PorschePhD

Air Fuel Ratio

JoeMag

On the CO adj screw, is there a stop for completely CCW and CW? Just want to make sure I can not screw this thing out.

fyi.. cold control pressure was 1.3bar ~10C and 3.65 warm and my WUR takes about 10 mins to reach warm pressure. The AFR's noted are at <5min run time.

PorschePhD

Your AFRs need to be read at operating temp. You can not take a proper reading before then.

I don't know of there is a stop or not. You will flood the chamber before you get to the full rich position any way.

JoeMag

My CO adj screw is NOT maxed out, took the flapper plate housing cover off and got more room and can turn more. Plugged up all vac lines except one to distr and pop-off valve and checked those for leaks. Will try running tomorrow...

On the CO adj screw, does it just richen/lean at idle or richen/lean out at higher rpms also? Based on pics in manual, looks like it just presses down on flapper plate bar so it only effects idle, but not sure...

PorschePhD

If you fatten it up say for example 3 % then you are doing so through the whole range. It is not just at idle.

DonE

If, as has been mentioned earlier in this post, you have a fully adjustable WUR, you will set CO for idle and then all other AFR's using the WUR. Once you learn how to adjust the WUR, you can then think of the CO screw as a fine adjustment screw. For example, I set my CO to .5% (lean), then set my WUR to the proper levels to acheive the AFR's needed, then tweaked the CO to hit the correct AFR's throughout the range. The CO ended up being 0%, but the AFR for cruise was 14.2 and WOT was 11.8. Enrichment came on at 4 lbs of boost.

Also, after the engine is up to operating temp, when you insert the adjustment tool, you can actually push the plate down and kill the engine. Once the screw is engaged, it should be fairly sticky to move in any direction. To get mine running in order to get it to a shop with a gas analyzer, I would start the car, get it to operating temp, then rotate the screw clockwise (slowly) until there was black smoke coming out the tail pipe (and the engine was at a rought idle). This is a real rich condition. I would then back off (counterclockwise) 1/4 turn. This almost always got me to 8 or 9% CO. It was still very rich, but I could safely drive it until I got to the shop.

JoeMag

Well, it really just needed a big adjustment on the CO -- about 1.5 turns rich to get from where I started down to ~3% CO (13.38 afr). I'm still very surprised that it needed that big of an adj after fuel head mod and WUR adj.

...I see where I got the 0.5 turns too, in the manual it says 0.5 turns is max adjustment that SHOULD be made (not 0.5 turns is the max adj that CAN be made).

What does this CO adj screw do to change the AFR throughout the rev range?

Thanks again!!

WERK-I

I think the adjustment screw adjusts the fulcrum point that the metering plate pivots on to the fuel delivery valve to the fuel delivery system(i.e. fuel distributor). So any change to the pivot point will translate proportionately to the movement of the metering plate.

diabolos88

Stephen,
so the CO still needs to be set at 3% even with your IA fuelhead mod?

WERK-I

JoeMag,
I'm very surprised, too. Since the CIS system is a mechanical system and the amount of fuel delivered to the injectors is based on system pressures, it sounds as though the fuel head may have been calibrated to a particular pressure differant than yours. Were there any setup procedures provided with the modified head? Have you modified your own fuel delivery system which is differant than the stock configuration?

PorschePhD

I think he modified the WUR which changes the control pressure and that is critical. System pressure stays constant within a spec. That spec will not really change much. So 5.2 to say 6 bar will not make much difference, but the control pressure changing from 1.9 to say 2.5 is huge. Control pressure changes the mixture. This is based on the lower and upper chambers applying pressure or releasing it on the plunger. System pressure unused simply bypasses back to the tank.

Your CO will depend on your AFRs at WOT full boost. Typically they can be brought down, but not always.

JoeMag

I did have my WUR reworked to be fully adjustable, however, before the mods I did not know what the control pressures were. It was noted by Brian (gent who worked WUR) that the plug that holds the bimetal (see arrow in pic), was pushed pushed down lower than he normally see's so maybe may starting pressures were lower than normal.

My fuel system has not been modified from stock configuration.

I did notice my fuel pressure (into the fuel head), did go up around 7-10psi after the fuel head mod. ...have a fuel pressure gauge that monitors that.