OK electrical guru's what the heck should I do now? (CIS air idle control valve meas) - PeachParts Mercedes-Benz Forum

Stretch · #1 11-14-2015, 08:49 AM

G'day Folks,

I'm still struggling with electrickery.

I want to test my air idle control valve on my M102.

Book says the current should be 580 mA +/- 50 mA after a 28 second period due to heater on air intake and at an idle of 700 to 800 rpm

So I got me the expensive cable

http://www.peachparts.com/shopforum/tech-help/372249-m102-m103-cis-test-cables.html

Plugged it into the parts I'm meant to =>

Connected the end to the multimeter

And the bloody engine stalls!

It seems like the impedance of this auto-ranging multimeter is too high (or summit like that) and that causes the engine to stop.

I've tried to make the measurement with "less good" multimeters I have with a switch-able range such as the one in this picture =>

And the bloody engine still stalls when I switch to the appropriate 0 - 1 amp (was it?) range...

....hmpf - not impressed.

Any suggestions?

One of those gucci clamp round a wire current meters?

Graham · #2 11-14-2015, 10:54 AM

How did you set your meter? It sounds like you would have to move the one lead to the 10A socket if current is over 400mA. Then set the dial pointer to 10A. To read up to 10A, the meter likely has a shunt inside that will add a certain amount of resistance to the circuit but not much.

I ask because I have at least once, forgotten to move that lead and then blown fuse inside meter! Looking at your picture again, I think you may have the meter leads in wrong sockets. Black should be in center (COM) and red on left (10A). meter manual

I have a clamp meter that will read DC (not all will). Not sure it would be very good at low currents. Need to check range and accuracy.

Stretch · #3 11-14-2015, 11:53 AM

Quote:

Originally Posted by Graham

How did you set your meter? It sounds like you would have to move the one lead to the 10A socket if current is over 400mA. Then set the dial pointer to 10A. To read up to 10A, the meter likely has a shunt inside that will add a certain amount of resistance to the circuit but not much.

I ask because I have at least once, forgotten to move that lead and then blown fuse inside meter! Looking at your picture again, I think you may have the meter leads in wrong sockets. Black should be in center (COM) and red on left (10A). meter manual

I have a clamp meter that will read DC (not all will). Not sure it would be very good at low currents. Need to check range and accuracy.

Thanks for the quick reply - I'm about to zip off and buy a clamp meter - may be I need to sleep on the idea before I end up spending more for little gain...

...the EX330 (my good) meter uses the leads in the position shown for currents up to 400mA

For 400mA to 10 Amps you need to swap the leads round as you said.

I tried both.

I had to fire up the engine with the multimeter disconnected to get the engine to start. Because the means the air idle control valve is disconnected the idle would run high (as it should to about 1500 rpm).

I then switched on the multimeter to the setting required.

I then connected the plugs so the air idle control valve worked - the engine bogged down and stalled 99 times out of a hundred!

Using a different cheaper multimeter I could get the engine to start with the multimeter connected but it always had to be in a range that was smaller then the range I needed for the measurement. Switching to the range I wanted made the engine bog down and the bugger stalled (or nearly stalled if didn't switch back quickly)

TnBob · #4 11-14-2015, 01:01 PM

I just connected my IAC with alligator clips ... one side direct to the MB connector, the other side to my meter and from there to the MB conncector.

Graham · #5 11-14-2015, 03:33 PM

Stretch - In the picture below, you don't have a lead connected to the COM port. You always have the black lead in the COM port and then you move from the main + port to the 10A port when you want to measure above 400mA.

From the manual:

Quote:

3. For current measurements up to 400mA, set the function switch to the mA position and insert
the red test lead banana plug into the mA/μA jack.
4. For current measurements up to 10A, set the function switch to the 10A range and insert the
red test lead banana plug into the 10A jack.

TnBob · #6 11-14-2015, 11:05 PM

Good eye Graham !
Soo true... com (common) is com regardless of whats being measured.

Stretch · #7 11-15-2015, 03:09 AM

Quote:

Originally Posted by Graham

Stretch - In the picture below, you don't have a lead connected to the COM port. You always have the black lead in the COM port and then you move from the main + port to the 10A port when you want to measure above 400mA.

From the manual:

Quote:

Originally Posted by TnBob

Good eye Graham !
Soo true... com (common) is com regardless of whats being measured.

Sorry to disappoint chaps - that picture was used as an example of the crappier types of multimeter I have kicking about the place. The picture shows me measuring something else that isn't related to this problem.

Graham · #8 11-15-2015, 10:06 AM

Quote:

Originally Posted by Stretch

Sorry to disappoint chaps - that picture was used as an example of the crappier types of multimeter I have kicking about the place. The picture shows me measuring something else that isn't related to this problem.

I had noticed that that was your other meter. But regardless of what you were measuring, the COM should have been connected.

Anyway, good luck with your trouble shooting!

Stretch · #9 11-15-2015, 01:06 PM

Quote:

Originally Posted by Graham

I had noticed that that was your other meter. But regardless of what you were measuring, the COM should have been connected.

Anyway, good luck with your trouble shooting!

I think this is a weird one because you need to use the two outer plugs for a continuity check - but anyway...

...I have ordered a clamp multimeter that measures DC current - I'll see how I get on with that.

Stretch · #10 11-24-2015, 09:13 AM

Just to update (despite my problems with leads) the solution was to buy a clamp amp meter and to feed that through a loop of wire going from one end of my test lead to the other.

Works a treat. I get a proper measurement and the engine doesn't stall because the meter isn't stealing all the juice.

TnBob · #11 11-24-2015, 05:04 PM

and what were you able to measure ?

Stretch · #12 11-24-2015, 09:44 PM

Quote:

Originally Posted by TnBob

and what were you able to measure ?

For the air idle control valve I was getting a pretty consistent 560 to 600 mA and the for the EHA I could see it slowly adjusting itself back down to zero amps.

Pretty cool actually to finally see something working as it should (even though I still have a stalling problem)!

TnBob · #13 11-25-2015, 09:07 AM

Ahhh... is it supposed to 'seek' ? 560 to 600ma ?

Soo...''Book says the current should be 580 mA +/- 50 mA'' and you are there.

Stretch · #14 11-25-2015, 09:44 AM

Quote:

Originally Posted by TnBob

Ahhh... is it supposed to 'seek' ? 560 to 600ma ?

Soo...''Book says the current should be 580 mA +/- 50 mA'' and you are there.

I'm happy enough with it. I can see that it is trying to do its best.

I have been told that the O2 sensor is always going to adjust slightly so you are going to get slight variations. (I actually found a note in WIS about this but I'm not going to tell you about it 'cos it will only piss you off!)

Note this spec is for the last KE generation - I don't think it applies to your car. If I remember correctly you need to measure some form of duty cycle at the air idle control valve to see if yours is behaving itself.

########

Even though this bit seems OK I'm still chasing my tail for the stalling problem. That's been dealt with in my Achtung thread...

...multi-tasking == multi-threading!

TnBob · #15 11-25-2015, 04:05 PM

I am sooo beyond being pissed... pls tell me.