Porsche Enthusiasts Club Forum

Hi all.

My 82 944 passed it's mot in january. Emmisions were slightly low, 0.716 on CO. The car had a misfire (pop) and i've been working to cure that.

I have:

Set the throttle position sensor so it works.
Replaced the vaccum lines under the manifold.
Removed, cleaned and tested the aux air valve
replaced the seals on the oil sepeator and O ring on the filler cap
new gaskets on the inlet
New temp senser for the DME
new plugs, cap and rotor. HT leads seem relatively new.

The fuel quality switch had been set to 3% lean - this has been put back to stock.

The pop has gone, but I tested the emmisions tonight and was horrified to see that they were 16% on co!!!

I have tried a differant fuel rail with regulator, damper etc - no differance
I reset the FQS to where it was - no differance.

We tried the gastester on another car and it seems fine.

Help!!!

Have you tried adjusting the mixture screw on the air flow metre?

Ive just had a MOT failure on the same thing, CO @ idle was 8% so using a 3.5mm allen key unscrew the mixture screw and if that doesnt provide enough adjustment remove the black cap and rotate the geared wheel (you need to pull back the metal spring clip jobbie (mark its origional position before touching it!)) rotate it 2 clicks clockwise and go from there using the gas analyser, using the geared wheel will make massive steps in the CO so dont go to far, then fine tune on the 3.5mm screw

I suspect the AFM is knackered. There is a trim adjustment but it only does a few % or so. The other thing is TPS but you say you've set this OK.

what part is the "trim" adjustment? using the internal adjustment of the AFM we were able to take it from 8% to 16% (2 clicks anti clockwise) then down to 1% (2 clicks clockwise) *from the origional position

this is what i mean, rotate the black geared wheel (lift the wire stop)

Hi Both,

Thanks a lot. I should have mentioned that the car runs rich all the time, i reckon it's at about 2 miles/litre. I have another AFM courtesy of cocacola that I can try.

I have set the TPS so it clicks, but have not tested the function of the switch itself - a job for tonight.

Thanks

That is not the trim! The trim is the small hex on the outside of the body (top right in the pic) & using that you'll get only 1-2% max adjustment.
Bosch say you shouldn't alter the internals at all. Generally the issue with knackered ones is the wiper wearing out the track & adjusting it to wipe elsewhere fixes it. Me I just got a decent s/h one!

Yeah, I know the internals is not the trim adjustment, and im sure your right bosch wouldnt want you adjusting the internals, rather charge you £800 for a new one, all you are doing inside is altering the the spring tension meaning more air volume is needed to move the flap, I adjusted mine, passed CO @ idle and checked the afrs on the rolling road and was fine throughout the entire rev range. Also if its rich @ idle it will be riich all the time! The ecu relies on the afm to tell it the volume of air and then applies the correct fueling, try adjusting that wheel....

The other issue is if someone had tampered with the ecu who knows what they've done to the rest?
Thanks both, I have another afm to try out if needs be.

I've tried two air mass meters. No difference. Tried the cog. No difference.

Suspicion had fallen back on the regulator/damper. If you suck the vacuum line you can taste petrol.

More details later when I'm not trying to do it on my phone!

Right i'm on a computer.

Interestingly when we first fitted the differant fuel rail emmissions fell to acceptable levels. We revved it up to purge the system of excess fuel and they sky rocketed afterwards. I dismissed this as a "blip" but the donor engine has been sat around for ages too.

I think either i'm very unlcky and have two lots of faulty pressure regulators or we have a wiring issue.

I've sanity checked my ECU/AFM part numbers and it looks like they are compatible - ECU is 0 261 200 006, AFM is 0 280 202 028. Unlikely that they'd be differant but you ever know!!

The next logical thing to do would seem to be to test the fuel pressure.

So can anyone recommend a guage that's reasonably cheap? There's loads on ebay, but obviously i want the right one.

How do you tell which of the regulator or damper is faulty without spending a fortune?

Thanks

The regulator controls the pressure & is a common failure. I've never had to change a damper.

I have a set of fuel gauges here but they weigh a ton, shipping back & forward would be a fortune.
A local Bosch main agent should able to check the rail pressure for you for not a lot.

Just a thought...Vacuum hose failure can cause oddities in running as well? Any obvious splits on any of it?

Im 99.9% sure the intake side is now airtight. It certainly wasn't before!