Porsche Enthusiasts Club Forum

Hi All, I'm still trying to get my 16vS engine to run right...

I'm not able to rev above 1600rpm without the revs dropping suddenly and then surging up again.

I double checked the crank - camshaft timing/TDC and it's set correctly.

I sprayed WD40 into the ICV under the manifold through the front aperture after removing the hose that runs to the bottom of the intake, as I've read they can stick. No difference once reconnected and left to idle. When I try increase revs it hunts at 1600 again.

I've also tried running with the TPS disconnected but the symptoms were the same... Still won't rev above 1600rpm before dropping back, then climbing up and so on ...

What else can I check?

Do you have a spare AFM to hand you can check on the car? My Pug 205 ran horrifically on a poor AFM, with it generally starting, but not revving at all.

No sadly not a S/S2 version. I can see the barn door move though as the air filter is disconnected - if I push the flap open wider the revs increase so it appears to be functioning - correct?

Can no-one offer any suggestions?

fuel pressure regulator possibly

Pushing the barn door open wider shouldn't increase revs too much I think. It should add more fuel but with throttle almost closed there won't be enough air so it should run rich and bog down. If the revs rise cleanly when you push the barn door but the throttle is at idle I'd say the engine is getting air from somewhere else to mix with that extra fuel.

I would bench test the AFM to begin with, easy enough to do and should at least prove that component out.

http://www.the944.com/afm.htm

OK guys thanks - I'll look into those ideas.

Could someone please confirm something for me on the S2 intake layout with the Idle Control Valve:

1) the arrow faces forward -> and the hose runs from the front of the ICV to the bottom of the intake chamber - correct?

2) the hose from the rear of the ICV runs to the intake boot via a fork in the hose?

I take it you are using the S2 AFM and not the S item IIRC?

Hi Chas, they're the same (according to PET anyway) and I think mine was off a S anyhow.

I pulled the whole intake assembly off this afternoon to check all the hoses etc.

Removed and tested the ICV - question about tho' - when closed should the hole be closed completely by the flap or is there a slight opening?

This is mine closed:



and open:



Is this correct operation with that slight open when "closed" or is mine not closing all the way?


Hallsy - I've got the AFM off and went to test it according to that webpage - what I can't figure out is where to put the multimeter pins inside the AFM - any ideas?

Edit- found it on Clarks: http://clarks-garage.com/shop-manual/elect-22.htm

The icv is partially open at rest iirc.

I have a photo of the icv orientation somewhere, I will find it!

Does this help?


20140224_173046 by Hallsy01, on Flickr

Right....

Popped off the AFM cover, it's been off before, the tracks were deep even the white ceramic was showing through in a couple of places, so I adjusted the slider thingy 'South' to get clear passage...

Started the car and same issue - won't rev higher than 1600rpm before dropping revs and climbing again, then dropping etc etc

Tested the AFM with 9v battery. Smooth voltage throughout with 8.7v ish at WOT when pushing the flap.

Connected AFM in the car with ignition on and voltage climbed and maxed out at 4.5v output at full flap. Huh?

Pulled off the connector lead and tested the voltage with ignition on; 4.97v across t4 and t3.

Is that the correct? Should that input voltage be 12v?

Hi Steve, sorry to hear you are still having 'teething' troubles!

I just had a re-read of the AFM bench test link that Hallsy suggested, it states:

The design of AFMs changed with the late 944 AFMs. There is no longer any intelligence to its output. This makes it much easier to design and cuts the cost. On the down side, it uses more resources of the CPU. The output is linear with the angle of door opening. If the door open full has a UP=4.5V, then the door half open will have a UP=2.25V. A quarter open, UP=1.13V, etc.

In the late AFM, the voltage being supplied by the DME UV has changed to a regulated 5V ±0.5V. This voltage is now very stable. The early DME voltage was typically 12V unregulated (8V minimum).

So, the voltage you are seeing seems to be about right. If I can think of any reasons other than those already suggested, I'll post them up...off to read the Bosch Fuel Injection manual!

Ah that's a relief Rhett! Thank you confirming that it's ok.

So... Fuel pressure next I guess. Off to machine mart in the morning.

Any other ideas chaps?