Tx4 taxi gen3 Vx 2 litre ecotec

[Fairwaypete]

Crank no start issue have got petrol coming up also lpg no spark at the coil packs but have power at the coil connections , got live data at the crankshaft sensor and cam sensor also have no fault codes or eml lights was thinking maybe a broken wire any ideas

[LPGC]

Is this the same taxi as in your other thread that would run on petrol but didn't want to switch to LPG unless you turned the engine off and restarted it, or is it another one and if so are you getting involved in fixing the LPG systems on taxis?

[Fairwaypete]

No this is a problem of mine that it broke down suddenly under normal driving conditions.

[LPGC]

By 'petrol coming up also LPG' do you mean you there is fuel pressure on both? The pressure could be residual even if the petrol pump isnt running and the LPG solenoids are closed.

Don't know if there's an immobiliser but that might be a good thing to check since you've found the crank sensor and cam sensor are working and there's power to the coils.

Is there power to petrol injectors / LPG injectors? Do either/both sets inject fuel? Is it trying to start on LPG (LPG injectors pulsing but petrol injectors not pulsing)?

Don't know about your specific setup, sometimes the LPG ECU connects to the cam sensor to get an RPM reading, sometimes it gets RPM from a coil pulse or just from petrol injector pulse. If it gets it from the cam sensor then if anything went wrong and it shorted that signal out it could prevent the petrol ECU seeing the signal... but you're seeing these signals on OBD so the petrol ECU must be seeing them OK.

[Fairwaypete]

Thanks for that will look into it further

[LPGC]

There is another thing to check.. If the diapghram inside the LPG reducer is busted and if there is a vacuum connection from the inlet manifold to the reducer, then gas from the reducer can leak into the manifold, so particularly if gas solenoids are open it won't start on either fuel because instead of the engine getting fuel and air the engine will get fuel and fuel. But if this happens you can often smell gas in the engine bay (and in a bad case it will come out of the air filter). The same could happen if an LPG injector were stuck open.

[Fairwaypete]

It’s got a new Brc genius vapouriser 1500 fitted recently the scs delta gd 16 Ecu has been refurbished as there was a misfire on gas but not on petrol all the gas filters have been changed the issue is the taxi broke down and there is no spark at the coils tried a spark plug in it no code showing up no blown fuses petrol pump is running gas solenoids are triggering rpm and cam live data showing up on laptop diagnostics

[LPGC]

I'm not familiar with the TX4 taxi conversions. Usually when a vehicle is converted aftermarket it retains its original petrol ECU and a separate LPG ECU is added, petrol injector pulse wiring between the petrol ECU and petrol injectors is cut (4 wires on a 4 cylinder) and a wire from the LPG ECU is connected to each side of the cut wires (8 wires) so the petrol injector wiring is routed through the LPG ECU. When running on petrol the LPG ECU connects the wires so the petrol ECU injector wiring is connected to petrol injectors, when running on LPG the LPG ECU disconnects the wires to disable the petrol injectors and places a dummy load on the petrol ECU side, the LPG ECU reads the would-be petrol injector pulse duration and uses that as basis for calculating LPG injector pulse duration.

The taxi setup might be different, the function of the petrol ECU and LPG ECU might be combined into the single ECU? This does seem to be the case because otherwise to cure a misfire that only occurred on LPG not on petrol you wouldn't be sending off the petrol ECU you'd be sending off the LPG ECU. Either way it seems a good bet that the refurb ECU is broken again.

Or if it does have a separate LPG ECU (or at least some sort of separate petrol injector on/off switching unit) with petrol injector wiring routed through it similar to what I described above the problem could be due to a fault with that switching unit. Most modern LPG ECU's have the petrol injector switch built-in but there have been plenty ECUs that used external petrol injector switching/emulation units. Obviously if you unplug a unit that makes the connection between petrol ECU and petrol injectors the engine won't run on petrol because the petrol injectors will be disconnected and if that same unit is used to read petrol injector pulse lengths to calculate LPG injector pulse lengths it won't be able to run on LPG either because the LPG ECU won't be able to read petrol injector pulse lengths.

If you get it fixed so it runs OK on petrol but the misfire is still present on LPG (or misfire re-occurs in future when running on LPG) it would be a good idea to check the LPG injectors before sending off the ECU for fixing, you can check injectors by moving electrical connectors and piping from injectors to manifold (to change which injectors serve which cylinders) to see if the fault stays with the same LPG injector or same ECU channel and wiring.

[Gilbertd]

What ECU is being used for fuelling is pretty much irrelevant. He's got no spark but has got a signal from the crank position sensor and the cam sensor, so they will be providing pulses from which the ignition pulses are derived. Depending on which ecotec engine is being used it may have an ignition coil block and HT leads or it may have individual coil on plug coils. In both cases, for there to be no spark on any cylinder it needs to something common. That might be that the ECU is not sending the pulses to the coils or it could be something as simple as a lack of power to the coils. They will all have, irrespective of what type it uses, a common ignition switched supply to them. Is that there? The ECU will then supply a ground pulse to the coil relating to a particular cylinder so the coil generates the spark. Is that present? A graphical meter will be able to show that immediately.

Running on LPG needs a better spark than running on petrol so a failing coil/coil pack or a bad connection in the supply would cause that.

[LPGC]

He did say there's power to coils, maybe it is the ECU

[Fairwaypete]

It has a custom built Ecu and the old original taxi ecu has been removed it’s a dual fuel Ecu that’s switches via a 4 pin round Brc gas switch

[Fairwaypete]

I actually swapped over the ecus with a known working unity

[LPGTX4#1]

Have you got this going?

[Fairwaypete]

Yes it was a broken wire at the back of the engine where it had been chaffing

[Fairwaypete]

Hi I have an eml light P0134 upstream 02 sensor replaced the sensor with a new Bosch part the light stayed out for 3 weeks the wiring looks fine the taxi drives fine

[LPGC]

The code points to 'no activity' which means the mixture signal that the ECU receives from the lambda/oxygen sensor isn't changing. It doesn't give any information about whether the signal being read points to lean or rich mixture etc, only that the signal isn't changing. If this happens only when the engine is running on LPG it could be because the engine gets too lean or too rich mixture for long enough to trigger the error code. That could be caused by a problem with a pressure reducer (e.g. leaking gas through its vacuum connection directly to the engine inlet manifold causing rich mixture), or worn / dirty / sticky LPG injectors, or incorrect LPG calibration (the length of time the LPG brain is pulsing the injectors for), or maybe something else.

[Fairwaypete]

Thanks for that the Brc injectors have done over 100,000 miles it had a new vapouriser recently

[LPGC]

Could be that the recent new reducer is outputting a different pressure to the old one. I don't know if your reducer is BRC, BRC reducers usually come preset at close to either 1.2 or 1.5 bar, the pressure can be ajusted by turning an allen socket but you won't be able to read the pressure or know what the pressure should be without being able to talk to the ECU.

[Fairwaypete]

I have the software on My laptop for the taxi and I have access to the live data the lpg pressure is roughly 1.5 bar the motor run s fine apart from the P0134 light the reducer is a Brc genius 1500 thanks for your help