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Crotchety Old Bastard
 
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You can run a fuel presure gage to the cockpit.
I have a mechanical gage permanently mounted on my WUR and had planned to add a sensor at that site and run an electric gage in the cockpit. Ran out of time for that but may pick it up again sometime this summer.
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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 06-20-2008, 06:08 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #61 (permalink)
one of the great unwashed
 
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Right now, I have my CIS test gauges semi-permanently attached. I'm looking for a fast response differential pressure sensor to mount permanantly, with the gauge in the cockpit.
I have tested the WUR with the mighty-vac, in addition to setting up boost settings, and it functions correctly.
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Patrick E. Keefe
78 SC
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Old 06-20-2008, 06:26 AM
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Cynical Misanthrope
 
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C'mon guys, get brave and run a mechanical fuel pressure gauge to the dashboard!
I actually did this once in a previous car, though the line and gauge came in a window so I could throw it out in case of leak. The car was leaning out on boost (later found a cracked fuel line in the tank) and I had to monitor rail pressure at WOT before I found this.
My WUR control pressure tap-in will stay in for the duration of my CIS-ness. My fittings are silver-soldered .
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Old 06-20-2008, 09:57 AM
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Quote:
Originally Posted by patkeefe View Post
Right now, I have my CIS test gauges semi-permanently attached. I'm looking for a fast response differential pressure sensor to mount permanantly, with the gauge in the cockpit.
I have tested the WUR with the mighty-vac, in addition to setting up boost settings, and it functions correctly.
I presume this means you have tested the WUR boost response fuel pressure function?
If so, that is not what I'm talking about. Your WUR is dumping fuel with no boost response function, upon hitting boost. The only thing I can think of at moment is that the fuel piston has been allowed to travel much further (not really big in mm terms - maybe 0.5-1mm) than it should to the air plate movement. About the only way I can think of this happening is the WUR pressure going 'soft' on you in response to a sudden airplate movement. This is different to testing the WUR boost signal effect to the pressure - it is comming at it from the reverse end so to speak when it is really supposed to be a one way effect.
If I have understood you right.
Alan
Old 06-20-2008, 01:33 PM
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Alan:
You are correct. If I feather the throttle, the enrichment is not as bad, but if I suddleny go to WOT, it's horrible.
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Patrick E. Keefe
78 SC
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Old 06-20-2008, 03:34 PM
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Alan:
After thinking about this, you have a good idea there. Since I have the oil out of the car, I will let the WUR get to warm control pressure, and throw the airplate open by hand to see if I can detect any measurable change in control pressure reading.

I have the oil out for valve adjustment. So far, they are/were good (4-5-6). I would rather eat gravel than adjust my valves, but I have to eliminate everthing. I am also going to go one range colder than I was running. I had NGK BPR6 platinum, changed that to Bosch WR8 (hotter and worse), so I'll go to BPR7 or WR4 (cold). Also going to try and squeeze the factory shielded wires in (brand new wires) and ditch the Clewetts.
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Old 06-21-2008, 06:52 AM
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Quote:
Originally Posted by AFM744 View Post
I actually did this once in a previous car, though the line and gauge came in a window so I could throw it out in case of leak.
I just did this recently with my 3.2 carrera. I used the CIS gauge kit with a longer hose and some fittings.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
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Old 06-21-2008, 09:49 AM
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OK, I think I have this figured out now. When I set the control pressure to lean it out on boost, the car won't hot start. Conversely, when I get it idling and running in non boost situations well, it goes pig rich on boost.

It's the idle air bypas. Since I ripped all of that crap out...I just have a WUR and an AAR, no AAV, decel valve, etc, I have no additional supplemental air at start up. My AAR just goes from the top of the throttle body, through the AAR and back into the bottom of the throttle body. The SC originally took air from the boot connecting the airflow plate to the throttle body; I don't have a connection on my low pressure side boot for that.

If I pinch off the AAR circuit entirely, the car just backfires on start up. If I unplug the AAR heating element, it acts like a decel valve until it gets really warmed up.

Anyone have a air diagram for the 930 so I can look it over?

Pat
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Old 06-21-2008, 07:18 PM
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What would an AAV look like? My 930 and SC have very similar AAR's - the little rotating disc on a bimetallic finger. I call that the AAR - maybe it is an AAV - but I've only got the one gizmo in both motors. As you say the SC takes it from the popes hat boot, the 930 takes it off the intercooler, and feeds it into the base of the throttle body. I suppose if someone was going to flog their cold 930 motor into boost, it would require a boost air load at the AAR also.
Other than a difficulty on cold start up, I'm not sure this would make much difference to your problem - the volume of air thru the slot is very small - enough to raise idle revs a few hundred with cold WUR fuel pressure.
You could block it off entirely (ie temorarily remove it and plug each orifice) and see if any difference. Perhaps easier to do with warm motor. But I can't see it could cause your problem.
As far as I can see, it is a WUR fuel pressure control problem. For whatever reason.
Alan
Old 06-21-2008, 07:56 PM
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Update:
Changed the IA head back to the rebuilt stock SC head. I had to re-rebuild the SC head...wrong o-rings. Now, The car runs at least, starts cold and hot and seems more stable. It is a bit lean, so I am tweaking the control pressure. My issues are now 180 degrees aff than with the IA head. Now, I have way overrich idle, and lean mid range. Also, the air plate assembly from my original SC/IA combo was a bit different than the one I am now using...the piston tip protruded a bit more from the one I have on now, so when I simply changed the fuel head, the geometry of the piston covering and uncovering the slits changed.

I am sending the IA head back for recalibration.
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Old 06-25-2008, 03:07 AM
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Pat - where the piston protrudes is not quite the issue - it is where the lip on the head of the piston sits in relation to the slits. This is adjusted by your idle mix screw. The fact you changed heads and have quite a different idle mix is expected - when I change pistons I have about 1 turn difference on the idle mix screw to pick up the same point/idle mix. Lean the idle off and lower the warm WUR pressure (lean mid range). You probably have done this.
If it still dumps loads of fuel without any boost signal at 3000 rpm (I suspect it might) - you would do well to try and monitor the WUR pressure at this point.
BTW - I don't drain my oil to to valve clearances - just run motor for few minutes to clear 'sump'. Then jack up on side - drains any oil back down the tubes. You may loose/catch a cup full when removing lower covers. Engine will cool down enough while you remove covers etc.
Alan
Old 06-25-2008, 12:56 PM
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Alan:
Yes, you were correct...I did that.
That oil goes everywhere whether I drain the sump or not...I hate adjusting valves.
I think I may be getting a handle on this, or at least developing a new baseline. The IA head is on its way back to Kansas.
Pat
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Old 06-25-2008, 01:27 PM
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I don't drain the sump - neither do I care for valve adjustments. But I find I drip very little oil if I do it as described - I place a catch tray under the valve cover as I remove it - catch about a cupful from the cover itself mainly - the rest has drained down the tubes. But you can't leave it like this o/night. You need to do the job then. The high tide slowly creeps up on you back to the valve case lip.
Have you tried the SC head out at boost? is it still dumping fuel too irrespective of boost signal?
Alan
Old 06-25-2008, 02:12 PM
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Alan:
I ran the car last night a bit at 3.2 bar warm control pressure. I was idling very rich, but the car leaned out badly. So, I went home and dropped control pressure to 2.8 bar. I haven't tried it out like this on the road, nor will I get a chance to until Friday. But, it doesn't seem to be dumping a lot of fuel in mid-range.
Pat
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Last edited by patkeefe; 06-25-2008 at 05:53 PM.. Reason: my speling was bad
Old 06-25-2008, 05:51 PM
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I presume you tried it on boost - mid range- and you are saying there is no fuel dump.
Will be interesting when you get the mid range mixture back to normal - less lean - to see what happens. But I struggle to see how the fuel head can do it without subversive help from the WUR - unless your SC fuel head just does not permit enough fuel for the problem to manifest itself. But I would not have thought you would be requiring more fuel than the SC head can provide at mid range revs - even at 5 psi(?) boost.
Alan
Old 06-25-2008, 06:25 PM
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I've been busy the past few days on other projects. I am really thinking I have some air leaks somewhere, as I am seeing some instability at boost. Even at really low control pressures, I can't fuel fast enough with the stock SC head when I get to boost.

I'm going to try and pressurize the whole air system and see if there are any obvious leaks.
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Old 07-02-2008, 03:30 AM
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Was wondering how you were getting on. One of the curious things about these turbo beasts - which took me a while to figure - is that at boost your air leaks which may have been causing leaness under vacuum, turn into boost leaks - so if my logic is correct, you should richen - all things being equal. Because now you are loosing air rather than gaining it?
Alan
Old 07-02-2008, 03:50 AM
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Alan,
I concur with your logic. I had problems before of this sort, which I was graciously helped out on by Rarlyl8 and Goran. In that instance, I had a blown up plastic airbox, which has since been change to stainless steel. Air leaks will definitely make it go rich, which becomes the only logical explanation of the over-rich conditions I am experiencing.

Pressurizing the intake system is another challenge, which I will attempt to tackle this evening.
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Old 07-02-2008, 07:21 AM
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I dont know what air intake system you are running - but I pressurised my 930 from the point leading into the inlet of the turbo basically. I never got complete seal - always loosing some gas. Whether it was all accounted for in the leak areas I could do nothing about - throttle spindle and air bleed idle screw, I don't know. I suspect some was still disappearing somewhere else - but nowhere I could readily detect or fix. Maybe the turbo spindle.
I found an engine rotation point that eliminated the valve overlap. Get your gas flowing, monitor your meter/boost gauge, and rotate your fan pulley - you will find peaks and troughs of pressure.
Alan
Old 07-02-2008, 12:49 PM
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Well, that was pretty easy to troubleshoot. The bottom seam of my blow up proof stainless steel airbox blew out.
Guess I can pull the engine tomorrow and get the welder warmed up.
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Old 07-02-2008, 05:30 PM
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