Garth S

I have a Jeff's new (old) spare MAF sitting here awaiting a trial in his '89S4 auto: he doesn't know this yet , and the wait may be a long one depending on the snow - but it will happen
I do not have a CO or A/F meter, so my best shot at setting the CO will be with a Fluke meter connected to the O2 sensor, left in open loop. So, where is a good spot to start with the 'mixture' screw in the MAF? Turn all the way in (rich) - and back out 'x' turns? - adjust for ~0.4v with the engine at operating temp?
Any guidance appreciated, for instinct says treat it like an AFM - but this is a first with a MAF .
TIA

Rich9928p

Unless you have a non-cat car, your LH should take care of keeping the CO in spec via the closed loop system. The non-cat cars have an adjustment to set the CO near the LH. No adjustment to the MAF should be required.

slate blue

The later style MAFs don't have a CO adjustment, I believe this went out around the time of the S4. You may have an old MAF if it has an adjuster, it shouldn't make any difference but thought you may appreciate the info.

Z

There is an adjuster screw physically on the S4 and later MAF, but it doesn't do anything. It's not connected to the LH like it was on earlier cars.

John Speake

The MAF is identical from the Euro S2 of 1984 through to the last GTS. Alll the MAFs have an adjiuster, and the multi-turn potentiometer in the MAF.

16v LH use the pot on the MAF - it is wired through to the LH ECU.

Early 32v use the pot on the MAF even though they have cats/O2 loop.

S4 and later have a remote pot above the fuse panel if they are non-cat because you can't physiically get the the pot on the MAF. So the wiring harness just doesn't connect to the pot in the MAF

If these later cars ar cat/O2 equipped, they don't have a remote pot.

But all MAFs are the same.

Garth S

Agreed - I have two sitting here: one 'new in the box', and another from a '85 US spec, plus one installed in the euro S4 . All are Bosch 0 280 214 001, and all have the 3mm adjustable pot open and ready to go.
With the one referred to in the first post, I know that someone has played with the adjustment screw - so back to the question of correct set-up:
Is there a recommended method 'starting point' ?
Rich, that the LH will fine tune is good to confirm, but some dufus has clearly been playing with the brass 3mm adjuster on this one.
Is the adjuster perhaps set to some specific initial resistance measured at one or two of the six pins prior to install? - and then the LH/O2 sensor loop applies the 'trim'?

John Speake

Hi Garth,

The starting point for a new MAF with no ageing is around 300 ohms, measured at pin 23 of the LH to ground. The pot above the fuse panel is a 20 turn multiturn pot, the same type as the one on the MAF itself. Clockwise increases the resistance. But this only applies to non-cat/O2 '88 and later cars

So if you had a 16v LH car (no cats) and the MAF is out of the car, you can set the pot to 300 ohms to Pin 6 to pin 4 of the MAF

For an early 32v, the same 300 ohms at the MAF would be a good starting point. An aged MAF will require more resistance to be used to get the mixture at idle correct.

Your '88 does have cats. The O2 loop with automatically adjust the mixture to stocih, as Rich has said.

If you disconnect the loop, it will go to a default setting, and you will achive nothing because the MAF pot is not wired into your car.

Garth S

Thanks to all for the correct feedback: Evident from the wiring diagrams ( who would think to look there first? ), the MAF adjustment pot is not in the loop for S4 cars. For what it may be worth to anyone with a car that uses this adjustment, Johns note of 300 ohms initial when new (pins 4-6) is valuable - and the one I had in hand gave 65 ohms/turn of the adjuster, decreasing when turned counterclockwise ...