9turbo51

My wife's S2 track car has developed a stumble at 5100 rpm. Every gear every time at 5100, and only at 5100, the car stumbles and the wide band flashes from high 12's to 17+.
Immediately the air fuel goes back to normal and the car runs fine to red line.
This one is baffling me. The car has Michael Mounts cam and headers and max hp chip.
Any ideas where to start looking?:

944meister

sounds like a flat spot in the airflow meter

9turbo51

Would that be that precisely repeatable? Not saying it's not, just don't know.
I won't get a chance to test before this weekend. I will respond with findings.

Ben951S

Yeah, what if you baby it past/to 5100? Not sure what that would say but is it 'WOT' to 5100 or any time at 5100...

9turbo51

Ah, I see the method to your madness! Good question, I will check it out. I'm a bit slow sometimes.
Thanks and will post my findings.

Eric_Oz_S2

Has the chip been matched to the cam and headers? Are you still running a nbo2 pre cat?

9turbo51

Yes the chip was custom burned by Russel at maxhp. Yes o2 is in the header. No cat, 2.5 exhaust. I believe the the car is in open lope at wot so o2 has no input.
"Patiently" awaiting Rouge's S2 tune...
Also, this is a new problem, just started a few weeks ago at VIR. I don't drive the car except when informed of a problem (by wife).
I did the mods to car a few years ago.

944meister

+944

what you've stated above pretty much narrows it down to the airflow meter, can't think of much else it might be. my guess is that your wife spends most of the time driving around in the 5100 rpm range on track and a spot has worn off on the afm board from the sweeper arm, which correlates with that rpm. <-- for having a wife that tracks

9turbo51

My wife has been instructing for years and does not "drive around" at any particular rpm. (sorry had to)!
That said I am leaning toward afm.
Just a little side note: I meet my wife at Summit Point (race track about on hour west DC) in 1994, we where both at your 3rd track event. Many years and thousand of $$$ later...
P.S. she had an '89 951 at the time, got destroyed do to "mechanic's" mistake.

Makis

Can't see why AFM will be the cause at consistent problems at 5100 rpm.
I think 5100 rpm in different gears will use different air intake depending of how the power is to be delivered, so the AFM unlikely cause this.
I would think the ECU fuel map had become corrupted and when 5100 is hit the ECU does not know what to do.

944meister

Now that I think of it, you're probably right, doesnt make much sense. Guess I need more sleep...

9turbo51

So far as far as I know this is happening at wot. As I stated earlier this my wife's track car. Being a track car or any car for that matter how often would you be at higher rpm other then at wot. I will drive it this weekend and test going past 5100 at other then wot. I have another good DME with an Authority chip in it which does not have enough fueling (even w/adjustable fpr) but could use for short test.
I will test in this order, and of course end test if/when at point I get good result:
* @ just enough throttle to get past 5100rpm.
adjust wiper arm to contact different arc on potentiometer if needed.
* change DME.
*If solved will put Maxhp chip in that DME.
if problem returns, will order new chip.
We shall see. Appreciate all input.
P.S. living in the sticks allows this.

Jfrahm

Re-tracking the AFM might be worth a try also:

https://rennlist.com/forums/924-931-...-your-afm.html

9turbo51

Interesting way of going about it. The plan is to switch to Rogue's maf conversion when he gets the s2 tune done. If need be I will probably do what they do at www.frwilk.com witch will increase pressure but only for, hopefully, a little while. P.S. Go Joshua!

9turbo51

I'm not worried about the tune at this moment. Just trying to fix a new problem.
Between my 951 track car and this car we really can't afford to be dragging cars around the county for someone else to work on. I will figure this out albeit with Rennlisters input.