Volvo 850 2.5 GLS 1996. We have an ongoing problem that we can't pin down. We're in a small island country with no Volvo dealers.

The engine starts and runs normally until warm. You can drive it for 20 mins or more in traffic, but after its properly warmed up it will start to hesitate and stall when you put the engine under load (foot down). It usually starts again and revs very well at idle and will pull away on the flat and even creep up a hill in idle with just a touch of throttle, but put foot down and it splutters and stalls. When cooled down it will pull and have normal power available, responding smoothly to throttle. There is no smoke or liquid discharge from pipe.

We have changed ECT sensor, coil, HT leads, plugs, fuel pump and relay, fuel system cleaned, has a new head gasket and engine cooling is normal with no coolant loss and normal pressure, fans work OK, temperature gauge rises to just over 3 o'clock position (normal). We don't have a Volvo diagnosis tool (I got a bluetooth OBD2 device and it says connected to computer, but gives no codes

The ECT sensor tested 1500 Ohms cold (room temp 25-30 deg) and 200 Ohms when hot. Does that look right?

Could it be throttle position sensor, a hairline crack in ECU circuit that reduces spark when warmed up, the throttle body (we did a basic clean but should we test it more?) If so can ECU and TB be tested?

Thanks for any suggestions!

 

I would have thought leads, but you already replaced those. Was there no change?

We did not get the 2.5 in the USA. Here in the usa, the engines we got in 1996 had mass air measurement, so the throttle is not really critical to the metering. If you are not setting any codes then it is kind of mysterious. You could have low fuel pressure, but you've already tried to address that.

 

Thanks FBP. The leads and general service made a difference, but not solved the problem. We're trying new ECT and TPS sensors. Takes time as mail takes 2-3 weeks to get here but it's not expensive. Some day I'll find out what the problem is.

Could it be the throttle body? I read that later Volvo models from 1997 had Mitsubishi throttle bodies that could have a fault leading to "hesitation, loss of power". ECU? There's not much more to change. Injectors?

 

Possibly clogged catalytic converter or exhaust?

 

Thanks, will get my techie to check that possibility.

 

This one solved. Cause was contaminated petrol tank. Vandalism. We found resin liquid/gunk in the bottom of the tank. The stalling gradually cleared up and has now completely stopped. Engine is running perfectly. I replaced the non-locking fuel cap with a lockable one.