switch back to petrol problem

[bonny]

https://photos.app.goo.gl/ngHb99CYEexjYNjq6

I have a new lead (thanks to Tinley for speedy service) and after failing to connect with an AEB download, got linked up with an Emer download.

If the above link works, you'll see I have a check box setting (currently enabled) for "switching to petrol for low gas temperature" and set at 15C. The basic switchover is set to Reducer at 30C.

I suspect it is the combination of the two which is causing my car to switch to gas as it warms, then switch back to petrol.

That being the case, what should I change?

Increase the initial switchover temperature and leave the low temp switch back enabled?

Turn off the switch-back?

I note that in the software, although the reducer temp hit 30C and the car switched to lpg, the gas temp indicated was lagging significantly behind the reducer temp. That suggests to me the switch over is set too low, I need to take off the switchback, or set the switchback temp even lower.

Your guidance much appreciated.

As a follow up, in the emer s/w if I make a change to the switchover, how do I save that into the running config/write that to the ECU? I can save to a file on the laptop, but not obviously load a changed config. When I exited the s/w and reloaded, I had the same settings as when I started....

Thanks
Paul

[Brian_H]

Start by having a look at your reducer plumbing. Top coolant system up, and see if the reducer is getting hot. It's possible its something as simple as an airlock, in which case slackening the highest hose and letting any air out might resolve it.

Otherwise it may be a case of looking at the plumbing to see if it's been connected to somewhere unsuitable.

On the software front not sure offhand, some of the older AEB software you needed to press the return key after changing any values to actually get them to change. Not sure what the emer software is like but it may be that.

[Brian_H]

It might be worth lowering that gas temp switch back, just reread your post and realised it was gas not reducer temp. But check how hot the reducer is getting at the same time, you should see it getting up to around 60 degrees at least once the engine is fully warm. If it's running cooler then it may be a plumbing issue. Check the actual reducer temp yourself as well as what the software says. It should be hot to the touch once engine temp is up.

[LPGC]

What vehicle is this and what LPG parts (besides the Emer ECU) are fitted (reducer and injectors)?

Does the problem occur when you put your foot down shortly after it has switched to gas when still warming up on a cold morning?

With the system set to switch at 30C if you put foot down a bit shortly after it's switched to gas it will see cold vapour temps and the reducer temp will fall below 30C.

The 15C switchback for gas temp is high, 2C would be more like it.

Some vehicle's heater circuits warm up much quicker than others, some reducers have better heat transfer (hot water prevents liquid gas from the tank remaining a liquid inside the reducer / hot water heats the gas output.... not quite the same things) than others and some injectors have performance effected less in cold conditions than others. Standard ECU temperature correction settings are not usually very realistic - as far as physics and injector performance are concerned only gas vapour temp needs compensating for, not reducer temperature, but some systems correct for both gas vapour temp and reducer water jacket temp by default... probably because it is expected that the gas temperature reading won't be very accurate because the vapour temp sensor is at the end of an injector rail rather than inline in the gas feed to the injectors. Some systems allow pre-warming the injectors while the engine is still warming up before it switches to gas, which gives the injectors a bit of a head start in terms of accurate performance when the engine has first switched to gas and is still warming up.

You may want to increase the initial changeover temp and decrease the 15C gas temp switchback as mentioned above. Depending on setup I would also likely expect to change some of the settings in 'adjustments' for temperature compensation to get fuelling correct during the warm up stage.

[Brian_H]

Taken from his other post to give some info, still need the other info though.

viewtopic.php?f=28&t=16718&p=120361#p120361

Hi folks,

I recently bought a Mercedes ML500 Sport which generally seems to run well on the LPG conversion it has, until more recently I notice it switching back to petrol early in a journey.

So, 2 questions:

1) What do I need in terms of lead and software to have a look at the setup and do some diagnosis?

The ECU is branded EMER, but I can see the details on the back stamped as AEB 2568D (I will try to work out how to add photos later) and it has a superseal (?) 4 pin connector on a fly lead from the ECU which I assume is for the diagnostic/setup connection.

2) once I've got a workable diagnostic setup, what am I looking for?

The car starts on petrol and I get a mile or so down the road, switches to LPG, no problems, all appears fine. I checked this morning just running in the workshop and the vapouriser is getting good and warm.
About a mile further on the switch shows the lpg light flashing and I'm back running petrol. No alarm for low pressure and no indication of a problem.

If I stop and restart the car, it will switch to lpg a bit down the road, then indicate I'm back to petrol again a bit further on. My local run is into town for shopping. When I start the car after shopping, it switches to lpg and stays on Lpg all the way home.

So, it's not a huge deal, but its a bit annoying and I'd like to sort it.

I did recently have to change the thermostat which meant draining some coolant and have had to top up coolant a couple of times recently. I wondered if there was air in the system/vapouriser preventing it heating up, but that did not seem to be the case when I tested this morning and I think that would impact the initial switch over to lpg rather than causing a switch back, but I may be wrong.


Your input would be very welcome.

Thanks
Paul

[LPGC]

Cheers Bri.

I've still got an AMG ML 5L V8 in the yard.

Certainly if changeover temp is set at 30deg on these motors the reducer and gas temps can plummet soon after changeover if the throttle is only tickled... with any reducer really because the water flow rate is only average and the decent sized engine can get through a lot of gas. Nothing too unusual about plumbing on the 5L V8 though, unlike the 6.3.

I expect this will have a Palladio reducer fitted which is a decent bit of kit with good water to gas heat transfer.

[Brian_H]

Sounds like the best bet would be to play with the temperature settings and monitor for what seems to be keeping it warm enough as you said above. What does he do to set the settings as asked above - I don't have one of the ecus to try it with, but it looks like its like the old method of pressing return after changing a value seems to be whats required?

[bonny]

Thanks for the input gents, all really useful and I think it is the temp difference between the gas and the vapouriser that's at the root of it and as Simon says, if that is the case, the cutback temperature is set way too high.

Yesterday, I managed to switch off the switchback setting and the car drove fine on a 7 mile run to town without cutting back to petrol at all once it had changed to lpg. When I checked the vapouriser temp by hand, it was too hot to touch, so the stated temperature in s/w at that point of 70C was probably accurate and reinforces the notion that its s/w config issue rather than plumbing, as the vapouriser is getting good and hot.

When I stared from cold with the cutover config screen up, once the vapouriser reached an indicated 30C, she switched to gas, but the software was showing a gas tempo of only 10C at that point, so this seems to be exactly what Simon was saying.

I haven't had a chance today, but will switch the low gas temp setting back on and set to a more appropriate value. The car is running well on gas and the swtich-over itself is not noticeable at all, so I think the general setup is pretty good just this changeover config needs getting right.

I'll feedback on the final changes. Thanks again gents.

[LPGC]

Some of the more recent AEB ECU's feature this switching back to petrol for low gas temps (as Bonny's does) but they don't allow you to set the minimum engine load (or rpm / pinj) at which the setting becomes active.

Bri, your Nevo ECU will allow you to set either/both a gas vapour temp / reducer temp at which the engine momentarily switches back to petrol and set individual minimum engine loads at which the engine will momentarily switch back to petrol. They are handy features because they allow setting a comparatively very cool changeover temperature (run on LPG sooner after starting to save more money) but with the safeguards of preventing problems due to injector performance issues (slower response when chilled with very cold gas vapour) or reducer issues (spitting liquid gas out causing high vapour pressure as liquid evaporates in rubber vapour lines), especially when used in conjunction with gas injector pre-heating settings. Both switchback temperatures (for engine loads greater than settable values) can be set at a temperature that is higher than changeover temperature. I often set changeover temp to 25 or 30C, reducer switchback settings to 25C at 20% engine load and vapour temp switchback to 0C at 20% engine load. 20% Load (according to the gas ECU) is a higher engine load than we might expect. I enable injector heating for ignition on reducer temps cooler than 30c, might as well use the injector heating function as it doesn't lengthen the time between starting the engine and switching to gas.

Currently got a 2003 L322 Rangerover (4.4 BMW engine) in the yard. Already converted to LPG with a Bigas system, the owner had a replacement engine fitted but the engine guy cut some of the LPG wires and left the rest bundled up in the ECU/electrics box, I was tasked with getting it working again. Took me little time to reconnect the wires etc but then I found it was set up to idle on petrol and the gas injectors at mid to high loads were pulsing for only around 3/4 the duration of petrol injectors. As I expected when I set it to idle on LPG it immediately ran rough (or stalled if it was cold) at anything approaching idle. Not surprised because the twin reducer was pushing 1.7 bar and the Bigas injectors don't like metering fuel accurately below around 3.8ms, the injectors fitted have the big nozzles and the big nozzles combined with high pressure were meaning the injectors would have to pulse for well below 3.8ms at idle and low loads. It was also set to changeover to LPG at 60C. All these things combined meant the owner didn't previously save much money by running on LPG because it was running on petrol far more often than it should and always at low engine rpms. I first turned pressure down to 1.2 bar and it ran much better, even idling OK on gas when warm but still idling running rough when cold and ginj still lower than pinj at medium to high loads. Turned pressure down to 0.9 bar and recalibrated again and now it seems good but I had to set a small petrol addition above 4500 above 12ms pinj because pressure falls to switchback to petrol pressure at high loads. The installer should have fitted slightly smaller nozzles really because engine cylinders are only 550cc and the petrol system idles with pinj of around 3ms, should have anticipated that they'd want the reducer to be pushing a bit more pressure to prevent switchback at high loads and that this along with the other factors should imply smaller nozzles.... Then I wouldn't have had to set a petrol addition. But at least now it will run on gas much more of the time than it probably ever did since the system was fitted and smoother with better fuel trims. I have since disconnected the gas vapour temp sensor and soldered a 1K resistor in it's place (so vapour temp reads constant 62C.. I couldn't find my box of electric components so I robbed a 1K resistor from a broken old 4cyl AEB ECU) because the gas temp sensor is in the body of injector rails where it is more likely to pick up underbonnet heat (or cold) than actual gas vapour temp and this meant it was leaning the mixture far more than it should for a long time during engine warm-up. The system compensates mixture for reducer temp anyway and for an extended period during warm-up the combination of over-leaning for reducer temp and over-leaning for gas temp meant it was leaned right off during warmp-up, also causing the gas injectors to be pulsed for well below 3.8ms and stalling before fuel trims could react.

[bonny]

All, just a closing update on this one and to says thanks again for the feedback which helped me to get it right reasonably quickly.

As per your guidance, I dropped the switchback temperature down to 5C and increased the initial gas switchover temperature ( I can't recall exactly but think I went to 40C). The car now switches to gas within a reasonable distance of home and doesn't cut back to petrol. Just as well as in the last 6 weeks petrol prices seem to have gone mad.

Thanks all.
Bonny

[LPGC]

Thanks for the update, very good!