Xantia 16v getting 12mpg!!! [Fixed]

sjj698 · Post by **sjj698** » 02 May 2010, 17:15

Hello All,

I am having Xantia problems...
(1.8l Xantia Petrol 16v) it is drinking fuel , roughly 12-17mpg!!

It drives fine, accelerates no problem (well it has never been a race car!), revs without hesitation and drives like it always did, except now it is thirsty. I normally get 30mpg and suddenly i have started to get 12mpg. It is not smokey.

Things i have done:
New air filter
Replaced the MAP sensor (for a second hand one, no difference)
There is no smell of fuel , and there does not appear to be a leek.
Did a compression test and all were looking good (190 - 205 PSI)
New stepper motor (Throttle housing)
You can easily push the car around in a carpark, so probably not a brake calliper stuck.

Took it to the garage and they could only find a temperature sensor error code in the ECU so i replaced the sensor, but it did not help. (the sensor was always telling the engine it was hot)

Things that i may try next:
I have tried to look for any air leaks in the manifold. Only when you first rev the car there is a small sound of air rushing but i think this is normal. Any ideas where common leaks occur. Blocking the air intake does not produce any obvious air sucking noises.
Lambda sensor replacement?

Questions:
Has anyone had any similar problems?
On the throttle housing there are 2 vacuum pipes, one goes to the engine the other has a long pipe that disappears into the wing. Anyone know what this does? I have tried sucking it and it is a bit restrictive.

1996 (P) 87,000Miles

Thanks for your time
SJJ

KP · Post by KP » 02 May 2010, 17:51

The only thing i can think of is the lambda sensor in the exhaust pipework is failing or failed and has caused this. Have you tried replacing the oil and filter as with that poor a fuel consumption i would imagine bore wash is occurring...

sjj698 · Post by **sjj698** » 02 May 2010, 17:54

Thanks KP,

I put new plugs and a filter in 4,000 miles ago (6mts),

other suggestions i have had are:

Faulty Throttle position Sensor.
Faulty Air temperature Sensor.

Hard to know what to replace first.

Steven

spider · Post by **spider** » 02 May 2010, 18:25

I'd still have a close inspection for a leak, as at 12mpg it must be going somewhere.

I'd imagine it would run horrendously if the mixture was that 'rich', having had a carb car that had a serious mixture problem, it would only run when warm at half throttle and above just to make it idle.

Back on topic, I'd have another look around for fuel leaks, its possible it may be evaporating before you can see it. Favourite place is the feed / return lines where they go to the fuel rail (where they are near the timing belt cover) , next area of concern is around the fuel tank and the fuel filter situated nearby (I assume its nearby as 406's have it next to the tank)

Pleiades · Post by **Pleiades** » 02 May 2010, 18:27

Hi Steven.

Fuel systems and computor controlled bits are not realy my thing! but it may be worth popping into any MOT station and asking the guys if they can just do an MOT emmisions test, they will most likely want a small fee but it will only take a couple of mins to do this.

The results should tell you something about what is happening.

The only suggestion that I have without any more info would be that a temp sensor may be lying to the engine and saying that it is too cold, therefore asking for more fuel.

Regards
Martin.

Post by **myglaren** » 02 May 2010, 18:32

Good call Martin.
I'd have expected a strong smell of petrol if it were running strongly enriched but perhaps not.

sjj698 · Post by **sjj698** » 02 May 2010, 18:34

Hi Martin,

I have got a new temperature sensor.
The exhaust was leaking and so they could not do an emissions test, i have since patched that and so will get an emissions test next week.

Thanks
Steven

sjj698 · Post by **sjj698** » 02 May 2010, 18:37

Hello All,

Yes it is a mystery as to where the fuel is going!
The exhaust is certainly sooty inside. I have checked the fuel lines near the engine and they look fine.
There is no smell of fuel anywhere...

Thanks for all the replies, i will keep you posted!
Steven

Deanxm · Post by **Deanxm** » 02 May 2010, 19:33

Where was the leak in your exhaust?

d

MikeT · Post by **MikeT** » 02 May 2010, 19:46

Hi Steve,

This is becoming my mantra lately but I would get it on a Lexia if you can. It will show if TPS, IAT, MAP etc is out of whack or has stored a code. Did the garage use a more generic code reader?

There's more than one temperature sensor (not sure total on your car but guessing three?). Which one did you replace?
All temperature sensors can be easily checked with a multimeter - on a good sensor, resistance between two pins or voltage from sensor output changes smoothly and progressively as the coolant heats up.

You can pull the spark plugs and check their colour to determine if it's running rich (no, suggests a fuel leak) but a sooty exhaust tells me they'll likely be black.

p.s. If it were my car, I would fear the CAT will be getting destroyed if it's running too rich.

sjj698 · Post by **sjj698** » 02 May 2010, 20:02

Hi Deanxm,

The hole in the exhaust was just before the back box, so should not have an affect.
I have since dome some miles with the exhaust fixed and the MPG is still poor

Steven

sjj698 · Post by **sjj698** » 02 May 2010, 20:09

Hi Mike,

yes i am worried about the CAT, i suspect that this may kill it! I have had a look and it is not easy to remove either and is ££££ sigh!

There are 3 sensors on the thermostat housing, the garage replaced the bottom (green) of the three.

I am not familiar with a Lexia, the garage are a 'citroen specialist', anyone know of a good garage around Southampton?

(I will pull a plug next week and have a look at it, judging by the exhaust colour it looks like it is running rich)

Thanks
Steven

sjj698 · Post by **sjj698** » 02 May 2010, 20:11

Hi Mike,

Forgot to ask, does the Lexia need a ODC II connector? My car is a P reg 1996 so has the older 'scart looking' connector.

Steven

Post by **myglaren** » 02 May 2010, 20:36

Ironically enough, it is Mike that is the closest Lexia owner to you

Lexia map

MikeT · Post by **MikeT** » 02 May 2010, 21:11

Hi Steve,

If the connector has three rows of 10 pins, yes it's the older type and yes they are available for the Lexia - unfortunately I don't have that adapter yet and don't know who to recommend you take it to.

I've got doubtful memory but I believe the green sensor is the one used for engine management decisions. Was the replacement tested by the diagnostic machine as working?

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Xantia 16v getting 12mpg!!! [Fixed]

Xantia 16v getting 12mpg!!! [Fixed]

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