Excessive petrol consumption...
Discussion
...not normally a topic that can be levelled at the Elise, but there you go.
I have a 5+ year old k-series based 1.8l S2 that's done about 55k miles. Recently it has suddenly started using more petrol than normal. This came on suddenly and unexpectedly - previously I was getting 200-230 miles out of a tank, now I'm lucky to get 160 even if I drive really carefully. This works out a 25% difference which I cannot put down to environmental, hard-driving or even imaginary factors.
The only thing I can imagine might have affected it is that my battery went stone dead a few months ago and required a jump start which I guess could have affected the ECU. Apart from that everything seems OK, car runs OK albeit there is a smell of petrol when I start it which may be anecdotal or not.
Anyone had experience with this? Anything I could check?
I have a 5+ year old k-series based 1.8l S2 that's done about 55k miles. Recently it has suddenly started using more petrol than normal. This came on suddenly and unexpectedly - previously I was getting 200-230 miles out of a tank, now I'm lucky to get 160 even if I drive really carefully. This works out a 25% difference which I cannot put down to environmental, hard-driving or even imaginary factors.
The only thing I can imagine might have affected it is that my battery went stone dead a few months ago and required a jump start which I guess could have affected the ECU. Apart from that everything seems OK, car runs OK albeit there is a smell of petrol when I start it which may be anecdotal or not.
Anyone had experience with this? Anything I could check?
You can check the plugs. If they are black and sooty to touch, the car is running too rich.
It could also be the car just needs a basic service - new plugs,( they could be old and failing ), new air filter. A blocked air filter enriches the mixture. The plug gaps are also important to performance and economy, too.
I do wonder, as you infer, how relevant this is to a computerised ( fuel injected ) car, as while the above is true of carb cars, I would have thought the computers/ECUs could compensate for these things??
You could ask a dealer for a computer check/print out. Oh, a blowing or holed exhaust can do the same, too.
It could also be the car just needs a basic service - new plugs,( they could be old and failing ), new air filter. A blocked air filter enriches the mixture. The plug gaps are also important to performance and economy, too.
I do wonder, as you infer, how relevant this is to a computerised ( fuel injected ) car, as while the above is true of carb cars, I would have thought the computers/ECUs could compensate for these things??
You could ask a dealer for a computer check/print out. Oh, a blowing or holed exhaust can do the same, too.
Possibly a fuel leak ?
Not necessearily obvious and the leak may only happen whilst the car is running. I am currently going through the same thing on my family car. The leak only occurs when the car is under load, it seems the sourceof the leak is not causing an issue when the flow is low i.e. cruising. (Having said all that, I guess you'd smell it if it was)
Not necessearily obvious and the leak may only happen whilst the car is running. I am currently going through the same thing on my family car. The leak only occurs when the car is under load, it seems the sourceof the leak is not causing an issue when the flow is low i.e. cruising. (Having said all that, I guess you'd smell it if it was)
Ok, a quick follow-up. Discovered, upon hard acceleration only, some smoke appearing from exhaust. Was unable to check the smoke colour, but there's definitely a smell of petrol so am assuming the smoke is due to unburned fuel as a result of an over-rich mixture.
My checks at this stage are thus as follows:
- Lambda sensor - may be indicating a cold exhaust permanently thus causing the ECU to overfuel the car even though the engine is in reality warm.
- ECU temp sender - may be indicating a cold coolant temperature causing the same effect as before.
Does these symptoms sound familiar to anyone? Any other checks I can make? Any other things that could cause an over-fuelling?
Full service to be done shortly anyway, but don't want nasty mechanics ripping me off for trivial faults!
My checks at this stage are thus as follows:
- Lambda sensor - may be indicating a cold exhaust permanently thus causing the ECU to overfuel the car even though the engine is in reality warm.
- ECU temp sender - may be indicating a cold coolant temperature causing the same effect as before.
Does these symptoms sound familiar to anyone? Any other checks I can make? Any other things that could cause an over-fuelling?
Full service to be done shortly anyway, but don't want nasty mechanics ripping me off for trivial faults!
Ok, Lambda sensor seems fine, checked using the instructions on the SELOC Wiki - warmed up the car and checked it with a multimeter - voltage around 0.5v, and rising each time the engine was revved.
This leaves the ECU temp sensor - would a fault here not prevent the cooling fan from coming on when the coolant was overheating? Or is the fan on a different sensor? It seems to work fine, comes on when engine hits 102C. And would a failure of this really screw the fueling up that much anyway?
Anything else I can check?
This leaves the ECU temp sensor - would a fault here not prevent the cooling fan from coming on when the coolant was overheating? Or is the fan on a different sensor? It seems to work fine, comes on when engine hits 102C. And would a failure of this really screw the fueling up that much anyway?
Anything else I can check?
tyronbarrett said:
Ok, Lambda sensor seems fine, checked using the instructions on the SELOC Wiki - warmed up the car and checked it with a multimeter - voltage around 0.5v, and rising each time the engine was revved.
This leaves the ECU temp sensor - would a fault here not prevent the cooling fan from coming on when the coolant was overheating? Or is the fan on a different sensor? It seems to work fine, comes on when engine hits 102C. And would a failure of this really screw the fueling up that much anyway?
Anything else I can check?
AFAIK the S2 has only one temp sender so if you're seeing normal readouts on the dash, then you should be able to safely assume that the ECU is also seeing normal temps. If the car was overfuelling, I'd expect it to be running pretty poorly so if your's is ok you can probably rule out ignition problems. You could check the throttle pot just in case. That just leaves the possibility of a fuel leak. Have a good look around the engine bay at the fuel lines whilst the car is running. Other than that I'm pretty stumped I'm afraid.This leaves the ECU temp sensor - would a fault here not prevent the cooling fan from coming on when the coolant was overheating? Or is the fan on a different sensor? It seems to work fine, comes on when engine hits 102C. And would a failure of this really screw the fueling up that much anyway?
Anything else I can check?
Gad-Westy said:
Just one more question, is the car performing ok? Just thinking about the possibility of binding brakes etc...
Seems to be quite quick still, but obviously I'm no pro driver, so a few bhp off the top would probably go unnoticed. The car isn't stuttering/surging like some of the FAQs suggest, and the idle control seems OK.I don't think it's flat tyres/brakes binding, I've checked the air filter now and that's fine too, haven't managed to pull the plugs out yet, I'll do that this weekend. It is definitely running too rich as there's often a smell of petrol fumes (in particular I get a build-up if I leave the car to idle somewhere) and the smoke on hard acceleration is always visible.
Thanks for everyone's advice so far though.
tyronbarrett said:
Gad-Westy said:
Just one more question, is the car performing ok? Just thinking about the possibility of binding brakes etc...
Seems to be quite quick still, but obviously I'm no pro driver, so a few bhp off the top would probably go unnoticed. The car isn't stuttering/surging like some of the FAQs suggest, and the idle control seems OK.I don't think it's flat tyres/brakes binding, I've checked the air filter now and that's fine too, haven't managed to pull the plugs out yet, I'll do that this weekend. It is definitely running too rich as there's often a smell of petrol fumes (in particular I get a build-up if I leave the car to idle somewhere) and the smoke on hard acceleration is always visible.
Thanks for everyone's advice so far though.
Sorry for the bump, just wanted to update this thread so that anyone searching could see the answer to my car's problem of excessive fuel consumption.
Ended up taking my car to Castle Lotus who diagnosed the problem as two faulty lambda sensors. I'd only checked one (the pre-cat one) in my tests and although it seemed to be making a decent voltage when run-up to temperature, my limited diagnosis skills made it impossible to say for sure that it was worth replacing both.
Anyway, I'm getting 200+ miles on a tank now so I should be able to get the £400(!) diagnosis bill repaid fairly quickly in fuel savings!
Ended up taking my car to Castle Lotus who diagnosed the problem as two faulty lambda sensors. I'd only checked one (the pre-cat one) in my tests and although it seemed to be making a decent voltage when run-up to temperature, my limited diagnosis skills made it impossible to say for sure that it was worth replacing both.
Anyway, I'm getting 200+ miles on a tank now so I should be able to get the £400(!) diagnosis bill repaid fairly quickly in fuel savings!
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