I theorised about the reversal of the a/f trend
to lean to rich (but then theory is often wishful thinking). I have not shimmed the wastegate (my only excuse is a serious lack of mechanical ability) and my boost drops of rapidly after peak torque, the result of a 14 year old wastegate spring and ever increasing exhaust gas pressure.
I seem to have some sort of afm / injector setup that has extra capacity. Even at a fairly std 10 psi peak boost @ 3250 - 3500 rpm it went leaner to richer and when I went to 13 psi peak boost at the same rpm range the trend remained the same.
I have a confession, we upped the boost to 14.5 psi and the trend still remained, but obviously I had the same knock/retard problem I had at 13psi so there was no point, although the torque figures just before the trace knock looked good.
What about the factory overbost protection fuel cut, my stock boost guage under reads by 1.5 psi
so I presume that at 14.5 psi the KLR is only registering 13 psi, just short of the 13.5 psi limit and as you are not doing fast gear shifts on the dyno there are no spikes and hence no fuel cut. <img src="graemlins/yltype.gif" border="0" alt="[typing]" />

 

Danno already pointed to the thread, but my 86 951 had a similar problem. I've got Autothority Stage II chips and the jetted banjo bolt. The Lindsey folks told me if I wanted to run the LBE with my setup to either dial down the LBE or go back to a stock banjo bolt. I tried both options and still ran hotter than I wanted to (half-way mark after a little "spirited driving") so I ended removing the LBE. I did like the extra little kick it added, I just didn't like the heat and to be fair to Lindsey my car was not stock - frankly I think the chips aren't tuned right anyway. Off-idle stumble, lean in spots, the typical story.

My solution to this problem was to order the GURU stage I MAP kit which I'm eagerly waiting for. (Danno and Travis....HINT HINT) <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />

 

Danno I have a Question for you: A while ago FR Wilk posted either here or on Pelican about changing which fuel map that your car uses by changing the shorting pins. Basicly there are four fuel maps in the DME for use in various places on the political planet and by disconecting the altitude compensator that is used in the USA version and installing the impedence shorting pin there is another fuel map available, ROW, that provides a different and richer map that is open loop. No O2 or cat.

I wonder if this would be causing the strange AFR changes in Hally's 951?

I bought the shorting pin at my local Porsche dealer and installed it temporarily in my '86 951.

I didn't have it dynoed but the car felt more responsive and slightly faster. The idle seemed to smooth out a little bit too. Running the car in this configuration for long with the richer mixture will damage the cat.

Maybe you can shed some light on this for us.

Thanks, Steve Frew.

 

Hmm, there are actually only three separate fuel & ignition maps in the DME. There 1)US&California w/cat, 2)ROW&49-state/no-cat and 3)Australia. Don't know why Australia gets their own map.

Anyway, they are different in the partial-throttle maps only. The full-throttle maps are usually identical across all three regions no matter which map you pick with the coding-plug.

I suspect MildMax's non-standard air-fuel curve is due to the AFM mod. That's OK though because he's not getting lean in the upper RPMs, which is definitely the exception to the rule.

 

Yeah but I would like to know why his car is that way so I could try what ever it is since it seems I will have to run my car the way it is for a little while longer

 

Danno,

I suspect the DME's had specific code for Australia due to the poor quality of unleaded fuel available in 1986. Unleaded (low octane) was only introduced into Aust in 1985/6. Leaded fuel has only just been phased out over the last 18 months!!! We also have 98RON available, this too was introduced only 3 years ago.....

The poor quality fuel has also caused problems for other car makers (notably Subaru Impreza WRX STI's with holed pistons)

Cheers
H2OCool'd

 

just to clarify a few things. As far as running hotter goes, because I run stock chips I set the LBE so that it gave 10.5 psi in the manifold. In this configuration I ran no hotter than without an LBE. Then having spent a lifetime off adding things like branch manifolds and exhausts to N/A cars and seeing a 2HP increase (or sometimes going backwards) I was seduced by the prospect of FREE POWER at last with my first turbo car.

Obviously it isn't this easy but I'm still trying.
Turning up the the LBE to 13psi in the manifold resulted in a car that on the seat of the pants dyno felt really frisky. When running at speed on the highway and giving it plenty of on/off boost
(staying on boost for long periods results in shortened life expectancy) the temp is absolutely normal (ie bottom quarter mark). The increase came once you left the highway and entered stop start traffic and low speeds. It still never got higher than halfway between half and three quarters. Putting on the aircon and taking it real easy (and a longer route home) normally gets it down.

As far as my unusual a/f ratio trend goes I think that a PO needed to replace injectors and looked around for something close and then fiddled the afm to get a car that ran. We have no smog testing/annual MOT type inspection stuff here, so this sort of bush mechanicking goes on all the time. I bought the car from the Porsche Centre (the official Porsche importers in South Africa).
They proudly announced that they had just fitted a new afm (it was seriously shiny and did look brand new), how where they to know about any previous messing around.

The dyno operator who adjusted my afm said he merely adjusted the offset and not the spring tension,using the dyno to check results until suitable ratios at WOT and cruise were achieved.

Seriously guys do not go down this road, this is stone age tuning, I said OK to it because I had no option(this is my only car, not a part time hobby). You have available to you very reasonably priced wategates, electronic boost controllers, chip sets, the guru MAP kit, these are precision tools compared fiddling with afm's.

<img src="graemlins/yltype.gif" border="0" alt="[typing]" />