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LPG Kit on my 4.6 RRC

1514 Views 6 Replies 5 Participants Last post by  jsp, 
T
Hello all,
Any advice would be appreciated regarding my LPG kit.
I have fitted a rebuilt 4.6 engine into my 1994 LSE in place of a very poorly 4.2.
It has an LPG kit on it that works briliantly to a point. It idles perfectly and revs freely all the way to the red line when parked but under load if i "boot it", it won't rev past 4200rpm. Lower down the rev range it has plenty of torqueif i ease back and let the revs rise slowly it will rev to 4800rpm.
It runs perfectly on petrol using the standard 14CUX ecu from the 4.2.
I am thinking that it is probable the vapouriser isn't capable of delivering enough gas to run the 4.6 at full chat. Does this sound right or am i overlooking something daft?
It is a slightly vague question but can I just swap the vapouriser with a higher capasity one or is it more involved?
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A
TerryG said:
Hello all,
Any advice would be appreciated regarding my LPG kit.
I have fitted a rebuilt 4.6 engine into my 1994 LSE in place of a very poorly 4.2.
It has an LPG kit on it that works briliantly to a point. It idles perfectly and revs freely all the way to the red line when parked but under load if i "boot it", it won't rev past 4200rpm. Lower down the rev range it has plenty of torqueif i ease back and let the revs rise slowly it will rev to 4800rpm.
It runs perfectly on petrol using the standard 14CUX ecu from the 4.2.
I am thinking that it is probable the vapouriser isn't capable of delivering enough gas to run the 4.6 at full chat. Does this sound right or am i overlooking something daft?
It is a slightly vague question but can I just swap the vapouriser with a higher capasity one or is it more involved?
Click to expand...
Try http://www.lpgforum.co.uk/ they might be able to offer you more specialized advice :thumb:
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p38arover
Is it an injected or venturi system?

What vaporiser are you using? As you surmise, the vaporiser may not be big enough for the job. The Landi Renzo one I had on my previous LPG system was rated for high power engines. A recommendation (for a venturi system) is the OMVL R90/E which is a two-stage converter
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jsp
sounds like Ron and you are on the money, my 4.6 with a single point vaporiser system revs freely but underload goes weak above 5000 RPM, mines got a 5 litre Holden commodore v8 mixer on it.
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V
TG.

Sounds like your 4.2 ECU isn't calibrated correctly for the 4.6 drop-in ! This might be a case where you floor it, the ECU replies by going into 'open loop' mode and isn't able to supply enough oxygen through the earlier 4.2 straw if I read this correctly.
By backing off and understanding your revs rising closer to 4800rpm, this means the ECU is operating in "closed loop" mode by matching the volume of air with the corresponding amount of LPG to initiate throttle response and complete combustion.

Is the filter element a standard issue variety or have you replaced this with an aftermarket item ? Your vapouriser is usually pre-set with said kits to facilitate engine capacities from 3.0-6.0ltr's in size, but I've heard of an instance with a past dyno mechanic who owned a modified Rangie experienced LPG gas starvation when the power potential of his donk was producing in excess of 200kW's(P38 4.6 V8 spec.) which is closer to 300BHP in the old money before these issues start to effect power.

Cheerio,


Vinniman
'88 Highline
Perth, W.A.
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T
Sorry for not posting the resolution to this sooner, i had completley forgotton I asked the question on here.
Aparantly the vapouriser i had on it was only good for "up to 190bhp" so it was too small even for the 4.2. I now have a bigas high flow vapouriser from tinlytech which is great. Between that and buying the leads to re-configure the LPG ECU so it fules my new lump correctly it is like having a turbo charger fitted compaired to it's previous configuration.
My current issue which nobody seems to understand is this:
ECU readouts:
petrol at idle:


lpg at idle:


petrol at 2500rpm:


lpg at 2500rpm:


Both lambdas read the same. Does that look like i have a pair of poorly lambdas or do they look normal?
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jsp
I assume you have a stepper motor controlling the LPG at higher rev's in order to maintain efficiency, and I would just assume it takes longer to adjust than the EFI ECU. Its simply regulating the the fuel flow to keep the engine at the lean/rich midpoint. Typically theres a stepper motor which reduces LPG flow untill the O2 sensor readings shows the engines running lean, then the stepper motor opens up untill the O2 sensors show the engines running rich, and the process starts over again. The EFI ECU does the same thing by adjusting injector timings.

I have a small stepper motor on mine and at revs I notice it only cycles about once a second from lean to rich, so yours is faster than mine.
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