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[Peter13]

Gents,

I have got a Technology Gas(same as D.T Gas) LPG system with Valtek rails in my 3.0. It has always had performance and MIL issues, in the beginning the car wasn't the best on petrol either. After solving every issue on petrol it seems to be an endless hassle to set the LPG correctly. I have just visited the shop where it was installed last week where the filters got replaced and I asked the guy to remap it. It has driven 600kms on petrol before. After doing the filters and the mapping I was quite satisfied for a while. I got the power back and there was no MIL, but only for 300km long
What I see:
- some minutes after it reaches the normal running temp it lights the MIL during modest acceleration(sometimes started at a gearchange, or is it a hesitation? - can't decide), MIL usually goes inactive when releasing the pedal

• O2 block learn map on bank1 went up to 155 (does it mean this side is running lean?)
• O2 block lear map on bank2 is 136
• the O2 integrators are moving between 125-130 on idle, I assume that is the normal

I think I'll try to record a log today on the way home to see what exactly happens before it lights the MIL.
Any other suggestions?
Thank you.

[feeutfo]

Assuming its a multi point system such as the stag we use here, sounds like the injector novel sizes are incorrect. TheBoy is familiar with Blm's on this ecu, and will probably tell you what the optimum figure should be, but basically the LPG mixture is off and the ecu is applying too much correction to get it right because the nozzles are the wrong size.

The installer should have sorted this for you apart of the instal.

[Peter13]

It starts from 5ms when idle(3ms on petrol), and it doesn't reach the fully open even on high revs. I think that is correct.
I'm suspecting the injector jets are in wrong position(too far from the head) and the system is disturbed by the EGR. Let's wait for The Boy's opinion.

[feeutfo]

See the guide index below in my signiature for LPG install info for v engines.

The nozzles need to be right next to the petrol injectors on the inlet manifold under the plenum chamber.

Sounds like they have cut corners and drilled holes in the plenum or such like?

[Peter13]

I'm pretty sure that mine is drilled into the inlet pipe somewhere around the middle of it. Not like this:

[Kevin Wood]

First things first - what codes is the engine ECU throwing to light the MIL?

It's probably going to be an issue with the mapping of the LPG ECU, TBH. Did the guy give it a decent road test, adjusting the map and checking fuel trims or did he just run through the auto calibration at idle?

Did he also check and adjust the vapour pressure and make sure it's not dropping off under load?

Fuel trim at idle is perfect - around 127, so no problem there.

Unfortunately, unless you can get hold of a comms lead and the software to talk to the LPG ECU you're reliant on the LPG guy to diagnose it.

[Peter13]

Hi Kevin,

the stored code is: 13 -O2 sensor open circuit (Bank1)
The O2 sensors are working fine, never seen any trouble on petrol.

However the guy went for a short (3+3km) drive, he didn't understand when he asked about the fuel trims and I told him the O2 integrator actual and the block learn values. He was expecting the rich/lean value in %, but I still don't know how to translate e.g. 155 to by how many percentage it needs to be richer/leaner to stay around 127.

Luckily I have got the proper cable and software to look into the LPG ECUs settings, but what should I look for?

Thanks.

[Kevin Wood]

OK. The fuel trims reported by these ECUs are not in percent but an 8 bit value where 127 is 0%. Below that, the ECU is reducing fuel and above that it's adding fuel, so 127 is the "aiming point". Sounds like it's spot on at idle but maybe it's out somewhere else on the map.

I would take it out for a drive watching how these vary on petrol, then again on LPG.

I'm not familiar with that system but I would be looking initially at the following parameters in general from the LPG system:

Vapour pressure - typically this should be around 1 - 1.5 BAR. Check it's stable when running on LPG and that it doesn't reduce too much when accelerating flat out (it might drop 0.1-0.3 bar typically).

MAP - Typically 0.3 at idle and around 0.95 - 1.0 at full load.

Temperatures -
Reducer temperature should follow coolant temperature
Vapour temperature maybe 10 degrees above ambient when driving. Feel the vapour pipe and see if the temperature reading is plausible

RPM - follows tachometer on dash.

If the basics above loom OK you need to have a look and see if the map needs a tweak. This is where systems vary. Typically most allow you to compare injector pulse widths on petrol and LPG. See if you can spot any areas where these differ and adjust the map to correct. You can also observe the fuel trims in the main ECU to work out where it needs tweaking.

[Peter13]

As far as I remember I have checked all of these points a half year ago based on your very good guide and didn't find any shortage. I'll check again one by one.

Fuel trims:

• Does anybody know what -+% percentage is covered by the 0-255 range of the trim? I hope it is lineary scaled at least:)
• If I look at the actual O2 integrator actual value, let's say it is 135. Does this mean it is richer than the desired 127 (and will move the trim to below 127 in long term) or vice versa: it shows the actual trim, not the resulting enrichment?

[Kevin Wood]

O2 Integrator value is a real-time value that's continually updating based on lambda sensor output IF the engine is in closed loop running. It allows a relatively small range of adjustment to occur instantly based on engine operating conditions.

The other values are long term values that are calculated based on the average Integrator value when running in that phase of engine operation, and stored in non volatile memory. In other words, if your integrator is averaging 135 at idle, the idle trim is increased so that every time the engine idles, that value can immediately be applied to get the engine running close to correct, and the integrator will then offset from there to make any small adjustments required.

Long term values are more about correcting for long term changes in the system - wear, small changes between fuelling accuracy at different altitudes, summer and winter weather, etc.

Of course if an LPG setup is slightly out in a particular combination of engine speed and load, this will, over time, cause the long term trim for that phase to wander off.