[agartthean]

This is about a 1986 Saab 900 S, with B202 engine (16 valve, dohc, no turbo) and LH2.2 fuel injection system.

With the Air mass meter (aka mass air flow sensor) connected the car has very little power, runs too lean. Disconnecting the Air mass meter helps a lot.

But the car has other electrical trouble, so before getting a new AMM i checked the connections at the AMM to the LH fuel injection control unit or ECU. I found a few differences to the "official service manual":
Connected are:
ECU pin 6 - AMM pin 1
ECU pin 8 - AMM pin 3
(but the manual says ECU 6 - AMM 3 and ECU 8 - AMM 1)
ECU pin 7 - AMM pin 5 (manual agrees)
ECU pin 14 - AMM 4 (= ground) (manual says ECU 14 - AMM 6, but it agrees that AMM 4 is ground)

Could anyone please check their manual and see how it should be? The wires in the car don't look like anyone has messed with them. And the car used to drive reasonably well before, although there was always some trouble after a cold start in the winter (engine stalling, quite possibly because it was too lean). After warming up it used to run well though, but it progressively got worse.

Thanks a lot.

 

[agartthean]

AMM stands for Air mass meter, i should say ...

 

[16saabs]

there are some OHM readings on the site somewhere (sorry )which give the readings if all ok. If you disconnect the amm the car then goes into 'limp home mode' and is usually as dull as yours sounds with your amm, but that's all it's supposed to do....get you home
cold start/run re weather conditions point to cold start sensor (blue end) that's between 2-3 cyl on inlet manifold, as once you are warm the car is ok.
does your CEL light come on(check the bulb works, might have blown/ disconnected), as this should light up occassionally on start etc if probs.
There is always the possibility your O2 sensor(lambda) is no good as it works in tandem sort of with the amm, to give the right fuel/air mix, so if one or the others out(had it) the other cannot work properly as ECU not getting right info to work with...as I understand it

 

[ludichris001]

First thing to check is that you have no vacuum leaks.

There should be around 2v on the orange wire for the AMM with the engine at idle.

There is also a small black fuse holder in the engine wiring loom, usually it's where the loom passes under the cabin inlet, and has blue/red wires going in/out of it. Make sure that fuse isn't blown (I have no idea what it's for but if it's blown the car won't run right) Twist the two ends to undo the fuse holder.

If all checks out ok, try disconnecting the oxygen sensor wire and see if that makes a difference while driving.

 

[Jim Mesthene]

Air mass meters can only be tested by substitution, despite what the 'bible' tells you.
You are reading the pin numbers from the back of the disassembled plug, right?

 

[agartthean]

Thanks for your answers.

When the AMM is disconnected the CEL is on, and the car is at least drivable. With the AMM connected the car is now essentially not drivable, so bad it has become.

I did check the temperature sensor that's on the intake manifold between cyl 2 and 3 (is that the cold start sensor?) and its resistance characteristics with respect to temperature are very close to what the manual says.

The O2 sensor i had checked in a propane flame recently, there was youtube video on how to do that, the voltages were fine and responding quickly after i had held it in the propane flame for some time, so that it got properly hot.

I had also fixed all the vacuum leaks.

The other things i will check on the weekend.

Does anyone have a bentley or other manual, with wiring diagrams, where the connections of AMM to ECU could be verified? I'm not sure if this is of concern ...

 

[agartthean]

To be more clear about the pin numbers: They are numbered as in my manual, see the photos.

The AMM's photo shows the connector from the cable side, the side where the metal clip goes up, as it is installed at the AMM.

The ECU shows the connector, when it is unplugged, the side where it plugs into the ECU. My connector looks slightly different, therefore a photo of the actual connector also. I interpreted the left side to be the more rectangular side.

 

[agartthean]

I got tricked by symmetry - how embarrassing
The ECU connector sketch in my manual was a bit misleading. I should have interpreted it the other way. Now everything is fine. Sorry to trouble you all with this.

My next question is about the AMM for the LH 2.4 fuel injection (Bosch number 0280 212 013) and the one for LH 2.2 fuel injection (Bosch number 0280 212 005):

Is there a more fundamental difference between the two than that the wires are swapped, and that the 0280 212 013 has only 5 wires instead of 6. Would the 0280 212 013 work
with the LH 2.2 fuel injection, if one changes the wires accordingly?

Thanks a lot.

 

[ludichris001]

They run at different temperatures and give different signal outputs. If anything it would probably either mask the problem or make it worse. It's best to just keep the -005 AMM

 

[agartthean]

thanks, that is convincing. I have ordered a new -005 meter ...

 

[16saabs]

thanks, that is convincing. I have ordered a new -005 meter ...

that will not be cheap

 

[agartthean]

that will not be cheap

USD 140 from partsgeek for a reman. It works great. All the trouble is solved, the car never drove that well in the last 3 years!!

(Initially there was some slight residual stalling, but that was due to a cracked spark plug. I found that out only today.)

 

[agartthean]

The new air mass meter from 2012 lasted for about 2 years, then slowly the performance drifted worse. After almost 3 years I bought again a new one, this time there is quite a choice on ebay and much cheaper. Again, all the trouble is solved.

 

[xander18]

Thanks for updating this thread! It pushed it to the top of the list so I would see it. I'm experiencing very similar issues with my MAF/AMM and you've confirmed some of my suspicions. Now just to endlessly refresh the eeuroparts tracking page until my new one gets here.

 

[c900]

I'm curious about this too as I'm unsure if I have a failed AMM (-019 version) with the 2.1 motor in my 1992 sedan. I've got a thread about the stall-out issues but specifically wondered if AMM's can and do fail yet ECU reports no faults associated with that?

Motor starts, but stalls out. Refer to 2.1 stalls out after starting following replacement of...

for all the gory details.

New AMM's are next to impossible to find, though they seem to crop up occasionally with a price tag north of A$1000.

 

[jvanabra]

I will sell you mine for A$900.

They absolutely fail without setting a CEL. Even on much, much newer cars.

What you describe sounds like fuel starvation.

 

[c900]

I'm thinking the same - which means FPR or the fuel pump itself. But dealing with the things I have access to and/or available spare parts for first. I don't have a spare AMM currently.