Porsche Enthusiasts Club Forum

Possible one of the elbows that is connected to the green pipe is leaking?

Very occasionally I cannot start my 944 2.5 lux and that happened today.
Remembering your touching those pipes changing the co I thought it worth a go, so I wiggled those pipes too..........the car started

I have never owned a car that seems to have miles of vacuum pipes going all over the place, why? what do they all control?

My car passed its MOT with no faults or advisories however the car does not have a nice even tickover but more a fluffy sound that normally on other cars is a rich mixture.

Hmmmm... well glad it's been of some assistance!

Update:
Ran a compression check yesterday; results:
#1: 13 bar
#2: 13 bar
#3: 14 bar
#4: 13 bar

So doesn't appear to be any issues there.

At a bit of a loss now, as I had the (new) plugs out for the comp test and definitely still running rich (look identical to the previous set), though on a long motorway run seem to be getting 29mpg, so it's clearly running ok.

Had more of the vacuum hoses off and can report the following:
- Vac hoses on the fuel side (FPR, FPD etc...) seems to be pulling 0.65 bar of vacuum. There was a small blockage in the rubber 'Y' between the FPR and FPD, though seemed quite easy to shift.
- Vac hoses on throttle body side seem to be pulling around 0.2 / 0.3 bar when revved (nothing on idle)
- Vac hoses on heater matrix valve seem to be working (valve opens when heater moved to hot)
- can't find any trace of leaks from hoses or rubber elbows (listening; visual inspection; spraying with WD-40)

As for earths/grounds....I'm now thinking this may be a red herring - running a cable from the battery neg terminal to various points round the engine bay (inc. AFM) made no difference to running or PD readings from earth to +ve (through admittedly, didn't have it on a CO meter at the time).

I'm now thinking either:
- weak spark....(though can't really back this up with any reason)
- DME fault, or
- DME temperature sensor (perhaps I misread the previous test resistance output)

Any thoughts welcome!

Long overdue update if it helps anyone else:

Root problem was essentially an intermittent fault with the DME temp sensor. By intermittent, I don't mean it was sometimes ok, but it was failing to provide the correct readings during part of the temperature range i.e. it was ok on the instant of startup, then rough during the warm-up period, then ok again at running temp. Changing it immediately solved the rough start-up issue, no question.

After changing this I re-emission tested it and it was 3.5% - not quite what I'd hoped for but an improvement of 1.5% and an almost pass.

Playing a little with the mixture (which I'd probably over-played with too much before) at MoT time brought it back down to around 2.5% which is a comfortable pass, if a little higher than it had been before.

Plugs look fine now after they've been ran for a while.

Looking back, it seems likely that the vacuum / fuel supply / earth lines of enquiry were red herrings....