Possible Inlet Leak 300TE Auto W124

[mark.porthouse]

Hi All,

As my LPG system has settled in it has started running slightly lean giving me the occasional slight misfire (explosion in the inlet manifold).

It did it again yesterday but this time I was unable to start the car on either petrol or gas. I'm suspecting a leak in the inlet manifold caused by the blow back. On the starter it will start momentarily but then immediately die on either petrol or gas. I'm imagining that at the moment of starting the mixture may be rich enough to compensate for an air leak, but the mixture immediately settles down and is then too lean because of an air leak. Also I have once or twice been able to start it and rev it highly and it carries on OK as long as I'm revving highly - no doubt because at that high an airflow the leak is inconsequential to the mixture.

I've searched around possible leak points and can't find a problem. Here are the ones I've identified (see attached jpeg). Are there any other ones? The car is an auto and there appears to be a vacuum line going down between the two firewalls (bulkheads) but I don't know where the other end is - I guess I could clamp it though.

What about the auxilliary air device? Is it possible it can be stuck open? I can't really figure how it mates to the inlet manifold either - it appears that its pipe goes very close to the head where it meets an electrical device of some kind.

Also, the under side of the airflow meter appears to be a large rubber thing through which the intake air flows down to the throttle body. Perhaps this has split? I can't feel a split but I can't feel around the whole thing.

Any advice would be most welcome.

Cheers,

Mark

 

[mark.porthouse]

Hi All,

Found the problem.

When I was looking at the idle control valve I was imagining air flowing through in the wrong direction. So when I imagined the correct direction and followed the hose from the valve to the bottom of the inlet manifold I found that the hose had blown off!

Now I have to try and reconnect the hose - which might be a little difficult as it is completely surrounded by pipes and leads!

Cheers,

Mark

 

[Glenn Smith]

probably the back fire that blew it off, you really need to find out why it backfired, do you have a leaky valve or incorrect timing maybe.

 

[mark.porthouse]

Hi Glenn,

I think that the low speed mixture (on gas) had steadily got leaner since installation. It was beginning to stall occasionally as well as misfire. This is possibly the diaphragm bedding in from new or possibly a build up of 'heavy ends' (oils within the lpg) in the mixer.

I've just tweaked what I reckon must be the low speed mixture screw (half a turn anticlockwise - for my reference!) and it cleaned up the idle a bit. I'll see if I still get any problems.

Cheers,

Mark

 

[John Hand]

Dear Mark,
I have just found your LPG threads whilst googling "W124 300TE LPG" and have joined the forum in order to ask the following - I can see you have had some teething problems; have you had time to form a view as to cost benefit analysis?

Regards

John Hand

 

[bolide]

If it's something you're planning, consider where the LPG tank will go and what capacity it can have in that location

Nick Froome
www.w124.co.uk