Volvo 740 Turbo chronic over fuelling - Bert
All
What would cause the engine system to develop this fault. Consumption had gone down to less than 15 mpg from near 30. Engine now refuses to start. G reg, 2.3litre. Mates tried the basics, someone said it could be the engine temp sensor. Any clues will help.


Cheers Bert
Volvo 740 Turbo chronic over fuelling - Andrew Moorey (Tune-Up)
Check the following first: Thermostat, does the temperature rise rapidly to normal. My old F reg 740 Turbo (250k+!) would be up to temp within a mile or so, If it is running cool this will increase fuel consumption. Airflow meter flap in air filter cover may be sticking, or coolant level low. Check these first and come back, by then I will have specs for coolant temp sensor. Incidentally are you sure of your consumption figures? I used to struggle to better 23mpg even on a run although bizzarrely on a late night cruise to the West Country on a deserted Mway at a constant ***mph it crept up to 26-27!
Volvo 740 Turbo chronic over fuelling - Peter D
I assume you have no cat but what feul system do you have. Injectors or carb and which one.


Peter
Volvo 740 Turbo chronic over fuelling - Bert
Peter
Have Cat & injectors, no other info yet.

Bert
Volvo 740 Turbo chronic over fuelling - Peter D
Check the temp sensor on the block should be a douple unit both measuring 1200 ohms to ground each. isf one is us the open loop default cold mixture is being used and she will drink.

Measure the air flow sensor and heating wire resistance as per the manual and check the micro switch is clicking on opening the thottle. Do this with the engine off so you can hear it.

Check the O2 sensor in the manifold again there are figures in the bbok giving you a voltage and an rpm but measure the sensor resistance to see if it is alive.

Good Luck



Peter
Volvo 740 Turbo chronic over fuelling - Peter D
Check the temp sensor on the block should be a douple unit both measuring 1200 ohms to ground each. isf one is us the open loop default cold mixture is being used and she will drink.

Measure the air flow sensor and heating wire resistance as per the manual and check the micro switch is clicking on opening the thottle. Do this with the engine off so you can hear it.

Check the O2 sensor in the manifold/exhaust again there are figures in the bbok giving you a voltage and an rpm but measure the sensor resistance to see if it is alive.

Good Luck



Peter
Volvo 740 Turbo chronic over fuelling - percy
Sorry, I know very little about Volvos. However I have always wondered about the fuel pressure regulator on injected engines. It is an item we don't hear much about, but I remember a friend with a misbehaving BMW saying that he could hardly keep the engine running, but the harder he drove it the better it was... The regulator was faulty, causing overpressuring. Some regs seem to have a vacuum feed from the inlet manifold which may give rise to trouble. Good luck.
Volvo 740 Turbo chronic over fuelling - Bert
I have now been told that the lambda sensor warning light illuminated itself on the dash. It was lit up every time the car was started, it was run in this condition for 3 weeks! before any noticable deterioration in performance or fuel consumption was evident! At about that time the car was connected up to a Volvo garage test unit, they reported that it might be! the ECU but they were not sure. The car has now gone to a Volvo specialist in the Medway area (non franchised). They have had it before & tried a different lambda sensor, but no difference, although they did not know whether it was a duff one or not.
I have read & passed on all info up to AM 25 September.
I will post the final outcome. It is not my car but was asked for help & this forum has helped before.

Cheers
Bert
Volvo 740 Turbo chronic over fuelling - Bert
Result, car back with owner & OK.
They found, the engine coolant sensor duff, as mentioned by contributor, wrong spark plugs fitted, ie not for turbo engine, number 3 plug lead breaking down & burnt rotor arm/distributor cap around number 3 post.
New sensor fitted, new plugs & leads, new rotor & cap, ECU reset, plus towing in to garage, about 10 miles all for £150.
Owner did renew the lambda sensor which he bought himself for another £150 or so, not sure on price.
Also he has been advised to change timing belt & have oil leak fixing by the filter.

Cheers all
Bert
Volvo 740 Turbo chronic over fuelling - Bert
Final final outcome, owner in the end had to get a reconditioned ECU, cost £274 from a place in Gillingham Kent.
The cars been OK for a while now
Bert
 

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