Map vac readings/location

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Budgetbond
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Map vac readings/location

#1 Post by Budgetbond » Mon Apr 05, 2021 11:31 am

Soz haven't updated much, I've been trying to review my system set-up, and I'm a bit unsure of my map vac line location and some of its readings are optimal.
For convenience sake I ran my vac line teed into an existing port v close to the throttle body that also powers a 'butterfly valve' (a flap that greatly reduces air flow into the intake up to about 4000rpm) and I'm wondering whether this is affecting its operation.
The lines are secure and airtight now, it does produce a vacuum, it works, im getting 102kpa engine off at idle petrol+Lpg 38-42_ish it's fairly steady but it doesn't increase by much, foot right on the throttle I can't really get it to read any higher than about 68kpa, nowhere near atmospheric like pressures.
Does that sound normal?
Corresponding gas pressure starts about 1.2 bar at idle and just generally drops a bit when I'm putting in more throttle, is that normal too?

If these don't seem right I was going to try and re-route the map nozzle to the inlet manifold.
I was just wondering whether there are any other general location tips I know it's preferable to be closer to the throttle body with shorter lines, but my reducer s at the exact opposite end at the cam chain end.
Is it better to drill into the runners or plenum and at any better angles (I'm looking to try and get a fuel efficient system) or does it make any difference.
I can't get my head around that if I pull off the vac line leaving an obvious air leak it still runs ok on petrol and gas without any emls so I'm thinking something's not normal!!

(I know my system need s a good proper calibration I know it's beyond me, im just trying to get it ready for that, my mapp s all over the place anything beyond idle I've tried driving around a bit on petrol normally just to lay some sort of petrol map line in the interim, I have noticed my exhaust is quite smoky, but not smelly, at revs and it does pop v occasionally I assume I'm running rich, am not sure whether I'm getting the best mpg at mo, but all else seems ok)

Any general tips there?

LPGC
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Re: Map vac readings/location

#2 Post by LPGC » Mon Apr 05, 2021 12:25 pm

Does that sound normal - No. Maybe you connected to a vacuum line with a one way valve (connected to a vacuum reservoir) instead of to manifold vacuum. Even if the pipe you connected to doesn't have a one way valve at the manifold, at the point that the butterfly valves open a momentary vacuum pulse can be generated in the pipe that feeds the butterflies and this can momentarily give a false vacuum signal.

General advice is to connect close to the throttle body. But depending on the design of the manifold it doesn't very often make a great deal of difference (as long as it isn't connected via a one way valve, a vacuum reservoir or anything that can create it's own vacuum pulses such as butterflies).

Go with the general advice for now.... But on some installs (and this may include yours) if the engine features extra injection but the LPG ECU doesn't have an extra injection filtering option it can be an advantage to tune the vacuum response by shifting the vacuum connection and/or adjusting the length of the vacuum pipe, a workaround/fudge because an engine that features extra injection should really be converted using an LPG ECU that features extra injection filtering.
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Budgetbond
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Re: Map vac readings/location

#3 Post by Budgetbond » Mon Apr 05, 2021 1:16 pm

Cheers Simon you're right there is a valve down the line thanks, thought it mite not be quite right or interfere, I'll try and drill midway towards the throttle body in the runners or plenum at right angles to the flow and leave a length of pipe on there for now.

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Re: Map vac readings/location

#4 Post by LPGC » Mon Apr 05, 2021 1:44 pm

Go for short pipes for now, would only opt for a longer length of pipe as a last resort and it isn't as simple as just fitting a longer length of pipe.
Full time LPG installer
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Budgetbond
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Re: Map vac readings/location

#5 Post by Budgetbond » Mon Apr 05, 2021 1:54 pm

Cheers Simon will do, I'll be heading to N York's on Mon 19th and coming back on Fri 30th if you can fit me in anytime then it'd be great to see your expertise in action or 'll have to arrange it another time asap when it suits you best

Budgetbond
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Re: Map vac readings/location

#6 Post by Budgetbond » Mon Apr 05, 2021 2:32 pm

Actually just thought another quick one, I could just disconnect the butterfly mechanism pipe and dispense with the mechanism tho it does help with mpg at lower revs and reattach the Lpg hose on its own there since I'll be running Lpg most of the time anyway, but would that make it better or easier Lpg wise?

Should I keep the butterfly mechanism and drill the manifold or dispense with the butterfly and just attach the vac hose to that port and suck it and see for now what d you think?

Am I better off keeping the butterfly in or out Lpg wise any difference or ease of setting up?

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Re: Map vac readings/location

#7 Post by LPGC » Tue Apr 06, 2021 12:39 pm

The 19th is out, already booked up. Play it by ear for the 30th?

Don't disconnect anything that should be connected like the butterflies.

If there is no existing vacuum port you could tap into (that doesn't have a one way valve) then drill and tap your own. If the engine has a mechanical petrol pressure regulator you could T into (edit - the vacuum pipe to) that.
Last edited by LPGC on Wed Apr 07, 2021 5:05 pm, edited 1 time in total.
Full time LPG installer
Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
Mid Yorkshire
2 miles A1, 8 miles M62,
http://www.Lpgc.co.uk
Twitter https://twitter.com/AutogasSimon
07816237240

Budgetbond
Junior Member
Posts: 208
Joined: Wed Jan 29, 2020 10:41 pm

Re: Map vac readings/location

#8 Post by Budgetbond » Wed Apr 07, 2021 2:37 pm

Cheers Simon I'll do that and cheers and also if you get any good days for you free-ish during that first week too keep me posted and I'll come down from the Coast and make a day out of it.

Budgetbond
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Posts: 208
Joined: Wed Jan 29, 2020 10:41 pm

Re: Map vac readings/location

#9 Post by Budgetbond » Mon Apr 12, 2021 8:04 pm

Ok so I've re-routed my map vac line to the inlet manifold ok in a fairly reasonable position I think and re-autocal ed and the map values do seem to be a little bit more responsive now, there s nothing physically I can really do now I think to my system, hopefully I'm en-route to enjoying good value running for quite a good long while now, thanks for your valuable tips.

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