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Author Topic: Problems with LTFT on LPG  (Read 9691 times)

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olm

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Problems with LTFT on LPG
« on: 04 March 2024, 01:59:14 »

Hello, I wanted to ask you a question regarding the LPG calibration since the conversion to Omega is quite common there. It turns out that it is quite common for the proportions of butane and propane to change and you regularly have to adjust the LPG times, but this time it is impossible to lower the LTFT, it ranges between 15-20% and it does not matter whether I add or cut it, I notice a change in the engine sound but the LTFT remains the same, when I change to gasoline it drops quickly and everything is Good, so I rule out that it is any sensor in the car, in addition to the fact that the problem coincided after refueling.
Could someone tell me what it could be? Thanks
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Re: Problems with LTFT on LPG
« Reply #1 on: 04 March 2024, 14:15:07 »

If it reverts to nigh on 0% on petrol, its the LPG thats the problem.  Note, with piggy-backed LPG, it will never be 0% on LPG, but should really stay single digits, or very low double digits, even with shittier LPG setups - assuming nobody still uses mixer setups.

From memory, a positive trim on those means its having to increase fuelling, negative is decreasing fuelling.

So if its fuelling up, thats not enough LPG getting in, if its trimming down, then not enough fuel is getting in.

Its most likely to be mapping on that bank, or a fuelling restriction, or a pressure difference between the banks.
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olm

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Re: Problems with LTFT on LPG
« Reply #2 on: 05 March 2024, 03:20:22 »

Yes, it is not the first time that this has happened to me after refueling, but with a slight adjustment to the calibration it was perfect. The problem is that now it does not respond and it does not matter if I add a lot or a little or even cut, the LTFT does not change. I can't find an explanation, but as soon as I put it on petrol it goes down quickly and works perfectly.
It happens in both banks equally
« Last Edit: 05 March 2024, 03:22:01 by olm »
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Re: Problems with LTFT on LPG
« Reply #3 on: 05 March 2024, 03:50:06 »

What's the thermostat doing? Coolant temp at ECU sensor Vs radiator temp Vs evaporator temp...

When did the issue start? ie sudden climatic change or just refuelled or change of use of the car...
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Re: Problems with LTFT on LPG
« Reply #4 on: 05 March 2024, 12:49:26 »

Yes, it is not the first time that this has happened to me after refueling, but with a slight adjustment to the calibration it was perfect. The problem is that now it does not respond and it does not matter if I add a lot or a little or even cut, the LTFT does not change. I can't find an explanation, but as soon as I put it on petrol it goes down quickly and works perfectly.
It happens in both banks equally
Both banks would therefore imply a fuelling restriction (if positive trim), so blocked LPG filter, kinked hose, tank or evap valve not fully opening etc.
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olm

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Re: Problems with LTFT on LPG
« Reply #5 on: 06 March 2024, 16:57:39 »

What's the thermostat doing? Coolant temp at ECU sensor Vs radiator temp Vs evaporator temp...

When did the issue start? ie sudden climatic change or just refuelled or change of use of the car...

The car temperature is fine. The problem came after refueling, I observed an increase in consumption and looked at how the LTFTs were. It is not the first time that it happens, it seems that they change the proportions at will and it is time to tweak, but this time the usual does not work and does not seem to lead to greater contributions or cuts
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Re: Problems with LTFT on LPG
« Reply #6 on: 06 March 2024, 17:00:39 »

Yes, it is not the first time that this has happened to me after refueling, but with a slight adjustment to the calibration it was perfect. The problem is that now it does not respond and it does not matter if I add a lot or a little or even cut, the LTFT does not change. I can't find an explanation, but as soon as I put it on petrol it goes down quickly and works perfectly.
It happens in both banks equally
Both banks would therefore imply a fuelling restriction (if positive trim), so blocked LPG filter, kinked hose, tank or evap valve not fully opening etc.

A curious thing happened to me today. I was traveling at 90km/h with LTFT close to 25% and when I stepped on it to go up a hill the STFT reduced approximately -20%. Then I tried to give several full throttle pulls and did the same thing, so much so that the LTFTs have gone down. The car responded and accelerated very hard.
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Re: Problems with LTFT on LPG
« Reply #7 on: 06 March 2024, 19:15:16 »

What's the thermostat doing? Coolant temp at ECU sensor Vs radiator temp Vs evaporator temp...

When did the issue start? ie sudden climatic change or just refuelled or change of use of the car...

The car temperature is fine. The problem came after refueling, I observed an increase in consumption and looked at how the LTFTs were. It is not the first time that it happens, it seems that they change the proportions at will and it is time to tweak, but this time the usual does not work and does not seem to lead to greater contributions or cuts
That suggests a fuel issue then although it sounds like the Italian tune up has made the LPG ECU think about what it's doing.

Perhaps fill the next tank from a different supplier and see if it improves further.

Incidentally does LPG get varied according to season :-\
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Re: Problems with LTFT on LPG
« Reply #8 on: 06 March 2024, 19:35:15 »

What's the thermostat doing? Coolant temp at ECU sensor Vs radiator temp Vs evaporator temp...

When did the issue start? ie sudden climatic change or just refuelled or change of use of the car...

The car temperature is fine. The problem came after refueling, I observed an increase in consumption and looked at how the LTFTs were. It is not the first time that it happens, it seems that they change the proportions at will and it is time to tweak, but this time the usual does not work and does not seem to lead to greater contributions or cuts
That suggests a fuel issue then although it sounds like the Italian tune up has made the LPG ECU think about what it's doing.

Perhaps fill the next tank from a different supplier and see if it improves further.

Incidentally does LPG get varied according to season :-\
I don't have another supplier in the area, and in theory Repsol is the best. I've already had several refuelings like this.
The proportions of butane and propane vary depending on the time of year, told myself.
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Re: Problems with LTFT on LPG
« Reply #9 on: 06 March 2024, 20:40:34 »

If they sell alot of it then the blend might vary alot according to the conditions.

The fact that the behaviour changed after refueling suggests that's the cause.

As an aside have you changed the plugs recently as LPG requires a much stronger spark than petrol and the quality of the combustion on one bank would certainly affect the trims.
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Re: Problems with LTFT on LPG
« Reply #10 on: 06 March 2024, 22:30:30 »

Yes, it has to be when refueling, but I can't imagine what could cause there to be practically no changes in the long-term adjustment no matter how much I add or cut, and also if I demand power the STFT drops drastically when it should go up.
The spark plugs have 20,000 km, so I doubt it could be
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Re: Problems with LTFT on LPG
« Reply #11 on: 07 March 2024, 02:01:51 »

Yes, it has to be when refueling, but I can't imagine what could cause there to be practically no changes in the long-term adjustment no matter how much I add or cut, and also if I demand power the STFT drops drastically when it should go up.
The spark plugs have 20,000 km, so I doubt it could be
I would check the plugs if only to rule them out. Start with the side that's showing the trim discrepancy. Do you have any LPG filters fitted between the evaporator and the injectors? And if so where/how.

Also do you have any live data for the LPG side of things... Injector timings etc.
« Last Edit: 07 March 2024, 02:05:18 by Doctor Gollum »
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Re: Problems with LTFT on LPG
« Reply #12 on: 07 March 2024, 10:07:06 »

Don't rule out injectors getting tired.  Many brands dont last as long as petrol/diesel injectors.

My last Omega, the injectors were worn after about 40k miles, with the symptom being lumpy idle, partucularly when cold, leading to occasional stalling.  In my case, rather than replace injectors, I just had it switching back to petrol under 1200 rpm and not switching back to gas until 1600rpm.  Had I known how long we were going to be keeping it for - the lack of LPG in my area made it unviable, but we kept on being able to get LPG on various journeys - I would have replaced the injectors.

The fact that it sounds like yours is over fuelling when pushed, and under fuelling at light loads, that does sound like mapping isn't right, or that the evap isn't getting the heat at lower loads.


In the UK, our LPG is mostly propane with a small amount of butane IIRC, presumably to stop the propane from freezing when cold.  I'm guessing this mix was always the same, as I never had to remap mine in that latter years based on time of year.
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Re: Problems with LTFT on LPG
« Reply #13 on: 22 March 2024, 19:38:13 »

Don't rule out injectors getting tired.  Many brands dont last as long as petrol/diesel injectors.

My last Omega, the injectors were worn after about 40k miles, with the symptom being lumpy idle, partucularly when cold, leading to occasional stalling.  In my case, rather than replace injectors, I just had it switching back to petrol under 1200 rpm and not switching back to gas until 1600rpm.  Had I known how long we were going to be keeping it for - the lack of LPG in my area made it unviable, but we kept on being able to get LPG on various journeys - I would have replaced the injectors.

The fact that it sounds like yours is over fuelling when pushed, and under fuelling at light loads, that does sound like mapping isn't right, or that the evap isn't getting the heat at lower loads.


In the UK, our LPG is mostly propane with a small amount of butane IIRC, presumably to stop the propane from freezing when cold.  I'm guessing this mix was always the same, as I never had to remap mine in that latter years based on time of year.

Yes, I thought they were injectors but something curious happened and I haven't responded until I was sure. After a refueling, suddenly the LTFT went to 0, surprised I wanted to wait for another refueling to see what happens.
Unfortunately, the same problem has reappeared after another refueling, always Repsol at the same station.
The strange thing about this is that you only see the problem if you connect the obd because the car works fine, no jerks and no MIL light
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Re: Problems with LTFT on LPG
« Reply #14 on: 22 March 2024, 19:43:35 »

Yes, it has to be when refueling, but I can't imagine what could cause there to be practically no changes in the long-term adjustment no matter how much I add or cut, and also if I demand power the STFT drops drastically when it should go up.
The spark plugs have 20,000 km, so I doubt it could be
I would check the plugs if only to rule them out. Start with the side that's showing the trim discrepancy. Do you have any LPG filters fitted between the evaporator and the injectors? And if so where/how.

Also do you have any live data for the LPG side of things... Injector timings etc.

Yes, there is a filter before the gas phase injectors. I have not touched one and there has been a refueling in which the fuel settings were perfect, now after another refueling they have returned. I thought it could be the station tank, that it came with some problem and renewing it would have solved it, but it seems not. And it is with each refueling that the problem appears or disappears, what can happen with the gas? And the most curious thing, the car seems to run well, although with a little less force if you step hard, although that's just my thing.
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