Injectors firing too early?

[Rokassileika]

By the way, is it possible to correct the mixture for particular bank only via AC gas synchro?

[LPGC]

You said the problems occur on LPG or petrol - If the idea is to keep it dual fuel so you can run on LPG or petrol you should do the diagnostics on petrol first. This is the most critical part of the diagnostics but it's often unclear whether you're talking about running on petrol or running on LPG. I'm still not sure whether you mean there are any problems when running on petrol. You need to clear all error codes and run only on petrol for a while to see if the problems occur running on petrol. If you switch to LPG at any time during testing running on petrol it could mess up the results of the running on petrol tests.

Are you thinking bank 1 and bank 2 injectors will be fed with different pressures because the injector rails are piped in series? The effect of piping the rails in series will be very small, this won't be a factor in the problems. If what you're thinking were true we could argue that injectors shouldn't be mounted on rails at all because the injector nearest the gas feed pipe would have a different pressure to the injector furthest from the gas feed pipe.

However - Check to see if the installer used a different type of spud on bank 2 to the spuds on bank 1. They may for example have used a conventional spud on one of the cylinder banks which might have a 3.5mm hole through the middle for gas to pass through, and used a different type of spud such as a long reach spud on the other cylinder bank which only has a 2.5mm hole through the middle for gas to pass through. Injector duty cycle is injector pulse duration divided by the available time for injector pulse duration (we sometimes call available time for injector pulse duration window). Window is affected by engine rpm, the engine rotates 10x per second at 600rpm or 100x per second at 6000rpm, so engine rotation time is 1/10th of a second at 600 rpm or 1/100th of a second at 6000rpm. The engine is a 4 stroke so the inlet valves open once every 2nd rotation of the engine so window is 1/5th of a second (200milliseconds) at 600rpm or 1/50th of a second (20ms) at 6000rpm. So if you have injectors pulsing for 5ms at 600rpm that is an injector duty cycle (dc) of 5/200 = 2.5%, or if we have injector pulse of 5ms at 6000rpm that is an injector duty cycle of 5/20 = 25%. The injectors pulse gas into the pipes between injectors and spuds, for any given injector pulse duration the injectors output more gas if the injector nozzle size is increased or if the pressure is increased but nozzle size has more affect than pressure. If the hole in the spud in the manifold is smaller than the injector nozzle size the spud becomes the metering device not the injector nozzle but given enough time between pulses (at smaller duty cycles) all the gas metered by the injector will flow into the engine. If the spud is smaller than injector nozzle size then at higher dc there isn't enough time for all the gas metered by the injector to pass through the spud into the engine before the start of the next injector pulse. If you have different size holes in manifold spuds on one cylinder bank compared to the other cylinder bank the effect on fuelling is negligible at low engine loads but the effect can be very big at higher engine loads.

You also need to investigate those temperature readings. If the engine ECU thinks the engine is only at 100F when really it is at 185F it might apply some fuelling enrichment that could mess up running on petrol or LPG.

[Rokassileika]

That would really make sense with the intake manifold spuds, thank You. I have never really tried to delete faults and drive only on petrol, but I did this once at summer i forgot i turned off the lpg for a while but did not feel the difference in power outputs. All I noticed was that at summer time when I added ~0.5 quart of ATF I couldn't recognize the car for 4 days after all that it got back to where it was. Anyway, these 4 days were very hot, so maybe less air played the game and it was just coincidence? I mean the hotter the air- the less dense it is the less fuel ECU commands to be put through the injectors. And the STFT for bank 2 is now not that far out of its path? Just like with the high moisture days. The more moisture there is, the less oxygen again- less fuel, bank 2 goes to norm? Just a theory maybe I'm wrong i don't know.

[LPGC]

That would really make sense with the intake manifold spuds, thank You. I have never really tried to delete faults and drive only on petrol, but I did this once at summer i forgot i turned off the lpg for a while but did not feel the difference in power outputs. All I noticed was that at summer time when I added ~0.5 quart of ATF I couldn't recognize the car for 4 days after all that it got back to where it was. Anyway, these 4 days were very hot, so maybe less air played the game and it was just coincidence? I mean the hotter the air- the less dense it is the less fuel ECU commands to be put through the injectors. And the STFT for bank 2 is now not that far out of its path? Just like with the high moisture days. The more moisture there is, the less oxygen again- less fuel, bank 2 goes to norm? Just a theory maybe I'm wrong i don't know.

Turn the LPG system off and from a cold start run it only on petrol while monitoring fuel trims to see if it runs ok.

If weather does affect anything it is more likely that affecting things like temperatures has more affect than percentage of oxygen in the air. Cold can affect LPG injector response but you need to have it running properly on petrol before diagnosing LPG faults.

[LPGC]

By the way, is it possible to correct the mixture for particular bank only via AC gas synchro?

Our previous posts crossed and I didn't reply to your post above.

Depending on which Stag ECU you have it probably is possible in a couple of different ways but if spuds are too narrow the only way to properly correct things is to fit wider spuds.

One way is in gas settings, click the 3 dots besides injector type selection. The pop up window allows you to set an offset (added on pulse time) and/or a percentage adjustment for each individual injector. You'd be using the percentage adjustment. The main problem with this method is that it would make fuel trims at low to medium loads more negative on bank2 than on bank1 becoming more correct as loads increase until at very high loads bank2 would go lean again if spuds are too narrow.

The other and better way is in the RPM/load correction table for bank2. But again if spuds are too small at very high loads bank2 would still go lean.

In both cases above at very high loads bank2 goes lean at very high loads because not all the gas in the pipe between injector and manifold gets in to the engine before the start of a new injection pulse. Also in both cases above it is difficult to get mixture correct across the full rpm range because when injector nozzle size is bigger than manifold spud size at higher dc's the output pipe between injectors and manifold gets slightly pressurised with LPG, while the rate at which gas will flow from injectors to the output pipe depends on the pressure difference between injector feed pipe and injector output pipe, while the rate at which gas will flow through the manifold nozzle that is too small depends on pressure in the output pipe versus manifold pressure. Normally when spud size is bigger than nozzle size the output pipe remains at close to manifold pressure, when spud size is smaller than injector nozzle size at high enough engine loads/dc the output pipe will be at some pressure between injector feed pressure and manifold pressure so it opens up a whole new range of things that need to be compensated for and the ECU doesn't have any settings (or readings) to properly address those aspects. The rpm/load correction table may seem to provide the solution but it doesn't. The only way to correct properly for spuds that are too narrow is to fit wider spuds.

We don't know if spuds are too narrow on bank2 yet, you still need to check that. If spuds are the same on both banks then if the problem is an LPG problem it could be a duff injector (or a crimped injector to manifold pipe). If not caused by an LPG problem but it runs properly on petrol it would be engine related but not something that manifests when running on petrol, LPG needs a hotter spark to ignite than petrol so it could be ignition related.

[Rokassileika]

Sorry for late reply. I have some news from my installer, he confirmed that the studs are the same size on both banks. I uploaded a video, sadly I can only use one interface at the time https://youtu.be/DXONJek2KVI What really got into my eye was the double LPG injection times reading at certain loads vs gasoline and reducer pressure going from 1.20 to ~0.98. Engine load reading looked funny, but since it is relying on LPG map sensor i think it is fair? I give more engine load from 1:03 seconds in video.

[LPGC]

Is point of gas entry into the manifold the same on both banks? We can see that the injectors are all forward facing in vehicle orientation terms, the injectors are all at the side of one cylinder bank. From the injectors pipes run to spud on the inside of the curve of the manifold on the forward facing cylinder bank. From the injectors pipes run to spuds in a position we can't see on the rearward facing cylinder bank so we don't know if spuds are on the inside of the curve or outside of the curve of the manifold on that cylinder bank?

Did the installer mean the spuds are identical on both banks? We know they will be the same outside diameter but is length and internal diameter the same? Internal diameter would make the most difference but length could also make a difference.

The Stag engine load reading is just an abstract figure, it roughly translates to rpm or map x pinj (petrol injector pulse duration).

Double injection times readings at what combination of rpm and pinj? It's not too bad to have this at low loads but is bad to have this at medium or higher loads.

[Rokassileika]

At 2:28 (youtube video) I noticed that at 0.93 loads (2880 RPM) normaly Petrol injection times should be 13.5 ms. On LPG the pinj drops to about 8-9 ms. This gives me an idea that the mixture is way too rich there. But then again, I notice that three injectors are showing 8.3 pinj whilst the other three are reaching almost 10 pinj (the lean side bank 2?). I'm not familiar how the order is set for LPG injectors when installing LPGs, but by the given cylinder layout bank 1 should have cylinders with numbers 1,3,5 and bank 2 2,4,6. The installer told me that they must be absolutely the same, i will take my small camera to see if I can see the position of how the spuds are sitting in the manifold. Will update soon, if I find the way to access it with a probe camera since everything is max tight around.

[Rokassileika]

Ok, so couldn't find my probe, but I tried to replicate the locations of gasoline injectors (blue) and LPG spuds (green).

[Rokassileika]

Forgot to mentiom- the bottom side in the drawing is bank 2

[Rokassileika]

Another small update for today. Yesterday I decided to play with LPG map in ACGasSynchro. LPG curve was looking like a hook (too rich in mid loads and starting to lean out in higher loads) I made it more straight and not that far away from gasoline map. The gas pedal became a lot more sensitive, I spinned the wheels yesterday by an accident going from traffic lights twice. Anyway, I checked for STFTs in Techstream, the problem with 70% engine load is still there it is less of a problem, but still there. Bank 2 somehow leans out more than Bank 1 still. I'm sure that I still have to correct the LPG map so will update You with how it goes. However, I still believe that the problem is lying somewhere else as LPGC mentioned before, maybe the spuds are too small not letting the LPG to flow fully in the cylinders.

[LPGC]

At 2:28 (youtube video) I noticed that at 0.93 loads (2880 RPM) normaly Petrol injection times should be 13.5 ms. On LPG the pinj drops to about 8-9 ms. This gives me an idea that the mixture is way too rich there. But then again, I notice that three injectors are showing 8.3 pinj whilst the other three are reaching almost 10 pinj (the lean side bank 2?). I'm not familiar how the order is set for LPG injectors when installing LPGs, but by the given cylinder layout bank 1 should have cylinders with numbers 1,3,5 and bank 2 2,4,6. The installer told me that they must be absolutely the same, i will take my small camera to see if I can see the position of how the spuds are sitting in the manifold. Will update soon, if I find the way to access it with a probe camera since everything is max tight around.

If 3 cylinders are reading 8.3ms pinj while the other 3 cylinders show 10ms pinj then if fuel trims are higher on bank 2 the 3 reading 8.3ms will be on bank 1 and the 3 reading 10ms will be on bank2. Also there's around 20% difference between 8.3 and 10 so we'd expect fuel trims on bank 2 to be around 20% higher on bank 2 than on bank 1.

If while driving with these pinj figures (8.3 on bank 1 and 10 on bank2) if you don't change throttle position at all but switch to petrol what do the pinj figures for both banks read then? Have you even tested to see if pinj figures stay similar on all cylinders when you're running under the same conditions (rpm and throttle position) or if the figures are different to the same 20% extent as they are on LPG when you're running on petrol?

If figures are OK on petrol (all pinj readings are similar) and if manifold spuds and injector nozzle sizes are all the same on both cylinder banks then potential problems with the LPG system include bad LPG injector(s). I haven't mentioned checking injector nozzle sizes before but it's worth mentioning... AEB injector nozzles are colour coded, the colour supposedly tells us what internal diameter they are but it's common practice to buy small diameter nozzles and drill them (very easy with them being plastic) to the required diameter - If at some point the injectors were changed perhaps someone bought the same colour nozzles but didn't drill them to the same diameter as the old injectors. One way to check for a bad injector(s) is to switch an individual cylinder to run on petrol when the other 5 cylinders are running on LPG while monitoring pinj and/or fuel trim readings - E.g. If one injector isn't flowing enough gas but the other 2 on the same cylinder bank are flowing correct amount of gas then fuel trims will be positive with the dodgy injector working (the cylinder it feeds running on LPG) but normal when that injector is disabled (and the cylinder it feed is running on petrol). But beware because injectors can occasionally fail in a way that sees them flow too much gas, so there is a (small) chance that the cylinder bank with decent looking fuel trims would be running lean if only it didn't have a failed injector flowing too much LPG. There is even a small chance that the problem isn't engine, LPG injector, nozzles, piping or spuds related... The LPG ECU could have failed in a way that sees it not send correct length pulses to injectors. The ECU sends a strong 'peak' electrical pulse for a short time to get an injector to open but if it continued to supply the injector coils with peak power for the full length of the time they need to be open it could damage the injector/coil by overheating it, so after the peak pulse comes the hold pulse which is enough power to keep the injector open. I have known ECUs (and more than Stags fair share) to fail in a way that sees either the peak or hold component of the pulse not work. But it isn't time to start suspecting the ECU yet.

[LPGC]

My second post today.

Just had a flick through your video, the shape of your map is wrong.

You could email me your map, I'd make a few changes including some changes I haven't mentioned so far.

Does your engine have a mechanical fuel pressure regulator and fuel return pipe running back to the fuel tank? If it does there will be 2 pipes running to the petrol rail/s on the engine. Don't confuse the evap purge pipe that will also run from the fuel tank to the engine bay with a fuel return pipe.

[Rokassileika]

There are no fuel return pipes, only fuel pressure regulator ( part number 23270-31010) by the given pictures I'm actually unsure how it works, i don't see any wiring or vacuum connections on it. As I mentioned I have already made some changes to LPG map, it is far from perfect, but the car drives much better, the P0420 is gone now too (still needs a lot of work on LPG map). Is there a way to send You some sort of AcGasSynchro file or do I have to email You pictures with each multiplier points and injection times without LPG being turned on? I tried to turn off LPG while adjusting the multiplier points for accurate pinj readings, but since the car is moving i found it really hard to adjust it. I guess I would need someone to drive the car for me while such procedure is taken.

[LPGC]

You could email me the file, my email address is in my signature at the bottom of all my posts.

If 23270 doesn't have a fuel return pipe connected it cannot be what we'd refer to as a pressure regulator (and usually what we'd refer to as a pressure regulator would have a vacuum connection like you've said). It could instead be a dampener that smooths out small fluctuations in pressure that occur when petrol injectors open/close, strictly speaking still a kind of pressure regulator but not what we'd normally refer to as a pressure regulator.

Anyway, you've answered the question about whether or not it has a pressure regulator, it doesn't. This means that petrol pressure isn't manifold pressure referenced, instead it will be atmospheric pressure referenced. This in turn means that effective petrol pressure (petrol pressure versus manifold pressure, since the petrol injectors output to manifold pressure) will vary with changes in manifold pressure. If petrol pressure is regulated to 3.5 bar above atmospheric pressure then effective injection pressure is 3.5 bar when the manifold is atmospheric pressure but will effective pressure will be higher when the manifold is under vacuum... If the manifold is at 0.3bar at idle (0.7bar of vacuum) then fuel pressure becomes 3.5+0.7 = 4.2 bar. This means that a given petrol injector pulse will inject a different amount of petrol depending on the manifold pressure... A given pulse length will inject more fuel when the effective fuel pressure is higher (at idle) than when the effective fuel pressure is lower (under load). The problem with this is that the LPG ECU bases LPG injector pulse length on petrol injector pulse length without taking into consideration effective petrol injector pressure, while at the same time LPG injector pressure is referenced to manifold pressure so a given pulse length of an LPG injector will inject the same amount of LPG regardless of manifold pressure (not quite as simple as that really). Ideally the LPG ECU should compensate for the changing effective petrol pressure, and it is possible with some ECU's including I believe your specific model of Stag ECU (it isn't possible with all Stag ECU's)... We can dial in compensation for changing petrol pressure not directly but indirectly, we know that petrol pressure is regulated and held constant above manifold pressure regardless of engine load so we can compensate for changing effective petrol pressure by compensating for manifold pressure.

Flow through a fuel injector is affected by changing effective pressures to the extent of the square root of the pressure, so we can calculate....
no manifold vacuum (1 bar map) so effective fuel pressure 3.5, square root of 3.5 = 1.87
0.1 bar manifold vacuum (0.9map) so effective fuel pressure 3.6 square root of 3.6 = 1.9, 1.897 / 1.87 = 1.014, so for 0.1 bar vacuum we should compensate by +1%
0.2 bar (0.8map), 3.7, 1.923, 1.029, +3%
0.3 bar (0.7map), 3.8, 1.949, 1.042, +4%
.....do the same calculation down to 0.8 bar (0.2 map).....
I set up a spreadsheet to do this for me automatically, I just enter the set fuel pressure and maximum manifold pressure (1 bar on a normally aspirated engine, more on a turbo/supercharged) and it works out all the figures for me. There's not point going below 0.2bar really because that's about the lowest manifold pressure an engine will see during over-run.
So if naturally aspirated and your fuel pressure is 3.5bar, if we do the calculation for 0.8 bar manifold vacuum 0.2 bar map we get the figures 4.3, 2.074, 1.109, +11%

That's if your fuel pressure is 3.5bar, if it's 4 bar all the figures will be slightly different. Been a while since I looked up fuel pressure on your model of vehicle.

We dial those figures into manifold pressure correction before we even begin starting the calibration or our map will always look a strange shape. Autocal never gets it even close to correct on engines that don't have manifold referenced petrol pressure. If we don't dial in the manifold pressure correction the strange shape map can work, kind of, but never great. We can set it up with the strange shape map and fuelling will be correct during cruise conditions but fuelling won't be correct for transient conditions such has changing rpm or engine load. This is because during cruise conditions pinj is very closely related to manifold pressure because manifold pressure is after all engine load and engine load dictates pinj, it's not quite that simple though because the engine has different volumetric efficiency at different rpms so compensating for fuel pressure is still better than not compensating for fuel pressure even for constant cruise conditions but the odd shaped map can work OK for cruise conditions +- a few percent of correct due to the changing volumetric efficiency. During the transients compensating for fuel pressure is far better than not compensating for fuel pressure, the engine ECU is programmed to give tip in enrichment that is correct for the anticipated rise in engine rpm, load and changing manifold pressure so without the fuel pressure compensation LPG tip in enrichment is wrong and this can be at least noticed in fuel trim differences (petrol versus LPG) following the tip in, at worst causing hesitation or even a misfire during tip in when running on LPG.

Usually the strange shape peaks at shorter pulse times than normal (you might guess this because there'll be most vacuum compensation at short pulse times), so your original map shape with a peak somewhere around 6ms is definitely incorrect because it is almost the opposite to peak at low pulse times, your original map peaked at around mid engine loads. This is exaggerated because you have the quick in response AEB injectors fitted which will push the peak even further toward the low load area than it would be with (say) slower Stag injectors fitted. This isn't a bad point about your injectors, it is bad points against your original map.

I don't know of any other installer who even thought about relative petrol pressure being a factor when calibrating an LPG system, let alone how to properly compensate for it, yet it should be a no brainer to anyone who claims to be a fuel injection field pro and all LPG installers are in that field. Most LPG maps I see done by so called pro LPG installers look to me like an amateur did them and that's not even including those that should compensate for effective petrol pressure differences but don't. Some of the manufacturers take notice of my advice when updating LPG ECU firmware / software and these days around 1/3rd of well known LPG system ECU brands support manifold pressure correction (read effective petrol pressure correction), the remaining ECUs that don't support it are missing a big trick and hugely compromised / disadvantaged because of it. I won't fit an ECU that doesn't feature it on any vehicle that has atmospheric referenced fuel pressure and these days that it most vehicles.

Send me the config file, I'll dial in the vacuum compensation, some rpm correction and adjust some temperature correction settings, then I'll email it back to you. But then you'll need to fine tune the multiplier points further because the final map should end up looking a bit smoother and less peaked towards the low load high vacuum end of the scale than it looks now.

[Rokassileika]

Sent You an email to cheapmotoring@yahoo.co.uk

[LPGC]

I downloaded it and have opened it using Stag software version 11.2.1.1 but this doesn't allow compensating fuelling for manifold vacuum, in terms of pressure compensation it only allows compensating for gas vapour pressure. There are still other things I can and will adjust in it such as temperature and rpm compensation but before I do that it's worth asking if you're running a version of software that does allow compensating for manifold vacuum? Which version of Stag software are you using?

What are your fuel trims like with the map as it is now fully warmed up at idle and at various combinations of rpm and manifold pressure, I'm asking for around 6 answers at various manifold pressures really?

[Rokassileika]

I'm using 11.2.1.1 as well. I checked my video file that I recorded when i changed my LPG map curves. Just after it goes into closed loop mode after starting the car it is something around -10% Short FT on both banks at 2.8 gm/sec MAF (The car was hot as much as I remember that time). Once i just start moving with the car i get Short FT 2 to 5% at MAF 6,50 gm/sec engine Load ~20-30%. At around 38% engine load i get Short FT From -3 TO 10%, Maf- 21 gm/sec (vehicle speed was 11 mph, forgot to observe the RPMs). 57% load i have Short FT -2% to -4%, MAF is 35 gm/sec. 71% load I have Short FT B1- 1.5% and B2- 20% MAF is 69 gm/sec. speed 22 MPH. Now if we would look at the files where I was recording on AcGasSynchro interface I have a MAP 0.86 RPM- 3500 pinj is 9.2 when should be around 11. then again- MAP 0.67 RPM-1620 pinj 5,5 when it should be ~7.

[Rokassileika]

As for what I have on the board is Maps, RPM correction, Deflection, Temp correction and Pressure correction

[Rokassileika]

This is my fourth reply, but heres what I noticed. I believe my ECU is Stag 300 ISA2. I would probably need Stag 300 Premium at least to achieve something better. It doesn't even read both banks for accurate injection times