Hi all, hope you can help a newbie on this forum.
I've got an 850 that is refusing to start. Appears to be no spark - I put a strobe light on the coil and got not flashes. It has been left standing for a few months, and just before that it developed a habit of refusing to start when warm, although it was fine when cold or normally hot. There are no diagnostic codes showing.

I don't know if this is relevant, but when I turn the key on, the temperature gauge goes to half way, pauses for half a second, then goes to full scale, hangs there for two seconds and then falls back. Absolutely repeatable. It started doing this yesterday, about the same time that the engine went from the occasional reluctant cough to absolutely nothing.

Many thanks for any pointers,
Pete.

How long ago was the spark-plugs there? Changed recently?
Check the distributor cap, and rotor arm. If nothing, test the distributor cords.

Check and replace if necessary the ECT sensor. If the ECT sensor going boink, this is what it'll do.

BTW, over time, ive seen the wire/cables broke giving the wrong impression to the computer.

Hi, I am also new. What a coincidence - my 1995 850 10-valve is doing exactly the same thing, except it will start but after about 10 miles it will cut out, do the temperature gauge thing and re-start after an hour or so. When in fault state there is 12v at the coil red wire but no spark at all at the coil HT connection, I checked all the relays, plugs etc and found nothing wrong. Thanks ampangbear for the advice about the ECT sensor - what and where is it? I checked the engine temperature sensor resistance and found it slightly low at 150 ohms when hot although this is within the normal range, I was beginning to suspect the EGR system. :puzzled: Thanks to anyone who can help, Alan

The ECT sensor is housed just below the thermostat-housing... at the left of the intake manifold, near the power steering pump/tank (if you're facing the engine).

It's below the top hose to the radiator...

Result!! Many many thanks Ampangbear, I was at my wit's end (not a long journey in my case). I renewed the thermostat as well, since I had to take off the elbow to reach the sensor. I did 40 miles with no problem, it would only do 10 miles between breakdowns before. The only trouble is that before I read your message I pushed and pulled everything, looked inside all the relays for dry joints, took out the crank sensor and looked at it, and now the idle speed is down to 550 hot or cold, with some hunting as if the idle solenoid is sticky. Would cleaning it help, or could it be another problem? Thanks again, Alan :banana:

Ampangbear, Sorry for the delay in replying, I've not been ignoring you. I have not had chance to try the suggestions here yet, hopefully tomorrow. I had the spark plugs changed 2 months and 4 miles ago (long story), and I have just changed the cap and rotor. Try the ECT tomorrow.

Alan42, I cleaned my idle solenoid and it seemed to help - I'd been having stalls at idle when cold for months, and it looked like it might have fixed it before this (*$&% latest problem put an end to testing. BTW I saw your post on alt.auto.volvo too, I was sure one of us had to get an answer!

Thanks all,
Pete.

Result! Turned out not to be the ECT sensor in the end. A wire had fallen off at the battery terminal. I swear I had looked for loose wires, and I still cannot see what it was supposed to have been attached by. Looking at the wiring diagram in the Haynes, I think it is the one that goes direct from the battery to the fuel/ignition ECU.

Also it is running fine now so it looks like cleaning the slow running valve did do the trick.

Thanks for your help,
Pete.

Hehe. No problem.

Glad you found out the problem.
:)