Well the old v864 in my 1980 Deville stopped shutting off the cylinders. It has about 90,000 miles on the motor. It was switching fine before. Here's what happened.

I took a 500 mile road trip and somewhere along the way, the car stopped switching from 8 to 6 to 4 cylinder operation. It's stuck in 8 cylinder mode now.

It has always run a bit rich. The timing has been done, a new oxygen sensor put in, and new plugs on the one half of the engine I could get to. Wires, cap and rotor are about 3 years old. My mechanic (a good one) says the fuel pressure is OK.

The 3rd gear wire going to the transmission is attached.

I have the shop manual, and managed to do the diagnostic code thing and got 19 and 30.

Any tips from people who have had their v864 goof up like this would be appreciated.

-istp

What tests does the manual say to perform when the switching quits? The ECM provides a ground to turn on the system once engine temp is to normal. Is the system protected by a specific fuse? Is the engine getting to normal temperature, 195 to 210 degrees?

I just read my initial post. I meant 1981 Deville.

I can't find any troubleshooting stuff in the manual with the symptom "v864 not switching around". I have no idea if there's a fuse for this stuff, and I'm pretty sure the engine temperature gets hot enough.

I did fool around a bit, and I could manually make it go into 6 and 4 cylinder operation (using the buttons on the climate control system).

Something tells me, I'm gonna be driving around on 8 cylinders for a while.

-istp :hmm:

Just taking a guess.... You said that it was running rich... most likely a bad sensor input... A temp sensor or a bad map sensor or hose to the map sensor.. one of these sensors could also stop it from shutting off cylinders...A bad air temp sensor could also cause problems, but less likely.
code 19 is a shorted fuel pump circuit...code 30 is idle speed control circuit problem....I have the factory manuel on this and some used parts for cheap if you can't find any...

I agree, a faulty temp sensor could be a cause. If the manual doesn't provide diagnostics, it surely describes how the system works and what signals it needs to engage.

I'm shocked there is still an 81' out there with the system that still works.