<img border="0" alt="[jumper]" title="" src="graemlins/jumper.gif" /> WOOHOOOOO!

Ahem, excuse me, can't conceal my excitement, but I'm getting way ahead of myself.

Since I bought my 928 almost 2 years ago it has had an annoying occasional hesitation. Over the past 6 months it got progressively worse, despite my efforts to fix it.

Finally about a month ago, John Speake wrote me and recommended I have him check out my MAF and possibly re-calibrate it. Having tried a million things I was slightly sceptical but also slight desperate, so last thursday I removed the MAF, wrapped it up and send it to England.

Saturday (yes, saturday) I got a call from John - my MAF is indeed way out of spec. if I want a replacment send? Oh yes! Monday I receive note that it has been send, Wednesday at 7:30 in the morning I have a new MAF - less than a week total. I immediately install it (without waiting for installation info from John - oops ), and head of for work.

AMAZING change - the car is a rocket. Even at 120mph it still accelerates like shot out of a canon. At the first red-light I discover a problem: It won't idle. Get in touch with John and he immediately responds, that I need to adjust CO - my mechaninc thinks the same, so off I go to the shop.

First reading is 14.5 - oops again. After turning the pot-meter all the way back it's down to 6.5 but still way out of spec. We start testing everything from fuel pressure to LH brain - no luck. As a final resort I suggest fiddling with the MAF pot-meter (though it's not supposed to be connected for S4 and above). Imagine our suprise when the slightest turn of the **** drops CO to 1.5-2. Weird but great!

Re-assemble the air-box, in comes the air-filter and the CO jumps to 6.5 again, almost choking the engine. Hmmm. Mechanic notes I got the filter in upside down (Apparently the arrows on the side do not indicate air-flow) so we flip it, and CO drops again.

Lesson learned: Apparently the filter touches the MAF when upside down, preventing air-flow at low RPM.

Anyway, John is my man of the day! I sincerely recommend his services to anyone with rough running/hesitation issues with the 928.

 

That "CO" potentiometer is nothing more than tuning meter for temperature compensation. If you aren't at the track every weekend, simply graft Porsche's original temp. sensor (from inside the afm) onto your maf - and you will get OEM automatic temp. compensation with the correct resistance between pins #1 and #4.
If you like playing with it, 70 dgrees F. is about 2k ohms. Check your plugs.

<img border="0" alt="[bigbye]" title="" src="graemlins/xyxwave.gif" /> <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" />

 

Isn't his MAF stock? 1987 S4?

-Joel.

 

Whos?

 

Yours. It sounded like "Special Tool" was talking about a MAF conversion from AFM, with the thermistor issue.

-Joel.

 

Yes, mine is stock, and frankly I have no idea what "special tool" is talking about - care to enlighten me ST?

 

ST - Niels' car has a hot wire MAF............

 

John- I will probably be sending you my MAF soon. I am waiting on a loaner from a Rennlister. (Thanks Sean!) Is it common to have to make other adjustments (CO?) after installing the rebuilt MAF, and if so can the adjustments be made by myself or only by a Porsche mechanic? Thanks

 

"Special Tool" is thinking about 944 MAF conversions. 928S4's have MAF already, which is nice.

-Joel.

 

Hi Charles,
I hope I will be able to help you out !

Any exchange MAF from me will have the idle mixture pot on the MAF set to a nominal value. The car will then run and idle OK on your 86.5, but you will need to do a final "tweek" of the pot with an accurate CO meter. And maybe an adjustment of idle speed.

The procedure is described on page 24-204 of the Workshop Manual. It says you need some special tools, but with a bit of ingenuity you could manage.

What is essential is an accurate CO meter.

Best regards

 

Hi Joel,
Yes I thought that the description was for a "flappy" !

Thanks !