# CIS-E Fuel Pressure Regulator...mods?



## wclark (Mar 28, 2001)

I finally took the GTI with its rebuilt engine (below) to the local DynaPack chassis dyno to get it dialed in. A/F, ignition timing and cam timing.
One of the things that surprised me was how much this engine wanted more fuel at WOT. We ended up rotating the A/F adjustment screw CW over 2 turns (from the 8-9ma setting) before we saw the power peak. The problem with that was that at idle the engine was wildly rich. For some idea of how far it was moved, it was 1 full turn CW past where the milliamp meter went to 0.0ma. and 1/8 turn will change things as much as 2-3ma. The car didnt idle below 1500RPM and on the way home it seemed the ECU would only start trying to control part throttle A/F (as seen by the A/F meter starting to move about) around 2500RPM where it would stumble for a moment then run OK.
Late last night I altered the "enrichment module" to 2K ohms and 3000RPM up from 1.2k ohms and 4500RPM up. I am not sure how much added fuel the ECU is delivering with the second parameters but the dyno graphs suggested above 3000 was where as much fuel as I could send was needed and this is the direction the Autotech unit goes for the higher output CIS-E engines. I also backed the A/F adjustment off about a turn until the meter began registering a couple ma at idle since I wasnt comfortable with where it was set.
I am thinking I need to increase the control pressure for the fuel some but havent seen anything in writing suggesting anyone has been able to do this with a CIS-E. I know it can be done with the CIS setup but that is completely different. One of my x-VW mechanic friends thinks some of the CIS-E external control regulators may have had an adjustment accessable from within one of the fuel nipples or the vacuum port but he isnt sure. Anyone heard of doing this?

Engine:
RD block and head. Head milled 2mm, port matched (minus anti-reversion steps) shaped and polished, oversized SS valves, tapered guides and light lifters, TT 288 hydro cam advanced 3.5 degrees. Intake ported and polished. Block bored to 92mm and trued, Wiseco pistons (9:1), ARP fasteners, stock 1.8 crank, lightened flywheel, large oil pump, trap door windage tray. The compression ratio calculates to 11.5:1. I run Sunoco GT100 and use a custom enrichment module similar to the one Autotech sells. I use a stock airbox minus the inlet labrynth and cold start air warmer with an ABD racing big bore air tube between the fuel distributor and throttle body. Distributor is stock Bosch with Magnecor wires, NGK plugs and MSD coil. Dual outlet cast OEM manifold, TT dual downpipe, race cat and 2.25" system with Flowmaster.


_Modified by wclark at 12:21 PM 9-15-2005_


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## wclark (Mar 28, 2001)

*Re: CIS-E Fuel Pressure Regulator...mods? (wclark)*

From a little research and some experiments this is what I have learned about the fuel pressure regulator so far.
There are 2 regulators. The CIS-E unit which operates around 75-80 PSI and the CIS-E Motronic (on 9A engines) that operates around 85-90PSI. 
The "adjustment" inside the return line nipple doesnt do anything as far as changing pressure on the CIS-E unit.
The diaphram on the other end does. A vacuum will reduce pressure about 5 pounds. Pressure will increase it from 75 up to as much as 90 pounds depending on the pressure applied (roughly 0-10 pounds on mine).
I didnt have much locating a used regulator from the 9A locally that wasnt either a rust bucket or over $100 (as part of a used fuel distributor). 
I am pondering ways to use the diaphram end. Pressure would be applied associated with the WOT switch, or better yet triggered by my fuel enrichment module... Since I dont have air pressure anywhere on the car, rather than adding an air pump I am thinking about using a fluid coupled system driven by a solenoid attached to a second diaphram or a small master cylinder of sorts and linked to the regulator with some hose. One thing I dont know is the max pressure the diaphram can handle reliably.
Update: I learned today that the metal in the center of the diaphram inside the can end ofthe regulator can be pushed directly (I used a small philips screwdriver) and increase the pressure. I am planning to use a solenoid connected thru a lever to multiply its force/mm to actuate the diaphram. It appears to only need to move a around a mm to increase the pressure from under 80 to 90. 

_Modified by wclark at 4:09 PM 9-22-2005_


_Modified by wclark at 3:51 AM 9-23-2005_


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## wclark (Mar 28, 2001)

*Re: CIS-E Fuel Pressure Regulator...mods? (wclark)*

Since this has become someting of a little blog on the subject, another update...
I tested the effects of increasing and decreasing fuel pressure on my running engine. I disconnected the O2 sensor from the Oxy Control Module to force it out of the loop so I could read A/F from the O2 sensor as it changed from fuel pressure.
Increased fuel pressure leans the engine and decreased pressure richens the engine. I had read this was the case for CIS engines but what I could find written regarding CIS-E was inconsistent. What I measured - at 3500RPM under no load - was increasing fuel pressure to around 90 PSI (from about 75) lowered the O2 sensor almost .1V and decreasing fuel pressure to about 70PSI increased it abut .05V.
My observations were based on the O2 sensor operating around .7V with the fuel pressure regulator operating with no applied vacuum or air pressure. That is slightly rich, probably around 13:1 or so based on this borrowed diagram:








I was able to also observe that my fuel enrichment module (a home grown product that operates similarly to the Autotech), in concert with the Oxy Control module WOT map, bumps the AF about .1V above the open loop .7V reading when the enrichment module resistance is set around 2k0 ohms. 
Based on the adjustments we did on the dyno for richening my goal is to be able to get the AF to 12:1 (or above .85V) at WOT at all RPM above 3500, while keeping it close to .7V open loop at idle and part throttle (by setting the idle richness adjustment). This seems to provide pretty good idle and part throttle response. That corresponds to around 5-7ma closed loop thru the differential pressure regulator. That is a setting more like what is called out for the stock 16V in the Bentley.


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## wclark (Mar 28, 2001)

*Re: CIS-E Fuel Pressure Regulator...mods? (wclark)*

A wrap-up on this.
Since I seemed to have some holes and inconsistencies in my understanding of CIS-E, I bought the Brobst book "Bosch Fuel Injection and Engine Management" from Bentley, then did some reading.
Armed with a much better understanding of the CIS-E (KE-Jetronic) I went back and made some measurements. I learned that one can make a HUGE difference in A:F by managing the differntial pressure regulator current, which is much easier to implement electronically than trying to develop ways to directly alter system pressure.
I learned that the TT method, altering the resistive value of the engine coolant temp sensor (which I had implemented), can be very effective in some early KE-Jetronic systems but largely ineffective in later ones which are programmed to ignore sudden changes in apparant temperature. Fortunately, my car doesnt ignore a sudden change in resistance (temperature) so the circuit I had in place just needed to be adjusted.
I learned that the Autotech method is different from the TT. It manages the diff regulator coil current directly. It inserts itself in place of the ECU control at WOT above a certain RPM and delivers a specific current (depending on the engine and level of mods this can be set to a fixed value between 15 and 23ma) which is much higher than the stock 10-13ma.
A little theory. The ECU richens the fuel mixture by decreasing the pressure of fuel that is in the fuel distributor lower chamber - on the bottom side of diaphrams in the fuel distributor and this increased difference in pressure between the injection fuel on the other side (upper chamber) of the diaphram increases flow from the metering slots of the control plunger. It decreases the diff pressure by increasing the differential pressure regulator coil current, which in turn reduces flow into the lower part of the fuel distributor. 
The thing that took me a little while to realize is that when you change the idle CO current, you are not "really" setting richness so long as the ECU is managing things by reading the O2 sensor and is not out of its current range to move the diff pressure regulator coil. If you attempt to increase richmess with the adjustment that moves the control plunger, the ECU will reduce regulator current to compensate. So something like stasis is maintained. However the ECU doesnt manage fuel with the O2 sensor at WOT. It supplies predetermined current to the diff regulator coil. So reducing the idle current thru the CO adjustment will increase WOT richmness by roughly the amount you moved the current from the nominal. e.g. if 10ma is normal at idle, going to 5ma will result in the ECU and distributor operating at about the equivilant of 16ma at WOT (it will still read 11ma on the meter but the offset of the metering plunger is the same as it would be with 16ma from the ECU under nominal adjustments). When I said "really" in the first sentence I meant that the ECU will still be able to control CO using the rich/lean/rich/lean approach it uses. However the "operating point" around which it moves is shifted so it will tend to be a little richer at times at idle and part throttle but not hugely - maybe enough to fail emissions though since emissions are very sensitive to very slight changes in A:F. 
Back to my story. I am running with the CO or "richness" adjustment set to read about 6ma at idle versus 10ma in the Bentley. This does seem to be slightly richer than stock at idle and part throttle and is needed to keep the engine happy with the ignition and cam timing I am running (if I go back to the stock 10ma the throttle response is poor). Anyway the ECU is managing CO based on the O2 sensor at idle and part throttle so this in theory doesnt correspond to a hugely "rich" setting while under dynamic ECU control...It is a little rich as I mentioned above about shifting the "operating point". Anyway what does happen at WOT is the ECU jumps to its preprogrammed 10ma-13ma (10 at lower RPMs), which is normal, but the fuel distributor is operating like it is at 15-18ma. with a lower pressure. Then at 3500RPM my enrichment module is switched in and with 2k0 ohms in place of the temp sensor, the ECU sets the diff press regulator current to 24ma. This, based on my guestimates (using the 02 sensor which read .9 around 4000RPM at WOT), puts the A:F just about where it was adjusted on the dyno when we had set the idle current below 0ma. I have more range than 24ma with this approach but will need to do some more time on the dyno to determine more precisely where the peak power setting should be.

_Modified by wclark at 1:05 PM 10-4-2005_


_Modified by wclark at 10:12 AM 10-5-2005_


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