LPG Removal

[HuwSy]

Aside from the tank, some pipes and wires about what else is there to take out? Where do the LPG feeds link into the existing engine/fuel system? How are the cables for engine management done etc. As Im considering LPG but only if its fully reversible or I know about all the parts that need to be adjusted 1st so i can get some spares in to storage before conversion. Thanks.

[S2central.net]

AFAIK - the LPG controllers are all 'piggyback' style and the LPG injectors are different too... The system I saw running on a local AAN could run either on petrol or LPG as the OE injectors, loom and ECU all remain... When you have LPG in the tank - it runs on that. The LPG controller must be mappable - dunno if based on MAF, speed density MAP or what.

[Stefen]

LPG delivery is based on its own MAP sensor. The LPG wiring is connected to each injector, so it can cut the power when switched over to LPG.
The LPG injectors are plumbed to nozzles which are drilled into 5 holes in the inlet manifold, just before the head.
If you had a spare inlet manifold you could remove everything else.

You can get LPG systems that switch to petrol when the throttle is fully pressed or above certian revs. This gives extra power compared to LPG.

Be careful though, as my Toyota has this done and wore the valves up into the head (as LPG has no lubrication). This is okay with hydraulic lifters, but with manually adjustable ones you need to take the cam cover off or shims (as in the Toyota) it's a timing belt off job and cams out every 10K. I was had!

[prj]

There are different types of LPG systems - some are more standalone than others.
Most systems tap into the injector signal and match the IPW supplied by the stock ECU proportionally.

That said, running LPG on a turbocharged car without having a full remap of the stock ECU to accomodate it is usually a very bad idea.
Because LPG burns much slower, it needs lots more timing advance. With timing advance calibrated for petrol, you have LPG burning at the valves and in the exhaust manifold at higher loads and having very high EGT's.
And piggybacks can't really advance your timing - only retard it. So there's the problem...

The difference is less pronounced on normally aspirated engines, because they can run lots and lots more timing, so you don't get so high EGT's.

[Jonnybravo]

Any kit is reversible, nothing that bad about swapping the kits over except using some common sense for where you route things.

Inlet manifold could ofcourse be either bunged or welded back up.

Most Toyotas and japenese cars in general do not like LPG, if yours failed that quickly then I'd imagine it would of fallen into the category of not being suitable for conversion from the companies point of view who I last worked for.

The problem with LPG like anything is that there are some very cheap and nasty kits out there, I did most of my training with Prins which personally I found the best system out there, ( after they sorted out a their emulator and reducer niggles ) the mapping system is nothing like as complex as other systems but you could never argue with the results and reliability on anything it was fitted to which is more than you can say for some other systems.

Good info from Dimitri there as ever, LPG on a capable ecu is a great way forward but understandably costs put people off. Ford are running a if not a few LPG powered Focus turbo touring cars backed by Mountune and I believe Prins so proof that it can work on a well stressed engine.

[prj]

Most turbocharged cars will actually make more power on LPG, because of the higher knock resistance, but it is important to keep an eye on EGT's to prevent damage to the valves, head, manifold, turbo...
The best way to do this is through a switchable setup connected directly to the LPG control unit.
So that you are running one map on LPG and the other on Gasoline and it's fully automated, meaning the moment it switches to LPG it switches ignition and fuelling as well and vice versa.

I haven't done this yet, but I am going to try it out on my friend's Audi V8 and see how it works out.
Fuel economy should get a lot better with more timing advance and correct AFR as well. As fuel cost is usually the prime reason for using LPG, it's a good thing

[S2central.net]

Would be interested to see how you get on with that... would love an S8 someday in the future, but it would have to run LPG to make it anyway viable but I would hate to be shortening engine life or performance as a result.

[prj]

As I said, it's not that bad on a N/A car.
Most modern production N/A engines run 30+ deg timing on torque peak - compare this 12-13 degrees on stock AAN plus the higher EGT's in a turbocharged car and you have an issue.

On a N/A car more advance will be needed mainly to improve fuel economy and performance.

[HuwSy]

Thanks for all the advice everyone. Much more to consider about this than i had thought. Although seems my 1st step is to get a spare inlet manifold so i can roll back all the changes if i ever need to.

@Stefen I like the sound of automatically switching between petrol and LPG at revs, although as @prj says some turbocharged cars make more power on LPG how would I know if this car is better suited to staying on LPG or auto switching back to petrol? Also do you mean more bhp or more torque? As the latter is more important to myself

@prj is the friends Audi your looking to convert a turbo one? Id like to know how this goes too. And what kit is used or what you would recommend to achieve this advance on timing and switchover. Does this require a different reprogrammable ecu for the petrol side of running too?

Thanks.

[prj]

@Stefen I like the sound of automatically switching between petrol and LPG at revs, although as @prj says some turbocharged cars make more power on LPG how would I know if this car is better suited to staying on LPG or auto switching back to petrol? Also do you mean more bhp or more torque? As the latter is more important to myself

Both. However, you need a remap to take advantage of it (and preserve your engine in a turbocharged application).

@prj is the friends Audi your looking to convert a turbo one? Id like to know how this goes too. And what kit is used or what you would recommend to achieve this advance on timing and switchover. Does this require a different reprogrammable ecu for the petrol side of running too?

That car is normally aspirated.
You are making a mistake thinking that the LPG is run by a standalone ECU - it is not.
It is just a piggyback, it still runs off the original injector signals and all ignition is done by the stock ECU!

If you run a turbocharged car on LPG without remapping the ECU and without MAP based cut-out (so that it switches when the turbo starts spooling or similar), sooner or later this will happen (pics borrowed from an A4 1.8T discussion):

[HuwSy]

You are making a mistake thinking that the LPG is run by a standalone ECU - it is not.

If you run a turbocharged car on LPG without remapping the ECU and without MAP based cut-out (so that it switches when the turbo starts spooling or similar), sooner or later this will happen (pics borrowed from an A4 1.8T discussion):

Rats, can the existing Audi ECU be remapped to suit or do i need a new one to be able to map it?

Thanks

[prj]

I am assuming your car is an S2?
Yes, it can, talk to MRC for example. Or I could do it, if I wasn't so far away

You'll also need some additional wiring and a switchable setup, which is wired into the LPG control unit, so that when it activates LPG your stock ECU switches maps.

Properly tuning for LPG on a turbocharged car requires a full cell-by-cell load tune on a load bearing dyno.
I'd personally say it's not worth it.

[mouse]

Does anyone here know if a petrol engine can be converted to LNG?
I know diesel motors can be (although I think current costs make it mainly viable for buses and trucks) .

It would be nice to one day fill up a daily driver from a gas point at home (with untaxed gas )

[prj]

If it can be injected, ignites from spark, and has sufficient octane - I don't see why not.
I think UrS4boy can chime on this fact - I have no experience with LNG or CNG, so I am not going to guess.

[HuwSy]

@prj Yup its an S2, ABY. You cant be far away if your "in your ECU" ha. May leave it for now until theres a few proven examples working or look into E85 if only for the thought that im fueling with basically alcohol.

@mouse my understanding that LNG is lower octane from reading previously but would be interesting to find out if its viable. Although i spent ages trying to wouk out how much a litre equivalent would cost converting the volume used by energy firms and pressure to no avail so i have no idea if it was cheaper or not at the end of it all.