No start when at warm temperature Topic is solved

[Pavel9]

This may be an old problem that has been discussed, but it has me stumped. 1997 Volvo 850 20 valve 5 speed non-turbo wagon. Engine starts well when cold but if you turn off, for about an hour (cool down time) it will not start again. It cranks fine but there no hint it wants to fire up.
1 Fuses seem to be all OK
2 Changed fuel pump although the OEM unit was working fine. No change.
3 Did not replace the fuel pump relay (#103) as the pump works fine.
4 Did not replace the big fuel filter yet as this seemed to be an unlikely culprit.
5 Put in a new fuel injector relay above the radiator. No change so put the OEM one back.
6 Inspected & cleaned the connections to the OEM cam position sensor. With the engine not warmed up, used a heat gun to heat up the cam sensor (aluminum cover) thinking it might be OK when cool but failing when hot. Again no change - engine started right up with a 70C cam sensor.
I read that on later models a ground strap from engine to trans could be causing a problem but this report said this happened at every start not just with warm restart as in my case...
What can I check next? I'm at a loss and any help would be appreciated.

Cheers, Pavel in Canada

[volvolugnut]

Have you checked/ replaced the coolant temp sensor?
volvolugnut

[Pavel9]

No, I haven't considered the coolant temperature sensor. Will check to see if a replacement is available or if I have to have it shipped by dog team!
Thank you!

[volvolugnut]

If you can read the temp with a code reader, it may tell you if sensor is bad.
volvolugnut

[abscate]

You can measure resistance directly, which is the best way to test it. Specs are in these Fora pages

[Vova585]

I would start with figuring out what is missing: spark, fuel, air. Given the fact that car starts great when cold, it is highly unlikely that problem is with the air, so lets ignore it for now. Fuel-starts and run great when cold, so most likely all is good here. You should have a pressure test port at the rail, so for piece of mind, attach it there and check if the fuel pressure is at spec upon you trying to start it. Spark would be a most likely cause. I think it still should be 1 ignition coil and distributor cap with 5 wires system?(my 98v70xc was, so just by analogy i assume ). I would check for spark from the coil to the distributor. If no spark- issue is likely the coil pack which has internal short upon warming up. Yes, ecm also can act up in such fashion, but coil pack is more likely suspect. Also agree with abscate about checking resistance from temp sensor on cold and hot and compare if adequate. Good luck

[abscate]

Courtesy of Rick Hale Parker

I think these are 1998 specs, they change in 1999

There are no error bars given on these so I would say +-20% as a guess for replacement

abscate wrote: ↑20 Oct 2019, 16:05
Check out the Engine coolant temperature sensor (ECT) and see if the resistance is in range.

Temperature : °C (°F) - Resistance Ω
0 °C (32 °F) - 7300 Ω
20 °C (68 °F) - 2800 Ω
40 °C (104 °F) - 1200 Ω
80 °C (176 °F) - 300 Ω
100 °C (212 °F) - 150 Ω

Vida: [Information]/ [Product specifications]/ [Specifications, electrical electronic]/ [Electrical system]/ [Specifications, electrical components]/ [Sensor]
Last edited by RickHaleParker on 28 Oct 2019, 20:25, edited 2 times in total.

[jreed]

Another item to consider / check is the crankshaft position sensor. Like the cam sensor tested/mentioned above, if it fails it can prevent the car from running.

[Pavel9]

OK... replaced the temperature sensor with a new one (not an official Volvo part), it was $35. No improvement, still won't start when warmed up. Will go back and check for any new codes...

[Vova585]

My previous advise stands. Warm the car to the temperature when it misbehaves and check what dropps(air, fuel, spark).