Stag Calibration

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patnut
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Stag Calibration

#1 Post by patnut » Tue Oct 06, 2020 12:30 pm

Hi Guys,

How easy is it to calibrate my stag LPG system myself? I understand this has to be done every so often.

I had an error code which stated car running lean only when running lpg so assume it needs recalibration to match petrol.

Is this easy to do I have the software cable etc and know my way around the software a little but don't know where to start with the calibration.

Also does the auto calibration do a decent job?

Thanks,
Pat

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Re: Stag Calibration

#2 Post by Fox vehicles » Tue Oct 06, 2020 9:16 pm

The auto calibration will normally do a pretty good job on most systems but it is important to check the mixture under drive conditions once you have done it. Especially in the open loop conditions You can do this with a simple code reader as long as it will show you the fuel trims and oxygen sensor reading. Of course, the system will need to be in good condition to have a good auto calibration result. You may find that the system is lean all through the rev range which could be down to a drop in pressure, sometimes all that is required is the pressure putting back to what it was when last calibrated. .I am not over familiar with Stag so probably not the best person to help, but I think Simon who is a regular on here would be able to help more on this, :)
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Re: Stag Calibration

#3 Post by LPGC » Tue Oct 06, 2020 9:56 pm

How well autocalibration works with most ECUs tends to depend on the engine/vehicle (what pinj is at idle) and injectors fitted/selected in software.
Usually if autocal is done with a brand new reducer and as soon as the engine is warm enough for autocal to run, reducer pressure drops a little as the diaghpragm loosens up and warms (softens), then the reducer outputs slightly lower pressure, then pressure correction adds a percentage to ginj figures to compensate for lower pressure, leading to slightly richer at idle. All this can happen at the same time as injectors are bedding in (when the response of injectors changes most over the service life).
Exactly how Stag autocal works depends on whether it's an old-skool Stag (300 / 400 / etc), bit newer such as featuring ISA2, or newer still such as Qmax. And then it can depend on whether you're talking initial autocal or what could be termed 'prolonged autocal' which can involve either/both of automatically momentarily switching back to petrol and comparing pinj's to steer multipliers or rpm correction (like doing a manual join the pinj/ginj dots manual method) or steering multiplier to keep fuel trims within a certain range.
The join the dots method doesn't work if the vehicle in question needs a fuel return fitted or if it runs anything like BMW's Valvetronic (some supposedly can with the addition of an extra gizmo that converts MAF readings into pseudo Map readings).
No autocal system is capable of adjusting temperatures or manifold pressure (effectively petrol pressure) corrections. Not to worry much about this one because most installers don't bother adjusting temperature compensation and probably haven't even considered petrol pressure compensation anyway.
No autocal system can properly adjust high load open loop fuelling particularly on vehicles that use narrow band lambda probes (most vehicles).
Basic autocal systems set only around 7 multiplier points, evenly spaced from around 3ms up to around 12ms, this makes for far too few multiplier points around the low load positions on most installs. A good manual map will probably have 15 multiplier points set with 7 multiplier points set between 1.5ms and 4.5ms where there is most difference between petrol injector performance and LPG injector performance in response/percentage fuelling terms.
The firm that fits most Stag systems and relies most on Stag autocal likes to sell their conversion customers an interface cable to 'allow remote tuning'. This is so that when the engine warning light comes on they can try to adjust the calibration remotely using the join the dots method. They talk about remote tuning as some sort of bonus to the customer only available through themselves but the real situation is that remote tuning can be done in the same way (not very well) on any system by taking advantage of remote desktop access software that is built into Microsoft Windows and the installer should have done a proper manual job of calibration to prevent the MIL light coming on in the first place.
One of the worst aspects of autocal systems is that their installers seem to realise that they can get better results by fitting slightly undersize nozzles or using slightly low pressure. This can mean that the combination of nozzles and pressure cannot supply enough gas to the engine for correct (rich enough) fuelling at high loads, but on the upside for the installer it can also mean that ginj is well above the critical minimal ginj at which temp correction and accurate multiplier become most important during the warm-up stage shortly after switchover to LPG from petrol, this can allow injectors that are not very linear/accurate to work well above the range at which they start to become nearly as linear as better injectors.
But.. On a vehicle that's easy to get good results on like (say) a P38 Rangerover, most autocal systems will do an OK (far from great) job. Not as good a job as they could on an equally simple install where the engine idles at 3ms pinj (compared to a P38 that will idle with a bit more than 3ms pinj) but OKish.
Autocal systems don't work well on engines that idle with pinj much away from 3ms (much below or much above 3ms) and even when they work properly they don't manage anything like as good as a proper manual calibration by someone who knows what they're doing, even if they injector spec is well suited and nozzles and pressure are well suited.

On manifold pressure correction - Most ECU's are not geared towards accurate calibration in the first place for a lot of moderately recent vehicles because a lot of recent vehicles use returnless fuel systems. In this I'm not talking about the obvious/familiar returnless systems like Jags/Fords/Volvos/some Mopar stuff, I'm talking about a fuel pump that delivers fuel to the engine at a pressure relative to atmospheric pressure rather than manifold pressure. A lot of engines are supplied with petrol at (say) 4 bar above atmospheric pressure, which means that when the warm engine is idling at (say) 0.3 bar manifold pressure the petrol pressure relative to manifold pressure is actually 4.7 bar, or on a cold tight engine that is idling at 0.4 bar manifold pressure the petrol pressure relative to manifold pressure is 4.6 (as opposed to 4.7) bar. If we double the petrol pressure (petrol pressure versus manifold pressure) to a petrol injector it will deliver 1.4x as much fuel. If pressure to LPG injectors is referenced to manifold pressure while pressure to petrol injectors is referenced to atmosphere the difference in reference pressures should ideally be accounted for because it can make for around a 6% difference in fuelling on a normally aspirated engine and more difference on a turbo'd engine. It may seem to some that the difference can be accounted for in rpm correction but that's only partially true, the rpm correction still won't properly compensate for transient conditions such as throttle tip-in and still won't properly compensate for unusual manifold pressures versus pinj and rpm that can occur during e.g warm-up or changing idle loads. A lot of installers may have noted they need to dial in an unusual shaped map (which basic autocal won't do) on engines with returnless fuel systems compared to engines with conventional mechanical fuel pressure regulators but a lot won't realise that their map is accounting for around a 6% difference if flow of petrol injectors across the range of manifold pressures on a normally aspirated engine without a fuel return. If petrol pressure is compensated for the multiplier map that should be dialled in starts to look more of a normal shape again... Except since effective petrol pressure is at it's highest at lowest manifold pressure pinj at idle will likely be lower than on a similar spec engine that has a mechanical fuel pressure regulator, this pushing pinj at idle to below 3ms.

Back to your question - How easy it is to calibrate your system yourself... This depends on what vehicle it is, what LPG components you've got fitted and whether you want to make compromises in the same way as some of the usual Stag installers do. If your install has components well suited to the vehicle and the engine's red-line is above 6000 rpm you'll at least want to set the maximum rpm whilst running on LPG setting to a higher figure than the default 6000rpm that every Stag install I ever see (a lot of them from all ends of the UK) seems to have left set at the default 6000rpm figure. I put right a lot of Stag installs, often recently fitted, often for customers who live close to the original installer, often which are supposedly covered by 'lifetime warranties'.

Still.. Not as bad as LPGTech autocal. Most of them are setup by the installer in 'tech mode' (continuous autocal mode). If the engine ever runs open loop for a period of time (perhaps because of a genuine engine problem such as failed lambda sensor or perhaps due to incorrect LPG calibration) the autocal continues to run using the dot to dot method and messes up it's own multiplier map. The only recourse is to recalibrate. If calibration mode is changed from Tech mode (often done in a day installers autocal mode) to normal mode the full recalibration has to be done again completely from scratch. Not to mention that around half of all LPG Tech ECU's in the UK were supposed to be destined for Eastern Europe markets and the software is locked (by ECU firmware) to the language of the country for which it was supposed to be destined. Good job I know my way around all software because I haven't mastered Polish yet ;-). Extra injection filtering doesn't work in LPGtech either, and it's reading of long pinj durations become confused (45ms pinj at 5000rpm is impossible).
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Re: Stag Calibration

#4 Post by patnut » Thu Oct 15, 2020 3:52 am

Lpgc thank you for the in-depth reply I drive an MG ZT 2.5l they put in a stag 300 premium system.

It looks a bit complicated and I didn't want to mess things up so might take it to a professional.

Thanks again
Pat

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Re: Stag Calibration

#5 Post by LPGC » Thu Oct 15, 2020 10:14 am

LPG systems don't go out of tune by themselves - The state of 'tune' is the calibration settings stored in the ECU. For an LPG system to be out of tune it was either not tuned properly in the first place, or something in software settings is enabled which allows the ECU to adjust it's own tuning calibration settings (which it has incorrectly done), or something physical has changed such as excess wear on injectors or leaking reducer diaphragm (both hardware fault conditions). Some might argue reducer pressure might change a little as the reducer ages thus affecting the state of tune but the ECU and settings should be able to properly compensate for this unless pressure has changed by quite a lot, which again would be a hardware problem.

You've said you had the lean error code, apart from that does it seem to drive properly?

If you're going to alter any ECU settings, first save the settings (click on parameters, then click on save).

Depending on how old your Stag 300 ECU is it may feature 'Autoadaption' in which case either OBD autoadaption or ISA2 autoadaption may be enabled. If either is enabled they allow the ECU to change it's own RPM compensation adjustment figures (change it's own state of tune). You could check in software to see if autoadaption is enabled - from the Map screen click on the autoadaption tab. If autoadaption is turned on (if the 'on' checkbox is checked) is OBD or ISA2 correction selected? In either case click on the 'rpm correction' tab, take a screenshot (to show us) and then click 'erase'.
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Re: Stag Calibration

#6 Post by patnut » Sat Oct 17, 2020 10:33 pm

Hi

I had the stag lpg system installed in 2013 so had it about 7 years.

The car runs fine the engine light and error code just come on when running on gas. I've attached a few screen shots below showing error code and other settings.

I do have autoadaption but it's not enabled.
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Re: Stag Calibration

#7 Post by patnut » Sat Oct 17, 2020 10:35 pm

Setup
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Re: Stag Calibration

#8 Post by LPGC » Sun Oct 18, 2020 8:40 pm

The engine isn't running in your screenshots but there are a couple of things to note...

The very high gas pressure reading of 3.07 bar likely points to a reducer problem (in which the gas entry valve internal of the reducer continues to allow a little gas to flow past it even during over-pressure situations). Whether or not this will cause a problem when the vehicle is running on gas depends on how severe such internal problem is but it will cause a problem during switching from petrol to LPG. The high pressure reading could also be caused if the reducer got too cold (a cold reducer can output liquid gas which the vaporises in rubber pipes).

The shape of the multiplier map (yellow line in bottom pic) is wrong, it would never be that bell shape with the peak at 15ms on any engine if the physical install is correct (appropriate injectors, nozzles and pressure). Normally if calibration (multiplier map) is something like correct the blue and green dots should quite closely match up on an engine that makes use of a throttle setup (not a Valvetronic or Valvetronic derivative) and if the engine doesn't need a fuel return to be fitted as part of the LPG install.

On your install they only match up / merge at around 8.5ms... However, if we did adjust the multiplier map to get the green dots to align with the blue dots on this install the shape of the multiplier map would then still be wrong (it would still start off low and peak at 8.5ms) and this also points to aspects of the install being wrong (or the engine being some type of Valvetronic setup which we know your engine isn't). Aspects that could be wrong could just be the faulty reducer already mentioned, or could be incorrect injector nozzle and working pressure combination, or could be due to other settings in the LPG ECU such as RPM compensation or the 'cold engine leaning' settings could be having a negative effect.

In the MAP screen, click on the tab for RPM correction, if any of the numbers in the table are not zero(?) post a screen shot of the rpm correction screen.

Let's see a few screenshots of the engine warmed up and running on LPG (so we can see pressure and temperature readings). At least one with the engine idling under no load, and one with petrol injector readings of around 7ms.

Hana red injectors are selected in software, does the install have Hana red injectors?
Thinking out loud - We don't know what size nozzles are fitted in the injectors(?) but if they're the old Hana red injectors they'd have 2.4mm nozzles.
I'd expect 2.4 nozzles to be about right for this engine at moderate pressure (say 1.4 bar) but the installer has set software reference pressure to 1.75 bar which is quite a high pressure. An installer might set a high pressure to compensate for nozzles a bit on the small side or in attempt to get a reducer that's a bit under-rated for the power of the engine to flow a bit more gas.
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Re: Stag Calibration

#9 Post by patnut » Sun Oct 25, 2020 3:37 pm

Hi yes they are Hanna red injectors 2.4. I replaced one that failed with a Hanna gold with a 2.4 nozzle adapter.
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Re: Stag Calibration

#10 Post by patnut » Sun Oct 25, 2020 3:39 pm

@ higher rpm

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Re: Stag Calibration

#11 Post by LPGC » Sun Oct 25, 2020 8:02 pm

No automatic entries in RPM correction is a good thing, to do fine tuning later you'll probably want to make some manual entries.

What model reducer is fitted? It's not very pressure stable on this install, this might be because it's very much under-spec'd for the install, or because the pressure adjustment has been wound up too much (it might be more pressure stable at a lower pressure like 1.6 bar at idle), or because it's broken.

I'd try adjusting pressure down to 1.6 bar when running on gas at idle (because at 2120 rpm pinj is 6.2ms, ginj is 7.2ms, yet delta pressure is only 1.46 bar). Then see how much pressure drops under slight load like the same 2120rpm 6ms pinj load in one of your screenshots.

Then see if pressure continues to rise when running on petrol but LPG solenoid valves are open - If there's quite a lot of high pressure pipe between the reducer solenoid valve and the reducer you can disregard 'LPG solenoid valves are open' but if the solenoid valve is directly attached to the reducer it's better to check for a pressure rise while running on petrol but with solenoid valves open.

Do you have the correct spec reducer temp sensor selected in software (it seems you don't)? If it's set wrong then in conjunction with the 'max ginj with cold reducer' settings enabled it could cause problems. We wouldn't normally see higher gas vapor temps than reducer temps, we can presume the gas vapour temp reading is correct if it's built into the pressure sensor.
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Re: Stag Calibration

#12 Post by patnut » Fri Oct 30, 2020 8:45 am

The reducer is OMVL not sure what model how can I find this?

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Re: Stag Calibration

#13 Post by LPGC » Fri Oct 30, 2020 10:14 am

Is it like this https://tinleytech.co.uk/shop/lpg-parts ... off-valve/ or this https://www.lpgshop.co.uk/omvl-dream-xx ... p-reducer/ ?

Any writing / stickers on it?

I had a Volvo XC90 3L turbo with Stag 300Qmax LPG ECU here for repair yesterday, owner reported it ran rough on petrol or LPG and sometimes refused to switch to LPG (switch beeped as though run out of gas at changeover). This had a KME Gold reducer with pressure cranked up.

The driveability problem was a failed wide band lambda sensor on bank1, which normal garages couldn't find because the Stag ECU had been wired to OBD which prevented their OBD readers connecting to OBD. It also seemed to have either a blown turbo oil seal, dodgy PCV system or knackered oil rings on cyl 6, it was quite smoky and fouling plug 6. The switching problem was due to the Stag ECU detecting a failed gas pressure sensor, actually the pressure sensor hadn't failed but pressure could reach over 3 bar at times while the engine wasn't running on LPG due to a failing reducer, the very high pressure reading was interpreted by the ECU as a failed sensor. Owner's gone away to have the lambda sensor fixed and investigate the oil burning before returning to me to have the LPG problems fixed.
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Re: Stag Calibration

#14 Post by patnut » Fri Oct 30, 2020 1:21 pm

I belive its the 2nd one dream.
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Re: Stag Calibration

#15 Post by patnut » Fri Oct 30, 2020 1:40 pm

The reducer temp sensor is what they selected at instal.

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Re: Stag Calibration

#16 Post by LPGC » Fri Oct 30, 2020 3:37 pm

It is an OMVL Dream reducer, HP on the sticker supposedly points to it being the high power (flow) version, the old versions of the Dream HP reducer would be good for the best part of 400bhp but more recent versions are not as good in terms of max flow / power handling ability as the old versions. Should be OK for your ZT though, if it's not broke anyway!

Pressure output would be around 1.5 bar as standard but pressure can be adjusted by turning the 10mm pipe nut / pressure adjuster brass hex fitting that the vacuum pipe connects to, screwed all the way in the HP reducer used to do around 1.7 bar. They're not the most pressure stable reducer but they're not usually prone to failing in a way which sees pressure reach 3+ bar.

All your screenshots show relatively cool temperatures for both reducer and gas. If the engine hadn't been running long the low temps could be due to that, but if the engine was fully up to temperature the low temp readings could point to an issue with not enough hot water flowing through the reducer. If there's not enough water flowing through the reducer the reducer and gas temps may drop to very low temps during driving, if temps fall low enough the reducer may output liquid gas (into rubber gas vapour pipes) which then evaporates in the vapour pipes to cause very high pressure in vapour pipes - The 3bar reading could be due to the reducer getting too cold?
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Re: Stag Calibration

#17 Post by patnut » Thu Jan 21, 2021 11:06 am

Error code went away after I increased the switch over temperature. I thik this is what created the error in the first place when I reduced it. Thanks for all your help especially LPGC.

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