LPG Discussion Forum

Peugeot 207 cc 1.6 lpg conversion
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Author:  LPGmalta [ Wed Aug 16, 2017 4:58 pm ]
Post subject:  Peugeot 207 cc 1.6 lpg conversion

Hi guys, a client wants me to convert his 2007 pug 207 1.6 to me the engine looks like the one fitted to the mini cooper. Is this a valvetronic engine, and if yes, should I use some special kit or something? Thanks in advance.

Author:  LPGmalta [ Thu Aug 17, 2017 4:53 pm ]
Post subject:  Re: Peugeot 207 cc 1.6 lpg conversion

Can someone help please?

Author:  LPGC [ Fri Aug 18, 2017 4:59 pm ]
Post subject:  Re: Peugeot 207 cc 1.6 lpg conversion

If we were gonna be pedantic only BMW makes Valvetronics... But we're not pedantic here and other manufacturers do make engines with similar technology to Valvetronic.

But as memory serves I don't think the Pug engine features that kind of technology. It may, however, not have a petrol fuel fuel return or pressure regulator that keeps petrol pressure relative to manifold pressure. On some vehicles petrol pressure is kept relative to atmospheric pressure instead of relative to manifold pressure and on that type of setup a lot of installers seem to struggle to get good results without realising why. On this type of engine, the problem is that relative petrol pressure fluctuates according to engine load.. pressure is at it's highest at low engine loads (when the manifold has most vacuum) and at it's lowest at high engine loads (when the manifold is at atmospheric pressure). Obviously, manufacturers of engines with this kind of setup map the petrol system to take into account the shifting relative fuel pressure, while LPG systems are usually plumbed so that reducer pressure is relative to manifold pressure (with a vac line between the reducer and manifold), leading to a mismatch in the methodology of the 2 fuel systems that causes problems... The LPG system assumes that (say) 5ms of pinj will send the same amount of fuel to the engine regardless of manifold pressure and engine rpm but this isn't true because 5ms pinj with the manifold at 1 bar could be the same as only 3.94ms pinj with the manifold at 0.2 bar, which I explain more fully below. Some people at this point will (partially correctly) point out that 5ms pinj will only ever occur at a certain manifold pressure because a certain manifold pressure implies a particular engine load... But they're only partially correct because that doesn't take into account the differences in how the engine breathes at different rpms.

If you do reference reducer pressure to manifold pressure in this usual way on such engine, you'll find 2 things: 1. Your map goes from an unusually high multiplier at low loads, and possibly to unusually low multiplier at high loads and 2. Fuel trims/fuelling shift unusually according to rpm. 2 Is because the engine's ability to fill cylinders with air shifts with rpm according to the engine's breathing characteristics at different rpm (cam profile etc) and will be able to fill the engine's cylinders to a greater extent when the engine is close to it's torque peak. A lot of LPG systems are capable of adjusting fuelling based on rpm but when we have a normal engine type setup with petrol pressure referenced to manifold pressure we don't usually need to make any adjustments for rpm if we fit decent quality and well matched (to the engine components) injectors / nozzles / pressure. Rpm adjustments can be used to correct differences in fuelling on this type of engine, it's just a messy way of doing it. And rpm correction is very clunky on a lot of ECU's and the feature doesn't seem to work very well on a lot of them.

It may seem you can get around the problems above by not referencing reducer pressure to manifold pressure but it isn't as simple as that. For starters, if this was ever going to work 100% your LPG pressure would need to be the same as petrol pressure but you can't run with an LPG vapour pressure of 3 bar! LPG pressure will be much lower than petrol pressure, so not referencing LPG pressure to manifold pressure usually means that if you get calibration decent at idle you won't have enough pressure to allow the engine to run properly on LPG at high loads.

Some example figures:
Petrol pressure constant at 3bar above atmosphere. Petrol pressure at full load (with manifold at atmospheric pressure) is 3 bar but petrol pressure at fast idle with 0.2 bar manifold pressure becomes 3.8 bar.
With LPG pressure referenced to manifold pressure LPG pressure might be around 1.2 bar constantly. We're used to seeing pinj at fast idle of maybe 2.7ms but the petrol ECU accounts for the 1.27* higher pressure at fast idle by reducing pinj from 2.7ms to 2.1ms, so your LPG system would run lean around idle without an usually high multiplier.
Without LPG pressure referenced to manifold pressure you might set pressure to 1.2 bar referenced to atmosphere, but now at fast idle actual LPG pressure would be 2 bar, which would be too much pressure because if nozzles in the injectors are big enough to flow enough fuel into the engine for flat out at 1.2 bar will mean the nozzles will be far too big to allow the injectors to pulse above their minimum duration at idle at 2 bar. Also, if petrol pressure shifts between 3 and 3.8 bar this is only by a factor of 1.27, while if LPG pressure shifts between 1.2 and 2.0 bar this is by a factor of 1.67... So not connecting the reducer to manifold vacuum actually implies bigger scope for calibration error (as engine breathing with rpm changes) than connecting the reducer to vacuum does.

A far neater and better in practice way of doing things on such engines is to fit the LPG system in the usual way with LPG pressure referenced to manifold pressure but fit an ECU that can compensate fuelling based on manifold pressure. It isn't the manifold pressure compensation that is important, but compensating for manifold pressure is the exact reverse of compensating for petrol pressure (which the system cannot read, or at least cannot act on). Set the compensation so that (in the above example) at fast idle with that 0.2 bar manifold pressure the compensation effectively increases LPG injector duration by 1.27* what the calibration says, the 1.27* gradually decreasing toward 1* when manifold pressure is at 1 bar (engine full load). I set a spreadsheet up to calculate what the compensation should be for any given petrol pressure / manifold pressure (including on turbo'd engines etc), and I use the info from the spreadsheet when entering all the figures into a KME Nevo ECU.

I have converted some similar model Pugs, similar year, and can't quite remember if the above is relevant... You'll have to find that out for yourself. But I do know that a lot of unrelated problems installers seem to have on similar Pugs are due to the more usual overly long pipe overly wide diameter (6mm) pipe lengths, poor choice of injectors, poor choice of location for gas entry (spuds / straws) on the manifold, @!## calibration. People seem to think there is a universal maximum pipe length that will allow decent results on any engine, but this isn't the case... In reality, you can have longer / wider pipes between injectors and manifold with big engine cylinders than you can with small engine cylinders. 10 Inch long, 6mm bore injector pipes might work OK on a 600cc V8 engine cylinder but probably wouldn't work OK on a 200cc cylinder. The manifold design of some Pugs/Citreons doesn't make fitting short pipe runs easy but on a smallish 400cc cylinder on an engine that might feature Atkinson type cycle (scope for fuel and air to be pushed back out of the cylinders on compression strokes) the effort for low volume in pipes has to be put in for good results. Also, mapping of some Pugs/Citreons can be confusing to the uninitiated because the fuel trims work a bit unusually.

Can often tell an engine that runs constant petrol pressure going on pinj at idle, vacuum at idle and pinj at full load at torque peak... Pinj will usually be unusually low at idle while still reaching maybe 16ms at high loads. But the same can also be true of engines that just feature variable valve timing, so there's a bit of reading between the lines when checking... To an informed installer this can be done by interpreting the shape of the map, or how fuel trims shift according to rpm, etc.

So summing up, I can't remember if the above is relevant here. Clicking the rather undocumented Valvetronic or Multiair check box (undocumented on most systems, i.e. check this box if the engine is Valvetronic without a thorough write up on what it actually does behind the scenes) may almost dial out some of the possible implications I described above. Almost but probably not thoroughly, because the Valvetronics and Multiairs will probably run a different petrol pressure to the Citroen, which would have to effect that 1.27* multiplier in my examples above, and that is still based on the assumption that the check boxes do exactly what I believe they do and work entirely properly (I think I know what they're supposed to do but I don't think they work entirely properly). If you want to fit parts that will do the job regardless of any of the above possibilities I would advise Nevo, single MJ injectors, short pipe runs, choice of reducer not overly critical but do connect vac pipes as usual.


Author:  LPGmalta [ Mon Sep 11, 2017 8:51 pm ]
Post subject:  Re: Peugeot 207 cc 1.6 lpg conversion

Dear Simon,

Thanks for your reply. I am using AC stag qbox basic, AC w01 injectors, 4 or 5 mm pipes between injectors and nozzles and 10 inch pipe runs. Hope it works.....this is my first one.....what a nightmare.

Author:  LPGC [ Tue Sep 12, 2017 7:50 pm ]
Post subject:  Re: Peugeot 207 cc 1.6 lpg conversion

Good luck then mate ;-)

Author:  agostino [ Fri Sep 15, 2017 3:37 pm ]
Post subject:  Re: Peugeot 207 cc 1.6 lpg conversion

I have the same engine, it was converted by Tubbs years ago.
Simon, its a valvetronic, no vacuum...I am not a fan of these engines also because they have poor torque.

King AEB, Magic Jet, can't remember the vaporiser
Toby told me it was a bit fiddly to calibrate at the beginning but managed to get it good.
it uses a fair amount of oil, its normal for this engine.

Author:  LPGmalta [ Mon Sep 18, 2017 8:01 pm ]
Post subject:  Re: Peugeot 207 cc 1.6 lpg conversion

I need help guys. I installed the system. Went to do an initial autocalibration, LPG system starts swapping from petrol to LPG injectors, cylinder 1, then 3 and everything is ok. As soon as system tries to do the same thing on cylinders 2 and 4, a pronounced misfire occurs and after some time the car shuts down cylinders 2 and 4. I have good gas pressure, tried different ecu and injectors but car still does the same thing. What could this be please? On petrol, car works ok. Any advice as I am lost...


Author:  LPGC [ Tue Sep 19, 2017 6:56 pm ]
Post subject:  Re: Peugeot 207 cc 1.6 lpg conversion

Thanks for the info Agostino (heh that rhymes)..

Sure you got wiring to petrol injectors 2 and 4 the right way around? If not just swap gas injector plugs 2 and 4.

When running on petrol (before the problem) what is the vacuum reading on screen?


Author:  LPGmalta [ Wed Sep 20, 2017 9:18 am ]
Post subject:  Re: Peugeot 207 cc 1.6 lpg conversion

Hi Simon, I just confirmed that at idle, cylinders 1 and 3 have a vacuum of -10kpa, whilst the "faulty" cylinders have 0 vacuum, wiring is ok, checked it and re checked it. At idle, car has 0.95 bar read through manifold after throttle body. I am sure the problem is because of the loss of vacuum which sucks in the gas, or not?

Author:  LPGC [ Thu Sep 21, 2017 9:38 am ]
Post subject:  Re: Peugeot 207 cc 1.6 lpg conversion

The vac readings seem to confirm it is Valvetronic as Agostino said.

All cylinders have the same vacuum... You have a very slight vacuum when the engine is running, no vacuum when the engine has stalled. This isn't the cause of you problem and doesn't provide any insight into your problem.

Did you try swapping connectors to gas injectors 2 and 4 ?


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