High fuel consumption?

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Freebird
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Re: High fuel consumption?

#81 Post by Freebird » Sun Sep 04, 2016 4:55 pm

Yep, bonkers...

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Re: High fuel consumption?

#82 Post by Freebird » Thu Sep 08, 2016 8:59 am

Well, it's early days but I filled up after 178 miles and the consumption was just over 20 mpg which is something like a 25% improvement.

I am happy with that, it now costs about the same to run as my E46 BMW 3 litre diesel so now I don't have to put up with that awful smell or that awful messy fuel.

Thanks again for all the help.

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Re: High fuel consumption?

#83 Post by robertXX » Thu Sep 08, 2016 12:02 pm

excellent ......well done all.

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Re: High fuel consumption?

#84 Post by LPGC » Thu Sep 08, 2016 6:50 pm

As mentioned in one of my previous posts, I believe the Stefaneli system may be supposed to light up green LED's progressively from cold until the reducer reaches fuel changeover temp (at which point the system will switch to LPG and green LED's reflect tank level as usual). In which case the state of LEDs with cold reducer could tell of reducer temp sensor problems even without the Stefanelli interface/software - If all greens are on even in cold conditions but change to reflect tank level when switched to LPG (which would seem the LEDs do reflect reducer temp before reflecting fuel level) this could be telling of a problem with the reducer temp sensor. If (as I also said could be the case) this Stefaneli system doesn't have a gas vapour temp sensor (instead uses reducer temp as only temp input used for mixture compensation) then this would also affect mixture when running on LPG.

Drive-ability on LPG seems to have been fixed but problems with automatic switching to LPG with engine too cold may yet remain and I'm not sure if correct lambda readings under all engine running conditions have been confirmed.

Still, nonetheless a good result. But I would advise at least checking lambda on both banks when running on LPG. Previously the engine needed cylinder head valve work, correct mixture at idle doesn't necessarily mean mixture will be correct while driving.

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Re: High fuel consumption?

#85 Post by Freebird » Tue Sep 13, 2016 4:05 pm

LPGC wrote:As mentioned in one of my previous posts, I believe the Stefaneli system may be supposed to light up green LED's progressively from cold until the reducer reaches fuel changeover temp (at which point the system will switch to LPG and green LED's reflect tank level as usual). In which case the state of LEDs with cold reducer could tell of reducer temp sensor problems even without the Stefanelli interface/software - If all greens are on even in cold conditions but change to reflect tank level when switched to LPG (which would seem the LEDs do reflect reducer temp before reflecting fuel level) this could be telling of a problem with the reducer temp sensor. If (as I also said could be the case) this Stefaneli system doesn't have a gas vapour temp sensor (instead uses reducer temp as only temp input used for mixture compensation) then this would also affect mixture when running on LPG.

Drive-ability on LPG seems to have been fixed but problems with automatic switching to LPG with engine too cold may yet remain

Simon
Hi Simon.

My LEDs do not do that, I get a red flashing LED as it warms up then the green "tank level" ones once it has switched over. The red one is on constantly if switched to petrol manually or if it runs out of gas. I can see a temp sensor in the reducer, but don't think there is a gas vapour temp sensor - I can't see any others anywhere.
LPGC wrote:and I'm not sure if correct lambda readings under all engine running conditions have been confirmed.

Still, nonetheless a good result. But I would advise at least checking lambda on both banks when running on LPG. Previously the engine needed cylinder head valve work, correct mixture at idle doesn't necessarily mean mixture will be correct while driving.

Simon
So, apart from checking that they flick, what else can I do? Pull a hose to look for an increase in V and squirt Butane to look for a reduction in V? If so how do I know the readings are correct?

Glen.

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Re: High fuel consumption?

#86 Post by LPGC » Tue Sep 13, 2016 5:25 pm

You just said the red flicks as it warms up but I thought you'd previously implied it changes over to LPG very quickly even from cold start / not much difference in changeover time between cold start and warm start.. Mentioned something about coming out of work and it switched straight to gas when you thought it should have run on petrol for a while before switching? Your Stef system may or may not be supposed to light up green LEDs as it approaches changeover temp. If it switches straight to gas all the time then even if LEDs are supposed to light up as reducer approaches changeover temp there may not be time for them to light before it does change.

Check that lambda flicks not just while the engine is idling but also while driving and at various engine loads - Run a wire from lambda signal and earth to inside of car and monitor V as you drive.

The butane / vac leak methods are useful for confirming problems are not due to failed lambda sensors - if you can consistently affect lambda V using those methods then this confirms the lambda probe is OK. Since you changed your lambda probes and lambda V has started to flick at idle you know your lambda probes are now OK and you also know mixture is OK at idle. Unless you have checked lambda V under various driving conditions you don't yet know that mixture is OK under various driving conditions. It might only take a problem with any of reducer, reducer pressure setting, pressure sensor, injectors, injector driver circuitry, temp sensor(s) or calibration for the mixture to be OK at idle but not OK while driving.

You've had to sort out worn engine valves previously, worn valves are usually caused by lean mixture, your lambda sensors seemed to be reflecting lean mixture when they were broke. Pause for thought here because broken lambda probes incorrectly reflecting lean mixture all the time should have the effect of causing the engine to run rich (if your pre OBD2 car doesn't have a limp home open loop mode, which is likely). A petrol injector pulse length that would give rich mixture should translate to the LPG system also providing rich mixture if the LPG system is working properly and calibration is correct. This is the important bit - your engine valve problem may have developed at a time when the LPG system should have been providing a rich mixture but a rich mixture would not cause engine valve problems. So, it could be that your LPG system was providing a lean mixture when it should have been providing rich mixture, which would point to a problem with your LPG system. Now that you've replaced/sorted the lambda probe issue(s) it could remain that your LPG system provides correct idle mixture but provides incorrect mixture while you're driving. Would be a shame to be blissfully unaware that mixture is lean while driving and have to sort worn engine valves again... at least worth a check of lambda voltage from both probes while driving. Following any change to lambda probes or LPG system (you've changed probes, I think you've had injectors to bits?) the calibration should be checked (or if that isn't possible then at least lambda should be checked)... Annual LPG system servicing also includes such checks to guard against un-noticed mixture problems etc - I don't think you'll have done such checks in the past, in which case won't know if the system provided correct fuelling even before any of the engine valve, lambda probe, injectors work needed to be done?

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Re: High fuel consumption?

#87 Post by Freebird » Wed Sep 14, 2016 1:21 pm

Gotcha

I will repeat the multimeter on the dash trick with both lambdas looking for a good swing in voltages.

On the subject of switching early, it usually takes 1/2 mile or so in the morning, but less in the evening as the ambient has been high recently. It now runs OK on gas once switched though whereas before the new lambda went in, it stalled and was sluggish. That time when it started on gas it had been sitting in the sun for hours.

It will start on gas if the engine is already hot though - is that normal? I seem to remember my previous cars started very briefly on petrol.

Glen.

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Re: High fuel consumption?

#88 Post by LPGC » Thu Sep 15, 2016 12:54 pm

Half a mile should be enough for warm enough changeover this weather and system may be set to start on gas if reducer is already warm enough.
Could be that your reducer temp sensor works properly some of the time but other times could be reflecting hot reducer when it is cold (usually implying intermittent short circuit).

Lambdas will improve matters anyway. Even open loop fueling (such as shortly after starting the engine) may be inadvertently affected by faulty probes.

Not saying there's a problem with mixture while you're driving, just worth checking and would expect (any installer) to check calibration/mixture while driving particularly after your type of problems.

Edit - In my last post I forgot to mention that certain injector and/or LPG ECU issues can create an imbalance of injector flow to each cylinder, an imbalance between injector flow means some cylinders get rich mixture while other cylinders get lean mixture. As long as the difference in flow isn't enough to cause rich/lean cylinders to misfire, lambda readings can still flick properly. So, even flicking lambda isn't 100% confirmation that some cylinders are not lean while others are rich. To check injectors flow the same it is possible with some (most modern) LPG systems to switch individual engine cylinders to run on petrol while other cylinders are running on LPG, if the system is calibrated correctly and all LPG injectors flow the same then switching any individual cylinder back to petrol shouldn't change the pulse duration of the other injectors. Bit more scare-mongering maybe :lol: but it isn't very unusual to find differences in injector flow rates, particularly with certain types of injectors when they're old/worn. Usually has to be a pretty bad case to cause VSR so don't worry! Older ECU's (like your Stef) are less likely to have the facility for switching individual cylinders back to petrol but on engines with multiple cylinder banks fed by multiple LPG injector rails at least differences in overall flow rates between injector rails can be performed by switching which rail fuels which cylinder bank... If injection pulse time per cylinder bank (noted in LPG software) depends on which rail is fitted to which cylinder bank then this probably points to the average flow of the injectors (3 in your case) on the rail giving the leaner mixture to be less than the average flow of the other rail (and vice/versa) but this still doesn't tell you if the leaner/richer or both rails have a problem injector or more. Less of a issue if all injectors on the same cylinder bank flow the same (even with a difference between average flow of rails) than if individual injectors on a rail flow differently but the only correct situation is if all injectors on both cylinder banks flow the same.

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Re: High fuel consumption?

#89 Post by Freebird » Mon Sep 19, 2016 1:11 pm

Well, I checked that both lambdas were flicking while driving along on LPG and they do indeed. The voltages are changing constantly between virtually zero and 4 volts, rarely if ever getting to 4.7 which is fully weak.

To my surprise they go very close to zero (fully rich) on the overrun - does that sound right?

The car seems to be running well now and fuel consumption is much improved since replacing the 456 sensor. Still don't know what caused the VSR and perhaps I never will.

Glen.

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Re: High fuel consumption?

#90 Post by LPGC » Mon Sep 19, 2016 3:29 pm

Freebird wrote:To my surprise they go very close to zero (fully rich) on the overrun - does that sound right?
Would expect a 5>0v sensor to read high voltage on engine over-run... unless you have 0>5v sensors instead of 5>0v sensors. If they are 0>5v sensors don't worry you that might have fitted the wrong sensors, you haven't! Lambda wouldn't flick nicely if you had.

But does the reading show 0v on over-run of either fuel? Does the reading go to almost to the other extreme on either fuel at full throttle high rpm? Thinking would expect lean reading on over-run and rich reading giving it some stick, at least on petrol. If readings are the opposite way around on LPG to on petrol then might expect LPG to be giving a minimum pulse time (that is rich but should be lean on over-run) and calibrated lean at high loads. But something else could be going on!

Likely 0>5v sensors?

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Re: High fuel consumption?

#91 Post by Gilbertd » Mon Sep 19, 2016 6:36 pm

Don't forget that the sensors are only capable of reading the amount of Oxygen in the exhaust. So if the throttle is closed off completely there will be virtually none going in so the same amount coming out. No Oxygen means a rich mixture but only if there is anything there to read, no air or fuel and it will read nothing.
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Re: High fuel consumption?

#92 Post by LPGC » Mon Sep 19, 2016 8:01 pm

Good point Gilbert.

Tbh I still wouldn't expect the exhaust not to get a flow of fresh air when fuel is shut off but you've made me think...

On the one hand - I'm so used to seeing lambda show lean mixture during fuel cut-off/over-run. And back in the day I'll have converted a fair few straight 6 Jags using single point AEB175 systems etc, I'd expect to remember odd fuel cut-off settings/lambda readings if lambda stayed rich (or didn't change) during fuel cut-off on over-run regardless of where I set stepper position.

On the other hand, I've always presumed around 0.15bar minimum manifold pressures I see during over-run conditions (on all normally aspirated engines I can think of) to be due to intake air flow, implying either throttle body (or ICV) is still allowing a flow of air into the manifold, which (another presumption) I'd always expected the engine capable of scavenging and pumping into the exhaust... But I suppose if the throttle (and ICV) were to close completely the 0.15bar manifold pressure could be due to the engine's inability to create more vacuum than 0.15bar, which might be due to the combination of compression ratio and engine valve timing perhaps?

Reckon if lambda swings to the opposite extreme flat out on petrol we could pretty much conclude sensors are 0>5v though? Or you might know for fact they're 5>0V on this Jag?

Simon
Last edited by LPGC on Tue Sep 20, 2016 11:27 am, edited 1 time in total.
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Re: High fuel consumption?

#93 Post by Gilbertd » Tue Sep 20, 2016 8:28 am

According to www.lambdasensors.co.uk the universal replacement for the Jag is the same as the universal replacement for my Range Rover and that is definitely 5-0V. Mine goes to 5V, or as near as possible, on the over-run so I suspect it's down to the engine mapping and how much air goes in under closed throttle. As long as it flips under normal running though, I think it's pretty irrelevant.
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Re: High fuel consumption?

#94 Post by LPGC » Tue Sep 20, 2016 11:10 am

Agreed all points. A couple of posts back I touched on methods to test LPG setup doesn't have a minimum injector pulse duration causing rich mixture on over-run (in case petrol over-run mixture is lean before fuel cut-off) and full power mixture goes rich.

In case mixture goes lean on petrol on over-run, goes rich at full power on both fuels and if system does compensate for gas temperature, then come colder weather it would be possible the rich low load running could extend to normal idling conditions.. a slight reduction in pressure might improve that (again only if it goes rich when it should). But as you say irrelevant and following Glen's successful result maybe a bit nit-picking :lol:

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Re: High fuel consumption?

#95 Post by Freebird » Tue Sep 20, 2016 1:11 pm

Hi Guys

They are definitely 5-0V where 5V = lean. it registers 4.7V with the engine off and ignition on - lots of oxygen around then.

Glen.

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Re: High fuel consumption?

#96 Post by LPGC » Wed Sep 21, 2016 9:59 am

Did expect Gilbert to be right on the 5>0v sensor spec, most comments since your last post have been about the mixture going rich on over-run.

Now lambda flick under driving conditions is confirmed, 'blissfully unaware' has been almost entirely disproved, I'm confident you won't have problems! The other checks I mentioned could still be done to entirely disprove potential issues but again could be considered nit-picking.

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