I've got an 88 740 turbo that is blowing out very rich smoky exhaust.It starts ok but doesn't idle well and won't take any throttle very well. The boost gage indicates normal boost. I took it to an independent volvo guy and he checked it out and couldn't find any of the ususl problems i.e. amm. leaks. ox sensor ignition fuel press regulator. He thought it might be the ecu but he doesn't mess with that part in case he is wrong. I got a used ecu and tried it and it didnt make any difference. In reading the various forums and FAQ section I think it may be the coolant temp sensor. I measured the voltage between terminals 5 and 13 at the connector and I got just over 11.0 volts with the engine cold and an air temp of about 70 degrees F. with the ignition on and I checked the resistance and got .452 K. ohms on the meter with the ignition off. Am I doing the test correctly? Do these results indicate a temp sensor fault? I sure hope that this is the solution. I know the sensor is under intake # 3 and will require intake manifold removal. I'd just appreciate some confirmation that I'm on the right track before I replace it. I'll probably replace it anyway. Thanks.

A quick look at the FAQs and it seems to me that your values are out of spec so that it might be a bad ECT sensor. BTW, I replaced one on my 940 and I was able to replace it without taking the manifold off (and without spilling too much coolant!) Check the wiring harness coming off the ECT, too.

Hope this helps.

Mike
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Mike Brown Greenville, NC 1996 965 113K 1994 940 135K 1986 244 137K

Try yanking out the connector with the engine running and see if anything changes.

What is your ECU model # ?

thanks for the help, my ecu # is 280000541, or 514 I can't recall exactly while I'm writing this. Joe.

Another way to easily confirm it is the sensor (especially if you have spare resistors lying around), is to check what the cold resistance value should be and insert matching resistor(s) into the pulled connector-plug. A quick check of the FAQs gives the following resistances - but not sure if they apply to your sensor or not.

32F (0C)-- about 6000 ohms within a range of +/- 10%
68F(20C) -- about 2300 ohms
104F(40C) -- about 1300 ohms
140F(60C) -- about 600 ohms
176F(80C) -- about 300 ohms
212F -- about 190 ohms

Check the wiring diagrams to figure out whether you have a single or dual-thermister ECT sensor - which would determine whether you need to use 1 or 2 resistors respectively.

Noel