Rebuilding AFM?

[zcacogp]

Chaps,

I'm not sure what I'm asking with this post, but will carry on anyway ... []

My S2 has failed the MOT again on emissions. High CO. Same as always. The tester was careless enough to put the probe in another car hence my car passed, but I'd like to solve the problem properly.

The same happened last year and I seem to recall that I did some things to make the CO readings come down, but they were still pretty borderline. I am strongly suspecting the AFM is nearing the end of it's days. It is 180,000 miles old and operates by pushing a flap in an airflow against a spring, and my suspicion is that the spring will lose it's springiness with time allowing the door to open more than it should and hence flowing more fuel, running rich and putting the CO up.

Taking the AFM apart and cleaning the tracks is a simple job, and one I have done before. What I am wondering is whether it is possible to tweak the spring tension up slightly, reducing the door opening and thus leaning out the mix and lowering the CO. Is this possible? Advisable? A very bad idea? Has anyone tried this? If so, how did you get on?

I know that re-built and re-calibrated AFM's are available, but they don't offer much change from £400 and that's a fair chunk of lolly. Does anyone know of a way of doing this cheaper?

(Alternatively, does anyone have a spare known-good AFM and an exhaust gas analyser, somewhere near London?)

All input to this ill-formed question welcomed ... thanks.


Oli.

 

[ukmastiff]

All I can offer is this. A 'tuning company' with a rolling road tampered with my afm and shagged it. It is a precision calibrated bit of kit.
Pro max who are good but lets face it not cheap charged me 300 for a bosch refurbed unit which I thought very fair.
It was about 3 years ago though.

As far as I know the car is still running superbly on the refurbed unit. If its definately the
Afm id get one and swallow the cost. However a knackered afm caused mine to run like a total dog not just a bit rich but my expertise ( on 944 afm's) is limited to my own one experience. Funnily enough on bmw engines with knackered afm im used to rich running and poor pick up at low revs ?
The
Regards Mas

 

[ChasR]

ORIGINAL: ukmastiff

All I can offer is this. A 'tuning company' with a rolling road tampered with my afm and shagged it. It is a precision calibrated bit of kit.
Pro max who are good but lets face it not cheap charged me 300 for a bosch refurbed unit which I thought very fair.
It was about 3 years ago though.

Remember the 944 was not the only car to come with a Bosch AFM (my 205 also has one). Several 80s cars came with them. Whilst you are not meant to fiddle with the screw, many chaps will for the right or wrong reasons (the 205 in my signature had it fiddled when it failed an MOT quite badly on emmisions according to the service history, with there seeming to be no ill effects; I reckon the distributor timing was out in hindsight though, with the AFM being misdiagnosed).

AFAIK, from when I have spoken to others, a refurbed AFM seems to be the way to go. I know of one renowned owner on here with a tidy S saying that he noticed a night and day improvement throughout the car's drivability when he changed his (albeit at a cost). It seems to be a similar consensus with the 205 chaps as well (not having a Porsche tag does not make them any cheaper it seems ).

If it were me, I would probably be tempted to check out the coolant temperature sensor (via resistance values if they are available) to see whether that is functioning correctly before moving onto the AFM. At that point I would probably attempt to clean it once more as you have previously, and possibly attempt to source the correct new spring (finding this out would be interesting mind you, but if you are willing to do the legwork ).

If you do end up having to go for a new AFM (I know that the secondhand replacement for my 205 was worse than what I initially had!) have you considered looking at the Augment Automotive MAP sensor replacements if his costs are comparable to a refurbished AFM?

 

[TTM]

Friend of mine uses an S as his everyday car and has been endlessly fiddling with the AFM to get the engine running right, to no avail. Tried different screw settings, cleaned the track, changed the spring tension, etc etc, and the car will still either run right when cold or right when warm, but not both.

Another AFM is probably the only way to go.

 

[edh]

I guess this will become more and more of a problem as the cars get older. My preferred option would be to get a MAP based ECU - if only someone would build one for the 16V instead of wasting time on 8V and turbos []

 

[Dockrell]

Oli,
I have an AFM for a 2.7 if that will fit - it's off a 130,000 mile car but was working well when I replaced it. I had the luck to get a new old stock AFM for a good price - this gives CO as 0.61% and HC at 63 - figures from my MOT yesterday.

As an alternative there seem to be a number of new 'hot wire' AFM's for the 944 range appearing on eBay at what appears to be a good price. I don't know if anybody here has tried them but that could be a better route - they appear to be a swop out replacement.

Mike
White 2.7 automatic

 

[TTM]

I have been running the SciVision MAF for several years on my S2 and I highly recommend it, but it's not cheap.

Seems to be even pricier now than it was when it came out.
http://dmeshop.de/product_info.php?products_id=33

 

[ChasR]

ORIGINAL: edh

I guess this will become more and more of a problem as the cars get older. My preferred option would be to get a MAP based ECU - if only someone would build one for the 16V instead of wasting time on 8V and turbos []

I guess with something like Emerald engine management along with the appropriate MAP sensor this could be done. Cheap however it would not be, even though that ECU is said to be great VFM.

 

[Dockrell]

Oli,
My spare AFM is Bosch part No. 0 280 202 064. After looking through my documentation the figures from the last MOT when that unit was used were:
CO 1.08%
HC 112.

Mike
White 2.7 automatic

 

[eddieedmo]

Oli

I replaced my AFM which had done nearly 176k miles with a secondhand one from a low mileage car and the difference was huge ,much smoother and power pulling like a train through the rev range.the Bosch nos is 0 280 203 029.The old one had very badly worn areas where the 3 arms swept and cleaning would make no differece they wear.
I also found a small split in the air box/wide rubber hose between the AFM nad throttle body.It was on the small side connection of it.This solved the irregular rough rich running after I replaced it.

Nick

 

[edh]

ORIGINAL: ChasR

ORIGINAL: edh

I guess this will become more and more of a problem as the cars get older. My preferred option would be to get a MAP based ECU - if only someone would build one for the 16V instead of wasting time on 8V and turbos []

I guess with something like Emerald engine management along with the appropriate MAP sensor this could be done. Cheap however it would not be, even though that ECU is said to be great VFM.

i was thinking more along the lines of augtronic - when Tom develops a board for the 16V S2 ECU

 

[944 man]

Tom said that he could run a 16v car on a more simple 8v DME. Without a doubt the ML2.x ECU is more advanced than the 8v cars kit (ML1.x & ML3.x), but its way behind Toms product so theres no need to keep it.

For an S2 keeper, expecially a daily driven car, Id guess that itd pay for itself quite quickly through the increase in fuel economy and youd see more power too.

I have a bit of a man crush on him, even though he appears to have auburn hair... []

 

[944Turbo]

I moved the spring round a couple of clicks on my coupe as I deduced the door was opening too soon, also lowered the arm to move the wiper relative to the tracks.
However I am not convinced this is your problem. (mine was more the door was reaching fully open too soon)

I had high CO and on the later turbos there is an emissions sniffer tube that comes up from the bottom of the downpipe. It is sealed with a rubbery cap. Mine had split and the readings were close too or over the failure line - replaced it and the following year it was fine. So could you have a leak in the system? (Didn't understand how this was affecting the CO but it was)

Also there is a bypass screw on the AFM (at least on the turbos) originally it would have been under a cap I believe this affects the idle mixture - have you tried playing with that?

Is the temp sensor (for the ecu rather than the guage) in the correct resistance range


Tony

 

[zcacogp]

Chaps,

Thanks for the replies. The consensus seems to be that a replacement unit (or re-built unit) is the way to go, and that repairing your own (other than changing the arc for the wipers) is not recommended. I am aware of the adjustment screw under the cap, and have twiddled it to no (great) avail. If you hook the car up to an emissions machine and twist the screw it actually doesn't change things much at all.

So, second-hand unit or rebuilt one? Promax seem to be the cheapest for a rebuilt one, but they say they have no stock at the moment. A hot-wire Air Mass Meter would be nice, although that would put me squarely into the realm of 'modified car' and I suspect my insurance company would have something (expensive) to say about that. Would it really make that much difference to fuel consumption Simon?

Hmmm. Decisions decisions.


Oli.

 

[Neil Haughey]

The screw is for idle mixture adjustment when the O2 sensor is disconnected but you also have to connect a jumper over 2 of the ECU connections, there is a part from Porsche that does this can't remember the number but this is what I have always had on my race car.