CIS - Running Rich
 

I'm helping a friend with his '80 SC (US market) car. Symptom: AFR indications of 10:1 and 11:1 are common under normal cruise and mileage is poor - 13MPG or less.

We've been messing with the injection and cannot get it to run leaner under part throttle/light load and WOT conditions.

Pressures have been checked on more than one occasion and are within specifications.

The car starts well under all conditions with no mucking about with controls.

Idle mix adjusted for ~stoich (14.7).

Vacuum leaks have been checked for.

Timing appears to be in check.

AAR verified to work.

Injectors changed. Checked for flow with bottle test.

O2 system seems to work with the 1.5V battery/ground test and dwell meter. I can't say 100% at this time as my memory is going bad..

So what's left?

Restricted exhaust?

New Dansk SSIs and 2-1 muffler..

Pressures?
 

What is the "system" pressure reading and what is the "control" pressure reading when first started running "cold" and then running for a while "hot" . 1980 was first year to add an O2 Sensor and control fuel mixture with a frequency valve..
Pressures should be read first , then go to Frequency valve operation. These systems are very easy overall and happy to help diagnose.
Mike

Mike

Pressures line up with information for 80 with O2: 20C=2.2 bar cold, warm 3.5 bar. System right where it should be, 5 bar.

Pressures look good... next place to go is Frequency Valve operation. Is it "buzzing" while engine is hot idling?
And can you adjust mixture and change its buzzing (frequency)?

Leaky cold start injector?

Do you adjust the 3mm allen screw that adjust the CIS plate height and mixture? Do you test if you have a sticky injector that are flowing more fuel that are suppouse to flow? Do you remove and clean the oil film, grease and dirt from the CIS plate and throttle body?

We connected a noid light and indeed it was operational.

As far as any buzzing goes..difficult to tell. Is it typically easy to hear/feel? Should I get out the mechanic's stethoscope?

One other thing - the PLX wideband has a narrowband output that is supposedly good for driving OEM gear but I'm starting to suspect that it may not be doing its job.

Even if the frequency valve was working, when is it most active?

smooth operation of the air flow meter? dizzy advance working fully? what is the ignition timing at idle and full advance? Full injectors weeping?

i'd be stumped too, keep checking and we'll crack it.

My guess is the cold start system (on my car it's a WUR) is staying on / open.

AFM plunger plate height set correctly?

To check FV buzzing, turn ignition to position right before start. You'll hear the CDI high-pitched whine. Then on the backside of the throttle body (facing the firewall), is an electrical plug - unplug that and you should hear a very loud, very distinct doorbell buzzer. That's the FV operational.

I'd bet money on that. Putting the aftermarket AFR system in probably is giving it the wrong signal. The 1980 had a particularly simple O2 system as well, no WOT throttle switch.

Someone else will have to check their files to see what the factory 1980 O2 box looks at as the narrowband range. I bet its' 0-1V as expected, but (for example) my AEM gauge outputs various 0-1V curves (even a 1-2V output!)

Jess,

Hook up an analog dwell meter to the test connector under the plastic cover on the left of the engine compartment and the CIS lambda system will tell you what is going on. You should have a steady 77 dwell on the 4 cylinder scale until the engine warms up , then a regularly fluctuating 40-58 when hot. Much better than guessing. Everything you need to know about the optimum tune for this system can be found by searching for CIS lambda.

Paul

I agree with Pazuzu's logic, get it back to 80 Bosch electronics... I think that facory O2 is a 0 to .9V range and with no heater the O2's are lazy (VERY SLOW)...afterall 1980 was the first year of the O2 sensor on the 911.
Mike

I found out the hard way that the PLX narrowband output is not compatible with the factory ECU. Jim Williams had similar experiences. I think we both assumed that it was just a simple voltage input to the ECU but apparently there is more to it than that. Speculation is that the waveform of the signal or the frequency of change is incompatible and the ECU doesn't like it. You would need oscilloscope traces to verify and I wasn't willing to go to that much trouble.

You can jump a couple of pins at the O2 sensor relay under the passenger seat to hear the FV click without the car running. Can't recall which pins off hand. I'd have to go back and look at the wiring diagram.

Pull the relay under the seat while the engine is running. If the engine rpm doesn't change the FV system is not working. Could be the relay is bad, the EC is bad or the FV is bad. Or possibly the wiring.

Did you flow test the ejectors?

Let us know what happens.

Thought I'd post some news. Seems the frequency valve isn't working as intended. It will only buzz for a moment.

Will also be installing old-school O2 sensor to drive the brain.

I'll post findings as we progress.

A lot of us have the O2 sensor unplugged and run the car in open loop. It was suggested by John Walker too.

The FV should be buzzing irregardless of O2 see sensor plugged in or not.

In my case it wasn't buzzing either. Turns out the FV/O2 ECU had a burnt circuit in it. Replaced that with a good unit and all's well.

Forgot to ask, does the car have bucking at around 2200 RPM?