Getting P0172 only on LPG

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xeno
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Re: Getting P0172 only on LPG

#21 Post by xeno » Fri Dec 27, 2019 8:24 pm

Yes that is what I meant to say: when I disconnect the hose from the PVC valve and plug the hole, or when I remove the oil filler cap, the LTFT values (on petrol) come in an acceptable range.

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Re: Getting P0172 only on LPG

#22 Post by Brian_H » Fri Dec 27, 2019 8:32 pm

You might be best to look into that first then, Some vehicles seem to get them gummed up and cleaning it out helps, so you might be lucky there.

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Re: Getting P0172 only on LPG

#23 Post by xeno » Fri Dec 27, 2019 9:11 pm

The PVC valve on my car is integrated in the valve cover. So I guess the only option there is to replace it.

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Re: Getting P0172 only on LPG

#24 Post by Brian_H » Fri Dec 27, 2019 9:42 pm

You might have some luck cleaning it by soaking in petrol? Might be worth a look around for a forum or similar dealing with your particular vehicle to see if they have any suggestions on how best to deal with it. Or maybe someone else here can suggest the best course of action?

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Re: Getting P0172 only on LPG

#25 Post by LPGC » Sun Dec 29, 2019 8:18 pm

The PCV having this effect could be telling... Positive crankcase ventilation means just that, i.e. airflow passes through the MAF, most air enters the intake through the throttle body but some air diverts through the engine crankcase before entering the intake manifold, either way air entering the manifold is usually metered by the MAF. So if fuel trims are more negative when the PCV system is working than when the PCV is effectively disabled (by blanking off the pipe to the manifold) then if airflow is the same the engine must be receiving extra fuel - in some situations (with certain problems) it can receive that extra fuel from the crankcase. Certain problems would include petrol being present in the crankcase, this is possible if a cylinder has been misfiring (on petrol) for long enough and/or if a petrol injector leaks because petrol can then make it's way past piston rings and into the sump from where it (it's vapours, usually increasingly as the engine/oil warms up and petrol in the sump is more likely to evaporate) can be sucked into the manifold by the PCV system. A petrol injector might leak if it is fed with higher fuel pressure than for which it was designed - Such as if the engine has a returnless petrol system but is run on LPG so fuel pressure to petrol injectors gets very high (because the petrol pump continues to run but no petrol is actually being used). In this case the fix would be to fit a physical petrol return (to keep petrol pressure actually correct and to prevent stress on petrol injection components), replace the faulty petrol injector (already broken by too much pressure in the past), change the oil and filter (get rid of the petrol in the sump) and re-calibrate the LPG system (an emulated fuel pressure probably wouldn't be the same as actual fuel pressure with a proper physical petrol return, fuelling on LPG is based on petrol injector pulse duration, petrol injector pulse duration on engines with returnless fuel systems is compensated for petrol pressure readings).

Some Chevy V8's do have a returnless petrol system, when I convert vehicles with returnless petrol systems I fit a physical fuel return (which does keep pressure within the normal working range and keeps stress on all fuel system components just the same as normal) but some installers fit a 'petrol pressure emulator', a kind of electronic 'fix' that returns an electronic petrol pressure reading to the petrol ECU that's within the normal working range but doesn't prevent actual petrol pressure rising to very high levels, the electronic 'fixes' can cause this kind of problem (and other problems such as worn out petrol pumps or petrol pump driver/PWM control electronics to wear out). Some BRC ECU's have built-in petrol pressure 'electronic fix' electronics... all electronic fuel pressure 'fixes' mask the issue/problem whilst causing extra stress on fuel system components (which can cause components to fail) rather than solve the problem, only a physical fuel return solves the problem.

Not related to your problems but I hate to see lube systems T'd into reducer and/or pressure sensor vac lines, lube fluid in these vac lines has the potential to make it's way into the pressure sensor or reducer where it can cause untrue pressure readings or even damaged components. Also lube fluid should enter the manifold in a fine spray, the smaller the nozzle size the finer the spray so lube fittings in manifolds should have a narrow bore but the vacuum connection for the pressure sensor and/or reducer will have a wider bore.
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Re: Getting P0172 only on LPG

#26 Post by xeno » Tue Jan 07, 2020 8:39 pm

I received my new lpg injectors today and went installing them immediately! But unfortunately it did not seem to fix anything :(. My LTFT values are still around -20 / -25 on LPG and on petrol around -15. I went for a drive to see if these values were really only when idle, but it seems that also when driving they stay around similar values as idle. So I guess my problem is not only on idle (the garage told me the problem was only on idle)

If I understand correctly from @LPGC my petrol injectors might be leaking because of high fuel pressure? I checked and I do have a returnless system:

"The Fuel System is a returnless on-demand design. The fuel pressure regulator is a part of the fuel sender assembly, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions."

I could replace the faulty petrol injector as you say, but how do I find out which one is faulty?

About the lube system, can I not just connect the lube hose directly to the manifold with a proper connector? Or what should be the correct way?

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Re: Getting P0172 only on LPG

#27 Post by LPGC » Wed Jan 08, 2020 11:10 am

Some vehicles which look in the engine bay like they don't have a fuel return do have a fuel return (for our intents and purposes), just that the fuel return isn't fitted in the engine bay. Your OBD tool shows live data (fuel trims etc), will it also show fuel pressure? Even if high fuel pressure caused leaking petrol injectors they would most likely stop leaking when running on petrol because petrol pressure is likely to be correct running on petrol... if you needed to fit a fuel return the lack of one would only cause high petrol pressure when running on LPG. A leaky petrol injector would be a long shot even with high petrol pressure but if a petrol injector leaks while the engine is turned off some of the leaked petrol will end up in the sump, and your PCV tests point a little to possibility of fuel in the sump.

You said you have a Flashlube system.... Is Flashlube actually the brand of lube system or do you have a different brand lube system? I ask because 'Flashlube' is often used as a generic term for lube systems in the same way as Hoover is used as a generic term for any brand of vacuum cleaner. How is your lube system plumbed in now? If you have a type of lube system often fitted with BRC LPG systems (not Flashlube) and you plumb it to feed into the intake manifold the vacuum in the manifold will quickly suck all the lube fluid into the engine because this system is designed to feed lube into a pipe that's above atmospheric pressure (gas vapour pipe between reducer and injectors) not designed to feed into lower than atmospheric pressure.

If you have trims now at around -15% I'd advise not using the LPG for a day or so, just use petrol and see if those trims come back to normal.
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Re: Getting P0172 only on LPG

#28 Post by xeno » Wed Jan 08, 2020 5:40 pm

I can read the fuel pressure; included with the freeze frame data when I got the P0172 code, the fuel pressure was 43 psi, which is within range (43-45 psi) running on LPG.
I could maybe later do a test what the pressure is running on petrol compared to LPG, but right now my LPG tank is empty so I first need to refill.

I have driven a full tank of petrol already (around 100L, I am currently only driving on petrol until this is fixed) and I don't think the values are improving. I think they are getting worse if any.

With Flashlube I really mean the brand Flashlube. This one: https://www.lpgonderdelenshop.nl/Flashl ... ver-Kit/en
You can see the drops and you need to adjust it for the proper amount of drops per minute.

So what can I do?

If fuel is leaking, does it mix with the oil? Can the vapors of it really make my car run rich? If then I replace the oil should the values be oke (for a little while)?

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Re: Getting P0172 only on LPG

#29 Post by Brian_H » Wed Jan 08, 2020 6:35 pm

Flashlube should be fine with that kind of dispenser, but you might need to use something like this https://tinleytech.co.uk/shop/valve-sav ... -manifold/ if the manifold has a low point after where you intend to connect it (if you think it might pool in the bottom end, which depends on the manifold design mainly - Some photos might help there if your not sure?)

Petrol could mix with the oil if enough was leaking - LPG generally won't do that. It may be worth seeing if you can check the oil (the dipstick will give you a bit of an indication to start with). I've known cars that get a lot of cold starts and short runs to have oil that stinks of petrol, it may be worth dropping yours into a clean container if your not sure and deciding what to do based on what comes out. Given the pcv issue mentioned before, this might be a good idea (but don't think of it as a permanent fix, you need to determine where the fuel is getting in from and stop it)

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Re: Getting P0172 only on LPG

#30 Post by LPGC » Wed Jan 08, 2020 6:44 pm

The fact that you can read the fuel pressure in OBD live data points to your model of vehicle not having a standard fuel return fitted...

You're reading normal fuel pressure when running on LPG but this doesn't necessarily mean that fuel pressure isn't climbing to very high levels when running on LPG - When running on LPG the pressure reading may be actual (in which case the LPG installer will have fitted a fuel return) or may be electronically emulated (in which case when running on LPG petrol fuel pressure will rise very high but the petrol ECU will read normal fuel pressure because of the electronic fuel pressure emulation). From an LPG installer's point of view the issue that needs to be addressed (if there's going to be any chance of getting the vehicle to run properly on LPG) is only the pressure reading, not the actual pressure... But actual high pressure can cause problems with the petrol pump, or the pump's driver electronics, or petrol injectors etc. So good LPG installers know that it's better to fit a physical fuel return than to fit an electronic fuel pressure emulator. A physical return addresses the fuel pressure reading while causing no more stress on petrol system components than normal, emulation addresses the fuel pressure reading but causes more stresses on petrol system components. If you have a physical fuel return fitted you should be able to find it T'd into the engine's feed pipe somewhere between the petrol pump and the engine... Or you may instead find a little electronics emulator box connected to fuel pressure sensor wiring.

Yes if a petrol injector leaks enough when the engine is off or when the engine is misfiring it can put petrol in the sump, petrol in the sump will mix with oil and it's vapours will richen the air/fuel mixture as they enter the inlet manifold via the PCV system. Too much pressure to petrol injectors could cause them to fail in a way that sees them dump petrol into the sump. This chain of events is a long-shot but very possible and would go a long way to explaining your richer running with the PCV connected. If we knew this had been happening it would be a good idea to change the oil and filter but you'd also likely have to replace a petrol injector.

The Flashlube link didn't work correctly at my end but from everything you've said about your lube it seems you do have a normal Flashlube. What are your concerns about the lube? Where does fluid enter the engine at the moment? How much lube has it been using?
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Re: Getting P0172 only on LPG

#31 Post by xeno » Thu Jan 09, 2020 4:22 pm

Maybe there is some confusion about the Flashlube system: it is already installed when I bought the car, I don't have any concerns with it. I think originally someone just asked if I had a lube system and I answered. So if all is fine there then it's ok to me.

Oke so my plan is to replace the oil and filter and start the car and measure the trims, both on petrol and lpg. If the trims are better this could indicate leaking injectors (maybe caused by missing fuel return). If the trims are not better it might be something else.

I will also take a sample so I can analyse the oil if the trims did not improve.

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Re: Getting P0172 only on LPG

#32 Post by LPGC » Fri Jan 10, 2020 7:58 pm

It was probably me asking if it had a type of lube system that pumped fluid into the injector lines... no worries because your lube system isn't that type.
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Re: Getting P0172 only on LPG

#33 Post by Brian_H » Fri Jan 10, 2020 8:58 pm

Is it a good idea for it to be on the vacuum line that feeds the reducer though? (and potentially the map sensor as well?)

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Re: Getting P0172 only on LPG

#34 Post by LPGC » Sat Jan 11, 2020 9:19 am

Brian_H wrote:
Fri Jan 10, 2020 8:58 pm
Is it a good idea for it to be on the vacuum line that feeds the reducer though? (and potentially the map sensor as well?)
No, if that's how it's connected it should be altered to use it's own manifold fitting.
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Re: Getting P0172 only on LPG

#35 Post by xeno » Sat Jan 11, 2020 3:35 pm

Today I went on getting the oil changed. First I took a measurement and the trims where around -15 on petrol and around -23 on LPG. The Fuel pressure on both petrol and LPG was around 43 psi.

Then I turned the engine off and noticed the fuel pressure started to slowly raise. Is that normal? I waited some minutes until it reached all the way to 72 psi and decided to start the engine again. Within some seconds the pressure went back to 43 psi.

Then I changed the oil + filter and nervously checked the trims again; they where the same as before! Same for the fuel pressure.

So i rechecked:
- Trims when I (only) remove the oil fill cap: all values around 0
- Trims when I (only) remove the PCV dirty air hose and block the manifold connection: all values around 0
- Trims when I (only) remove the PCV fresh air tube and block both the manifold and the hose: all values around 0

So the situation before and after the oil change seems to be the same. The fuel pressure going to 70 psi seems to be a problem? Did the new oil mix with leaking fuel that quickly to influence the air/fuel ratio again? Or might there be something else going on?

I took a sample of the oil and will send it to blackstone labs. But that might take some time to arrive, but then we should know if there is too much fuel or not in the oil

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Re: Getting P0172 only on LPG

#36 Post by LPGC » Sun Jan 12, 2020 10:55 am

I'm not sure on whether fuel pressure rising to 72psi after you've turned the engine off is normal but I wouldn't think so.

Does it run OK on petrol now? Assuming it does..

You're getting the same figures after changing the oil and filter as you were before, which seems to rule out petrol in the oil... I wouldn't bother sending a sample of oil off to a lab for testing, seems an unnecessary expense. A failed PCV valve could maybe skew trim figures if it sees the engine burning oil that enters the inlet manifold from the crankcase, so I would check the PCV. Problems with the engine itself (blow-by, worn rings, worn valve stem seals, compression) could all have the potential for upsetting trims but I wouldn't worry much about these unlikely potentials at the moment. No harm done by changing the oil and filter, you've ruled out a potential problem and given the engine an oil service.

The -15 trims on petrol are perhaps a bit excessive but this may not point to an issue. Engine management systems (particularly those that respond to fuel pressure) can have a fuel trim system that's a bit more complicated than just the usual set of ltft's and stft's, so you may not be seeing or taking into account all that the engine management is doing regards fuel trims. Or could just be that your MAF is over-reading air flow a bit. Still, the difference between the -15 trims running on petrol and -23 trims running on gas point to an LPG calibration and/or LPG hardware issue - would try adjusting LPG calibration so trims on LPG match trims on petrol. In time (and when the engine management system has passed all it's IM readiness checks) you may find that the -15 trim becomes much closer to zero but if you run on on LPG with the more excessive -23 trims it is unlikely to pass IM readiness checks.

Do you have an interface cable and software for your LPG system?

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Re: Getting P0172 only on LPG

#37 Post by xeno » Sun Jan 12, 2020 4:59 pm

I checked the service manual and found:

"Ignition ON, engine OFF, command the fuel pump ON with a scan tool and observe the fuel pressure gage while the fuel pump is operating. Verify the fuel pressure is between 345-414 kPa (50-60 psi).
⇒ If the fuel pressure is greater than the specified range, replace the fuel pump module."

So I guess it should not exceed 60 psi.

I already payed for the oil sample, so I will sent it anyway, in that case we will at least know for sure what is in the oil and maybe even spot other problems.

Also from the service manual:

- "The normal Short Term FT (fuel trim) parameter should be between +10 percent and -10 percent, with near 0 percent the optimum, with the engine running at operating temperature."
- "The Long Term FT parameter should be between +10 percent and -10 percent, with near 0 percent the optimum, with the engine running at operating temperature."

I do see higher values also when driving around, but as you say it is difficult to make conclusion seeing the system is so complex. What does strike me though is that after removing the oil cap the values are near 0 percent, so optimum! But yeah, maybe it has always been like this, I know you get an error code after (-)25, and that is what is happening on LPG.

I would love to know more about calibrating the LPG system. I only have OBD interfacing at the moment. What kind of cable and software would I need to get for the LPG system?

Also you said you would check the PCV. How can I do this?

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Re: Getting P0172 only on LPG

#38 Post by xeno » Mon Jan 27, 2020 2:36 pm

I brought the car to the specialist today for the MOT test.
All was fine except off-course the problem of running too rich.

I asked them to perform a fuel pressure test to see if there is any petrol injector leaking. But they said all injectors are working good. They said actually all the values are good, so they don't understand what can cause the LPG to run too rich.

In the meantime I also received the oil report. I will add the report to this post. The did not find any fuel in the oil, they did find potassium, which is in antifreeze.
I have done an oil test before because I was loosing coolant, which turned out to be a cracked cylinder heads. The cylinders heads have been replaced and since then I am not loosing coolant. So it is really strange they found potassium.

I hope someone can help me! If there is any test I can do I love to hear it.
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Re: Getting P0172 only on LPG

#39 Post by Brian_H » Mon Jan 27, 2020 6:49 pm

Its possible (though not very common) for a failing vapouriser to leak coolant into the gas. This in turn can then get into the engine via the gas injectors and might end up in the oil. Though I'd have thought you would have noticed losing any significent amount of coolant and mentioned it already. Has the vapouriser had any attention recently?

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Re: Getting P0172 only on LPG

#40 Post by Gilbertd » Mon Jan 27, 2020 7:24 pm

If that was the case, it is likely it would also be pressurising the cooling system so giving symptoms similar to a blown head gasket.
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