Basic CIS Tuning Question

[wcarson]

Hi guys,

I'm hoping to get some easy and elementary advice from the CIS experts out there. I have done a lot of reading, and have some clue as to how the system works, but I'm hoping for some quick guidance.

Here's my summary:
1982 3.3L 930, K27-7200 Turbo, Kokeln IC, SC330 cams, Mildly ported heads, single plug stock ignition, Euro heat exchangers, Borla Muffler. STOCK 0.8 Bar Boost.

Brand new (Rebuild) CIS Fuel Distributor and new Leask WUR (The car has run great and the motor has 6K miles on it, but I recently had an issue with a failed fuel distributor, hence the rebuild of the FD. I also just got a new Leask WUR and also had my euro injectors tested and cleaned too). So now I'm trying to tune the new CIS set up.

I have installed an AEM Wideband 02 system for tuning purposes.

The Leask WUR came with the following info (I have not tested these numbers):
Cold Control Pressure 1.5 bar at 22 degrees C
Warm Control Pressure: 3.65 Bar
Enrichment Pressure: 2.4 Bar

My issue is this: I set CO to 3% with a Gunson Gas Tester. AFR at idle cold was 11-12:1, then when warm was 14.5:1. It drove terribly. With even minimal load, like 1/2 throttle, no boost, flat surface, it would be lean at 15:1 AFR and hesitate and buck a bit.

I then started to richen the mixture up with a 3mm Allen wrench and doing mild street driving, then getting more and more on throttle and boost while slowly making adjustments to the mixture.

I am now at warm idle AFR of around 10.5 :1 (Very Rich I would think) and the car seems to run and idle very well. But getting into heavier throttle while building boost at lower RPM's, I get lean areas where AFR is up to 13-14:1. This is in lower rpms on heavy throttle as boost is building. As the boost builds to higher levels, the AFR richens up to around 11-12:1, but at higher RPMs on full boost, it starts to drift up to 12.5:1 up to 12.8:1 or so. Currently warm cruise AFR is between 12-13:1.

So I need to lean the car out a bit when on low loads and cruise but richen it up when boost is building and at full boost.

What specifically do you all recommend adjusting with the mixture and the Leask WUR? I am thinking I will need to set the mixture screw back to leaner to achieve an AFR around 13-14:1 at warm idle, then perhaps drop the warm control pressure to richen the AFR when under load. And I may also have to lower the Full Throttle Enrichment pressure if it's still lean when on full boost. Does this sound accurate?


Many thanks in advance!!!!

[T77911S]

who rebuilt the FD. i assume cast iron

leave your pressures alone. trust me, i have been down this exact road. very rich idle and lean cruise with a cast iron head. even had my FD rebuilt TWICE. finally determined it was just a bad FD. i now have an aluminum one with the FV removed and all is good.
you dont have a good understanding of how the pressures work. the CP effects ALL RPMS, the enrichment effects boost AFR. if you drop the CP you will just lean it back out with the mixture screw and be back where you are. only difference is at what RPM the lean cruise happens.

do you trust the gunson.
what is the CO when it runs good.
what is your timing. does advance work properly.
also make sure your plugs cap and rotor are in good shape
this does not sound like an air leak issue but check in the intake man bolts anyway.
is your blow off valve vented to atmosphere are recirculating.

[wcarson]

T77911S-
Thank for the input. My FD is cast iron- I got it as a rebuilt unit from RarelyL8 Motorsports. My old unit was also cast iron and worked well unit it leaked. I had it all dyno tuned (by an experienced shop in Southern CA) and AFR's were on the rich/safe side but overall great across the board. I don't really trust the Gunson Gas Tester- the values always seem to drift all over the place. I do trust the AEM Wideband though- it indeed seems very accurate.

Not sure on my timing- but everything has run perfectly for years until my FD leaked and I got the rebuilt unit and Leask WUR. The engine has not been touched since or changed in any way, other than I've taken the fuel system off and now reinstalled it with refurbished components.

Yes- I agree that I don't have a great understanding of CIS tuning. What is the fundamental difference between changing the mixture (3mm Allen Wrench) and dropping the warm control pressure on the adjustable Leask WUR? You are implying that they are essentially equivalent- ie, If I lean out the mixture and also drop the control pressure a bit to richen things up, I'll be right back where I started. My understanding was that I could lean the mixture out so that it won't be so rich at idle, then slightly drop the control pressure so that it will more rich when under load across the spectrum.

[wcarson]

Hopefully someone can give me a good summary of the difference between setting the mixture (with the 3 mm allen wrench) and setting the warm control pressure.

Basically to get my car to run in acceptable A/F ratios when under load and getting on boost, the car is running way too rich off boost. If I lean it out with the mixture screw and then lower the warm control pressure a bit with the Leask WUR, will that help with the current situation?

Thanks in advance!

[Alan L]

T77911S is correct, as usual. The idle mix screw sets how open the metering slits are for idle airflow.
Read - idle airplate opening. Dropping the CP has a similar effect - because it softens the control pressure on top of the metering piston in the FD. Making it easier for the piston to open the metering slits for a given airplate setting - read idle airplate opening. In addition - it has the same effect across the whole throttle range. Whereas the idle screw sets a baseline opening, which becomes inconsequential as you progress to WOT.
I tune my idle by ear. Warm engine, then tweek the allen key one way slowly until your hear the engine note change. With practise it is quite distinct - hitting the lean/rich mark. Take note of the o'clock position of the allen key, now reverse the tweek until you hear the engine note change again. Note the o'clock position. You should not be more than about half a turn between O'clocks.
Now hit the mid spot. That will be as close as any other tuning method and the car should be happy at idle. Various engines are happier at various idle AFRs.
Alan

[wcarson]

Thank you- this is helpful.

My plan is to check all the control pressures and also the system pressure. Proving everything is as expected and within the range it's supposed to be pre-set to, I will lean out the mixture so my idle is better (with CO at 3%) then lower the warm control pressure so the AFR across the range are richer.

[Alan L]

Your WP is correct for the 3.3. You could come down a fraction (0.2)
You need to set that first.
Tweek the idle mix last. Changing the WP will change the idle mix. But changing the idle mix will not change your WP. You still not quite getting it.
In fact your AFRs look reasonable. There is a tendency to run lean on trailing throttle. But 10.5 idle is too rich. If the car sounds sweet at this AFR, then you likely have an airleak somewhere.
Best you go looking for some airleaks before tweeking anything.
Alan

[wcarson]

Ah- got it- that makes sense to lower the warm CP first, then re-set the mixture. The car idles alright when warm at the current rich condition, but it idled much better at the initial leaner mixture setting. And when cold, it barely idles because it’s so rich now.

I’ll check all the pressures before I change anything. Thank you Alan for the input- it’s very helpful.

[Alan L]

Yes - verify pressures first.
Your boost dump pressure (2.4) is very low. If in fact true, I can only think it is to gain as much fuel as possible. Dropping the WP by 0.2 wont have any real effect on your top end AFRs if you are at 2.4 on dump. Anything from 2.4(and below) up to around 2.8 has no real effect - you are already getting what the FD can provide.
Alan

[wcarson]

Alan- Thanks again for your wisdom. The boost enrichment pressure was custom set by Leask and RarelyL8 for my set up of SC330 cams, ported heads, K27-7200 turbo, etc.

Our cars are probably pretty similar in terms of motor set up. Mine made 351 wheel HP on the dyno when it was built years back. It was running the euro FD that was modified for increased flow by Imagine Auto (who used CIS Flowtech) with a stock WUR. The AFR's were on the rich but safe side and it ran great for the past 20 years on that set up. Now I've installed a rebuilt stock euro FD and the adjustable Leask WUR. So hopefully I can make this set up work.

Thank you again. I'll report back once I actually check the system pressure and control pressures. Many thanks from a Yank to a Kiwi! I lived in WA and NSW growing up but never spent much time in New Zealand. I know it's a beautiful place.

[Alan L]

As Brian will tell you I am sure, at around 400 RWHP you are on the limit for CIS - without major mods to the FD.
I have struggled for a long time to get enough fuel at the top end - and basically my AFRs are like yours - leaning out beyond 12.5 around 6000 rpm. This is common.
I have done everything I really can to get another 5% or so of flow to make this top end workable.
So what you experience in that regard is probably quite expected.
Getting AFRs 13-14 as you come on to boost is normal - pre boost dump. It is quite safe -you don't have full boost in that mid range and those numbers are about where you would want them.
Then the problem begins - at boost dump - they drop to pig rich (depending on set up), then progressively lean out as the revs climb - until you basically run of of fuel - if you are generating sufficient power. If you are running a stock engine you have fuel to spare at the top end and can afford to dial that rich dump back.
Otherwise - thats where the Leask switch comes in to play - delaying the dump as long as necessary.
Your idle settings have virtually nil effect on any of this and are an independant process really - just for getting idle right. But at this low end of the rpm, any airleaks become a major contributor.
It would pay to be sure you are not dealing with airleaks before ripping into the CIS too hard to combat your rough running problem.
Alan

[wcarson]

Hmmm. Interesting about the 13-14 AFR on load as boost is building. That's vey good to know that that is safe. I didn't like seeing those numbers go high like that before boost dump. I'll report back when I get more info- hopefully by the end of the week. Many many thanks.

[Alan L]

As the boost starts to pick up, the car is making more power. So it is asking for more fuel - it is breathing faster.
But your WUR WP at this point has not changed - so it starts to lean out. The boost dump usually comes in around 0.5 bar of boost. So at 13-14 AFR at low boost, you are quite safe. Normal optimum AFR in a NA engine is around 14-14.5. So you are still slightly on the rich side with low boost. If it did not lean out like that, when you got the boost dump it would probably near kill the engine with fuel. You need it to lean out a bit before dumping more fuel in.
The limitation with CIS/turbo is there is no progression. All or nothing sort of thing. So an abrupt transition thru the boost phase.
Yes - NZ is a beautiful country. Travelled to more countries than I could count. This place still has it. Not without issues, but still the place to be, for me.
Alan

[wcarson]

Quick update- the system pressure is 6.2 bar, within spec, cold control pressure is 1.5 bar and warm control pressure was 3.65 bar, just as it was supposed to be set at.....RarelyL8 included a spec sheet from Leask that had the preset values listed. Spot on. I decreased the warm CP to 3.4. I then leaned the mixture at idle so the AFR is 13.5 when warm. I also refit all the air intake and intercooler fittings and hoses and re-tightend all the clamps very carefully.

It idled beautifully at warm AFR of 13.5. But when doing a test drive, again, similar to before, as a rolled on just a bit of throttle it leaned out to AFR of 15-16. I richened the mixture allen screw a bit on subsequent test drives, gently rolling on more and more throttle.

Here's where I am now: Idle warm AFR is 11.9-12.0. It still idles great. Cruising at a constant speed in 3d or 4th gear on flat surfaces AFR is 13.5-14. But when I roll onto the throttle at around 2000 rpm, it leans out transiently to AFR up to 15.3, then starts to richen up rapidly. When AFR is in the low 15's, there's really no boost yet. As boost starts to build, it gets richer pretty quickly. At full boost, it's dipping into the low 10's.

Overall it seems to run great. I don't mind keeping it on the rich side- but my main concern is the transient lean condition at AFR in the low 15's when I'm rolling onto the throttle before boost builds......... Is this safe? It only lasts for a second or two and there's certainly not much boost, if any, built at this point.

Here is a quick video of a 2nd gear pull- you'll see it starts out at AFR in the high 13's at cruising constant speed, then I roll onto the throttle, in the end flooring it as boost builds. You'll see very early in the video the AFR leans out the low 15's for a second or so.

https://www.youtube.com/watch?v=6VdkVpr9UxE


Here's a similar video on a 3d gear pull. I started the video right AFTER I applied the throttle so the video starts at AFR in the low 15's.

https://www.youtube.com/watch?v=yze1cW0nPgg

As always, thanks for the input!!!!

[Alan L]

Your car is behaving like pretty much all CIS 930s. And your tuning response is pretty much as I would do.
If it is running fine, ENJOY it.
Depending what your AFRs run to at the top end on boost, you may be able to decrease the boost dump a bit (get out of the low 10s). Or if you don't have one, fit a Leask rpm switch - controls/delays when the dump comes in. That way you even out the big up/down AFRs on boost.
The lean AFRs pre boost are not an issue if it running fine. Remember - your static compression is a lowly 7:1.
Alan

[wcarson]

Thank you Alan- as always, very useful. I was hoping you were going to respond and it sounds like all is alright. The car certainly runs well- no stuttering, hesitation, etc. It's perhaps too much information now that I have the wideband 02 system installed- I now need to learn to not be preoccupied with it every time I drive the car! I did do a WOT run in 4th gear on sustained full boost for a good 7 or 8 seconds. The AFR was a steady 10.5 to 11. Plenty of fuel there. So I could likely try backing off just a bit with the enrichment.

I've mentally committed myself to driving it more often than I have been the last few years. Thank you again for your help. It's truly appreciated.

[Alan L]

Try a 2nd or 3rd gear pull in to higher rpms - top end of where you are comfortable. Note AFR.
If they are still in 11s, you need to lean it out a bit - raise WP. Or reduce boost dump a bit. Latter prob better option - don't need leaner off- boost AFRs.
Note your AFRs just before the boost dump comes in. That will tell you if you need to increase WP a bit. Ideally it should be getting up between 12.5 -13. If not - two choices. Increase WP, or fit a Leask rpm switch. Has rpm pills you insert to get to the desired rpm (AFR) before the dump comes. Then you don't go so low in AFR, because you are already at higher rpms.
It is as problematic running the engine in low AFRs as it is lean ones. Too much fuel is diluting the oil in cylinders and depositing soot on everything. Cleaner burning = better performance and engine life.
You don't need to be studying AFRs once you get it set up. Extremely (indispensible) useful for diagnostic and tuning. Once you have that set, forget and drive like you stole it.
I have my AFR right in front - above my steering wheel. In a race I hardly get a chance to check - down a straight, 3rd or 4 th hard pull and no cars trying to nail me. Maybe 2-3 times a race. Once I am happy I am safe, I forget it and just wring its neck.
Regards
Alan

[Alan L]

Once you get some spare time and feel like giving the 930 some TLC, checking for airleaks is always a useful exercise. Below boost they contribute to lean running, at boost they make it more rich.
Typical places are hose joints, cracked hoses, IC plumbing (O rings etc), injector blocks (the plastic ones crack). It is win/win if you eliminate any. Better running car.
Alan