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Revs dropoff when pushing in clutch at lights.

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Hello folks,


I posted this to ford forums but didn't get much response so I figured I'd try here as many of you probably have similiar setups.

I have a BA XR6T that used to have a BTR auto that I killed with 12+ PSI and liquid LPG injection. I fixed that by putting a BF turbo T56 and extreme clutch with lightened flywheel and a manual tune.

It goes great however there is one small issue.

When I put the clutch in to stop at the lights, the revs drop way too far.. down to 400 before slowly climbing back up to 700 or so. Occasionally it will stall.

When I put the pedal box in I didn't get around to putting a clutch switch on.. I was wondering if the switch does anything other than the cruise control. I mean to say does it do anything to tell the PCM that the car has the clutch in any reason other than cruise control?

Also I read somewhere that the PCM needs to know that the T56 is in gear or in neutral.. when I put the box in, I wired up the reverse lights and connected up the wires where the neutral safety switch so it would turn over... didn't hook anything up that would tell it I was in gear or not though. The question is.. should I have?

I know that having a lighter flywheel will make it drop revs faster but it shouldn't be like this surely. Auto boxes usually hold revs so I know this is adjustable in the tune, but where? is there a name for it in tuning schemes? Holding revs after instant disengagement?

I'd really like to adjust this thing to hold revs briefly before dropping down slowly to 750 or thereabouts... Of course it's possible that I naffed up setting up the pedal box and should have hooked up the clutch sensor and/or a neural switch to the PCM so it would do this itself. The manual tune on the PCM now is based on HAANFG4.


I should add a couple of things, the revs dropoff happens in both Petrol and LPG, and the ignition system in my car includes Brisk racing silver plugs, recent version WeaponX 80k coils (dwell turned to match) and a Herrod JMS voltage booster so I can run big gaps for a good idle and still have no spark blowout up high.

Any thoughts would be very much appreciated.



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Tune needs adjusting.  The car can infer neutral from road speed so doesn't need a clutch switch.


Do you have a tuner? If not I can sort it out for you with HPT.

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Thankyou sir.. it was done originally via encrypted BEB and Binary Editor. but I've got the actual bin file off it now.     I think I might know at least partially what the problem is..    I discovered the Boost varied LPG regulator had come loose and was dumping too much LPG in.   So the PCM was trying to account for that by leaning it out.. and that made it a pig when it was on Petrol. I found an installation manual for the Icom JTG system that talks you though how to set it and tomorrow I'm going to try to buy a gas pressure guage and match it up as best I can.


That explains why it always runs better just after the KAM data is cleared...  With any luck I will have a schema I can use soon and I'll be able to fine tune it myself.  Think I'm going to swap it to LPG only too.. no warm up on petrol and then swap.   All that does is confuse the PCM.  The JTG fitter I spoke to said that starting on Petrol is a silly tradition from older LPG systems..   (the JTG has an in tank pump and return line, it's very similiar to a Petrol setup.) Apparently no need to run Petrol at all unless I get stuck somewhere with no LPG.   Should make tuning it easier too.

Edited by frankieh

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These injected lpg systems cold start on petrol for a number of reasons The main one you will have problems with is cold start enrichment (çhoke') Gas dosent like cold start enrichment -you are mixing a vapour fuel with vapour air ( the liquid will vapourize in the manifold before it gets to the combustion chamber) as opposed to liquid petrol mixing with vapour air -idling when cold with no heat or turbulence to aid fuel vapourizing  you can turn off the cold start enrichment to over come this but if try petrol it will run like bag of crap when cold. If you don't regulary use petrol it will go óff' 'in the tank & destroy your petrol system Anything after amonth & the fuel can go stale ( stinks like old paint varnish & is excellent for killing grass)

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