Help about Air Mass Meter, Multimeter and 1990 16v Saab900i

[lando1]

Hi. Few days back I was on this site asking about a sluggish 1990 16v 900i I just bought. Some helpful folks adviced I check the Air Mass Meter resistance between pin #3 and #6 which should be around 380 ohms (or between 300 and 450 ohms to be within spec). So I went out and bought myself a shiny new multimeter, took the Air Mass Meter out the car and set out to measure the resistance between the pins. First thing is, the pins aren't numbered, so I don't know how to work out which is #3 and which is #6. Any ideas? Still, as there are only six pins I tried the only two permutations possible, setting the multimeter on 2k and then 20k. With one permutation, I get no reading at all ; with the other I get no reading on 2k but then get 18.79 on 20k or 1.88 on 200k and so on... which is nowhere near or anything like 380 ohms. What does it mean? Am I doing it all wrong? Am completely lost now. Any advice or tips would be really appreciated. Many thanks.

[ProfZ]

If you're looking straight at the AMM's terminals, the rightmost is no. 1 and the leftmost is no. 6.

Give this a try, and let us know what happens!

[lando1]

Many thanks. If I look straight at the terminals - facing Bosch AMM box with airflow arrow pointing left to right - and make the leftmost pin from the AMM box #6, the reading I get with the multimeter set on 20k is 0.99. Makes any sense?

[cdaly]

Sounds like 990 ohm (assuming the 20k setting on the meter uses the . to mark the Kohms. Sounds way high if so...

[lando1]

:-??

[Ben]

An image speaks a thousand words; looking at this image: http://img.villagephotos.com/p/2003-...231/amm001.jpg

You will see a screw next to where the red wire attaches to the AMM, turn this anti-clockwise to lower the AMM's resistance.
Have the Multimeter on the 2k setting while you are doing this.

Ben.

[lando1]

Thanks a lot for the photo and info, Ben. One thing though, I was told to check the resistance between pin #6 (leftmost) and #3, and on the photo, though it's not too sharp and so hard to tell, the black test lead seems to be connected to either pin #1 or #2. Is that so? Is it wrong to connect to pin pin #3?
Cheers.

[Smackrazor]

I just tested my AMM and all of the pins gave a resistance of about 30 except pin 6 and 3 which had an infinite resistance. Does this mean my AMM is broken or is my multimeter broken?

Edit:
Bought a new multimeter, tested it on resistors and get the right value, test it on the pins on my AMM again and get infinite resistance. Tested another AMM I have on my other wrecked Saab and same story. What's going on?

[lando1]

Know the feeling, smck...

Ben, I took the AMM out again and re-read resistance between pin #6 and #3 (as in the image linked above) with mm set on 2k. The reading I get is .994. Did it a few times to make sure and always comes back the same: .994. Would such reading make for a "sluggish" drive? What are the symptoms to be expected from the AMM being set so high above 380? I'm asking because the car isn't going all that bad really and I just would like to check before breaking the AMM's adjustment screw's red seal which is untouched. By the way, just in case it's relevant, my AMM number ends with 017.
Thanks again.

[ProfZ]

Originally Posted by Smackrazor

Edit:
Bought a new multimeter, tested it on resistors and get the right value, test it on the pins on my AMM again and get infinite resistance. Tested another AMM I have on my other wrecked Saab and same story. What's going on?

Dumb question--are you testing the correct type of AMM? The "380 ohms" test only applies to the LH 2.2 AMM, which has a metal body.

Later (2.4 and 2.4.2) AMMs have plastic bodies, have different pin parameters, and cannot be adjusted.

It's certainly possible, too, that you have one bad AMM and that the one from your wrecked car is also damaged...

[Smackrazor]

Oh.... yeah I'm teting a 2.4 and a 2.4.2 AMM... ops:

I pulled the fault codes from my car and it said everything was working fine which was good enough for me.

[lando1]

Well, guess I better switch cars again until I get to find out a little more about AMMs settings and symptoms. So it's back on the road for the old 8v carbed one and away with the 16v injection one.

Quite spectacular really...

[Smackrazor]

What you can do for an AMM test is let the car warm up, then rev the engine to 2500 rpm and shut it off. After a second the platinum wire should light up (glow) and then go out.

[lando1]

Cheers, smkrazor. Just did the test this evening and the wire glowed and faded. So this much of the AMM's okay, I guess.

Just signed up on an <<Audi>> website (I know, but it got them Bosch injecttor systems too, I'm told) and the guys there turn out to be quite helpful; possibly just taking pity on a poor Saab owner who can't use his new second-hand car. So still hoping to sort out this AMM thing soon.

[WSAABI]

I tried to sort out Drivability, starting, rough idling and stalling issues on two different cars for a while (its too embarrassing to say how long and how many "expert" Saab mechs I contacted)

In the end, I'd replaced the AIC (a good idea), tune up (plugs, cap & rotor), Used several high test injector cleaners (the last being Redline's), traced the vacuum lines over and over again (finally replacing them all) and adjusted my AMM (original equipment) countless times. The AMM seemed to test fine and the resistance between #3 -> #6 contacts was adjustable & within spec.

So I figured it was some still lurking ghost in my machine.

Only because I stumbled upon an eBay auction of New AMM's for the silly price of $58 (I know what you are thinking... and they might be, I dunno) so I bought one. I should have gotten a couple. It TOTALLY fixed my drivability, starting, idling ETC!!! And power!

A lucky break indeed. $277+core charge is steep but baring a freak eBay deal, I would have done it long ago had I realized the potential.

After testing mine and thinking it was good for so long, I can only suggest getting a new one if your problems are similar. Search eBay (buy with caution) you might get a deal too.

Edit::
I just looked to see if the deal was still availible.
Here it is

[lando1]

Many thanks for the above and Ebay link, wsaabi. Only thing is I had a look at the AMMs on Ebay and they all end with #005. Mine ends with 017. From what I've managed to gather about the AMM thing so far, they're not interchangeable. But I'll look more into it just in case this isn't so. Cheers.

[deniss]

So the fact that AMM lights after engine shut-off like it should doesn't mean it's working properly?

Also, why can't you measure its resistance with an analog multimeter? can you really damage it that way like Bentley states?

lando1 - the eBay AMM deal won't fit your car because he states it's up to 1988 model year only, and yours is a 1990.

[Smackrazor]

The 380 Ohm thing is only for certain model AMM's as listed above. Later model AMMs have different readings, so the only way to test them is if the platinum wire glows.

[deniss]

yea, that's what Bentley's states. in their test sequence, it's obvious that if the wire glows, you need no further tests of voltage or resistance. i assume then that if either voltage or resistance is wrong, the wire wouldn't glow at all.

anyhow, i went ahead and ordered that AMM from eBay for $59. never hurts to have a spare, and this particular Bosch part number is exactly what's specified for my Saab in the official parts catalog.

[lando1]

Car working fantastic.

Turned out to be a faulty throttle valve (thank you Ben for advice and link to page on how to clean it in other tread). Haven't resolved the AMM resistance discrepancy though. Pin #3 and #6 still make for a 994 Ohms reading. Could be on account of the AMM itself (i.e. the 380 ohms doesn't apply to the 017 Bosch AMMs). Or then again, could be something else. Still aim to find out.

Now she's purring and I've become a little more familiar with its workings, I need to learn how to read the trouble codes stored in the ECU. How is it done and what's needed to do so. Any ideas anyone? Thanks.