Basic query re: 8mm v 6mm outlet valves

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Basic query re: 8mm v 6mm outlet valves

#1 Post by kayble » Tue Mar 27, 2018 10:14 am

Hello all,

Car & conversion: '98 740i M62B44 4.4 non-vanos engine - conversion is Prins VSI2 with Keihin yellow 73cc injectors & Emer single hole multivalve.

I transplanted my conversion from a srapped 540i and all appears well under normal usage. However, at the extremes of the rev range under WOT, the car will loose power, as if it's being starved of fuel. Fair to say that under normal, even 'spirited' usage, this is not a problem.

The car has 8mm polypipe runs for tank fill and outlet to the reducer but, from memory, the single hole multivalve has a 6mm outlet to feed the reducer, and an adapter is used to step up to the 8mm polypipe.

Working relatively blind here - in that I know I should be hooking the conversion up Prins diagnostics to see what's happening with fuelling under hard WOT acceleration at the top end of the rev-range, but a thought occurred to me: should I in fact be using a multivalve with a 'native' 8mm outlet (seen a Tomasetto item that has this), versus a multivalve with a 6mm outlet that's then stepped up to 8mm?


EDIT: just to say that I've recently serviced the system, with new reducer solenoid and gas phase filters.

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Re: Basic query re: 8mm v 6mm outlet valves

#2 Post by Brian_H » Tue Mar 27, 2018 11:43 am

If the current one has a restriction (as it would given that its a 6mm outlet) this may explain your issue, Although as you say hooking it upto the diagnostics would give a better idea whats going on. Equally the placement of the valve can have a bearing on it (it should be as far towards the back of the tank as possible, though this is only likely to be a problem if it isn't when the tank is running towards empty, and more of an issue with a torroidal tank where the tank can be rotated to allow it to fit better).

Given the mapping probably hasn't been adjusted (as you say you haven't got the software to do it?) it could be a mapping issue (which may have been present on the original vehicle anyway).

Swapping the multivalve wouldn't be a bad idea, be aware they need to match the tank when ordering (tank diameter size and orientation angle as well as type of tank), although at the same time seeing whats happening with some diagnostics might help (even the petrol side diagnostics would give some sort of clue whats going on as they will be trying to correct the problem, although seeing the LPG pressure would be far more useful as a starting point).

It might also be an idea to pull the tank solenoid post off and give it a good clean up if you suspected the front one to be a problem. They do sometimes get a bit gummed up and that might be just enough to cause the problem, though I'd think its a long shot (best to do that once you've run the tank to empty though where possible - which since yours will run on gas is easy to do!)

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Re: Basic query re: 8mm v 6mm outlet valves

#3 Post by LPGC » Thu Mar 29, 2018 10:10 am

Does the problem happen every time you boot it or just after booting it a lot of times? If it happens every time I think it's unlikely the 6mm restriction at the tank will be the problem if the rest of liquid feed is 8mm.

Which Prins reducer is fitted (small or big version)?
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Re: Basic query re: 8mm v 6mm outlet valves

#4 Post by kayble » Wed Apr 04, 2018 1:31 pm

Happens each time when at high revs WOT acceleration - no such symptoms on petrol - its as if the gas is struggling to keep up when the engine is at the top end of the rev range with full bore acceleration requested by the driver.

Reducer is a Prins 180/101010/B with an 8mm inlet valve/solenoid - which from what I can glean is a reducer capable of working to either 180BHP or 335BHP applications dependent on whether a 6mm or 8mm gas inlet valve is installed on the reducer?

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