Stag LPG, running lean and very hot gas.

Hello Everyone,

Sorry for me writing in English, I explained in this topic Is this okay?
and there were no: "NO, don't do that!" So I thought I'd give it a try.
Reply in German is okay with me; I think I can translate it enough for myself.

Now the problem; since a few weeks I have a BMW E60 523i automatic and it has a STAG 300 Premium build in.
Now here in the Netherlands, there is almost no LPG company that wants to work on it as they don't know the brand.
When running on LPG, the errors of being lean pop up (lambda = 1.003) and the power is very low; I can't get the car to drive more than 100 km/h.

I bought a cable with software to dive into the ecu of the LPG system, set the pressure on the converter (is it?) to 1 bar and its a bit better. There seems to be no information as to what the pressure should be, so I presumed 1 bar out of the things I could find.
On petrol, the power is okay.

In the "Dry-gas" hose to the engine, there is a vacuüm meter and gas temperature meter build in.
The temperature of the gas is read out as 72 degrees celsius.........that seems a bit high, doesn't it?
But I have no idea how bad that works out on the running/power of the engine.
I also have no idea how to get that lower.

The injection times seem okay; there is a multiplier and it does a x 1.2 at lower injection times.
At higher petrol injection times, the multiplier goes lower, even beneath 1, so I think I should put that up a bit, right?

For me, my thing is: when I dive into such a problem, I think a lot and get stupid I don't see the obvious anymore.
I mean; how hard can it be; injectors are opening and a bit longer than the petrol injectors, pressure is okay (measured after the filter, filter is new) and so: it shouldn't be lean.
Except for the injectors itself.......I'm thinking of that right now, writing al this.
There is no brand on the LPG injectors, I noticed when I got them out for cleaning in an ultrasone bath (nothing coming out of it, they seem new too).
I looked at the opening; they also seem wide enough (2,4 mm) for a 130 KW 6-cilinder.
In the software of the LPG system, one has to choose a brand of injector and mine already says "AC-DIAC 3 ohm".
So, the ohm seems important; the ecu needs to know how "fast" an injector can be.
Measuring the resistance of the LPG injector when hot, gave exactly 3 ohm, so that should be good.

Now I have no clue why it is running lean anymore. Gas temperature?
Is there someone with knowledge or info on the STAG systems?
Any help would be very much appreciated, thanks in advance.

 

Ah, yes sorry: it is a N52 engine.

 

Okay, that could be to smaal then? I will up the pressure to 1,2 or 1,3 bar.

For some reason, I didn't get the lines; there is only the multiplier line in that screen. I do have the manual for how to install and how the program works, but I can't get clear is to how I am supposed to get those lines.
Will work on that some more and post it when I found out.

 

I do see the manifold pressure in the bar, but no line.
Also, it is visible in the start-up screen, but I can't remember the value it was. At the moment, I can't look it up again; I'm not feeling well and its so hot outside. That may not a smart move for me, so the doctor said.

But no vacuüm due to the Valvetronic seems right.
However, I was under the impression the system didn't really need a manifold pressure signal to calculate the engine load? I mean; it mimics the signal of the petrol injectors, right?
On the other hand, I can adjust the multiplier: when petrol injects longer, the load is higher, right? Then LPG doesn't do enough, so I set the MP higher on higher petrol injection times and look up in the LTFT and STFT if I'm about right.

You mean that, did I understand correctly?

 

I had to think about it, but there is an angle I had in my head the whole time and I just now realise I did not mention it here; sorry about that!
The thing is; when I floor the pedal, it has even less power. Making it come back again, gives some more power again.
So in my head it is: more throttle, more air intake, "same" lpg quantity and thus: more lean.
That was the angle I was coming from and therefore I thought to upper the MP when higher injection times (= more throttle I presume) happen.

But you are right: I will increase the pressure first and see what happens.
I will get it as perfect as I can get it and then - if needed- I can always mess around with the MP a bit.

Do you think the LPG temperature of 72 degrees celsius has something to do with it too?

 

Sorry for the late reply guys, haven't been well. Stil am not well, have some serious medicine and not allowed to drive at the moment.
So, I did get the map, but only standing still on the driveway......

What occurs to me, is the map is at 0,94 in the screen, also in the "corsair" and does not go down at all. That must be because of the Valvetronic I presume?

The car was not completely hot at the time of the picture, but when it got hot, the pressure dropped and I had to give it almost a complete turn counterclockwise to get it to 1,2 again.

The fuel trim is about -7 but when I keep the rpm at 2500, the injector time is the same (even just a bit lower, I set the same MP range for that) and the trim is -30
So I made a dip in the MP line between 2 and 8 ms petrol injection time; when driving on the motorway, the times will be in that range and it the trim should be more okay.

But some things bother me:
- how can the gas line be lower than the petrol line?
- how can there be dots on the lower parts when the map is so high?

 

Sorry guys, I wasn't stubborn or hardheaded when I said I had to think about it.
That was just; I had to think what you meant.

On hollidays now, big gasleak on the dry gashose from the reducer again! Had to buy me some tools to make it proper this time and cut a section off. Wow, what a lot of gas that was!
Btw, indeed, mp higher didn't work, pressure up did!

 

Oh, that would be an old line you mean?
So I have to make myself one, let it "record" somehow, right?
I will try some more to get a decent line.
Thanks!

 

Sorry guys, its not that I ignore the problem of the system not being able to cope with the Valvetronic!!
The thing is; this is SO bad, that can't be how it was when it was first build into the car. It will never be perfect, I understand, but sometimes not even being able to reach a 100 kmh, can't be right.
At the moment, a new system is not in the cards (or wallet for that matter) and I am trying to get it halfway decent, so I can take it out on the road.

Meanwhile I have been driving with the laptop on it and tried to adjust the mp to the fuel trim.
What seemed weird is that the first bank is completely different to the second: +25 to -8 for instance.
I also see the petrol injection times for all of them the same, but a way higher injection time on lpg for the first 3 cilinders......
I thought the multiplier worked for al 6 cilinders, right?

It is pretty weird, I don't understand anymore.
Apparently the fuel trim works on the multiplier too?
Per bank?
I have to save up for a new system; this one is weird......