BC

What is slight failure mode again for the MAFs? Hesitattion at low rpm, such as when you floor it from a stop?

FlyingDog

From the pic, it looks like DR's filter is a Kool-Blue by Accel filter.

Louie928

It's been a long time, but I'm sure in this case I had a new, or cleaned, Porsche filter as well as a newly cleaned & drained K&N. Like you, I wanted as few variables as possible when I was doing tests. When I used to run K&N filters, I had two. I would have one cleaned and set aside in a plastic bag to drain. Then when I swapped filters I'd use the cleaned & drained one and put the other one away after cleaning and re-oiling that one. I also noticed that with the K&N filter, there would be a thin layer of fine dust inside the airbox if wiped down with a clean cloth. The airbox stayed clean with the stock Porsche filter. After never seeing a performance improvement with the K&N plus the less effective filtering, I gave up on them. I didn't have any MAF problem using them. In the 928, they just don't work very well. I made the same test a few more times in the GT development cycle hoping that the K&N would net a few more ponies but it never was to be. I have some dyno comparisons that show the K&N even worse than these two. I didn't dig through enough records to find them.

heinrich

I was there with Louie and we tested on my 299rwhp S4, which benefited from stock over KN. Better horses with stock

James-man

I like horses. I will try orange at the next dyno day, if for no other purpose than to be redundant.

John Speake

Hi Brendan,
Yes, partial MAf failure shows up as weak mixture when off loop, so - poor response to throttle input (esp. at less that WOT)

I can't think why K&N give less power, unless it is affecting the fuelling by changing the airflow patterns through the MAF ?

Were you monitoring A/F ratio when you compared K&N to stock, Louie ?

Regards

BC

Are the MAFs the same throughout thier use? i.e, 84-95? Or are there different settings? I assume so.

Jim bailey - 928 International

the same mass air is used for 84-euro 85-95 USA but starting in 1987 the mixture adjustment circuit on the mass air body is no longer used.

heinrich

John, because of airflow. The KN (I saw it with my own eyes with Louie) loses power. My theory is that the grid (I like to call it chicken wire) causes turbulence. When you view airflow downward in a straight path, the stocker is smooth as butter, but the KN is more of a fine grid of obstacles to the air.

heinrich

Brendan I swapped 87, 88, 85US and Euro MAFS around and they all work fine. However there WERE idle differences between them. A MAF from one car made another car idle less smoothly and vice versa.

BC

Since i fixed all the vac leaks I thought the next step was possibly maf, as the Euro had a K&N on it. Its gone now, and its running better, but still has the tip off hesitation.

heinrich

That MAF is good. Had forgotten about the KN I had installed .... original was old so I grabbed what I had, i believe that KN is new, FWIW. I'd look for air leaks Brendan. Around the MAF maybe, or intake ...

heinrich

Although idle is just fine, and with air leaks you'd expect trouble there.

John Speake

Brendan,
The Euro is more sensitive to MAf ageing than the S4 and later cars. Anything over 2% ageing and a Euro looses the edge off throttle response.

Yes, all MAFs are the same 84Euro - 95 GTS.

heinrich

I do believe I tried a brand new MAF. But I don't remember for sure.