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High negative LTFTs on Subaru Tribeca
http://lpgforum.co.uk/viewtopic.php?f=28&t=14212
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Author:  Brian_H [ Thu Aug 31, 2017 9:49 pm ]
Post subject:  Re: High negative LTFTs on Subaru Tribeca

For the price of a bottle of ic12 i'd give it a try as a first step - I've known it to improve problematic injectors previously, If they are gummed up with lube that might be enough to clear them (couple of applications on each rail). Though to be fair i'd have expected your specialist to have sorted that out with the leaked lube fix etc. I'd certainly give the cleaner a go before touching the software settings if you now have the access to them. It might be worth posting some screenshots of the settings if you have the software though?

Author:  DJB1 [ Thu Aug 31, 2017 10:52 pm ]
Post subject:  Re: High negative LTFTs on Subaru Tribeca

No haven't got software or cable yet. The worsening features suggest a mechanical fault rather than software. Yet again, I'm getting the occasional P0420 error code (cat below efficiency) which has previously signified internal destruction of one or other cats. I think that when I accelerate hard (which I like to do), the ECU switches to open loop and major over fuelling is occurring. Either that or the non oem sports cats are not up to the job.

Author:  Brian_H [ Thu Aug 31, 2017 10:57 pm ]
Post subject:  Re: High negative LTFTs on Subaru Tribeca

DJB1 wrote:
No haven't got software or cable yet. The worsening features suggest a mechanical fault rather than software. Yet again, I'm getting the occasional P0420 error code (cat below efficiency) which has previously signified internal destruction of one or other cats. I think that when I accelerate hard (which I like to do), the ECU switches to open loop and major over fuelling is occurring. Either that or the non oem sports cats are not up to the job.


Simon can confirm, but it may be possible to switch cylinders between fuels - this can isolate the fault to a bank etc. (newer AEB ecus allow this, not sure with BRC)

Could equally be the calibration is off - either its wired with banks crossed over, or its running with a combination of nozzle size/pressure that just won't work as Simon pointed towards above. Depends if its ever worked with the settings you currently have? Though no amount of calibration will correct dodgy injectors perfectly.

Author:  LPGC [ Fri Sep 01, 2017 8:54 am ]
Post subject:  Re: High negative LTFTs on Subaru Tribeca

BRC Plug n drive does allow switching individual cylinders between fuels and it's a check worth doing. For conclusive per injector comparisons it's necessary to do it at idle and under load while closed loop.

The standard cats are reliable, if the fitted cats are 'sports none OEM', how do we know they're reliable and wouldn't break in the same time period running on petrol as running on LPG anyway?

Summing possible LPG causes up we're looking at lube flow, lube gumming/damaging injector(s), poor injector/pressure combination, poor calibration at high loads.
Other issues can cause the same effect too, such as crimped injector to manifold pipe(s) - This would make effected cylinders run leaner than others particularly under load, lambda will reflect around the average mixture on each bank so if some cylinders are leaner than others on a bank it implies some cylinders will be richer. Not all gas in a rich cylinder will be burned, the remaining gas (particularly in conjunction with the remaining air from the lean burning cylinder) can then overheat the cat.

Something must be wrong with the lube system or mixture if the cylinder heads are suffering vsr.

Simon

Author:  DJB1 [ Fri Sep 01, 2017 5:22 pm ]
Post subject:  Re: High negative LTFTs on Subaru Tribeca

Thanks Brian_H and Simon

The VSR issue may have been due to the lube being inoperative for a while (broken wire to float switch) or because lube was plumbed in upstream of filter. Both were addressed some time ago. I don't know whether the sports cats are reliable but I was assured by fitter that he has fitted this type to hundreds of cars most of which are high performance and very few have had problems. I suppose that he might be lying but he seemed trustworthy and has replaced burnt out ones at cost price.

If lube blockage of injectors is an issue then I'm sure that I will have it having now done about 100000 miles on LPG. I'm not willing to spend much money on this car. I've had my money's worth but it's a good work horse and apart from the 20 mpg on petrol, it's not that expensive to run now that I do all the maintenance myself.

Author:  rich r [ Sun Sep 03, 2017 9:14 am ]
Post subject:  Re: High negative LTFTs on Subaru Tribeca

Don't forget that the EZ30D engine is prone to a little VSR over 100,000 miles even when run purely on petrol, so unlubricated LPG will definitely accelerate what would already be going on.

The standard cats on the Legacy/Outback/Tribeca 3.0s are indeed generally reliable until well over 200,000 miles - there are some reports on the Australian Legacy (Liberty) forums of the original cats and exhaust system still being perfectly fine after 600,000km (375,000 miles). That is of course assuming that the engine is running within acceptable a/f ratios on all six cylinders. There have been reports of certain types of sports cat fitted in the front cat positions failing and being sucked back into the cylinders, especially with better flowing headers.

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