aguk928

Well I got my shark running, and through its MOT (Road Worthiness) test. Yet I have a problem or two. Any help would be much appreciated.

I have an 85 S2 Auto, being in the UK I guess Euro spec. After doing a top end rebuild I reinstalled all the Induction system and found that on the Air Flow Sensor a cardboard ring (homebrew) had been installed. Now here is the situation, with this ring installed the engine sounds and idles reasonably well but runs very rich and the fuel economy is down to about 5-7 mpg, plugs very sooty. If I remove the ring the engine runs rough and after a few minutes starts hunting. Idle pulsates, hit the gas and it improves put it in D and starts again pulsating till it dies so now it appears to lean.

What are the possibilities please?
Faulty MAF?
Faulty Brain?
or a faulty idle control valve?
vacum leak?
or all of the above?

Some suggetions would come in real handy.

Many thanks.

John Speake

When you say a cardboard ring - can you descibe it ? Does it just have a smallish hole in it for the air to pass through ?

I have seen the same before. I does sound as though the MAF is toast. I can test your MAF for you on my test jig. See my website.
Regards,

aguk928

Hi,

Thanks for such a quick reply.

Well this cardoard ring apart from being cut from a piece that says Vauxhall on one side (Any shark would be upset with that), reduces the MAF diameter by about 1". Interesting way of recalibrating the MAF!!!

Is there anyway that I can do a so called quick and dirty test of the MAF, I do have a reasonable amount of electronic test and measurment gear.

Again thanks

aguk928

Re the quick and dirty test I see that on your web site you give a great run down on the MAF and the type of tests that I was looking for for starters. Will do them and then I have a feeling I will be asking for some costs to recalibrate the unit.

Thanks for the great info.

Mattman928

I am wrestling with the exact same problem (5-7 MPG) and sooty exhaust and plugs (I don't have any cardboard). So far I have replaced (MAP, coils, rotors, plugs, wires, temp sensor, Tested the Throttle position sensor).

All I have left to test is the Brain and the Oxygen sensor. I actually placed my brain in another car and it ran fine, but I've heard of instances where brains that were failing, would run fine in one car, and not another.

I'll keep you posted

John Speake

Hi - I'm surprised you managed to get the car through the MOT running as it does !

The checks on my website are for gross MAF failures. The MAf has to be withinn about 2% of correct calibration to work properly in the car. To check this your need a flow jig, as I have.

Chris Sanderson of Loe Bank Motors is at Bury, Lancs. he carries one of my MAFs in stock. He is very knowledgable on 928s

Or you can send me your MAF for a calibration check. You can mail me off list at info@jdsporsche.com

Regards,

aguk928

Hi John

Yes I would say that it was boarderline on passing the MOT as the HydoCarbons where high but they where prepared to pass the car as they where not grossely to high, this was with the cardboard ring installed.

My guess is that the MAF is giving to high a voltage for a given air mass moving through it possibly and with the cardboard ring installed the air mass is reduced and the MAF starts to give a voltage within range for the LH brain, but its calculations are telling the fuel system to put in to much fuel. Thus to rich.

Now in trying to understand the system, I would guess 3 possibilities of a combination. The platinum wire has thinned to much, or it is gunked or the calibration pot is off.

Looks like the MAF needs checking either way.

aguk928

Matt,

Will be interesting to hear your progress.

Best of luck!!!

John Speake

quote - "Now in trying to understand the system, I would guess 3 possibilities of a combination. The platinum wire has thinned to much, or it is gunked or the calibration pot is off. "

Ageing will weaken the mixture, overoiled etc the same. the idle mixture pot has quite a range, but it sounds as though someone has already found they can't adjust the mixture properly.

I will check the cal for 20GBP.

aguk928

Thanks John,

It looks excactly as you say someone already tried setting the mixture and had to resort to changing the airflow with the cardboard ring.

I certainly will be looking to arrange in the near future your testing the unit (Thanks!). There are a couple of things that I would like to do to first so as I can get the next stages of repair/restoration started while the MAF is away with you.

Out of interest, I disconected the MAF conector and found that I was getting similar idle hunting as with the cardboard ring removed. I wonder if this would be as expected? Or does this show the presence of another fault as well. Because without doubt as soon as the cardboard ring is inserted the idle stabalizes and the car becomes drivable, yet when without it hunts, surges, dies, and has no pickup under load running very rough, until the RPM hits about 3000.