B234F high fuel consumption

[zzuzi]

Hi All,
I bought Volvo 740 2,3 16 valve 1989.But there is a problem-the fuel consumption is 11-12mpg,it has a bad idle too,sometimes when i release the throttle the engine dies.I used the diagnostic and for the ignition there was no fault codes,but i couldn't do the ECU diagnostic-The LED just don't blink.When i place the cable into socket 2 and press the button(the ignition ON is to KPII)the LED lights,but when i release the button the LED don't flash,so i can't even get a fault code.I replaced the oxygen sensor(Lambda sonde),checked the engine coolant temperature sensor,the AMM,the spark plugs and cables,the connection between the OBD LED tester and the ECU but everything is fine.Do you have any suggestions how to find the problem?
Many thanks!

[Diesel-do-nicely]

I would suspect the ecu has gone to its break down setting. If you can , try replacing it and see if there are any changes.

[rogerthechorister]

Surely if the ECU has gone to breakdown mode the lambda light should be on.

Be wary of the ecu - I'm pretty sure the ecu for the B234F is specific to that engine and Ithink it is unavailable new (and a stupid price even if available new). Even if you get a replacement ecu do not throw the old one away someone may be able to resurrect it.

[Doug2942]

Just had my ECU repaired by 'Bluestreak' for £225. Also had my injectors overhauled by Jim Athan. What a difference !!
Had poor tickover, lambda light on & getting 12-13 mpg running around.
Currently checking mpg since putting it all back together.
Doug

[Diesel-do-nicely]

[QUOTE=rogerthechorister;839879]Surely if the ECU has gone to breakdown mode the lambda light should be on.


not always if its faulty.

[Doug2942]

Following my recent post, I filled up today & recorded a mpg of 15.5.
Whilst this is an improvement I'm a bit disappointed after the various jobs done, had hoped for 20 plus as it used to be.
Doug

[Diesel-do-nicely]

Originally Posted by will2942

Following my recent post, I filled up today & recorded a mpg of 15.5.
Whilst this is an improvement I'm a bit disappointed after the various jobs done, had hoped for 20 plus as it used to be.
Doug

so the repaired ecu had the fault warning light extinguished for £225, great.
Check that the engine tempature sender signal to the ecu plug is 2v when cold and 5v when at operating temp, or its the other way round, doesnt matter , it must be different . That way the ecu is getting the info the car is heating up, a good indicator is the colour of the spark plugs, no black soot.
Just a bit off topic but...
This may be not whats wrong but i had a job on a Ford RS mexico MK2 escort that despite the 1740cc re-bore and twin 40 webbers , BVH and 4 branch exhaust could still be beaten by an ordinary 1600cc version.And did 10mpg.
After checking the timing and valves / compressions i decided to see if something else was up.
Turned out the diff in the rear axle was nearly solid.
When you spun the rear wheel while it was up in the air the opposite rear wheel rotated freely, however 2 people could hardly move them both together in the same direction.
Stripped the diff and fitted new bearings and pre-load washers .
Taa Daa , the car went like a rocket and 10mpg was now 25mpg

[Diesel-do-nicely]

http://www.volvoclub.org.uk/faq/Engi...eratureSensors