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one of the great unwashed
 
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CIS Fuel Pressure regulation

This relates to the overall enrichment problems a few of us are having, mostly those with the IA mods and the Leask ancilliary devices. Yeah, I know we have a few concurrent threads going on this, so I thought maybe I could try and consolidate.

I want to try and turn down the fuel volume in the fuel head on the SC fuel distributor, the 930 is essentially the same, I believe. I don't have a really good mental picture of the internal fuel flow in the head itself, mostly regarding the inlet at the head, internal bypass and the return back to the accumulator. I do understand the internal working of the head, and pretty much how flow is regulated via the WUR, I am trying to find the volume regulation before or at the head entry. I believe the volume is somehow regulated by the needle valve resident in the head near the fuel inlet. I wish I had a picture to post so I could point to it.

Anyone know how this regulates volume? I pulled mine out this morning (the needle valve) and found it has one single shim for spacing. Maybe the thing needs more or less shimming? The carrier has a 16mm hollow bolt, and the guts themselves are attached to a 4mm hex allen screw (the needle).

So far, the enrichment issue is kicking my a$$. I want to exhaust all of my options before I send it back to IA for recalibration. Besides, I don't learn anything sending it back.

TIA
Pat
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Patrick E. Keefe
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Old 06-06-2008, 07:12 AM
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Patrick, do not really understand what you are trying to do?

Is your car running to rich & where, or are you not getting enough fuel to support the boost you are running?
Old 06-06-2008, 08:21 AM
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Yeah, I pretty much understand exactly what I am trying to do, The car is intolerably rich, especially early on boost, and still has enough fuel to support good AFR at redline. I need a bit less fuel volume, and I am looking for the simplest way to accomplish this, short of putting a throttling valve in the fuel delivery line. I can find the link to the other three threads on this in a minute.
Pat
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Old 06-06-2008, 08:31 AM
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Here's the concurrent similar issues:

http://forums.pelicanparts.com/showthread.php?t=401064
http://forums.pelicanparts.com/showthread.php?t=412190
http://forums.pelicanparts.com/showthread.php?t=410826
http://forums.pelicanparts.com/showthread.php?t=409641
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Old 06-06-2008, 08:45 AM
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I have an '87 930 with the IA head and B.L. WUR.
I have the CIS gauges for checking system and control pressure and an innovate LC-1 and G3 AFR gauge in the car.

When I removed the shims you're talking about (mine had 2, a thick one and a real thin one) the system pressure went from 95psi down to 75psi.
I put the thin one back in and fuel pressure went up to 80psi.
I didn't touch the CO adjustment or the WUR.
Idle and 40mph steady speed got a little bit richer, like from 14.3 down to 13.5 and boost enrichment got leaner.
Midrange boost around 4000rpm went from 10.1 up to 11.5
Midrange felt a little stronger and didn't stink like unburned hydrocarbons as much.

But, boost up around 6500rpm went from 12.5 up to around 13.8 and thats too lean up there for the 1.1 bar boost I'm running. I also heard some detonation with the windows rolled up at high rpms.
So, after seeing and hearing that on one test run I put the 2 shims that were under the spring in the fuel pressure regulator back in.

hope that helps.
Old 06-06-2008, 09:26 AM
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Thanks, JF
I am going to screw around with the shims, and readjust the control pressures again. I can get either good cruise and rich boost, or good boost, but then it gets so lean I have trouble restarting the engine hot. Massive PITA.
Pat
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Old 06-06-2008, 10:10 AM
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Is this the volume control???

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Old 06-06-2008, 01:25 PM
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Took the shim out, got it to 65 PSI. Fiddled with the WUR and fuel head. Getting more driveable. Turned the boost up to 8 PSI, and it fueled OK.

Goes pretty good at 8 PSI.
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Old 06-06-2008, 05:54 PM
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Pat how do you know this isn't a WUR issue? I"m hoping all the issues you have will go away with a digital WUR
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Old 06-06-2008, 06:47 PM
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As I mentioned in another thread, before removing the two shims in my IA fuel head, my system pressure was easily over 100 PSI. I mean when I flipped the valve on my CIS pressure gauge test kit, the needle just pegged itself!!! I'm now dialed in at just 90 PSI with no shims. My AFRs no longer dip down into the 10s! The lowest I have seen on a third gear pull is 11.4, which quickly jumps up to 11.7.

Brian Leask indicated to me that you can file the shims down to fine tune your pressure...in other words, play with it...
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Last edited by sand_man; 06-06-2008 at 07:04 PM..
Old 06-06-2008, 07:01 PM
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For mods, I have 3.4L Ps&Cs, 7.3:1 CR, SC cams, HFS Turbo, twin Plug heads, IA fuel head, Leask WUR and Solenoid, OBX headers, 965 intercooler, ARP rod bolts and head studs, .80 bar waste gate tweaked to .90 bar with a Joe P manual boost controller.
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Old 06-06-2008, 07:07 PM
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The problem is running out of adjustability. You need both the flow rate and the system pressure to be within spec for your application.
When the flow rate is brought to an acceptable level by lowering the system pressure you begin to affect other things such as injector and WUR function. Both those devices, and probably others, are set up to function optimally at specific pressures during specific times and temperatures. For example, the cacking presser for a 930 injector is ~40psi. The cold pressure that you might see with a system pressure of 65psi could very well drop below 40psi. Even at 60psi the spray pattern of the injector might be affected - I don't know that, just throwing it out there.
Pat, if I were you I might try to mimic the 3.0L 930 specs for the fuel system as a starting point. Your C/R is higher and boost lower but the resulting power and fuel needs should be similar I would think. Again, I haven't done any math and don't know the particulars of your engine.
Refresh my memory; will a 930 fuel head fit work with an SC air metering assembly? I just remembered I have a 3.0L 930 fuel head. It hasn't been used in a long time but you are welcome to give it a try.
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Old 06-06-2008, 07:21 PM
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Well, when I started tweaking everything tonight after work, I checked the system pressure. I inadvertently left the valve closed to the WUR, and stated the car, and it started right up! I was at 4 bar control pressue prior to this, but by leaving the valve closed, I had the WUR completely out of play. Pressure with the valve closed is 65 PSI, which is getting close to the minimum opening pressure of the injectors. I actually ran the car for a few minutes before I realized the valve was closed. It was running a bit lean, like in the high 14's..

From this I have deduced that the WUR is not the culprit in the over-enrichment issue, it's the sheer volume of fuel passing through the head to the injectors.I have a stock later model SC CIS system I purchased from a fellow Pelican coming. I'll swap out the fuel heads when it gets here and see how that works out. I will lkely need to send the fuel head back to IA for recalibration. Im thinking a stock fuel head will suffice, along with the Leask components.

I'll play around with this some more tomorrow,and see where that goes.

Post script:
Brian, I guess I was writing at the same time as you. I agree completely with what you say here. I just have no adjustability with the IA head. I appreciate the offer for the 930 head, I may well take you up on it.
Thanks!
Pat
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Last edited by patkeefe; 06-06-2008 at 07:26 PM.. Reason: Saw new post as was writing this
Old 06-06-2008, 07:22 PM
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I picked up a used late model SC CIS system. I took the fuel head off, and disassembled it last night. Pretty simple system, really. I cleaned it all out; it was in pretty good condition. All the passages and slots were good. I am going to reassemble it after golf today.

Now, I figure, since I have the Leask stuff, I should be able to get my adjustability back. Also, I can jerk the pressure back up with the shims, and drop control pressure with the WUR. So, we shall see how this works out.

I'll probably send the current head back to IA, as Stephen says he can recalibrate it. WIth the new head, I can get a new separate baseline, and determine what degree of recalibration will be necessary.

Pat
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Old 06-14-2008, 06:05 AM
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The SC fuel distributor is cleaned out, reassembled and installed in the car. I pressurized the system, and it doesn't leak. That in itself is a small miracle. Pump is making 74 PSI on this head, and the control pressures rose from cold to warm setting with the ignition only on. So, these are good signs.

Next, to get it running...gotta put the air inlet boot back on...after golf, of course.
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Old 06-15-2008, 11:44 AM
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Quote:
Originally Posted by patkeefe View Post
Yeah, I pretty much understand exactly what I am trying to do, The car is intolerably rich, especially early on boost, and still has enough fuel to support good AFR at redline. I need a bit less fuel volume, and I am looking for the simplest way to accomplish this, short of putting a throttling valve in the fuel delivery line. I can find the link to the other three threads on this in a minute.
Pat
Why have you not considered increasing the WUR pressure? You say too much fuel at boost and good AFR at redline. Are you concerned at dropping AFR too much at redline?
I guess the real issue lies with too much at the start - in which case, (I'm guessing) this may have a better response curve - in that the WUR pressure controls the metering piston response to the air plate movement. The initial response may be more delayed than the redline response at WOT.
Alan
Old 06-15-2008, 02:47 PM
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Alan, I have had control pressure set from 2.8 bar to over 4 bar, and all points in between. If I raise it much past 4 bar I may as may as well not even have a WUR.

CIS typically leans out at higher RPM, so what I meant was I have the fuel to support boost at redline. The way I see it, it's easier to blow something up from detonation at 6500 RPM than it is at 3500 RPM. The mid range just has too much enrichment.

The simplified look at the fuel delivery is that the control pressure basically sets the pressure differential inside the fuel head, and the plunger off the air plate sets the volume to the injectors. More airflow past the plate, more fuel delivery (the slots get uncovered in the metering device). So, volume delivery to the injectors is somewhat independant of the WUR, but the pressure of the injector squirt is controlled by the WUR. I think the IA head gives more volume per unit pressure.

I may take the IA head apart to see how the thing was modified.

Pat
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Old 06-15-2008, 06:49 PM
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Pat,
If you do not have any fuel to spare at the top end, then I agree - just reading your post I got the impression you may have had some margin there too.
I'm not sure I agree with your bit about the WUR controlling the pressure to the injectors. This is set by the system pressure. In the pic attached, the system pressure/injector fuel is held in the waist of the piston. It is the top part of the barrel head (I can't do arrows etc) that moves over the metering slots. It rides up as more fuel is needed, opening the slits more. More fuel held in the waist can move thru the slits. The WUR pressure sits on the head of the piston as a resistance to the waist moving up in response to air plate. So, the WUR pressure defines how far the piston can move for a given air plate deflection. Harder pressure = leaner mix (less slit open). But the fuel delivery pressure is the system pressure.
But given the system seems linear - ie slits parallel, and air plate/piston linear, there is not much one can do to vary the range within the travel. There is a non- linearity in the air plate venturi volume - but you can't fiddle with that either.
Have you checked the piston/bore - since you had them apart. I found replacing my piston (worn/scored) has tightened the AFR range up. You can imagine a fair leakage across the top skirt with 50 psi differential pressure (WUR vs system).
This will find its way into the slits - beyond what the air plate says.
It amazes me this crude system works as well as it does - the two pressures rely on the interference fit of the piston in the bore to seperate them.
Regards
Alan
Old 06-15-2008, 07:47 PM
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Alan:
Funny, I was just reading your thread about lag when I saw you mentioned the custom piston you have, and was going to ask you about it. I was a bit unsure of how the differential was maintained. I thought it was maintained by the smaller of the two pistons...after all, there are only two moving parts in the entire system, and the smaller piston, I figured, allowed more fuel to bleed back off the control pressure side, thus increasing volume ultimately to the injectors. Your explanation makes sense to me.

Anyway, the IA head has a really nice piston and bore...no scratches or nicks in the bore. The one I just rebuilt was a bit scratched, but I cleaned it up, and it moves freely.

Thanks!
Pat
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Old 06-15-2008, 08:01 PM
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Pat, One of those is the original (you can just make out some scores) and the other I made.
The metering is defined by the lower edge on the top skirt - this is the defining line over the slits - ask me what happens when the skirt lip is fractionally out of round.
The circumference above the lip on the head of the piston is the 'seal' if you want to call it that. ie the only thing that seperates your WUR pressure and system pressure. The tolerance is about 1 thou in the bore. Even at 1 thou you could imagine fuel leaking thru a gap that big with 50 psi behind it. If you have wear, or a score, the flood gates open. So, your cleaned up piston may have moved freely - as it needs too, but what leakage did it have? I suspect this is a major part of trying to tune ageing CIS systems - the AFR range simply becomes too wide to optimise with the limited options available. You could postulate the leakage is constant , therefore tunable. But as you fling the piston up the bore under WOT I suspect the leakage allows the piston to overfuel - ie degrades the WUR/system pressure relationship - which was stable at idle, or low opening.
Regards
Alan
Old 06-15-2008, 08:13 PM
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