Interpreting data. VS s3 Log

[Dylan]

Wow that's terrible. Sure the wide bands ok? What's the narrow band voltage at idle?
I've never delt with duel fuel or even gas alone I avoid it at all costs.

[MAGP]

At idle it sits around 14.7-15 and randomly leans to 16.8 or so.

It should cycle between about 14.3 to 15.1 or so. Anymore than 0.4 away from 14.7 indicates something is wrong. Likewise if it doesn't go richer than 14.7 something is wrong.

Under load it leans right out to 19+.

This is on petrol? have you made sure the MAF is calibrated correctly?

I've never delt with duel fuel or even gas alone I avoid it at all costs.

LPG is quite a good fuel, you just need to understand how it is different to petrol to get the best out of it.

[Dylan]

I'm sure it is good fuel but I've never needed to work with it. And as you said need to understand it don't really want to practice on someone else's car. But i have heard good things when it's all set up right.

If this car is duel fuel I'm wondering how the gas controls are integrated to the engine ecu? Coud it be effecting some signals like maf or air temp?

[MAGP]

If this car is duel fuel I'm wondering how the gas controls are integrated to the engine ecu? Coud it be effecting some signals like maf or air temp?

Unless it is liquid phase injection the actual injection should not be changing anything. Liquid phase does change air temp drastically.

However the way you've worded this you are, correct me if I'm wrong, talking about the actual wiring in of the LPG hardware to the ECU. The only way this can cause a change is if it has been wired in incorrectly causing some sort of feed back. To make sure no feedback occurs the LPG wiring would need diodes in the wiring for each injector.

The injectors will need extra relays after the EFI relay to control the petrol side and the LPG side when selected by the LPG switch which would then also select Map A or Map B. If this is not done it is possible settings could be wrong for the fuel being used. So to exclude this from being a problem an accurate wiring diagram or explanation would be required.

[Dylan]

Thats what I'm wondering. I've never wired any LPG before so no idea on how invasive it is.

[MAGP]

In the vast majority of conversions only the injector wiring needs modification but I have seen conversions where people have butchered other circuits.

After reading this thread a couple of times my guess is there is something wrong with measured airflow. If the engine starts out lean and gets leaner with more throttle % it indicates to me the MAF frequency is wrong and the % error increases with more airflow. 1 other possibility is the injectors, assuming they are working properly and getting enough fuel from the fuel system, are sized incorrectly.

At face value everything in this thread points to either of those 2 possibilities.

[Whyzee]

The LPG side of things doesn't interfere at all, it's a sequential vapour injection system. The only inputs to the LPG ecu are the petrol injection timings. The factory injector plugs plug into the LPG harness, which then plugs onto the injectors. No relays or mods to the engine harness. I've totally disconnected the LPG wiring, but no difference. The injectors are correct (only just been purchased - genuine Bosch).

Im thinking it must be a MAF problem. I unplug all other sensors and it exhibits the same problem - but when I disconnect the MAF (I assume in this case fueling is determined by the TPS), it richens when it should, but obviously not the right amount. The wideband has been recently calibrated and seems quite accurate. I can get good power out of it when I change the LPG map to the correct afr's. And when it's running lean it seriously lacks power and even backfires through the intake if it reaches near 20:1 under any sort of load.

I have another memcal that I can try with a different tune on it.

The dizzy couldn't exhibit these problems, could it? It's about the only thing I haven't changed yet

[Dylan]

Wouldn't of thought the dissy could contribute BUT if it's a wiring problem then who knows.
You said earlier you've tried different MAF's?
If so then it must be un measured air after the MAF but if gas doesn't have the same symptoms then?
Back firing out the intake is a good sign of a lean condition or mis timed injection. Haven't got low battery voltage?

[Whyzee]

It does the same on LPG. But I've tuned the LPG to compensate for the short petrol injector timings so it's drive able.

Yeah I've tried 5 different MAF sensors now - all second hand though

[Dylan]

Might be best to tune the petrol then too save the motor?