Rear ECT Ignition Temperature Switch 960 Disappeared!

ibismachine · Post by **ibismachine** » 31 May 2010, 07:03

Here were the symptoms: Running rough on start for about the first 5 minutes with white smoke out the exhaust. Typical head gasket issues. Losing about a pint of antifreeze a day. Seems like too much for the amount of white smoke I was getting. Next issue - Erratic idle but mostly zooming up to 3000 rpm. Problem points to ECT temperature sensor - the one in between the back of the engine and the firewall. I went to see the sensor and it had disappeared. The hole in the block was there but there is no trace of the sensor or the wires that connected it. I have removed the harness as far as I could - coil connections, injector connections, crank position etc.. but no broken wires or even any sign of broken wires.

Two questions (please):

How are the ECT sensor wires routed back to the brain?
How come although the block is full of antifreeze it isn't leaking out the hole where the ECT was?

DanR · Post by **DanR** » 31 May 2010, 09:28

Your ECT is located at the t stat housing up front at the upper radiator hose. 1996 and newer use OBii and they went to one sensor for both the gauge and the ecm.

You might have a head gasket leak, but would pull the spark plugs and inspect, if it has been a while with these symptoms, then the culprit cylinder's spark plug should be nice and clean. A pressure test would then be required to confirm.

Your idle problems might be water shorting out spark plugs that are wet, until the engine heats enough to boil that moisture away. Or if it is not a leaking head gasket you might have a vacuum leak, a bad throttle sensor, or idle speed motor.

But you never had a coolant sensor at the rear of the head.

Looks like you have an oil leak though, could be the rear cam seal or the sometimes the oil filler gasket leaks but the oil travels down hill to the rear of the engine.

Keep us posted on what you find.

DanR '94 964 352,000 miles (118,000 on the new engine)

ibismachine · Post by **ibismachine** » 31 May 2010, 12:48

Dan,

Thanks for your post, but I have a couple more questions. I have attached wiring information on a V90 6 cyl 1997 and it shows that sensor (17) in place. So..I believe you when you say I never had one because it unscrewing and disappearing with all of the wires doesn't make sense, but what goes in the hole in the picture, and why am i seeing these sensors in other (later) Volvo 6 cylinder engines?

Thanks and God bless.

ibismachine · Post by **ibismachine** » 31 May 2010, 12:54

BTW spark plugs are clean and show no telltale leaking - simple compression test shows all cylinders within 5%. Idle speed motor working fine. Additional info: Temperature gage is erratic - dropping from midway to off in a second and rising back up a second later. Unrelated symptom arrived at the same time: transmission EWS overdrive lights blinking like a Christmas tree! Time to throw in the towel? Thanks!