K-Jetronic throttle flap reset

[Onne]

Hello all,

As you may know I run my Merc on LPG... Which sometimes results in a backfire through the inlet.

Last time I had someone out to reset the position of the main flap under the inlet.
Any ideas?

[Onne]

I forgot what actually happens... It struggles to idle on LPG.

When I come to a junction, traffic lights etc it seems to surge and subsequently stall. Starts straight back up, which makes me think the hoses are all on ok.
Running/idling on petrol absolutely fine.

[ChasR]

What sort of a system are you running on the Merc?

I was always led to believe that backfiring on a mixer system was generally down to a lack of LPG (they need to run a little richer than the equivalent sequential system).

Saying that my old Mondeo V6 used to misfire/backfire on a sequential system, although it did also have the Ford V6 'moosing' issue. Making my own makeshift anti moosing pipe (basically a longer pipe going from the airbox pipe to the idle control valve) near enough stopped the moosing and also cured the misfiring issues.

[Onne]

I'm running the old style vapouriser (single point injection), with a long pipe (1,5m) from the vapouriser to the actual ring on top of the injection mouth:


1 being the vapouriser
2 the radiator
3 the air filter housing
4 the gas injection ring
5 the long pipe

I've been told before that the length of pipe is not ideal, as the gas could (potentially) reliquidify.
Only had the one backfire, and it sometimes misses when cold

[Tepper]

Resetting the flap is pretty simple but it requires a bit of disassembly. I did this write-up a while ago, ignore the bit about removing the metal plate holding the injectors in. Oh and you can remove the fuel distributor and air meter as one assembly. Have you checked that the 'throttle' flap (it's actually a basic mechanical MAF, the throttle is underneath) actually needs resetting? Here's the write-up, there's another page on the same website that tells you how to reset the plate once you've got the whole lot off the car.
mercedes-190.co.uk/topic/6693576/1/#new

[Onne]

Thanks for that, looks a good write-up. Shouldn't be too hard to do either, as long as I have the tools.

Fingers crossed for good weather!

Weird thing is though that it runs fine on petrol, but it would be more sensitive for vacuum leaks when running on LPG.

[ChasR]

When I had a similar issue on my old Mondeo of doom (not the beige 3.0) it was down to a blown vapouriser (instead of giving out 1.5bar of pressure it will chucking out more like 3Bar!) (it would either idle at around 2.3krpm at the lights or try and stall on you). Backfiring however seemed to be cured by the moosing pipe modification.

I hope it is a simple issue for you and not the former!

I don't mean to rain on your parade but some sources (PPC if you trust their information...) seem to think that is not a great idea to run a mixer setup on a K-Jetronic system IIRC due to the possibility of the metering head getting damaged through bacfires and changes in the airflow as a result of putting a venturi in the air inlet tract.

[Onne]

I have been told the same, but on the other hand also that it is a very strong system.

And to be honest I haven't had many problems with it, only thing that tends to happen is hoses being blown off.

Saying that, I'd love to convert it to sequential, but that is rather a lot of work...