figured out what they were. I believe the reading was 20ma.

The early Mercedes CIS-e ran at 8mA if I recall [perfect fuel mixture]. They eventually figured out that 0mA was a better deal because if the fuse blew or the system did not work, the basic fuel system would run.

When the engine is cold, there is a set correction. This amount of current is dictated by the CIS-e ECU. Once the engine is warmed up, the O2 sensor will vary the mA reading so the fuel mixture is correct.

You certainly could search the internet for better information that I could give.

If you have the amp meter installed backwards, it will only read backwards, not blow any fuse. So instead of a positive reading, it would be negative. The meter fuse blew because the current was over the fuse rating.

[arne2]

Thanks, that's helpful. I know that I did have it up to temp, at least for part of the time. The Bentley gave some very high number for ignition-on-not-running, something like 110 mA. No, I don't get that much by a long shot. More like 1.1 mA when not running.

Ironically, the ~2.4 mA reading is right in the middle of VW's spec. But it is suspect in my mind since it doesn't change much.

Who knows how long the fuse in my meter was blown. Decades, perhaps. I can't remember when or if I've ever used the ammeter functions before this. I've had this meter for probably 40 years. It's been through a lot...

[arne2]

Rapidly coming to the conclusion that my ECU may be bad. No real surprise, as it has spent years lying loose in the rain tray, bouncing around and sitting in water from clogged drains.

Here's what I've noticed.

It always flashes codes for bad idle switch and faulty Hall sensor. Both of those items were documented bad in the past, but both are now fine, tested in every way possible. Those codes can not cleared. They just repeat over and over.

The DPR is supposed to show between 90-110 mA with the ignition on but engine not running. Mine reads 1.7 mA. Consistently reads ~2.6 mA at idle, warm, cold or in-between. No amount of adjustment changes the reading, even ridiculously large changes that severely change the mixture and how the engine runs.

Unless someone has a better idea, I'm probably going to hunt down a replacement ECU soon.

[Butcher]

The cob webs are clearing, Mercedes is 70ma. If it failed the key on/engine off test, the ECU was bad. No other tests needed. California ECU's were 65ma. This test also confirmed if your ma meter was hooked up correctly [right flow].

I think you are going in the right direction if the engine off test is that far off. The other option would be that your specs are wrong. As long as you confirmed the specs are correct, just buy/find another ECU.

[arne2]

Makes sense, thanks. I've located a replacement ECU. Hope that finally puts this all to rest. I've got a few other mechanical things to address, then clean up the wiring mess from the hack engine swapper, then some welding before paint. A fair ways to go yet.

[arne2]

[gereonb]

About to do the DPR measurement myself on my 16V PL CIS-E, will let you know what I find, what was the plus/minus ? I assume plus on the loom side and minus at the DPR.