[Engine 850 2.0 LPT] Mysteriously high fuel consumption

[Norwegian]

Gents,

Just wanted to throw this little problem at you: Low mileage, no apparent reason. I'll be most thankful for any and all suggestions that may shed some light on it.

Engine is a 1996 2.0 Low Pressure Turbo @ 175 PS, with a modest 250 000 km on the clock. Around town I struggle to get more than 17 to 20 mpg even with an egg on the accelerator. On highways, the absolute best I can hope for is about 27 mpg, at constant 100 km/h, but at the end of the day it is more like 23 mpg. Surely, with careful driving I should get more out of it?

Now, the funny thing is that the engine runs absolutely smooth at all revs. No burbling, no hunting, no rough idle, nothing.

I do have a distinct feeling that it runs rich. When starting it always have to turn over at least 5-6 times, when it starts it runs momentarily high (1500 revs), then drops to normal. Starts slightly faster when warm, but not as quickly as most other cars I have owned. Some say this is just the Volvo way - is it really? Smells of petrol, too, when starting. When accelerating it lacks that last oomph that I've felt in other cars with comparable engine size. Smooth, but not entirely willing, if you see what I mean.

Stuff I've done recently (and which have changed absolutely nothing):

FCP tune up, with dizzy cap/rotor/OEM plugs/OEM plug cables/air filter/oil filter/fuel filter/PCV-kit/Lambda sensor/engine oil new. Old PCV wasn't too clogged, but very brittle.

Cam belt, tensioner, roller new.

Rear cam seals, both turbo oil pipe seals (did stop the dripping, though).

Vakuum lines seems to be ok, no apparent leak from induction line either. Drop of oil hanging under the turbo, always, but no apparent blue smoke.


So, what may be the cause(es) of consistently low mileage without rough running? No fault codes stored, by the way.

- Vacuum leaks, after all? And if so - where, most likely?
- Faulty MAF?
- Late valve timing?
- Tired turbo (will refurbish soon anyway)?
- Wrong fuel pressure?

[Luxobarge]

Any binding brakes (check wheel temperature after a run)?

Tyre pressures OK? (many of us run the cars with the tyres 2-4 PSI higher than Volvo standard as depicted on the fuel filler flap).

If there are no codes stored, then that rules out a lot of issues with the engine management system.....

[Norwegian]

Originally Posted by Luxobarge

Any binding brakes (check wheel temperature after a run)?

Tyre pressures OK? (many of us run the cars with the tyres 2-4 PSI higher than Volvo standard as depicted on the fuel filler flap).

If there are no codes stored, then that rules out a lot of issues with the engine management system.....

Brakes ok (new, no binding, no heat). Even the hand brake works well, yay!
Tire pressure a good 10 % above flap values - summer tires, alloys.
Mostly alone in otherwise empty car, so no deadweight.
No engine light.

[DaveNP]

What does the tailpipe of the exhaust look like? if it's running rich I would expect it to be sooty. (I appreciate this is a vague measure but compared to the average car) We had a problem with my wifes Nissan which the ecu claimed to be running OK or lean, the exhaust pipe was thick with soot, the problem was due to a faulty lamda sensor, I see you've replaced yours, what brand did you replace it with? some of the cheap ones are not reliable.

[Norwegian]

Originally Posted by DaveNP

What does the tailpipe of the exhaust look like? if it's running rich I would expect it to be sooty. (I appreciate this is a vague measure but compared to the average car) We had a problem with my wifes Nissan which the ecu claimed to be running OK or lean, the exhaust pipe was thick with soot, the problem was due to a faulty lamda sensor, I see you've replaced yours, what brand did you replace it with? some of the cheap ones are not reliable.

Good call!

Tailpipe is indeed sooty. Lamba is Bosch model specific (FCP). But wouldn't a bad lambda present more noticeable problems than just bad mileage?

[slipkid]

Mine was the same. All sorted with new coolant temp sensor and thermostat. Genuine Volvo coolant temp sensor was about £35 from the main dealer. Seems like everything else has been ruled out. Hope you get it sorted.

[SonyVaio]

MAF and FPR
Tyre pressures
Alignment
leaking intercooler or boost pipes
Ambient temp sensor (fuel & air mixture)

[DaveNP]

Originally Posted by Norwegian

Good call!

Tailpipe is indeed sooty. Lamba is Bosch model specific (FCP). But wouldn't a bad lambda present more noticeable problems than just bad mileage?

So with the sooty pipe it would be running rich, I would expect a Bosch lamda sensor to be good. The wifes Nissan ran OK despite the problem with the lamda. The suggestion of a dodgy temp sensor could be the answer but if it's a sensor not working right rather than a total fail it gets to be a guessing game as there will be no code for a 'failure'.

[Rob.D]

Hi Norwegian,
I just thought I'd throw this into the mix... If your tailpipe's sooty have you considered the state of the injectors? My local Volvo man does not favour fuel addatives to clean the varnish off. Instead he blows them through with an airline and detects a difference in the whistling sound once the gunge has been cleared-out. If removing the injectors then new seals and O rings may be a good investment.
Hope this is of some use.
Regards,
Rob

[TXC]

Check for ruptured fuel pressure regulator on this (if it has one, conventioal vac type on end of rail), will drink excessive fuel if it's sucking extra fuel through, also this will cause extended crank times and loss of full perfamance due to lower fuel pressure.

Also, a fuel leak exrernally under pressure will also give rise to similar symptoms, some fuel leaks will only occur under pressure, engine on.