CIS AFR problems

[wreckah]

yes indeed,

you set the idle AFR , and the CIS takes over from there.

if you want to start WOT tuning etc...then i think it's better to go away from the CIS. I cannot see many tuning options within the stock system without hampering driveability, cold start, etc...

If it's a track car only, and fuel consumption is not an issue, you could do a very dirty trick with the wideband module: Disconnect the WOT switch so the car always uses O2 sensor input, and then use your analog output programming to make the engine run a fixed AFR all the time. I did this for a couple of months because it was the only way for me to drive the car (other components were broken): i set the AFR around 13 at all times, and it actually drove quite well. (better than stock when you're on it). Idle was marginal, as was cold start. But we could drive the car (it was our only car for a while).

Now i'm running bitz kit, and i'm never looking back

[Walt Fricke]

If one is not bound by racing class rules, many options are open. Not so where there are rules, and using the Innovate to, in a sense, run the FV is not allowed by the rules I have to follow. Adjusting the existing system is one thing, but adding another system (this is a clever approach, to be sure)is not on for me.

[Walt Fricke]

Don G - do your A/F traces look anything like the ones I showed? With or without smoothing? Without smoothing mine look more like a seismograph. Your RPM trace is good? Solid?

[T77911S]

what WUR do you have?
is the O2 sensor connected and is the system running closed loop?
what is the max timing?

system pressure:
if you lower system pressure that could make it run richer. here is why, hopefully short version.
system pressure is in the lower chamber pushing up on a spring trying to close a valve.
if you lower that pressure, the spring will open the valve more, thus letting in (out)more fuel making it richer. the only counter part to this is you will lean it back out with the mixture screw and going back to what I said in my other long post is again, the AFR';s across the RPM range will all be related to the idle setting AFR. hey that was pretty short.

back to the CP.
if you set the CP to 3bar and adjust the idle to 14.5, nothing really changes as far as AFR's if you set the CP to 3.6 and idle to 14.5. set the CP to spec and leave it. only reason I would alter the CP is if the engine has been modified.
this is what is incredible about this system, it is almost idiot proof as long as you keep setting the idle to the same AFR. the system takes care of the driving AFR's

just as a note, my 77 with the 033 WUR was pretty rich at WOT. don't remember the numbers.

calibrate the LM, with engine off and I would remove the O2 sensor. make sure it reads what it should in open air.
set timing to spec
set idle to spec
set CP to spec
adjust mixture to spec
new plugs

run some WOT tests.
shut it down before it idles and pull some plugs. I will usually just pull one from each side unless I see an issue, then I will pull more.

one other thing, if running vac advance make sure it is connected properly.
is the vac retard connected? you should not need it.

[Walt Fricke]

Well, the '77 CIS and the 81-3 US CIS are not quite comparable. The '77 has that vacuum feature altering the CP, so the load alters the CP, does it not? The later US SCs don't have that. Instead, they have the Lambda system, if you use it. But even if you don't use it, you still have the frequency valve part to help you start and run at WOT.

Since in open loop the FV on cold start on time is, per what I read, the same as the WOT FV on time when cold, warm, or hot, a duty cycle of 65%, it is tempting to think that if I set my idle AFR at 13.2 cold, WOT should end up the same. Warm and hot idle are 50%, but WOT is 65% for both.

I can try this, but what about the shape of the throat where the butterfly-like air measuring plate resides? At low RPMS, with little air flowing, the plate is in more or less of a tube. At mid-throttle RPMs, the plate is in a funnel - the higher it rises, the wider the throat, and a 50% increase in air flow won't create the same rise/FD plunger open area change as the same coming off idle. And at some point the throat widens at a smaller angle. Even leaving aside the FV aspect, doesn't the shape of this three angle funnel complicate the notion that idle AFR will stay the same up through WOT?

[Walt Fricke]

By the way, although I don't think of my engine as being modified (stock pistons, cams, TB and all the CIS stuff other than always open loop, stock CR, etc., the exhaust system puts the car maybe 20 hp over stock, which means more air is entering the cylinders at higher RPMS, needing more fuel. The metering valve ought to compensate - more air, higher flapper position, higher plunger slot, more fuel.

[wreckah]

hi Walt,

next to the Lambda brain, you should also have a enrichment relay, that does something too, but nobody knows exactly what...metal box underneath the passenger seat, next to the computer.

cheers, Jan

[Walt Fricke]

Right. It looks like it gives you 3 seconds of a higher duty cycle (richer mixture) with a cold or warm engine (75%)when going from idle to cruise, and when going from cruise to idle with a warm engine. This per Jim Williams' fine chart where he measured things (after all, he is an engineer).

I haven't tested mine, though I opened it up to confirm it wasn't burned up or rusted and so on, and that it was getting power.

Since I can expect the engine to be over 35 degrees C after a warm-up or formation lap while on the track, I think it has no effect on my lap times

[T77911S]

Originally Posted by Walt Fricke

By the way, although I don't think of my engine as being modified (stock pistons, cams, TB and all the CIS stuff other than always open loop, stock CR, etc., the exhaust system puts the car maybe 20 hp over stock, which means more air is entering the cylinders at higher RPMS, needing more fuel. The metering valve ought to compensate - more air, higher flapper position, higher plunger slot, more fuel.

usually the better flowing exhaust provides better scavenging of exhaust gasses making it run leaner at WOT. usually you see guys trying to richen the WOT either to be safe or they are leaning out.

[T77911S]

Originally Posted by Walt Fricke

Well, the '77 CIS and the 81-3 US CIS are not quite comparable. The '77 has that vacuum feature altering the CP, so the load alters the CP, does it not? The later US SCs don't have that. Instead, they have the Lambda system, if you use it. But even if you don't use it, you still have the frequency valve part to help you start and run at WOT.

Since in open loop the FV on cold start on time is, per what I read, the same as the WOT FV on time when cold, warm, or hot, a duty cycle of 65%, it is tempting to think that if I set my idle AFR at 13.2 cold, WOT should end up the same. Warm and hot idle are 50%, but WOT is 65% for both.

I can try this, but what about the shape of the throat where the butterfly-like air measuring plate resides? At low RPMS, with little air flowing, the plate is in more or less of a tube. At mid-throttle RPMs, the plate is in a funnel - the higher it rises, the wider the throat, and a 50% increase in air flow won't create the same rise/FD plunger open area change as the same coming off idle. And at some point the throat widens at a smaller angle. Even leaving aside the FV aspect, doesn't the shape of this three angle funnel complicate the notion that idle AFR will stay the same up through WOT?

I am aware they are not the same.

what WUR do you have?
are you running closed loop?
what is your max timing.

if you are certain you are too rich at WOT, and the plugs show it too and there is noting else wrong, then disable the WOT switch on the TB. run a steady 50% DC.


the funnel.
the middle section is designed to lean out the mixture at cruising speeds.
I look at the funnel kind of like the program map in EFI. at a given RPM (based on airflow) the system provides a certain amount of fuel.

CIS is not a performance system. throttle response is lacking and the ability to customize the tuning is not there. throttle response comes from the overshoot of the sensor plate when you give it gas unlike a carb that has accelerator pumps.

I don't know what the 3.0 runs for WOT AFR normally so I don't know if you have a problem or not. that's why I just mentioned how my 2.7 ran and also to go back to original settings.

as mentioned if too rich, try removing the WOT switch, if open loop or even closed loop.
max timing may not be advanced enough.

[Walt Fricke]

T7 - I have the same WUR you have/had - the 033. Don't know quite how this came to be, as I bought the engine used out of Seattle (where it had started life on a stock Targa, and had not been hot rodded at all) years ago. However, by the simple expedient of not attaching to a vacuum source (and the '82 SC doesn't have a source for this up on the TB - it has the two lines to the distributor, which work, and one line to the top of the WUR, but its function is simply to provide clean ambient air pressure to the upper chamber. The lower chamber's tube is just exposed to engine compartment air. This is just like how the proper late US SC WUR is set up. Control pressure is control pressure.

I only run open loop - no reason to run closed in a track only car, and a number of reasons not to run closed loop.

I'd have to hunt up my notes, but the distributor advance is within spec but toward the advanced end of spec.

Looking at what others have posted, and what racers and engine builders have said works best, 13.2 or thereabouts at WOT is what I want. It is just possible that this is how Porsche designed it to be.

Thank you for the suggestion about disabling the WOT enrichment. If I can figure out which of the three wires to pull from the throttle switch (the top one?), that should do it. Jim Williams' site says that the idle and WOT positions on this switch produce a closed circuit to ground to their respective pins on the mini-brain under the right seat. If I pick the top wire, I have maybe a 50/50 chance of getting it right, and I should be able to see what is happening on my scope looking at the pulse widths. This should show up right away on the track.

[T77911S]

with you being in open loop, when you go WOT, is your DC changing. this is why I asked about open or closed loop. not sure but if in open loop then the DC of the FV goes to a default and never changes, no?

033, for some reason I suspected you had a different WUR than spec. the 78-79 used a different WUR. that one had the vac control on top I think, the 033 is on the bottom. I was going to say you should be ok with the 033 but I am second guessing that now.

WUR's are design to provide a change from CCP to WCP as you know. that difference can be around 2 bar. with the vac not connected to the 033 you are in the "rich" mode or lower WCP mode. if you try to set it to spec, around 3.5bar, there may not be enough range to go from cold to warm CP.

back to the FV.
connect your scope to the FV, remove the switch from the TB and manipulate it by hand if you can to see what the DC does.

timing,
check full advance with timing light.


I had the SC TB on my 2.7 along with the 033. there is a connection, I think on the rear, that can be used for the WUR. not that you need it because you are already rich. the TB came off of an 80.

[don gilbert]

My WUR. Did this yrs ago to my car and several others. You can not tune for crap with stock wur. Full control of afr at all times with this set up. Just dial in the press. you want for cold starts,,,raise it up to 55 and let the 02 system take over, or lower it to 40 for a nice rich mix when you want one.

[Walt Fricke]

T77 - the port on the SC (at least for the 80-83s, with the FV and mini brain, only provides a source of filtered atmospheric air. Arguable it is a bit below atmosphere because of the resistance of the air filter and the various bends (total of 270 degrees, pretty much) the air has to make before reaching the throttle, but I think that is de minimis. It looks just like a vacuum line, but isn't.

The 033 does have top and bottom ports, which can be used for whichever flavor (leaning or richening) you need. I put a vacuum (Mityvac) on each one of them, and with the fuel pump running watched the control pressure on the gauge. Quite dramatic changes, though I wasn't being scientific and comparing vacuum with pressure change. It proved the chambers were intact, and the aneroid disc was also intact and doing its job as a variable base perch for the smaller, inner spring.

Don - I wish the rules allowed me to do something like what you have, but they don't. Stock parts are stock parts.