Can this ECT possibly be faulty?

quahog pearl · Post by **quahog pearl** » 14 Nov 2012, 10:42

I have been having hard starting issues for over a month. I recently changed the wire set to Bougicord and plugs to Bosch (there were 2 NGK's and 3 Denso in there, only 1 of them torqued enough, gaps were all over 1mm

) The car runs a little better I think, or I'd like to believe that. But it ran well before and runs great now. Only ignition code is 214 - intermittent RPM sensor, which for some reason I cannot clear. When I disconnected the ECT to measure resistance I got open circuit. It turned cooling fan on(makes sense I guess) and set fuel code 123 - faulty or disconnected ECT. Reconnect, and code is easily cleared. Temperature gage appears to work exactly as it should. I'm puzzled because I was expecting to see resistance on this sensor that would change with coolant temp. Is there a digital protocol superimposed over an analog signal? I believe the ECT runs both the gage and inputs to engine management, not sure how. Ideas?

Post by **cn90** » 14 Nov 2012, 10:53

I post all info on ECT here:
https://www.matthewsvolvosite.com/forums ... hp?t=52203

On ebay, there is a seller selling the SWF ECT for $39.

Post by **jblackburn** » 14 Nov 2012, 12:22

You should be able to see resistance - 3000 up to 250 ohms - on the sensor. It will not show voltage. Your meter set to the right setting?

quahog pearl · Post by **quahog pearl** » 14 Nov 2012, 12:47

jblackburn wrote:You should be able to see resistance - 3000 up to 250 ohms - on the sensor. It will not show voltage. Your meter set to the right setting?

Yes, but thank you. I always doublecheck my settings before I start(goes back to the 70's when I had an analog meter and you had to "tare" the ohms to zero first to be accurate.) This is why I posted, even though it sounds like I don't know how to use the meter. I must have rechecked this 6 times as I couldn't understand how I could keep getting infinite resistance across the 2 ECT switch pins, yet the gage on the instrument panel works fine.

Post by **jblackburn** » 14 Nov 2012, 12:52

Haha, ok - just making sure. You're testing at the connector pins themselves? What about if you go up to the solder joints on the sensor itself?

There should only be a resistance signal from the sensor as it heats up - not sure why your meter isn't reading it.

quahog pearl · Post by **quahog pearl** » 15 Nov 2012, 10:17

I will check at the solder joints. I've been having better luck starting recently as I discovered something quite by accident. I can crank and crank until it finally starts OR if I crank a little and then release key so it is "run" (position2?) it will start. This works even if I crank for just a second. I wonder if there is an issue with the throttle position sensor or injectors are operating differently between start and run

Post by **jblackburn** » 15 Nov 2012, 10:19

ORRRRRR

Try this. Flip key to II, wait 2 seconds, then turn off, and then flip back to start.

IF that works, you've got a bad check valve at the fuel pump assembly.

quahog pearl · Post by **quahog pearl** » 20 Nov 2012, 10:52

Checked the ECT again last night. Resistance 2400 ohms, cool engine. This morning, 6400 ohms, cold engine (-2C). I was using my old meter on the wrong range before. I guess I should get a nice Fluke like the one I use at work, before senility sets in completely. Still starting poorly, but I doubt it's the ECT

mazda4d · Post by **mazda4d** » 20 Nov 2012, 15:15

This is regarding your starting issue, because I did have a similar problem with my 1994 850. First, the car would start when cold but not when hot. I had the code for the rpm sensor that kept coming back, and then the car wouldn't start at all... So I changed the rpm sensor (75$) and the car started right away. It seems that the rpm sensor fails when hot, thus preventing the ignition system from giving a spark, but work when cold, so giving the 2-1-4 code in A6 - RPM sensor fault intermittently.

This worked for about 6 month, then the started stalling, but with no code. It seems that when cam shaft sensor is going, it will may not give you a code 3-1-4 (cam shaft position sensor absent/faulty) or 3-2-4 intermittently (A6 or A2), but it will keep the ignition from working, even without logging a code. The cam shaft sensor is supposed to pulse, to regulate the spark, if it doesn't but stays steady within the range, then it's ok for diagnostic but not working for the ignition!. So I got one from the scrapyard (because I had no code and wasn't sure) and problem fixed! (for 20$ vs 125$) The car now runs and starts better then in the last 3 years! (What's funny is all that was done in 2011 and I have a 94, and I see you have a 95).

So basically, it seems like a rpm sensor fault will keep from starting only, but if you get a pulse and the car starts, then you're ok because the computer probably uses other info the keep firing the injectors etc. As for the cam shaft sensor failure will keep from starting but can also stall a running engine.

PS : I did also have the ECT fail on my 2006 xc70, the engine temperature gage would not bulge, but this never affected the engine control. If your temp gage works, your ECT should be ok.

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1994 850 sedan, 2006 xc70