930/03, AFR 10.5 at redline...

[ArvidW]

Hi,

At the 911 Technical forum I was advised to ask my question here:

Hi,

Recently I've been working on a 1972 911 targa with a 1978 3.0 ROW SC engine (engine code 930/03) which belongs to a friend of mine. Together we have rebuild the engine with new rings, bearings, studs, wiring loom, bolts, valve guides and gaskets.





Quite a lot of time was spend on re-instating the CIS injection with rebuild/checked/new components. The car runs great, starts and idles fantastic when cold and performs excellent (0-62mph in 6.8 with 2 large blokes in the car)

The only thing I (as a EFI guy) don't like are the mixtures when driving: (Innovate MTX-L wideband)
- Idle: Tuned for aprox 14.5 AFR
- Part load 60-140kph: 13.2-12.8 AFR
- Full load 2-4krpm: 12.8-12.5 AFR
- Full load 4-5krpm: 12.0-10.8 AFR
- Full load 5-6.5krpm: 10.8-10.5 AFR

System pressure: 4.9bar
WUR hot pressure: 2.9bar (3.2 with > 0.1bar vacuum)
WUR cold pressure 2.3bar @ 22dgC
The WUR was shimmed with a 0.15mm shim to be exactly in the middle of the spec when hot.

Is it normal that a CIS car (non-lambda) runs so rich at WOT? (part load also seems rich to me..)

In two weeks i'm going to have the car dyno tested (dynapacks) and I would like to gain a few ponies by running it less rich. What options do I have to adjust mixture at WOT that doesn't influence mixture at idle?

I've tried:
- Searching for vacuum leaks: Replaced some hoses + injector bushes
- Mixture screw: Large impact on mixture at idle, neglect able impact noticed at WOT
- Vacuum line WUR: removed the vacuum line, stopping vacuum leaning --> mixture at idle richer --> leaned mixture at idle back to 14.5 with mixture screw. --> No significant impact at WOT
- Swapped vacuum line WUR: --> Vacuum enrichment instead of leaning (WUR 2.4bar @ 0.6bar vacuum) --> readjusted mixture at idle to 14.5 --> runs aprox 0.2AFR leaner at WOT but 1.0AFR richer at part load (I could have expected that..)

Still not the result I was looking for I've read the bosch K-jetronic manual and mixture at WOT seems to become rich due to the steep 3rd cone in the sensor air funnel. Changing that shape is a bit too much work for my liking..

I know of the existence of the FrankenCIS, which I genuinely like as a ex-megasquirt user. Unfortunately it's not my car and my money..

[gavinc69]

Alot of guys with CIS on engines 'shim' the fuel head to give more fuel so I guess you could remove shims to reduce it, may help.
You can google 'shim Bosch CIS Furl Head' etc or I have some info on it when I tried it on my CIS :

Go to page 12

Turbo Conversion on 3.0 SC Winter Project

[flightlead404]

Have you checked the p/n on the WUR to make sure its the correct one?

[smurfbus]

I would try different system pressures to find the optimal compromise. And check the wur part# too.

[ArvidW]

Thanks for the responses !

@gavinc, do you recon reducing the fuel pressure will alter the air fuel ratio mainly at WOT or for the entire operating range (from idle to WOT)

@Flightlead, yes, the WUR is the correct type (0 438 140 045) for a 1978 3.0SC

@smurfbus, could you give me an indication how big the lowering of system pressure should be? Should I try 0.5bar to start with? Or more?

[smurfbus]

Just like tuning other values on EFI go with small changes and then you can see if it goes worse or better. You engine being NA I dont know how it reacts with system pressure but after couple of steps you will see where its going.

You need to compensate the control pressures (can you?) when you're done with changed WOT values (system pressure). I'm totally clueless on NA engines fueling so take this advice as a guess.

[Alan L]

Lowering the WUR pressure takes you richer across the board. 0.5 bar would be a good place to start. It equates roughly to about a 0.5AFR on my beast. You can tune the richer idle out of it, but it has minimal effect across the rest of the AFR range.
it seems to me a bit odd to get increasing richness with rpm. Wonder if some other issue somewhere.
Alan

[Alan L]

Sorry - your AFR already too rich at top - need to raise WUR pressure - by about 0.5 bar for start. The problem is this will raise your Cold pressure too. If it goes too far out of spec and begins hard cold starts, you may need to knock the pin on the WUR for the cold pressure.
Again, if idle too lean, correct with idle adjust.
Alan

[ArvidW]

@ Smurfbus, yes I can adjust the control pressure. Last time I used a washer which I filed to give the correct control pressure:






@ Alan L: I'll shim the WUR to give 0.5bar more control pressure, adjust the idle AFR with the mixture screw and try again.

Could the enrichment at high rpm (airflow) be caused by the shape of the CIS airmass measurement "bowl" ? That above 4500rpm the metering flap goes into the 3rd cone and starts giving a rich mixture?

[Alan L]

Well the cone is designed to provide more than a linear air/fuel mix, yes. But that should basically sort itself out to a stable AFR thru the range - that is the whole point.
I can't help feel something is not quite right.
Can't remember when I last tweeked my SC WUR, but I think you should not have to shim it - screw the allen screw in the bottom in by about 1/4 - 1/2 turn to get 0.5 bar. That pushes the spring against the diaphragm a bit harder = higher WUR pressure.
Alan

[ArvidW]

It took me a while to find the allen bolt you where implying. Apparently it's carefully hidden by some Bosch engineers.

After careful examination I have to conclude the Allen adjustment screw will have exactly the same effect as the shim I installed. Both increase the preload of the inner spring. I'm still very grad you gave me this tip as adjusting is way easier than filing down washers I've found some of your posts stating the 1/4 turn is 0.25mm so I can remove my shim and make a baseline at 1/6 turn.

Tomorrow I'll start working the control pressure, and monitor AFR's. I'll keep you posted.

[kenikh]

Too much fuel on top? Just add boost!

[JFairman]

That'll work!

[Alan L]

Yes, the pitch of the thread will either be 1 or 0.8mm. So 1/4 turn will be 0.25 or 0.2mm which is equiv to about 8-10 thou shim. But much easier to just adjust the screw - which is what it is there for.
Alan

[Jeff NJ]

Originally Posted by kenikh

Too much fuel on top? Just add boost!

See, that is the kind of out of the box thinking I've come to expect here!

[Alan L]

Well, a shame to waste all that fuel. Or, spread some around to the rest of us that suffer from 12.5 AFR on boost before redline.
Alan

[kenikh]

FWIW, my car is close to your AFRs at redline using a k27-7006. I like the added safety margin. I call it my gasoline intercooler.

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[Alan L]

Kenikh, what fuel head and cams are you running?
Alan

[kenikh]

Euro/early fuel head and 993SS cams

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[ArvidW]

I just performed a leak test to verify everything was OK before adjusting the WUR. I made a closing plate to seal the rubber booth near the CIS flow sensor as wel as a closing plate inc hose connection to pressurise the system via the exhaust (engine @ TDC for some valve overlap)





Installing the CIS flow sensor closing plate is a pain in the ass, so little room in that tiny engine bay :roll eyes:

Unfortunately I found two air leaks:
- Filler cap of oil tank (not an issue, with vacuum it will pull the cap down and seal properly)
- Throttle body shaft (see video). There is some play on the shaft and if you wiggle it the leak becomes smaller / larger. I think I should fix this first..

https://youtu.be/9kWrn6_REbw

@kenith, I wouldn't complain if this SC ran 10.5's (AFR or quarter mile...) with a k27