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Cynical Misanthrope
 
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C2T WUR with two bimetallics and control pressure

Gents, I'm trying to get my control pressure to behave. It starts up at 1.7b, which is fine, but it stays there no matter how hot the car gets. And the wideband (and fuel gauge) reflect this.
I've adjusted the upper bimetallic post up and down, and I have it topped out now that it's no longer affecting control pressure. I have 12v from the WUR heater plug, and I have ~40ohms on both heater elements, so I suspect they are both working.
I cannot find any info here about this mysterious second bimetallic. I dialoged a bit with Rarly, but he isn't familiar with the two-strip WUR either. My next step is to begin adjusting the bottom strip in the same fashion as the standard upper one; anybody disagree?
Thanks for your input!
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 06-17-2008, 09:21 AM
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Cynical Misanthrope
 
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So I ripped out the WUR, uuuh-gain. Since I only know about the more common 930 WUR by your pictures and descriptions I'm speculating that the entire lower section of my WUR is differn't. Below my manifold pressure diaphram is a second big chamber, and a pushpin that goes to a coil spring on the bottom. This spring is acted on by a 2nd heated bimetal. However, at room temp this spring is not depressed by the bimetal. I was reassembling this and contemplating disabling the lower section when the heating ceramic crumbled... :-/ OK, no more contemplating. Second observation, the upper bimetal has a two-stage heater with it's own tiny bimetal switch. When it's really cold the switch is open and only heats half the element, thereby maintaining lower control pressure longer in severe cold.

So, if my control pressure is not rising with warmup, either by heating element (within 120sec) or by conduction (after 30min), then the bimetals aren't acting on the springs. According to the Bosch CIS manual, the bimetals compress the springs when cold (lowering control press) but lift completely away from the springs at operating temp... so my WUR should be giving me 3.5-4b even if I take out the bimetals, right?

Thanks for reading my thoughts.
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.

Last edited by AFM744; 06-18-2008 at 09:54 AM..
Old 06-18-2008, 08:45 AM
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Cynical Misanthrope
 
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Doh!

Once I drew this out in complete diagram it came to me. The manifold diaphram center has a smaller concentric spring and a threaded preload adjustment for that spring seat. Initial conclusion was this threaded adjustment would preload the manifold pressure enrichment ...uh, the other way. Once I looked at the drawing and saw that this adjustment also carries the spring pressure from the bottom main spring I realized I've successfully raised my manifold pressure enrichment diaphram (rather than lowered it) thus why my control pressure is stupid-low, and why I'm getting single digit A/F ratio on boost.
But I had to completely disassemble this thing and draw it out in 2D with fuel pressure vs spring vs diaphram loads to SEE how this relic works.



Now to start ordering more EFI parts...

EDIT: Yes I could've just sent the bloody thing to Brian Leask, a saviour for these cars. But I'm the kinda person who *might* ask for help when, but not before I need a coronary bypass. I concede that I can't do that myself.
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.

Last edited by AFM744; 06-18-2008 at 10:12 AM..
Old 06-18-2008, 09:52 AM
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Crotchety Old Bastard
 
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I have not been able to find any new info on the C2T double metalic strip WUR just yet.
One (or more) or the SC models had 2 strips. They were used to fine tune the warming curve for a cold environment. The part numbers were Euro, I assume 911 slated for sale in the far North.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 06-18-2008, 01:49 PM
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Cynical Misanthrope
 
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Thanks for jumping in Brian! The tiny bimetal switch on the top element has a screw adjuster for setting what temp the switch opens. But in NorCal we rarely see <32F and my car is a garage queen so I certainly don't need extended cold enrichment. My objective until my EFI stuff shows up is to get my control pressures somewhere in the ballpark and try to keep this car from single-handedly facilitating OPEC's takeover of the Western world.
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 06-18-2008, 02:03 PM
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I think the second chamber is for altitude compensation.
Old 06-18-2008, 03:19 PM
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Cynical Misanthrope
 
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As far as I can tell it's just another spring in free air. Nothing that would respond to altitude or absolute barometric pressure.
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 06-18-2008, 04:19 PM
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Cynical Misanthrope
 
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#304 I stand corrected! The bottom is not an open spring, I looked at it with a small mirror and you're right, it is a brass accordion diaphram presumably for altitude correction. Thank you!!!
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 06-18-2008, 06:01 PM
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Crotchety Old Bastard
 
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I have read about the altitude adjustment on some WURs but have never seen that model in person. I recall someone making the statement that all the 965 WURs had that feature.
Looks like we have the answer!
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 06-18-2008, 06:58 PM
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Hey Jon,

Did you get this sorted out yet? I was just wondering how you were checking the warm up feature on the WUR. When I checked mine I had to run a seperate 12v source to the WUR to heat the bi metalic plates. The car has to be running for it to get 12v's. Took me a while to figure this out after jumping the fuel pumps to check system/control pressure. What ever you do...don't mess up the WUR as they are rediculously expensive to replace.

BTW...I just remembered, I still owe you the manuals!
Old 06-18-2008, 10:29 PM
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Cynical Misanthrope
 
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'Sup Jeff! I have a T and a line tapped into the control pressure line between the fuel head and the WUR. I have the gauge on the side of the engine compartment so I can watch it while the engine warms up. This is a *temporary* configuration.
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 06-18-2008, 10:38 PM
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Cynical Misanthrope
 
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More info:
According to Adrian Streather's 965 writeup (very handy and on RL) this WUR is specific to the 3.6. I guess that's possible as I have a late '92 3.3 (#251).

So, while I was trying to adjust the bimetals to set my control pressures it was the threaded adjuster on the manifold pressure diaphram that I had so far off. I thought this would affect only my boost-enrichment, but was in-fact the hot control pressure. My control press was ~2bar, (very rich for cold) and since my bimetals were backed all the way off 2bar was also my HOT control pressure. This explains the eye-watering fumes and plummeting fuel gauge.
I reset the diaphram adjuster and started it up cold with 62psi on the control pressure and it runs great (it's 98F right now). Reset the idle mix 13.9 with the narrowband O2 unplugged. Obviously I'd have to pull this WUR out and get the bimetals reset to drop the cold control pressure... but this WUR will be in a box in my shed by the time it's cold here again.


What remains to be seen is what on-boost fueling looks like. With that low control pressure it was atrociously rich at boost onset, but 6-7k WOT was awesome. If it's now too lean I'll try messing about with the system pressure to see if I can fill out that top end. Maybe I'll make a mess again, either way I'll learn more.
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 06-21-2008, 01:27 PM
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