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PostPosted: Tue Jan 24, 2017 11:33 am 
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Joined: Mon Jan 28, 2013 10:57 am
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This situation is a bit complicated so I will give a bit of back ground.

2006 Subaru Tribeca (H6 3 litre) with BRC plug and drive fitted at 42000 miles. Currently at 128000.
Both cylinder heads removed 3 times due to:
1. valve seat recession combined with leaking head gasket (valve seat recut and valve clearances set)
2. re-do head gasket in close succession to 1. due to missed cylinder head crack
3. further leaking head gasket due to failed thermostat and over heating. I also re-set valve clearances on bank 1 inlet valves which were tight. Generally runs well since with no overheating or coolant loss.

Had to replace full exhaust 6 months ago and chose to replace both cats (with 'sport cats'). Have since had to replace one front O2 sensor (AFR) due to failure immediately after new cat (damaged in removal I supect). Prior to this, I was getting a p0171 code due to spikes in a defective o2 sensor. No codes since O2 sensor replacement.

Current problem: I have drivability issues. Mainly off-throttle running which is a little irregular. It also sometimes stutters on acceleration. MPG has worsened a little. I monitor ECU parameters using a wireless OBDII reader which connects to my phone. All parameters look fine except long term fuel trims which are persistently negative (around -10% on both sides). I've checked a few things but discovered today that whilst running on petrol, the trims revert to normal (near 0%). Makes me think that the LPG system is overfuelling.

I've lost faith with both of my local BRC installers (original installer fitted Flashlube pipework incorrectly which effectively rendered it useless perhaps leading to VSR , second one didn't know that faulty float switch in lube bottle disabled lube pump so unknowly ran without functioning Flashlube for weeks). Would prefer not to go back to either of them.

Suggestions?


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PostPosted: Wed Jan 25, 2017 6:41 am 
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Joined: Sun Jun 21, 2009 4:14 pm
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Yes take it the Simon at LPGC!
He's the only person I trust with my lpg.

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PostPosted: Wed Jan 25, 2017 1:42 pm 
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Yes I would love to but he's 250 miles away!


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PostPosted: Wed Jan 25, 2017 3:55 pm 
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Joined: Wed Sep 29, 2010 5:01 pm
Posts: 2943
Location: Yorkshire
57jam89 wrote:
Yes take it the Simon at LPGC!
He's the only person I trust with my lpg.

Cheers Simon!
DJB1 wrote:
Yes I would love to but he's 250 miles away!

So only about half the distance some of my customers come ;-)

What are the trims when engine is under load just before the point at which it goes open loop, and how do they compare to trims on petrol?

Simon

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2 miles A1, 8 miles M62,
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PostPosted: Thu Jan 26, 2017 2:06 pm 
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DJB1 wrote:
Yes I would love to but he's 250 miles away!


He's 177 miles away from me!

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PostPosted: Wed Jul 19, 2017 8:51 pm 
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I finally took it to BRC specialist who had the car for 24 hours. The main issue is recurrent burning out of new cats fitted a year ago. I'm on number 3 and 4 having replaced both sides once. The problem that I can see from OBD reader is that on petrol it runs with positive trims (i.e. correcting slightly lean condition) but on LPG, the reverse is true with a tendency to very negative long term trims (typically minus 9). My concern was that the calibration of LPG is abnormal and relative to petrol running, it is overfuelling. I understand that the BRC ECU piggy backs to main ECU which governs emission control via AFR sensors. However, the BRC ECU must adding more fuel compared with main ECU. This change over from petrol to lpg is the problem I think since it must struggle to regulate correct fuelling with these rapidly changing fuel trims. I also worry about when it goes into open loop on lpg. I suspect that given the trend to overfuelling at mid throttle, it'll be seriously over fuelling at wide open.

The BRC specialist adjusted the lpg correction at idle - he didn't mention any other changes. I can't say that it's any better now. On petrol, it's fine. Long term trims around 0-3, short term trims hover around -5 to +5. On LPG, they are all over the place. On light throttle (MAF below 25), short term trims are positive (up to +15). On acceleration, (MAF above 25), they are very negative (-10 to -15).

Here's my question:

Is there adjustment to BRC settings that will correct this? I figure that it needs more fuel at light throttle and much less at mid or full throttle.


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PostPosted: Thu Jul 20, 2017 9:14 pm 
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Joined: Mon Jan 23, 2012 12:21 pm
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Location: Milton Keynes
DJB1 wrote:
I finally took it to BRC specialist who had the car for 24 hours. The main issue is recurrent burning out of new cats fitted a year ago. I'm on number 3 and 4 having replaced both sides once. The problem that I can see from OBD reader is that on petrol it runs with positive trims (i.e. correcting slightly lean condition) but on LPG, the reverse is true with a tendency to very negative long term trims (typically minus 9). My concern was that the calibration of LPG is abnormal and relative to petrol running, it is overfuelling. I understand that the BRC ECU piggy backs to main ECU which governs emission control via AFR sensors. However, the BRC ECU must adding more fuel compared with main ECU. This change over from petrol to lpg is the problem I think since it must struggle to regulate correct fuelling with these rapidly changing fuel trims. I also worry about when it goes into open loop on lpg. I suspect that given the trend to overfuelling at mid throttle, it'll be seriously over fuelling at wide open.

The BRC specialist adjusted the lpg correction at idle - he didn't mention any other changes. I can't say that it's any better now. On petrol, it's fine. Long term trims around 0-3, short term trims hover around -5 to +5. On LPG, they are all over the place. On light throttle (MAF below 25), short term trims are positive (up to +15). On acceleration, (MAF above 25), they are very negative (-10 to -15).

Here's my question:

Is there adjustment to BRC settings that will correct this? I figure that it needs more fuel at light throttle and much less at mid or full throttle.


Sounds to me that you have a mismatch between the pressure and nozzle size - Do you have any access to the software? (its not easy to get hold of some BRC software anyway). You've given some of the info Simon had asked for in January so hopefully he might see your reply and answer, though i'd suspect he may need some more info to go on.


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