Porsche Enthusiasts Club Forum

Dear All, Great forum ! The old 89 944 2.7 failed its MOT on emissions ...amongst other things. I am guessing air flow meter which I intend to tamper with asap.

Just reading Haynes (which is USA as far as I can see and mine has no CAT) ....does engine temperture sensor or throttle switch have a significant role in emissions ? I haven't tested them yet but as the car is old they will probably need replacing.

Any thoughts gratefully received.

Also any advice on getting these parts ? I have done a few google searches but not turned up a temperature sensor. I think I may be confusing water temp and engine temp. Maybe they are same sensor ???

By the way the car starts and runs well for 150K.....as far as I can see just running a bit rich. Plugs and air filter are new.

usually there are three temp senders (not sure about a 944)

one for the ECU, one for the fan switch, and one for the gauge.

If the ECU one is faulty, it could be telling the ECU the engine is cold, thus making the engine run cold start enrichment, so even when warm it will be overfuelling...

So yes it could be that.

Airflow they should be able to adjust for a small fee while its on the tester.

Also make sure air filter and sparkies are clean.

Have a look here http://www.clarks-garage.com/ Air flow meter operation & testing. It's a good article. I believe you can get a new one from euro car parts for sensible money if you have to. The temp sender is part of the AFM.

Assuming it has seen plugs & an air filter recently then AFM is favourite although the throttle position switch (TPS) could be a possibility. My local Bosch dealer wanted around 200quidish for a new 'un. How far is it away, AFM will normally be miles out 5-8% or so.

Guys, thanks for the replies. I need to talk to MOT guys today but I recall it should be less that 3.5 and it was 4.5...? They fiddled with AFM adjustment and got it better but not enough...I have cleaned and re tracked AFM so will fit that today. Also need to test the engine temp sensor. Will keep you updated.

Check the air filter & more importantly ignition, plugs & points, it makes a huge difference on 944s. ALso if very marginal an oil change could make a difference if it hasn't been done recently.
Oh & give it a good thrapping on the way to the MOT as it'll clean it out.

Incidentally MOT level is 3.5% but actual Porsche level is around 1.8% depends on model, so it's more poorly than you think.

Guys, quick update. Re tracked the AFM...fairly easy job. Checked the engine temp guage ...reading a little high on the resistance so changed it but I doubt it was the real problem.

So..thought plug leads. 2 of them were very very high resistance...300K ohms seems to be what they should be...so a new set from GSF and off I go. Also cleaned rotor and cap.

You can see its better already as at cold start exhaust is barely visible. It use to be very noticeable.

Its in on Friday so will see if we can hit the magic 1.8 % or whatever. With 2 pots basically mis firing no wonder it failed the MOT.

Plug leads should pay for themselves in a few weeks in saved fuel !

Thanks Ian.

fingers crossed

Good luck the 944 is extremely sensitive to ignition condition. I suspect it is because it is a very big bore.

Guys. thanks for your support. deliberate mistake...plug leads are 3k not 300...anyway...

MOT passed at 3.1 %.

My mate at the garage reckons he has never seen a 944 less than 2% so he was very pleased at what we achieved. I see the spec in Peter Morgans book is less than 1.....!!!!!!!!

Next problem is it won't pass in 12 months because of rust around the rear suspnsion mounts....I think another post is in order !

just checked my emissions results, CO at 2.298% so should be ok for a while

Glad you made it!

Mine was around 2% with a s/h AFM so yours is still a little high.
Rust around the suspension mounts is a pain & potentially expensive, mine failed on this nearly 2 years ago. This was the resulting work....
http://www.pbase.com/tr7v8/porsche_repair_pics

The first MOT my 2.7 it was 1.8%, which really pleased me. A year later (and about 10k miles) it was around 2%.

Not sure it should be <1% though, if all is singing

Jim, & all, thanks for the suppoprt. The pictures of suspension rust look painful. What sort of money to get that sorted ? i fear mine will be as bad if i start cutting !!!

cheers Ian.