CIS behaviour when coasting

[Vereeken]

Grateful if the CIS experts could chime in.

What can I ecpect from the 1982 CIS system on a EURO SC (no lambda) when coasting (so lets say 60 in 4th and then letting go of the throttle but remaining in gear- I believe that is coasting).

What should I see on the Innovate LM1 ? Should I see an AFR that comes close to 20.9?

So what I am asking is in fact if the air flow sensor falls to close when coasting thus closing the ground to the fuel pump relay and effectively closing the FP delivery for as long as you remain in coast.

Or is CIS nod designed in this way and does the air flow sensor remains slightly open thus delivering Continuous fuel even when coasting?

Michel

[RarlyL8]

All engines idle when the throttle plate is closed. You should see a low spike in the AFR that recovers to idle level ~13.5 give or take for CIS. Coasting is engine breaking which will pull air back through the exhaust and may scew your AFR reading depending on where the O2 sensor is located.

[T77911S]

if you let off the gas with it still in gear and RPM's abpve idle as in slowing the car with the engine, yes, 20.9.

[Vereeken]

hmm ok, I thought that modern engines cut off any form of injection when lifting the throttle to comply with exhaust regulations. I was wondering if they achived the same goal with the throttle plate give that it can make contact with it sseating position and shut the relay down.

So it looks like my CIS is also behaving as it should when letting go of the throttle in gear. I see a spike in AFR to about 18/19 and then setlles back to 13.7.

Thank you.

michel

[Vereeken]

Ok, what I meant is what T77 describes.

On the throttle in gear , let go of throttle in gear but fairly above idle RPM.

So If I understand you the engine should work as a giant air pump.

If I do not see that (I see only high 18s 19s) and only for a couple of seconds to what does that point?

The car runs great but I seem to remember being able to see 20.9s long ago before I overhauled the system.

Is this the seat of the air sensor ( the little screw with which you can alter the height where it sits in the throat) not adjusted properly?

Michel

[javadog]

Originally Posted by Vereeken

hmm ok, I thought that modern engines cut off any form of injection when lifting the throttle to comply with exhaust regulations.

CIS is not a modern system. The fuel cutoff when coasting in a 911 started when Porsche introduced the Motronic system on the 1984 Carrera 3.2.

JR