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Fine Tuning CIS AFRs...oxymoronic?

Hey guys-
So I've been doing lots of fiddling, even more searching and reading but still I scratch my head.

Car is a '91 964T (basically same fuel system as a 930).

I'm in Denver at 5200 ft - and I have an approximate 20-25 minute loop I do for "tuning" - mix of stop n go and highway. All systems should be fully up to operating temperature. What's on my mind is cruising AFR. Take for instance Sunday - I did a long drive - 3 hours, mountain curvy roads, get up to 9000 ft, etc. - I had fiddled with the WUR and my cruise AFR was too low - consistently 13. 5 to 14.0 - and for 2.5 hours I was thinking "okay I need to lean out cruise tonight after the car cools down". When I get back into Denver and it's 90 deg F outside - I stop for gas and at the hardware store - then my cruise AFR is up to 15.0 - 15.5 for the last 20 minutes. I'm thinking it's a function of heat - intake air temps, oil temp, engine temp, etc - but the inconsistency is throwing me off. As the car sat those two times there was probably some heat soak, but I would have thought 5 miles highway cruising would bring temps back in line. Regardless - can't drive in perfect conditions all the time.

Next - still scratching my head why my full throttle AFR is 10.8 - the piston on the back of the WUR is pushed all the way in. 1 BAR boost so don't want to increase. I'm confident there are no boost leaks but I have not done a smoke or pressure test. Does my altitude make it hard to lean out the system due to thinner air? Assuming not but...gotta ask. General question: Do people reduce system pressure at the fuel head/distributor (remove shim I believe)? My strong preference is not to mess with the FD.

Thoughts appreciated - thanks
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Brandon
'91 911 Turbo
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Denver, CO
Old 06-04-2018, 07:39 AM
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^^^ All I can say is DITTO! Same conditions.
Cruise fluctuates from 13.5 to 15 and I can't get out of the 10's on full boost with the disc all the way in and a 4800RPM delay pill.

But I have only spent a hour or less messing with it. I need to get on a dyno and really pin down my full boost numbers and watch what happens at what RPM to dial it in.
I'm not going to worry about it until I can do that.

Being in the 15's with no load is nothing to panic about. I'm hoping leaning out the idle and warm pressures will help my on boost lean out.

I'm wondering if the air plate sensor will have an affect on the rest of the system.
So, if I set idle AFR a little lean at 14 will it help me dial in the cruise and on-boost settings in for the WUR better??
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Old 06-04-2018, 08:05 AM
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Brandon, what is your system pressure?
If you have a hard time adjusting your boost afr, I recommend removing shims from the CIS relief spring until you are near the low end of the spec and then reset your afrs.
My idle afr can get really high if it's hot out. It's because the engine heats the bimetallic strip in the WUR so it's operating opposite of a cold start. After some driving the fuel cools the wur off and everything returns to near normal.
I actually made a delrin insulator for the wur base but it had no effect.
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Last edited by 911nut; 06-05-2018 at 09:40 AM..
Old 06-05-2018, 09:34 AM
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Quote:
Originally Posted by 911nut View Post
Brandon, what is your system pressure?
If you have a hard time adjusting your boost afr, I recommend removing shims from the CIS relief spring until you are near the low end of the spec and then reset your afrs.
My idle afr can get really high if it's hot out. It's because the engine heats the bimetallic strip in the WUR so it's operating opposite of a cold start. After some driving the fuel cools the wur off and everything returns to near normal.
I actually made a delrin insulator for the wur base but it had no effect.
OK so it is OK to reduce system pressure by removing a shim(s) to get boost leaned out. I was hoping to not have to go there....I guess I will tho....

Good thought on the phenolic spacer, tho.
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Denver, CO
Old 06-05-2018, 12:09 PM
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The -160 WUR of the '91 C2T has an extra diaphragm for altitude compensation. How old is your WUR? Has it ever been rebuilt? Is this a new situation?
I would not mess with the FD other than verifying system pressure is within spec, fine tuning is done with the WUR.
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Old 06-05-2018, 05:31 PM
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Quote:
Originally Posted by 911nut View Post
Brandon, what is your system pressure?
If you have a hard time adjusting your boost afr, I recommend removing shims from the CIS relief spring until you are near the low end of the spec and then reset your afrs.
My idle afr can get really high if it's hot out. It's because the engine heats the bimetallic strip in the WUR so it's operating opposite of a cold start. After some driving the fuel cools the wur off and everything returns to near normal.
I actually made a delrin insulator for the wur base but it had no effect.
engine heat really has no effect on the WUR.
just do a pressure test and see.
if by chance engine heat does raise the pressure then I would check to make sure the WUR is working like it should from the bi metal strip. the heating element should heat it enough so engine heat has no effect on it
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Old 06-06-2018, 04:05 AM
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I would not change sys pressure to adjust boost afr.

I don't know the 160 but if it has a diaphragm in it I would pull a vacuum on it to test it.

why do you wait for the car to cool to adjust the AFR? how are you adjusting the AFR?
how does it run? 15's are ok for cruising.

the top of the 930 runs very cool, especially when driving. after a long drive check the IC and intake, not much heat other than what is coming up from the turbo.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 06-06-2018, 04:16 AM
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If you have a lambda valve you should switch to Franken CIS and if you have wild swings in barometric pressure use two MAP sensors. Use one for MAP and one for ambient pressure. MS will do automatic adjustment.
Old 06-06-2018, 06:56 AM
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Quote:
Originally Posted by RarlyL8 View Post
The -160 WUR of the '91 C2T has an extra diaphragm for altitude compensation. How old is your WUR? Has it ever been rebuilt? Is this a new situation?
I would not mess with the FD other than verifying system pressure is within spec, fine tuning is done with the WUR.

Brian,
Recall that, after you recommended I should run system pressure to the max, I could no longer lean out my boost AFR. I had to lower the control pressure to get the adjustability back.
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Old 06-07-2018, 05:57 AM
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Making test loops from 9000’ to 5200’ is going to throw a big wrench in your tuning, BTDT

The factory altitude compensation is better than nothing, but still not precise, more like a good compromise.

Keep your test loops in the 5000’-6000’ range, something like Denver to Castle Rock, or Denver to Fort Collins, depending where you’re located, and get everything nailed down. Then you just need need to live with a richer mixture as you get to 9000’ and higher. Keep good records of your adjustments, because you may want to go on a long drive closer to sea level some day, which would probably require a slightly richer mixture.
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Old 06-07-2018, 07:06 AM
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Guys-
Apparently I wasn't clear - or comments taken out of context - all good - easy to happen on forums...

My WUR was done by Leask a few years ago - I'm confident it's good..
I like to give the car time to cool/sit/reduce fuel pressure before disconnecting fuel lines at the WUR to reduce gas squirting everywhere. Just the way I do it.

My 20 -25 minute test loop does not vary from 5200 to 9000 ft! :-) That was just a 3 hour drive I did Sunday. My test loop is at my home elevation - ~5200 ft.

Yeay I know 15's OK for cruising - point was it was at 13.5 -14.0 for 2 1/2 hours then it jumped up to 15.0+ for the last 30 minutes...

My goal in all this is to get full boost at red line up from 10.8 closer to 12.0. the WUR adjustment is maxed out as it sits.....

I will check my system pressure today or tomorrow. I don't recall specifically. If it's at the high end of spec I don't see why not lower system to low end of spec so full boost can be leaned out a little. Our thin air in Colo may make it tough to lean out full boost....

As an aside I'm running 1 bar boost and can easily lower it back to .7 or .8 if/when I go to sea level. Will take like 2 minutes (I have an adjustable wastegate Fredmeister made for me a few years ago).

Thanks guys!
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Old 06-07-2018, 01:16 PM
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check for an air leak. under boost that WILL increase the mixture.

are you adjusting the WUR correctly.


if you are removing the CIS gauges just leave them connected for testing. I probably had mine in there for over a year.

post your CP's
WCP,
regulate your air down to about 10psi, apply air pressure to the WUR and check boost CP.
system pressure.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 06-08-2018, 02:51 AM
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Quote:
Recall that, after you recommended I should run system pressure to the max, I could no longer lean out my boost AFR. I had to lower the control pressure to get the adjustability back.
It is possible to pull the control pressures out of their normal range of adjustability by having a high system pressure. Typically leaning out boost is not the direction needed, enrichment is the goal. In this case the engine is not modified to the point where AFRs are too lean on boost so the starting point needs to be stock system pressure.
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Old 06-08-2018, 09:36 AM
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System pressure is 6.75 Bar. Spec is 6.1 - 6.8 Bar on a 964T. So Iím at very upper range....
Old 06-08-2018, 08:29 PM
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When I go from a track at SL to one 3000Ft ASL, my AFrs drop (richen ) by over 0.5. I have to tune for the track - but I don't have a 964 WUR.
Alan
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Old 06-15-2018, 10:16 PM
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Quote:
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When I go from a track at SL to one 3000Ft ASL, my AFrs drop (richen ) by over 0.5. I have to tune for the track - but I don't have a 964 WUR.
Alan
That's an interesting data point. What do you do? just adjust [the 3mm] at the fuel head? Or something more involved?
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Old 06-16-2018, 08:34 PM
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Raise WP by about 0.5 bar.
Alan
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