Why does it still enrich?

[911st]

Ben,

I do not know if this is of use but Dave posted the following and it looks like a good starting point. I still would allow a margin for a CIS car because of it's less than accurate, consistent, or adaptive nature.

On boost in the 10's is probably what Porsche intended.

Originally Posted by David

[timc]

FWIW, Mine has had the same upper 9's way in to boost for the last 70K miles, AFR's are perfect everywhere else thru the RPM range. Bought a BL WUR last year, installed, same thing. No vacum leaks anywhere. Engine completely stock except: No SMOG, Fabspeed muffler, BL WUR.

[Helmsy]

UPDATE:

So I swapped out my injectors for some other (vitually new) injectors to see what effect it might have. I also put in some W4CS plugs.

AFR exactly the same (dips down to low 11s and blips 10.7 on lift off from WOT) but shutdown is better. I noticed one little pop (almost inaudible) about 10 secs after shutdown but at least the engine stops now soon after I turn the key.

So what I have concluded:

- The RPM switch doesn't necessarily stop a rich condition at WOT on boost.

- I may have a fuel head problem ie. flowing too much fuel or maybe it's just normal and this is why andial, etc. installed fuel controllers?? NOTE: I have a euro car ie. no lambda frequency controller.

- Drives better with the new injectors however I still noticed slight surging on low cruise (fine tuning needed). Tuned to ~13.9 idle ~14.2 cruise. I will need to drive it and start and stop it a few times before I am certain the shutdown is ok.

The tests were done with my stock wur so I will swap back to my BLWUR and bang the disc in and screw it up tight again and at least live with mid-high 11s on boost.

Any suggestions at this point would be greatly appreciated.

[mooney265]

First off, I'm not suggesting that the following idea would necessarily apply to your particular situation, but I'm just asking:

What if you had a cylinder or two that had massive compression or leakage problems? Then, wouldn't a Sh$T load of air be escaping through the rings or valves thus creating a very very rich situation in that particular cylinder [or two]?

This highly rich cylinder[s] would therefore bring the average AFR at the tailpipe down? And, would be amplified under boost or high stress situations...

Just thinking out loud...

[Helmsy]

Anything is possible and sometimes thinking out loud brings the best ideas.

I can't help but feel it's something to do with fueling either the head or flapper or control pressure dropping for some reason. I tested fuel delivery and more than enough fuel is coming from the pumps.

I will need to get it into the shop soon for some unrelated work so I might get them to do a leakdown test and have a look to see if they have any ideas. I was thinking of putting it on the Dyno to see exactly what is going on.

[911st]

Do you have an Andial Fueler on your car?

Based on your idle and cruse numbers it does not seem you have a higher flow FD. Also, to my limited knowledge, when Andial was doing builds they did not use the modified FD's.

Thought the injectors were probably the biggest part of your run on issue.

As you have installed good used injectors, one still could still have a slightly lower pop pressure. If so, it will be the last to equalize pressure after shut down.

[Helmsy]

No I don't have a Fuel controller on my car. Just a stock standard euro FD. I just thought maybe that's why people used them.

+1 on the pop pressures. I will check them when I get a chance. Any easy way to easily check them in the car?

[911st]

You can sort of check balance in the car but not pop pressure to my pressure. to my knowledge.

Some of the old car repair shop's will sometimes have a CIS injector tester.

Or you can send them out to an injector shop.

[smurfbus]

Originally Posted by Helmsy

UPDATE:

AFR exactly the same (dips down to low 11s and blips 10.7 on lift off from WOT) but shutdown is better. I noticed one little pop (almost inaudible) about 10 secs after shutdown but at least the engine stops now soon after I turn the key.

Tuned to ~13.9 idle ~14.2 cruise. I will need to drive it and start and stop it a few times before I am certain the shutdown is ok.

The tests were done with my stock wur so I will swap back to my BLWUR and bang the disc in and screw it up tight again and at least live with mid-high 11s on boost.

Any suggestions at this point would be greatly appreciated.

That low 11 is perfectly fine and better than the 10s you had earlier. When you say screw it up tight you don't mean the 3 allens on the bottom? Those set the enrichment trigger and you don't want to make it trigger earlier and IIRC tight is earlier? Even though you have blocked the enrichment with the pill those trigger bolts might affect mid range AFR?

Why not try a leaner cruise like 14.7 or even 15.3. I had it like that and while the spool was not optimum it still was good enough for me and MPG was better too. You can still have 13.7-9 idle.

One option is to install an additional injector controller on the lambda port if the richness bugs you that bad but I would just accept the safe rich on mid revs and just drive it. I had lean issues and that was the reason for the AIC in my case but at the same time I could dial mid range much leaner (need to address the lean spool though)

[Helmsy]

Low 11s is fine it's just I would prefer not to have to bang in the disc a long way and am curious as to why the thing still enriches even tho I installed the rpm switch. I cant recall but I think screwing in the 3 allen screws raises the threshold for boost enrichment.

It is curious to me that adjusting the wur to be so tight and virtually not enrich has an effect on the afrs under boost however the rpm switch doesn't stop it. I believe it may be a control pressure issue where pressure drops under boost but not because of the wur.

Is it possible for the fuel head or pressure regulator (in the fuel head) to flow more fuel than the wur is set for? ie. wur is set for a certain pressure but somewhere in the fuel system the pressure drops under boost which causes a rich condition? Just thinking out loud.

[911st]

Can control pressure drop with acceleration because of something other than the WUR's effect?

Interesting question!

I still think it is mostly the programing built into the metering cone profile.

However, control pressure (CP) basically comes from leaking off system pressure (SP) through a very small measured hole inside the Fuel Dist.

The WUR then leaks off said potential to maintain the desired CP.

Thus, I would guess the only way for CP to drop would be for SP to drop below CP. If that happed for any reason like a faulty fuel pump all bets are off for the motor running well at all.

If this could happen it would probably go very lean as there would not be enough pressure to push the needed fuel quantity through the injectors.

I have heard of this effect on modified 930's more than a few times so I believe it to be more in the range of normal.

However, if the FD is adjusted to flow more fuel, this condition is increased. We saw that on the first high flow FD we did.


It was noted to set cruse AFR leaner and that one might still be able to maintain rich enough idle AFR's.

This would require a higher SP and fattening up the screw at the FD. Higher SP will make the metering arm ride higher and decrease fuel delivery. Adjustment at the FD screw will advance the metering pin having an effect mostly at idle and a percentage of that effect as the air flow rates progress. Thus, you may have to increase SP more than you think as you will lose some of your improvement when you bring back some fuel to support idle.

I do not know how much you can raise SP with the BL WUR. I would call Brian L. to see if you do not have any supporting documentation. I would also put a gauge on it if doing so.

[Helmsy]

Thanks again.

I will try raising SP with my BLWUR and theoretically it shouldn't be as rich throughout the rpms. I have tried leaner before (14.7) and if i recall correctly it didn't idle or run as well however that was on old plugs.

I may need to try different plugs and gaps too to get it running smoothly on a leaner tune. I currently have W4CS with about 0.035' gap (MSD Ignition). I seem to remember posts relating to our cars liking to run a little richer especially with 964 cams.

[911st]

Most gas motors seem to need 14/1 to idle well.

CIS more so than most as it dose not atomize fuel well.

Also, the 930's CIS does not have any provision for acceleration so something closer to 13.2/1 off idle makes for better pre boost acceleration.

However, they can cruse well if lean.

[smurfbus]

You adjust the system pressure with shims in the fuel head pressure regulator on the right side of the FH. I have 7.3bar now and I found out on my car it was the best setting for more fuel. More pressure did not provide more fuel in my car. But with higher SP you fuel pump need to be in good condition. 7.3 bar very high for todays standards.

[911st]

I used to think higher SP would make for more fuel across the range.

However, it does not seem to but it can extend fuel delivery capacity at top end.

It helps to understand that the head is designed as a pressure regulator that will maintain an accurate Differental Pressure no matter what. Even if there is varations or degradation in the fuel system like with the fuel pump, accumulator, fuel filter or such. It is this Differental Pressure's effect, not system pressure, that ensures we deliver the same amount of fuel to the injector's at any expected point of operation.

Thus, changes in SP should not effect AFR's.

So why might we increase SP?

Because it extends the pressure range available at the injector. And sense the only way CIS can vary fuel delivery is changes in injector pressure. Remember, we are stuck with a 100% duty cycle.

For example. say the operating pressure range it the injector might run from say 25lbs to 90 lbs. If we can extend that to say 25 to 100 lbs, we should get more fuel delivery potental up top.

With this it makes makes more sense that increasing the SP might only effect the upper rpm AFR's.

But only if the metering plate dose not stall. CP and or the metering cone's design might limit access to the last part of the metering pins travel where this increased potental might be accessed.

Lowering CP under enrichment lets the metering pin advance further accessing additional metering pin range and thus higher delivery pressures at the injectors.

Thus, combining higher SP and lower on boost CP, assuming the fuel pump has the room, both might come togeather to help AFR's at the highest part of the RPM range more so than just lowering on boost CP.

However, with the lower CP on boost can again come exaggerated AFR's with the triggering of boost enrichment.

With shiming we probably should expect an increased potental for run on. With shut down the higher SP take longer to leak down to the injectors pop pressure.

Sorry, got carried away again. I love the CIS puzzle.

[Helmsy]

Wow thank you so much.

Very valuable information right there and helps me to understand this puzzle a little more.

I meant in my last post I will raise CP in my BLWUR and try it with a leaner cruise, not SP as I stated.

So far shutdown seems ok although I haven't really had time to drive it much.

[Helmsy]

OK so I thought I would revive this topic in order to update others in case they have similar issues and also to get some help with a new problem.

Car shuts down fine now with the new injectors.

I still have my stock WUR installed as my BLWUR doesn't hold boost pressure. Is the WUR supposed to hold boost pressure or instantly bleed off??

Anyway I can't seem to get a hold of Brian so I am running with the stock wur (anyone know if Brian is away atm?).

I tuned it to cruise at 14.6 and idle at ~14 operating temp and it seems to run really well however, it seems to go lean and rpm drop whilst warming up until it gets hot.

After about 5 mins driving on a cold rich start (12s) the cruise afrs are fine however idle afr is up around 16-17s (rpms ~800) until it gets hotter and then after about 10-15mins it's back to ~14.

Could it be my plugs or gap, timing or something else? (running W4CS gapped 0.035') Should I open up my AAR slightly to raise rpms during warmup or will that not affect the lean condition?

Any ideas are greatly appreciated at this stage.

[IMONBOOST]

I am sure the BLWUR should not bleed pressure.