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Alan L's Avatar
 
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Leaness happens every time. But once during my CIS test, it suddenly dropped back from AFR 13.5 to around 11 without moving the throttle from the lean spot. It has not done this before - so I suspected the piston sticking. It is still a bit of a long shot, but the clearances are so tight in the fuel bore, and I don't know what level the fuel filters filter down to but particles bigger than a couple of thou would cause binding. There is a very fine screen around the entry ports to the fuel head chamber, and it was completely clean, but even that fine mesh may be too large for some particles. For all I know my tank is full of fine grit. The original head did have scoring on it - which the bosch guy says is dirty fuel.
It is possible my tank has never been cleaned in 25 years , and I don't know the age of the filter. I went to change it routinely when I was originally going over the car - but like a lot of fittings, could not budge the unions, so left it. Went on to other things.
I can't remove the Mercedes bit until I can make a new WUR/fuel head fuel line. It is an integral part of the fuel plumbing. I am stuck with it at the moment. Tried fiddling with the settings on it last nite - adjusting it while engine running and watching AFRs on throttle movement. Didn't seem to have any effect either way.
But I have found a place that can source the appropriate fuel union fittings. Have some on order. Then need to make new fuel line so can bypass the gizmo.
Meantime, pulling tank today/tonite.
Regards
Alan
Old 07-29-2008, 01:50 PM
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Are you sure the part between the WUR and fuel head aren't a part left in from an andial set up.If you could post a pic. , some one might be able to tell you for sure what it is. Good luck AL
Old 07-29-2008, 01:56 PM
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I tried to find the posting I made when I queried this bit originally. I just deleted the pic of it from my files in a clean out few days ago.
But from the Bosch part number the device was concluded to be an additional fuel enrichment thing - which derives from a Mercedes. Not sure, but I am guessing it is supposed to provide more top end fuel? The car originally had an EBC and appears to have been running boost beyond 0.8 bar - it came with a hand written note over the boost gauge - Do not exceed 1 bar or engine will brake - Japanese version of english.
It is a small bell like chamber which interrupts the fuel line between head and WUR. It has an adjust screw that protrudes from the bottom of it.
Alan
Old 07-29-2008, 03:00 PM
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I was looking for something else - and just found a pic of it in another file.
Alan
Old 07-29-2008, 03:17 PM
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That looks like ordinary 3 bar BTR. SAAB used it on their early K-Jet Turbo cars (in conjunction with electrically operated switch) to drop control pressure at WOT and thus make the engine go richer.

You can connect boost signal (from plenum) to it's nipple BTR will hold pressure @ 3 bar + boost/vacuum.

Is your hose connected? This might be the missing link. If you can connect it you might be able to get consequent behaviour troughout the boost range.

It usually siths on EFI fuel rail and it's primary objective is to hold fuel pressure constant over the injectors regardless of boost. If you connect the nipple to it (assuming it's connected in such way that it helps) it will react to the boost/vacuum and either fix your problem (richen on vaccum, lean on boost) or just make things worse.

It's worth a try. Take a boost signal after the throttle and connect it to BTR nipple. Do a run with AFR.

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Last edited by beepbeep; 07-29-2008 at 03:34 PM..
Old 07-29-2008, 03:32 PM
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It all depends on how it's connected. As it sits now, it will introduce constant 3 bar pressure difference across it's two fuel connection (and actually compensate AFR for barometric pressure. Neat, huh?).

Once you connect the hose to it:

If it's connected so it increases control pressure with boost, the effect will be that your boost AFR will lean out and your trailing throttle will get richer.

If it's connected so it lowers the control pressure with boost you will get even more boost enrichment and more leanness on part-load.

If first thing happens, you'll get the behaviour that you want (which is good) but base map might be shifted after all your fiddling. Thus you might get consistent 14:1 AFR both on boost and light load. Then it's just a matter of lowering the control pressure until it's down to 12's and you're square.
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Old 07-29-2008, 03:40 PM
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Now we are getting some where. This sounds hopeful.
It is fitted as is in pic at moment. There is no hose to the nipple. So, I am just getting constant fuel pressure across it?
The way it is hooked up at moment, lower line comes from WUR. Upper line goes to fuel head.
If I hook it to plenum, on vac it would pull the diaphragm down and allow lower CP - hence allow more fuel on low throttle? (Precisely what my problem is).
On boost would harden CP by pushing up on diaphragm, and lean boost off a bit?
My boost fuel range seemed reasonable. But I am desperately short of fuel pre boost.
I should hook a hose on to the nipple from the plenum - vac/boost signal.
This nipple is adjustable - does this mean I can fiddle the range of boost/vac signal?
"Thank you for your time."
We may be making progess.
Alan
Old 07-29-2008, 03:57 PM
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Edit: There is a spring and a membrane. Membrane is actuated with the nipple.

Fuel comes from the top and is held there with a spring to 3 bar (typical). Rest is dumped to the left.
If there is a vacuum in the hose, membrane lifts the spring a little and pressure in top hose is reduced. Other way around if there is boost.

I don't know how this thing is connected in your system so I cannot say what will happend. If you connect the hose it will either make your problems worse or flatten the boost/vaccum AFR differences.

If nipple is not connected it will only introduce constant pressure loss across the valve.
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Old 07-29-2008, 04:10 PM
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I just re-read "nipple is adjustable". This rings a bell! If you screw the nipple into the bell, your pressure coming from the top will be higher (as spring tension will be greater).

They are usually not adjustable. There is just a nipple and membrane underneath it. Yours might be.
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Old 07-29-2008, 04:13 PM
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This is how SAAB solved fuel enrichment in K-Jet in 1979. It was laughable and got replaced year after.

Once speedo went "fast" or throttle was WOT:ed, valve 3 opened and 4 (which is basically just a BTR) dumped control pressure 3 bar, making it go rich. Laughable really...

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Old 07-29-2008, 04:24 PM
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Many thanks Goran. I have many Q's about it then - why would it be on my engine?
I will hook up vac to it and see what I can get it to do. Presumably it is supposed to make my system work better, but if I take it off, I would be back to normal 930 system?
It sounds like it would be making the fuel piston harder to work in the fuel head - especially for small throttle movements.
Alan
Old 07-29-2008, 04:35 PM
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What does BTR stand for?

No wonder you have problems Alan.
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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.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 07-30-2008, 09:53 AM
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Quote:
Originally Posted by beepbeep View Post
It all depends on how it's connected.

If it's connected so it lowers the control pressure with boost you will get even more boost enrichment and more leanness on part-load.

.
The fact the car had an EBC, and the stock spring seems to give me 0.8 bar, and the fact the engine had recently been thru major mechanical failure/rebuild, and had a note attached to it warning against boost over 1 bar, I suspect it has been hooked up for the scenario Goran has suggested here. Given that CIS seems to have a tendency to lean out on boost, if you want to push it to 1 bar, you would have to do something more to stop it melting, and get whatever performance needed. The intercooler is stock.
So, taking Nathans advice I have tried to simplify the process, in the hope of identifying the source of the problem. I have removed it. Now I am just waiting on fittings so I can put my fuel line back together and put the CIS back into the car.
We will see - but I think this is the right way to go.
When I first posted a query about this bit when stripping my car down, we identified the part and the fact it was a fuel enrichment device. Since my problem is a fuel leaness (pre boost) I figured this probably was assisting my fuel system more than hindering. But Goran points out it can work in several ways - depending how it is hooked up. It is gone now.
Regards
Alan
Old 07-30-2008, 12:57 PM
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I hope it works out for you Alan.

Hopefully when all is well you could then refit the unit and tweak it to help richen up the AFR if needed. However, the problem I see coming is that it will want to enrich throughout the whole rev range once you are on boost. Usually these cars run too rich at 3500rpm if they are not lean at 6000...
This is where the utcis comes in with it's mappable MAP x RPM table.
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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.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 07-30-2008, 02:34 PM
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I'm very close to buying a digi WUR. If I can't get it sorted this time, that is the plan.
Up til now, my boost AFRs seem reasonable - eg they will start at say 11.5 and lean to 12.2.
Which seems OK to me - could be better via digi WUR - but seems tolerable.
The problem has been that it leans out to 14+ under these same WUR settings in pre boost range. Without this extra gizmo, this may all change.
If I get a digi WUR I will also have to invest in/borrow a lap top.
But cross that one when required. Has to be simpler than the time I've spent so far.
Alan
Old 07-30-2008, 02:46 PM
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