V

v8dude

New Member
Hello All,

Just wondering if anybody could offer some help.

I've got a V8 Disco with a 14cux ecu and I like it...! What I don't like is the amount of fuel that its using. I've clocked it at 10 mpg which I'm sure is a bit low even for that beast of an engine. It also hunts for the idle when first started and you can also smell excess fuel. I've made a roverguage cable and cranked up the software (fantastic piece of kit) and the first obvious problem I can see is that both lambda sensors show their readings constantly at -100% in the short term and never swing positive. Is this likely to be a lambda sensor error or are they in fact reading that there is too much fuel in the mixture and the fault is elsewhere. There's also a stag LPG system on there as well but I'm trying to get it to run properly on petrol first.

As you can tell, I don't know much about petrol engines.

Thanks in advance for any help.

Dave.
 
10MPG isn't far off the mark. There isn't a lot to go wrong with the ECU, but the O2 sensors can and do fail. They're titania sensors not your more usual type. And they're about £100. Each.
 
v8dude said:
Hello All,

Just wondering if anybody could offer some help.

I've got a V8 Disco with a 14cux ecu and I like it...! What I don't like is the amount of fuel that its using. I've clocked it at 10 mpg which I'm sure is a bit low even for that beast of an engine. It also hunts for the idle when first started and you can also smell excess fuel. I've made a roverguage cable and cranked up the software (fantastic piece of kit) and the first obvious problem I can see is that both lambda sensors show their readings constantly at -100% in the short term and never swing positive. Is this likely to be a lambda sensor error or are they in fact reading that there is too much fuel in the mixture and the fault is elsewhere. There's also a stag LPG system on there as well but I'm trying to get it to run properly on petrol first.

As you can tell, I don't know much about petrol engines.

Thanks in advance for any help.

Dave.
Click to expand...

The lambda should oscillate between low and high about every second. As said, your lambda sensors could have died.

You should also check all the other usual suspects - air flow meter, throttle pot and coolant thermistor. It also helps if your ignition timing is correct - it will have been changed to suit the LPG. Also check/set your base idle and remove and clean the stepper motor (idle stabilisation valve). You might also want to consider doing a compression check as well (make sure you do wet and dry). HTH
 
Cheers Kev,

That's quite a lot of stuff to go at. Where do you think I should start? I'm not massively concerned about the mpg but its definitely not running properly and I'm still sure that 10 mpg is not good. It's very snatchy at idle and then sometimes it will stall. A lot of hunting for idle as well. As I said before you can smell the fuel.

As the Lambdas are both reading negative would that make the ecu open up the injectors to add fuel or is it the other way way round? It might be an idea to start at them if this is the case. I've moved the idle control valve in roverguage and that seems to behave normally.

Where to start?

Thanks again for your help.

Dave.
 
Give it a service and sort the sensors out.
But depending on how you use it 10 mpg is not unusual.
Afterall it is a 2 ton brick on wheels.
What mpg were you expecting to get?
 
V8 doing 10 mpg no that’s not right, maybe on an excessively high mileage engine that just about clapped out. I ran a V8 1989 that was doing 15mpg and that was high mileage after a rebuild 20mpg unless you have a heavy right foot.
My guess would be you problem lies with the airflow meter, but as already said tune the engine to petrol, when LPG is used the engine is tuned for LPG not petrol, so the normal occurrence when switched over to petrol the engine runs lumpy and may backfire causing damage to the airflow meter, timing and running with LPG is critical all ignition parts must be tip top condition.
 
3.9? if so has it not got a thing built into the LPG side to adjust the Advance and Retard like an A&R power amp so that it adjusts the timing accordingly to which fuel your using? Guess you have to do it manually with 3.5 carb?

Also I was reading up on the Lamda sensor readings and operations today on an unrelated fault reader, dunno if it has anything of interest to you in this:

http://ecumate.com/docs/Ecumate inst.pdf

As Kev says they should oscillate every second or so.
 
Last edited:
gunny said:
v8 doing 10 mpg no that’s not right, maybe on an excessively high mileage engine that just about clapped out. I ran a v8 1989 that was doing 15mpg and that was high mileage after a rebuild 20mpg unless you have a heavy right foot.
My guess would be you problem lies with the airflow meter, but as already said tune the engine to petrol, when lpg is used the engine is tuned for lpg not petrol, so the normal occurrence when switched over to petrol the engine runs lumpy and may backfire causing damage to the airflow meter, timing and running with lpg is critical all ignition parts must be tip top condition.
Click to expand...

+1
 
mrnice said:
3.9? if so has it not got a thing built into the LPG side to adjust the Advance and Retard like an A&R power amp so that it adjusts the timing accordingly to which fuel your using? Guess you have to do it manually with 3.5 carb?

Also I was reading up on the Lamda sensor readings and operations today on an unrelated fault reader, dunno if it has anything of interest to you in this:

http://ecumate.com/docs/Ecumate inst.pdf

As Kev says they should oscillate every second or so.
Click to expand...


Thanks. This is really good.. Lots of info the pdf!
 
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