High negative LTFTs on Subaru Tribeca

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DJB1
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High negative LTFTs on Subaru Tribeca

#1 Post by DJB1 » Tue Jan 24, 2017 11:33 am

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?

57jam89
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Re: High negative LTFTs on Subaru Tribeca

#2 Post by 57jam89 » Wed Jan 25, 2017 6:41 am

Yes take it the Simon at LPGC!
He's the only person I trust with my lpg.
Nissan Skyline 350gt Lpg fitted by Lpgc.

DJB1
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Re: High negative LTFTs on Subaru Tribeca

#3 Post by DJB1 » Wed Jan 25, 2017 1:42 pm

Yes I would love to but he's 250 miles away!

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Re: High negative LTFTs on Subaru Tribeca

#4 Post by LPGC » Wed Jan 25, 2017 3:55 pm

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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57jam89
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Re: High negative LTFTs on Subaru Tribeca

#5 Post by 57jam89 » Thu Jan 26, 2017 2:06 pm

DJB1 wrote:Yes I would love to but he's 250 miles away!
He's 177 miles away from me!
Nissan Skyline 350gt Lpg fitted by Lpgc.

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Re: High negative LTFTs on Subaru Tribeca

#6 Post by DJB1 » Wed Jul 19, 2017 9:51 pm

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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Re: High negative LTFTs on Subaru Tribeca

#7 Post by Brian_H » Thu Jul 20, 2017 10:14 pm

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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Re: High negative LTFTs on Subaru Tribeca

#8 Post by LPGC » Sat Jul 29, 2017 9:35 pm

DJB1 wrote: 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.
Yes, on most BRC systems including yours, the software has a couple of simple sliders to (respectively) adjust calibration at idle loads / adjust calibration at off idle loads.

Perhaps the reason the guy you took it to didn't adjust the off idle settings was because he didn't actually drive it? I won't say anything that could be seen as questioning whether he knew what he was doing, or fobbing customers off with only a bill ;-)

Trims being at -9% during closed loop on midrange loads (compared to petrol trims of +3% during same conditions) could be a pointer toward overly rich mixture during high load open loop conditions but that isn't necessarily the case. In my experience plenty BRC installers don't seem to address pressure / nozzle size issues (as per Brian's post)... not usually a problem on most vehicles but can be a problem on engines that idle with small petrol injector pulse duration such as on most Subaru engines. Your short term trims shifting between +10/15% on petrol and around -10% on LPG points to a long term situation that would see more of a difference between -9% and +3% which would point to more of an issue with LPG calibration.

But, even then, since the engine will spend the majority of it's time at low (idle like) and midrange loads, I still wouldn't expect repeated cat burn outs if fuelling seems anything like OK at idle and midrange loads anyway. This may point to a different problem such as failing LPG injectors giving some engine cylinders very different mixture to others - If the BRC system were fitted with BRC's lube system which flows lube into the engine via the LPG injectors I would suspect this to be the case.

Simon
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Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
Mid Yorkshire
2 miles A1, 8 miles M62,
http://www.Lpgc.co.uk
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DJB1
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Re: High negative LTFTs on Subaru Tribeca

#9 Post by DJB1 » Sun Jul 30, 2017 8:59 pm

Thanks Simon and Brian.

The specialist drove the car some distance (that's why he kept it overnight). He logged the trims and showed me the record.

I did an ECU reset and things seem more stable now. On petrol, LTFT sits between 0 to +5 (most of the the time around 2-3) but on LPG it's drifts down to -6 and never lower. The short term trims are negative on acceleration and this is more marked on hard acceleration.

I take your point about injectors - not sure how to test whether they're ok or not. I'm beginning to conclude that the new 'sports' cats might be the problem after all, the original cats were just about working (and weren't burnt out) at 10 years old. Nothing much had changed in the car except that I had to replace exhaust because of terminal corrosion. I have no doubt that reducing the fuelling on LPG ('gear' setting in the BRC software?) will help the trims but I doubt whether the cats will last any longer.
Last edited by DJB1 on Sun Jul 30, 2017 11:21 pm, edited 1 time in total.

Brian_H
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Re: High negative LTFTs on Subaru Tribeca

#10 Post by Brian_H » Sun Jul 30, 2017 9:19 pm

DJB1 wrote:Thanks Simon and Brian.

The specialist drove the car some distance (that's why he kept it overnight). He logged the trims and should me the record.

I did an ECU reset and things seem more stable now. On petrol, LTFT sits between 0 to +5 (most of the the time around 2-3) but on LPG it's drifts down to -6 and never lower. The short term trims are negative on acceleration and this is more marked on hard acceleration.

I take your point about injectors - not sure how to test whether they're ok or not. I'm beginning to conclude that the new 'sports' cats might be the problem after all, the original cats were just about working (and weren't burnt out) at 10 years old. Nothing much had changed in the car except that I had to replace exhaust because of terminal corrosion. I have no doubt that reducing the fuelling on LPG ('gear' setting in the BRC software?) will help the trims but I doubt whether the cats will last any longer.
Might help to confirm which type of lube system is fitted (if any) - following the pipework should give you the answer to this, if your not sure post some pictures. Though injectors can fail for other reasons, if you have access to the software on some systems you can switch cylinders between fuels, this would allow you to isolate individual injectors, Not sure if BRC systems allow this, and even if they do you will struggle to get the software usually. but if you can get access to that then switching some off should allow you to see if it behaves better with the trims.

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Re: High negative LTFTs on Subaru Tribeca

#11 Post by LPGC » Sun Jul 30, 2017 9:25 pm

The specialist could/should very easily have adjusted calibration to bring trims on LPG more in line with trims on petrol. Having driven the vehicle it is surprising he didn't take his laptop on that trip and adjusted calibration during it.

Didn't the specialist test and comment on the condition of your injectors? Easy to determine an injector(s) that perform differently to the majority of injectors - compare trims when individual cylinders are switched between fuels.

Yes the 'gear' setting.

Must have misread your original post, wrote my last post thinking you'd implied you'd had to replace cats a few times.

Bri and mine posts crossed.

Simon
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Re: High negative LTFTs on Subaru Tribeca

#12 Post by DJB1 » Sun Jul 30, 2017 11:34 pm

I'll clarify the cat situation. About a year ago, the exhaust system fell onto the road. It needed to be replaced and oem system was £3600! I opted to go for custom stainless steel system for much, much less. As it had nearly failed an mot on emissions, I thought it wise to replace the 2 main cats and chose sports cats. Apparently the old ones were a bit clogged but were fully intact. Bear in mind this car has had head gaskets done twice so had every reason to think that the cats might be past their best. I have now had to replace both cats (the new ones, left and right) because they seem to have burnt out.

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Re: High negative LTFTs on Subaru Tribeca

#13 Post by DJB1 » Sun Jul 30, 2017 11:37 pm

Ps I don't have access to BRC software but have read manual online. Having said that, I could get cable and software off eBay.

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Re: High negative LTFTs on Subaru Tribeca

#14 Post by Brian_H » Mon Jul 31, 2017 5:57 pm

DJB1 wrote:Ps I don't have access to BRC software but have read manual online. Having said that, I could get cable and software off eBay.
I was thinking BRC was like Prins, but it looks like the software etc is slightly more easily available. http://lpg-kits.com/ does have a version listed with a serial connection for £19.99 if you have a laptop with a serial port, or £29.99 with a usb interface. At least you'd get slightly better support off him than some random eBay seller who may have issues understanding you later on if theres a problem.

I have a suspicion that some of the more advanced features may require a dongle/unlocking to work so you may have to end up going to an installer to do anything on that, though I'd suspect your problem is more basic (either injectors failing - may only be one of them) or its not quite setup right. The software would help you determine what that problem might be (TBH the cable will help if you get issues in the future as you should be able to see whats wrong if it won't switch etc as well)

Does it have the lube going into the injector feed if its got one?

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Re: High negative LTFTs on Subaru Tribeca

#15 Post by DJB1 » Tue Aug 01, 2017 12:09 am

Yes lube does go into injector feed.

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Re: High negative LTFTs on Subaru Tribeca

#16 Post by LPGC » Tue Aug 01, 2017 7:56 pm

For certain results only buy a proper BRC cable. Before I bought mine I tried various supposed BRC specific cables with mixed results.

For the type of diagnostics I mentioned (checking injectors) it can help to be familiar with what you are doing.

I implied lube going in through injectors could cause problems in an earlier post.

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Re: High negative LTFTs on Subaru Tribeca

#17 Post by DJB1 » Thu Aug 31, 2017 8:32 pm

I'm now coming to the conclusion that one or more injectors are clogged. I've noticed that there is quite a bit of oil (likely to be lube) around the gas pipework leading to injector manifolds. Not sure if this signifies a fault with injectors or just a minor leak but this wasn't evident a year ago.

Quick question: does IC12 injector cleaner work?

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Re: High negative LTFTs on Subaru Tribeca

#18 Post by Brian_H » Thu Aug 31, 2017 9:26 pm

Depends on the fault - if they are gummed up yes, its not able to repair damage though. Its worth a shot. It might be as much a fault with your lube system - how quickly does the level drop?

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Re: High negative LTFTs on Subaru Tribeca

#19 Post by DJB1 » Thu Aug 31, 2017 10:05 pm

Not that quick. The delivery rate was adjusted recently (by BRC specialist) but it leaked before that. Seems to be worse on bank 2 side.

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Re: High negative LTFTs on Subaru Tribeca

#20 Post by DJB1 » Thu Aug 31, 2017 10:07 pm

Sorry should have specified that now, trims are trending towards negative on mid to full throttle and positive on light throttle or idle. This does not happen at all on petrol.

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