[Engine 850 2.0 LPT] Mysteriously high fuel consumption

[Norwegian]

Thanks for good inputs, all! As I'm probably not the only one with this or similar problems, I'll try to go forth in a logical and consistent manner (I did say try), so that this thread may also have some value as future reference for others.

Originally Posted by slipkid

Mine was the same. All sorted with new coolant temp sensor and thermostat.

Originally Posted by SonyVaio

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

Coolant temp sensor: Car heats up fast regardless of ambient temp, coolant temp gauge rises quickly to 3 o'clock and stays there, heater works well. Thermostat ought to be ok, I think?

Is the coolant temp gauge and the EMC supplied from the same sensor, or are there two different sensors?

Ambient temp sensor: Computer displays correct ambient temp at all times. Is it the same sensor for fuel/air-mix, or a different one?

MAF: How do I test it?

FPR: 3 bar above manifold pressure at the Schrader valve, is that it?

Originally Posted by Rob.D

Hi Norwegian,
If your tailpipe's sooty have you considered the state of the injectors? My local Volvo man does not favour fuel additives 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.

So far I have a hope that the answer is somewhat simpler and cheaper than the injectors. Fuel quality is fairly good here, too. But if nothing else works, I'll certainly look into it.

Originally Posted by TXC

Check for ruptured fuel pressure regulator on this (if it has one, conventional 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 performance due to lower fuel pressure.

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

Will check. How about the coal canister system, any possible malfunctions there that could tie into this?

[TXC]

FPR: 3 bar above manifold pressure at the Schrader valve, is that it?

That's the measurement? Or are you describing the regulator?

What does the pressure do at ignition off?

[Norwegian]

Originally Posted by TXC

FPR: 3 bar above manifold pressure at the Schrader valve, is that it?

That's the measurement? Or are you describing the regulator?

What does the pressure do at ignition off?

No, just me mentalizing procedures there :)

My neighbour has a complete workshop and I believe he's got a professional fuel pressure kit, too. Will measure as soon as he has the time to help me.

[Norwegian]

Still working this issue - some updates:

- Fuel pressure ok, vacuum regulation works well (35-45 psi depending on throttle position)

- Coolant temp sensor works well, gives the expected resistance values at different temps (found a chart somewhere).

- Lambda regulates quickly, but is covered with soot

- MAF cleaned with special CRC MAF-cleaner, but it wasn't really dirty and cleaning made no difference at all.

- Throttle house cleaned, but again, not really dirty and made no difference.

- purge valve doesn't appear to leak (no suction on canister side), but may not open as it should - no ticking when starting the engine, however that would be an environmental problem, not an mpg-problem, right?

Emission check @ 2000 rpm:
CO % vol: 0,01
CO2 % vol: 15,4
HC ppm vol: 9
O2 % vol: 0,07
Lambda: 1.004
AFR: 14,8

... all of which is wonderful, but it doesn't explain this:

23 mpg long term (last 2000 km, mixed driving), nigh impossible to get more. And there is still the soot problem, as well as the lack of power. No wheel spin even at stand-still, full kickdown.

Still no fault codes or EML, but my reader can't access live values or long term fuel trim.

I have put in an instrument cluster with a boost gauge. Needle will go about 1/3 of the way, maybe slightly more at full throttle and 5000+ revs.


Things to do:

- Check vacuum lines again
- Rebuild turbo. That is really only because I have the parts and want to see the inside of it, not because I have any indications that it is particularly bad.

[SonyVaio]

Without checking back through the thread, have you checked/changed the TCV??

[Norwegian]

Originally Posted by SonyVaio

Without checking back through the thread, have you checked/changed the TCV??

Funny thing going on there. When I bought the car, there was no TCV (or BCS, boost control solenoid) present at all, not even the bracket. The pressure hose from the turbo was connected directly to the waste gate actuator, and the electrical connector was pegged on a plastic blind connector on the air filter box. The setup looked pretty original, in fact.

I experimented a bit with a manual boost controller, which brought up the boost pressure at high revs (3500-4000 and up), but did nothing for the mpg and low end power. I then got a BCS off Ebay a few months back, which again did bring the boost up just a little bit, but nothing in the low end and no change in mpg.

Waste gate opening pressure is checked and within limits, btw.

As for the injectors: We have pretty good quality petrol here. I've added injector cleaner at every tanking anyway for some months, but no apparent change.

[SonyVaio]

Interesting!

So how was the boost dump being controlled on the original setup (original to you anyway)?

I'll have to have a look at VIDA to see what it has listed and the setup.

[Norwegian]

Originally Posted by SonyVaio

Interesting!

So how was the boost dump being controlled on the original setup (original to you anyway)?

I'll have to have a look at VIDA to see what it has listed and the setup.

The way it was connected, the boost nipple on the turbine housing was connected directly to the wastegate actuator, and the dump valve to the vacuum tree. I've since inserted the BCS between the boost nipple and the wastegate actuator, resulting in a small increase in turbo boost.

[Norwegian]

A quite illuminating article on emission analysis: http://www.autoshop101.com/forms/h56.pdf

A pre-cat exhaust leak can cause the symptoms I experience, while the cat alter the emission values so they appear to be normal.

The long term fuel trim value will certainly be helpful now. Will have to get it read somewhere.