Getting P0172 only on LPG

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xeno
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Getting P0172 only on LPG

#1 Post by xeno » Sat Dec 14, 2019 3:24 pm

Hello,

I have an Avalanche 2008 with a BRC LPG system.

Recently I am getting P0172 (System too rich) error code.
I checked the STFT and LTFT (on idle) and when I run on gasoline they are around 0 (or at least between -10 and 10). When I switch to LPG the LTFT bank 1 (same bank as P0172) changes to around -20.

On top of that I recently received a P0301 Misfire on cylinder 1.

The LPG specialist also seemed to identify cylinder 1 as a problem because he replaced the bougie, bougie cable and LPG injecter for that cylinder, except this did not seem to solve the problem.

The LPG specialist does not really seem to know what we can do next. Could anyone here help me with a solution?

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Re: Getting P0172 only on LPG

#2 Post by Gilbertd » Sat Dec 14, 2019 8:15 pm

Not sure what an Avalanche is or where you are (although bougie, literal translation, candle, is what the French call a spark plug). The LTFT dropping to -20 means it is detecting a rich mixture so leaning the mixture but obviously not enough so you are getting the fault code and misfire. If it was a faulty lambda sensor then it would be the same on petrol so it looks like it could be a fault in the LPG system. Does it have a vacuum take off on the affected bank? A leaking diaphragm in the reducer could allow gas to enter the inlet manifold through a vacuum hose.
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Re: Getting P0172 only on LPG

#3 Post by Brian_H » Sat Dec 14, 2019 8:41 pm

Looks like its probably a Chevrolet truck we are talking about here. Given you mention banks, I'd wonder if the other bank is showing the opposite correction to the one your seeing on bank 1 (Assuming its a engine with multiple banks, which the only options appear to be between 5.3l and 6.0l all in V8 format suggest it probably is).

The vacuum take off is easy to test for once you locate it, equally its worth finding out where it is located and if its close to cyl 1. Pull it off when the engine is running and see if you get any gas leaking out of it (the hose coming from the vapouriser)

Its possible incorrect injector wiring may be causing problems (petrol injector breaks not matched up correctly to lpg injector, or hoses crossed over). It might also be that the banks aren't correctly married up in the software, though I don't know if the BRC software does anything with that - Simon might reply on that point with any luck.

Has this been a recent conversion, or has it been fine for a while and suddenly started doing this?

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Re: Getting P0172 only on LPG

#4 Post by LPGC » Sat Dec 14, 2019 10:49 pm

Which BRC ECU is fitted? They don't allow software routing but some allow individual cylinder trim adjustments, doubt this is the problem though.
With the info so far I can only advise same as Brian and Gilbert have. Also worth checking the installer hasn't replaced the wrong LPG injector and make sure all petrol injectors turn off when running on LPG (stethoscope / pipe to ear to petrol injectors).
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xeno
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Re: Getting P0172 only on LPG

#5 Post by xeno » Sun Dec 15, 2019 9:22 am

Thank you for the advices!

I see I missed some details; yes it is a Chevrolet Avalanche 2008 with a 5.3l V8 engine. I live in the Netherlands, I thought bougie was an English word :) But I meant spark plug indeed.

I have 2 banks, and bank 2 seems to run fine, I do not see that it has an opposite correction, or at least; I see values between the -10 and +10 range on idle.

I have 2 reducers in the system of the type 'BRC 1500 Genius MB' (https://www.lpgwebshop.com/en/brc-reduc ... -12mm.html)
There is a hose going to the top of the intake manifold, this could be a vacuum take off I guess, I can easily reach this. This one is also close to cylinder 1. I will check if there is gas coming out of this hose.

The conversion has been done like 10 years ago. I always had a rough idle, and every now and then a catalyst converted code (P0430), which I always cleared because my garagist said it was because of the LPG installation. I started looking into this issue since I got P0172 error codes.

The BRC ECU is the 'Fly SF'.

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Re: Getting P0172 only on LPG

#6 Post by xeno » Sun Dec 15, 2019 11:11 am

Ok, I just tested the vacuum take off. Both reducers have a hose on the top that are connected to each other and to some sort of switch and go to the intake manifold. There I disconnected the hose, plugged the hole in the engine with my finger and checked if LPG comes out of the hose when the engine was running. There did not seem to be a leak from this hose, I felt or smelled nothing.

Also with the hose disconnected I checked the fuel trim values but they did not improve.

I did notice that the threaded hose connector was very loose. This for sure must have been leaking. So I reconnected it correctly and connected the hose again.
It looks like this improved the values a little bit (or at least the rough idling), but the LTFT Bank 1 was still too high on around -14. When switching to petrol all the fuel trim values are fine.

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Re: Getting P0172 only on LPG

#7 Post by Gilbertd » Sun Dec 15, 2019 11:23 am

Try disconnecting the petrol injector on number 1 cylinder. If that cures the problem it might not be shutting off the petrol to that cylinder and dual fuelling.
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Re: Getting P0172 only on LPG

#8 Post by LPGC » Sun Dec 15, 2019 4:41 pm

2 Reducers so the question needs to be asked - Are the gas outlets of the 2 reducers plumbed together somewhere in the system (a pressure balance pipe fitted)? If not and if the 2 reducers are giving a different pressure then the injectors fed with most pressure will inject more fuel, so to prevent such problems a balance pipe should be fitted.
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Re: Getting P0172 only on LPG

#9 Post by xeno » Sun Dec 15, 2019 9:33 pm

I will try to disconnecting the petrol injector and see what that does.

For each reducer the output gas line goes to a fuel filter and then to the injector rail where 4 injectors are mounted. The output of the injector rails are connected to each other.

Does this mean I am missing a 'balance pipe'? Or is the injector rail the balance pipe? Do you have a link of how a balance pipe looks like?

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Re: Getting P0172 only on LPG

#10 Post by LPGC » Mon Dec 16, 2019 9:34 am

The connection between injector rails will serve as balance pipe, you have one (the pipe between rails) so we can rule this out.
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xeno
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Re: Getting P0172 only on LPG

#11 Post by xeno » Mon Dec 16, 2019 6:49 pm

Today I used a screw driver to listen to the injectors for cylinder 1 and 3 (I could not reach easy any further).
When not running on LPG I could clearly hear the ticking of the injector. After the engine switched to LPG I did not hear anything anymore. So this seems fine.

Are there any more tests I can do?

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Re: Getting P0172 only on LPG

#12 Post by LPGC » Mon Dec 16, 2019 9:57 pm

P0172 points to mixture too rich on bank1.
P0301 points to misfire on cylinder 1 (which is on bank1).

On the Chevy V8 bank 1 is the left hand drive/US driver side and UK nearside/passenger side if the car is right hand drive. Cyl 1 is the front cylinder.
The above error codes in combination point strongly to an issue on cylinder 1 but, that said, a misfire could be caused on cyl1 if mixture on cyl1 is leaned off too much because another cylinder (or cylinders) on bank1 run too rich.

So the LPG installer probably swapped the front injector on the (UK) nearside bank of cylinders? If he swapped any other injector put the one he removed in the front of the UK nearside / If he did swap the front injector on the UK nearside try swapping the one removed with those further back (cyls 3 5 and 7 with Chevy cylinder numbering).

Hehe just remembered you're in a left hand drive country anyway.. So you should be looking at the driver side bank of cylinders.

Do you have a lube system fitted?

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xeno
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Re: Getting P0172 only on LPG

#13 Post by xeno » Tue Dec 17, 2019 10:44 pm

Cylinder 1 is on the right side of the car if you stand in front of it looking towards the car. For me that is on the drivers side (because I live in the Netherlands). The cilinder 1 is also the first one, by that I mean the closest cylinder towards the radiator.

For that cylinder the LPG Installer replaced the injector. I can see that clearly because it is very clean.
I don't have the old one, so I can't try swapping any other injectors.

I could try swapping all 4 injectors of bank 1 to bank 2 and vice versa and see if the LTSF has switched bank.
I don't know how difficult that is, they seem to be relatively easy to reach. Are there any instructions on how to do that?

Edit: And yes, I have a lube system fitted.

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Re: Getting P0172 only on LPG

#14 Post by LPGC » Thu Dec 19, 2019 11:09 am

So it seems the installer swapped the injector on the cylinder for which the misfire code was generated, which would be the most sensible and intuitive one to try first (if going down the road of swapping injectors)... But just because this cylinder had the misfire code doesn't necessarily mean that this cylinder's injector is the one at fault - If for example 2 or all 3 of the other injectors on that bank of cylinders flowed more gas (on average) than they should (because those injectors have a problem) it could cause those cylinders to get the correct amount of fuel (despite broken injectors) and this cylinder to get a very lean mixture causing this cylinder to misfire!

Yes it's a good idea to swap injectors on cylinder banks. Swapping them should be a simple case of removing/fastening pipe clips?

What type of lube system is fitted? :rolleyes: A type often fitted with BRC installs causes injector problems.
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xeno
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Re: Getting P0172 only on LPG

#15 Post by xeno » Tue Dec 24, 2019 11:48 am

To remove an injector I guess I need to disconnect the wire connector and then remove it from the rail. With LPG I am always afraid that the gas will come rushing out.

The lube system is from Flashlube.

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Re: Getting P0172 only on LPG

#16 Post by Brian_H » Tue Dec 24, 2019 12:04 pm

if you want to play it safe, shut off the gas from the tank either using the shutoff valve fitted on it, or by removing the plug from the solenoid and run the engine on gas till it errors (for low pressure) then you know its as empty as possible. Or for injectors if the front solenoid is accessible, unplug that and do the same.

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Re: Getting P0172 only on LPG

#17 Post by xeno » Fri Dec 27, 2019 3:24 pm

Today I took the time to switch the injectors on different banks, except when I checked values for LTFT I noticed that they where a bit high on gasoline as well; bank 1 was around -15 and bank 2 around -12. When turning on LPG bank 1 would be -30 and bank 2 -25.

So now the LTFT being too low is also a problem on gasoline, although the values for LPG are definitely a lot lower.

When I take off the oil filling cap (or remove the 'PCV fresh air tube' and plug the hole) the values increases for both banks with around 10% (when running gasoline of LPG). For gasoline that means the values become in the acceptable range. I am not sure if this is normal, or maybe indicates that my PCV valve is broken.

After switching the last set of injectors I noticed that the values had changed: Bank 1 was -20 and bank 2 was -30. So it seems that at least this injector should be replaced?

I also figured out how to disconnect the gasoline injector electronic connectors, so after the car switch to LPG I disconnected them all, but saw no change in the LTFT values.

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Re: Getting P0172 only on LPG

#18 Post by Brian_H » Fri Dec 27, 2019 3:43 pm

Disconnecting the petrol injectors won't entirely rule them out - any that leak due to a bad seal will still leak (you'd not normally notice that on a petrol only vehicle as they would compensate for any leakage by adjusting the trims anyway).

The trims will adjust when its on lpg, which with a correctly working and calibrated system shouldn't be a problem, But if the calibration is off (either due to a problem with the system causing incorrect fuel supply, or it wasn't done right in the first place) they will drift away from where they should be.

Simon (LPGC) has asked about the lube system - how or where does it connect to the manifold (we know its a BRC lube system from what you've said, but its worth checking this to clarify now). If your not sure, take some photos of the setup and post them here if possible. What would be useful to know is if the lube pipes connect before the injectors (so that the lube would be flowing through the injectors).

You need to prove to yourself what the petrol system is working like normally - to rule out a problem with it causing a problem thats more apparant on the lpg side, Best thing to do there is to drive it on petrol for a day or two to let it adjust itself back, then check your trims again at that point to see if they look more like you'd expect (a dodgy MAF sensor can throw the trims off, particually if its got contaminated causing it to underread, If you have any access to live data do you know what the MAF is showing and if it looks correct?)

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Re: Getting P0172 only on LPG

#19 Post by xeno » Fri Dec 27, 2019 6:17 pm

I don't think the lube system is from BRC, as far as I know it's a 'Flashlube'. It is connected with a T connection to the vacuum line between the intake manifold and the reducers. So the lube would not flow thru the injectors I would say.

I tested the MAF according: 'With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be within 2-6 g/s at idle.' Mine was around 6.

I am curieus if I have a PCV problem (for the petrol side), for LPG I am considering replacing all 8 injectors with new ones. I don't think the previous owner ever changed a LPG filter so it would not surprise me if they are just worn (after 10 years) and closing too slow. I found them reasonably priced here https://lpg-megastore.com/public/catalo ... =128287087

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Re: Getting P0172 only on LPG

#20 Post by Brian_H » Fri Dec 27, 2019 6:57 pm

If you have a problem with the PCV it will potentially still be a problem on LPG as well - possibly worse as your hardly using any petrol either. Is it possible to disconnect it and plug the holes left to see if it improves the problem before you try to spend money fixing it.

You might find running it on petrol to help with that as well, The best way to approach that sort of issue is sort the petrol side first, then sort the lpg side once your happy the petrol side works correctly.

Good chance the injectors are either not sealing as well as they could or completely affecting fuel dosage given the age of them. Though would expect your installer to be able to diagnose that (bear in mind if they are leaking, when switched back to petrol they will still leak until the pressure is gone from the front end of the gas system as well, which might take a few moments with a small leak, making the petrol trims appear to be wrong as well)

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