930 CIS suddenly running lean

[sigchuck]

Hi guys, I have a rebuilt/refreshed 930 fuel injection system on my 83 911. It is a non-lambda 78-79 system, and I have an Innovate box to monitor AFRs.

Recently, the car has begun to lean out under load - both boosted and non-boosted. I don't think that this is the result of a defect with the Innovate box or 02 sensor, both of which have around 500 miles on them and sensor having been properly calibrated. My idle reading is still fine and where it was previously, and the gauge does go slightly rich when I suddenly let off the throttle (around 12:1 momentarily). I've also checked for vacuum leaks.

The WUR appears to still function normally for the warmup cycle and warm idle is a consistent 1000 RPMs after 5 or so minutes.

The lean condition is apparent when the car is cold and warm, but again, only under acceleration. I'm far from a CIS expert, but it almost seems like it's not sensing vacuum/boost (though I haven't really tried much boost because the AFR numbers are somewhat alarming at 16 under partial throttle).

Everything was functioning fine until it wasn't. Any thoughts on whether this might be a diaphragm issue with the WUR? If the diaphragm was damaged, would it be leaking fuel from the top port? In my case, there are no fuel leaks. I have also check CCP and confirmed it's within spec.

Thanks for the help and please don't hesitate to let me know what other information I can provide!

[1979-930]

Is the car stock?
It could be the in the WUR or fuel head.
Rebuilding the WUR or getting an adjustable WUR from Brian Leask at RarlyL8 might be needed.
16 on boost is going to pop that engine.


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[slow&rusty]

It's easy to temp. hook up a boost gauge with a rubber hose somewhere between the intercooler to the manifold to verify boost.

Also when you accelerate or tip into the throttle, you should see the AFR numbers drop, is that the case. Partial throttle doesn't tell us anything.

Which Innovate are you using?

Also there is a 930 section on this Forum, where you will get some additional experienced responses.

[sigchuck]

Hi guys, I was actually in the process of taking off the WUR this morning. I had tested CCP again last night and was getting readings all over the place - from 2.4 to 4 bar - which was quite a surprise considering where they were a week or two ago (in spec). The good news is that my system pressure is consistent at 6.5 bar, so I'm hoping that means no FD issue???

My innovate box is an LC-2 with a gauge made by John Bell.

A somewhat pleasant surprise was that the screen was entirely covered with debris (see attached). The downside is that I have no idea where the debris could have come from. I was in a hurry this morning and was removing so I could ship it off for service, so I haven't had a chance to recheck it now that I've cleaned the screen. I did initially swab it with a q-tip before blasting with carb cleaner, so I'll check that with a magnet once I'm back home.

The fuel system has been completely replaced over the past 3-4 years, from the tank, to the pump, to tunnel lines, filter, and all soft CIS lines, so this is somewhat perplexing. The FD and WUR were also rebuilt within the past 500 miles.

One thought was that I bought my test kit used and the valve (unbeknownst to me) was completely shot and leaked very badly. I replaced it with the valve from a Harbor Freight kit, so maybe the plastic ball valve in the metal housing is shaving tiny bits off every time I open and close it? I guess I'll be able to make a more educated guess once I see whether the debris is magnetic or not.