StoogeMoe

Here's a pretty good site that gets into the details of how the maps are used.

DME Tuning

If you read the whole thing, there is a part that reads

"When the DME senses WOT, the AFM and O2 inputs are ignored. The IDC is set solely by RPM."

I had the disassembled code at one point, and if I can find it again, I can verify that it is indeed true.

DarylJ

That's the part I don't get. What is the difference between the two flows - open is open. What changes to affect the volume of air coming through the throttle body once it's at WOT and the bar door is all the way open?

Or are you saying that there is one flow for barn door fully open and not WOT and another for barn door fully open + the WOT signal? That would make sense, but I can't see how else the flow could be affected once the barn door is fully open other than the throttle body.....and one would think Porsche would have flow matched the two components so that maximum flow through the throttle body is exactly fully open for the AFM barn door.

I'm not claiming to know any of this for a fact. I'm trying to make this fit logicially in my head based on what I know of other cars and what sensors the 944 has.

Makis

I agree the AFM should be fully open when maximum flow (fmax) is achieved, i.e when the throttle body is fully open and we are running at full engine rpm. However it is suggested in this thread that the AFM is fully open for flows (let say f1) , that is clearly smaller then fmax. This means that the AFM cannot effectively be used to measure flows between f1, fmax. If you have WOT we can estimate the flow, but if we don't then what?

DarylJ

Well, that was my point - it seems odd that that there is a scenario where that can happen (wide open AFM at other than fmax). That's what I was trying to get through my head. I can't imagine why allowing that was a design decision, but if it was, it was likely Bosch's and not Porsche, and my have something to do with the fact that theses were designed for multiple different applications.

Jon C.

Hello, I know this is an old thread but I am having this issue as well but mine stumbles at 5k and it goes back to normal acceleration at like 5400. I would think a valve spring would be an issue from 5k onward to reline at that point.

911buzz

Hey Jon C, I have an 88 944s and am having this problem too. We installed a wide band sensor and it is definitely going full lean. I have replaced/tested almost everything. Plugged in 2 different DMEs today with same results. I will test replacing the AFM this sunday. Mine looks very good internally but this seems like the only part that fixed the OPs problem.

I will post up if this fixes my issue.

Charlie

RGS

@911buzz how did the test turn out?

911buzz

Sorry it took so long to get back to you. I had a race last weekend and needed to deal with getting car ready. We won so it was worth the effort.
I finally got a chance to really dig into the AFM today. I went to Clarks Garage and read the test procedures for the AFM. What I found was thet there were dead spots in the wiper track.
A quick adjustment to the wiper arm and it seems to be working fine now. I still need to test on the street but it has no miss fires at full throttle anymore when free revving it.
heres the page from Clarks. http://www.clarks-garage.com/shop-manual/elect-22.htm

911buzz

Update, car is working great. Now for sale on Bring a Trailer.