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Hard to tell with those graphs since boost isn't logged along with RPMS. The spike to 14 on the first rpm run up could be lean (if it's a WOT run) or it could be fine (if it's just rpms building with high vacuum, low throttle input).

12.7 under heavy load is lean, especially if it's at torque peak.... but I see the afrs drop into the 11's.

Old 09-15-2010, 07:37 AM
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Great thread.

Quote:
Originally Posted by PorscheGAL View Post
As mentioned above, the LM-1 can log RPM. I just added an LMA-2 and just hooked up the sensor for RPM. Boost is next. Still working on how to configure the RPM on the graph. I'm just a Noobie at this.

Thanks to everyone for their input my lean AFR readings after extended trips. It is just scary to see such a jump.

Stephanie,

What are you doing here?

Is it cruse for the first part, then acceleration, then throttle lift?

What I think I see is a small lean surge at with acceleration, over rich at first throttle lift, a major lean spike from the metering arm over swing shortly after throttle lift, then stable AFR again.

Thx.

Last edited by 911st; 09-15-2010 at 08:39 AM..
Old 09-15-2010, 07:41 AM
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PS,

Stephanie,

Do you still have your de-accel valve in place or have you removed it?
Old 09-15-2010, 08:39 AM
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Quote:
Originally Posted by 911st View Post
What I think I see is a small lean surge at with acceleration, over rich at first throttle lift, a major lean spike from the metering arm over swing shortly after throttle lift, then stable AFR again.
I agree with this analysis...the major lean spike is probably throttle lift. My afr graph looks a lot like yours PorscheGAL
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Old 09-15-2010, 09:02 AM
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Quote:
Originally Posted by infraredcalvin View Post
I have the opposite "phenomenon" going on where I go rich after letting off the throttle (makes sense if it's the fuel dump DonE refers to).
infrared, just wondering about the WUR in your car. Yours is a '76 or '77, yes? For some reason its stuck in my head that the early turbo WURs behaved differently than the later cars. I seem to recall reading that the early turbo WURs respond to vacuum, while the later ones respond to pressure (and vac has no effect). No 1st hand experience here, but it might explain your AFR graphs vs. GAL's. Food for thought at least.
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Old 09-15-2010, 09:07 AM
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I have an LM2 and I'd noticed this kind of AFR 'step change' myself.

In the evening: Drive my car for 15 minutes (AFR at idle around 13.5), park up for 2 hours, drive home (AFR at idle around 14.1).
Following day: Drive my car for 15 minutes (AFR at idle back around 13.5)...
Old 09-15-2010, 11:28 AM
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Quote:
Originally Posted by PorscheGAL View Post
As mentioned above, the LM-1 can log RPM. I just added an LMA-2 and just hooked up the sensor for RPM. Boost is next. Still working on how to configure the RPM on the graph. I'm just a Noobie at this.

Thanks to everyone for their input my lean AFR readings after extended trips. It is just scary to see such a jump.

Stephanie,

911st is right - your engine is on the 'over-run' (i.e. lift off the throttle)

Here's mine (with Boost in Red):


When the black line (RPM) dips, the blue line (AFR) rises.

Here's a smoothed version of the same picture:


There's a lot of noise on the Boost signal. (Trying to find ways to reduce this.)
Old 09-15-2010, 11:37 AM
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I am thinking the Control Pressure Dampener as installed on the Porsche 930SE, RUF, and some other CIS cars might reduce this lean spike.

I suspect that should this metering plate over swing occur with a shift and instant WOT, as under racing conditions, it might create a significant lean issue that could result in motor damage.

Here is what the dampener looks like and it is installed in the control pressure line between the Fuel Distributor and the WUR:



Here is some discussion in trying to figure out what it was supposed to do: Control Pressure Dampener from 930SE

Stephanie's graph looks to be an excellent representation of what can happen with throttle lift on CIS and kind of brought it all togeather for me.
Old 09-15-2010, 02:44 PM
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TJ930,

It took a while to get comfortagle with your graphs.

I think I am seeing what I suspect in the non soothed one.

Along about 9 it looks like you make a shift. With the quick drop and recovery in boost the AFR curve has two lean spikes.

I think one spike is from the over swing with lift.

However there appears to be second lean spike when boost starts to come back with WOT. It looks like it might be a big lean surge as the motor starts gulping air before the metering arm can respond.

I could be wrong.

Can you isolate the area between about 9 and 9.5 and expand it?
Old 09-15-2010, 03:08 PM
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Quote:
Originally Posted by 911st View Post


Stephanie,

What are you doing here?

Is it cruse for the first part, then acceleration, then throttle lift?

What I think I see is a small lean surge at with acceleration, over rich at first throttle lift, a major lean spike from the metering arm over swing shortly after throttle lift, then stable AFR again.

Thx.
Yes, I wanted to record a session of cruising, then acceleration and slowing (throttle lift.)

This is what my car usually looks like; unlike the drives over an hour where it leans out prior to load. This doesn't worry me as much as the leaning prior to load.

Also, my decel valve is still in place, but I have considerable "rumble" when decelerating. I have check all connections, and all looks good.

In all, my graphs looks different in how far I drive. Most drive last 30-40 minutes, but when I drive to Myrtle Beach it is a 3 hour drive oneway. About an 1 to 2 hours into that drive, I see a leaning to 14ish AFR.

I will look into the control pressure dampener link. Thanks
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Old 09-15-2010, 05:56 PM
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Quote:
Originally Posted by RarlyL8 View Post
Pat, do you vent your BOV to atmosphere?
In an effort not to sound stupid, but i don't think the 76's have a BOV. I also have removed my decel valve. this run was not quite a wot, i was getting on the freeway in some traffic making my way to the fast lane, so i was on and off the throttle somewhat erratically as i was merging. i do need to log boost, bec it would be nice to see what is happening during boost.

I have a rebuilt 76 wur i've read that it does work a little different - parts were scavenged from another 76 wur and a new mercedes wur and reassembled in my wur - that's about all i know. I called BL about rebuilding the leftover parts - he told me not to get rid of the 76 housing bec it was hard to find, the repacements are really later model wurs.

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Old 09-15-2010, 10:35 PM
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