None firing Merc

[del mar]

Morning,

1993 R129 300sl

3 litre straight 6 engine.

If left for a week or so, it isn't keen on firing, lots of spinning but can take 10 -15 mins to fire. Once running car runs fine, and will stop and re start without issue but the first starting is a real hassle.

Last year I changed plugs, distributor cap and rotor arm car has only done a few thousand miles since, but recently it has been a pain to start.

What am I missing ?

thanks

Del

[E-bmw]

Fuel draining back to the tank/airlocks in the fuel lines? Fuel pump not priming?

When you next try it spin it up & check for wet spark plugs before it starts.

Ignition timing?

Get it checked (not sure if this engine is fully electronic or uses a dizzy?) so may be a non-starter. Sorry!

[stevieturbo]

so presumably you're telling us it does wind over ? and it winds over at a decent speed ?

Does it have spark during this period ? Does it have fuel ? Assuming it is petrol of course.

Basics as always.

[GreenV8S]

If it's a petrol engine, the initial cold start would depend on cold enrichment. No idea how it's provided on that car. If that's provided electronically, I'd check sensor and wiring (should just need a resistance measurement at the ECU plug). If it's provided mechanically, check the choke mechanism is operating.

[del mar]

Thank you gentlemen.

Turns over at a good rate.
Will check for spark and damp plugs this weekend.

Fuel level is low - orange light is on but needle is not on the "floor"

[paintman]

Put some more fuel in.
I agree that it sounds like the fuel is draining back to the tank, possibly a pinhole or a leaking joint somewhere between the tank pick-up & the point where the fuel goes into the inlet manifold.
Is there a clear section in the fuel line that would allow you to see if there is air/lots of bubbles?

Appreciate it's a diesel but I had a similar problem with a Sprinter - every morning would start & run for a couple of seconds before stopping after which a fair bit of cranking - but only around 30 secs or so - would see it run fine & be OK for the rest of the day.
After much head scratching I found it to be the small spring loaded valve assembly in top of the fuel filter: http://www.ebay.co.uk/itm/Mercedes-Sprinter-Fuel-F...

Edited by paintman on Friday 16th December 14:52

[GreenV8S]

paintman said:

Put some more fuel in.

^^^ That.

[Old Merc]

Does your R129 have the M104 engine?
If so the wiring from the coil packs to the bulkhead could be at fault.I changed the spark plugs on my R129(moving the coil packs and wiring out of the way) and created all sorts of starting and misfires.
Mercedes supply a very handy loom kit,all fitted,good as gold ever since.
There is a poster on the Mercedes section on this forum called R129,he knows everything about this model.

[PositronicRay]

Old Merc said:

Does your R129 have the M104 engine?
If so the wiring from the coil packs to the bulkhead could be at fault.I changed the spark plugs on my R129(moving the coil packs and wiring out of the way) and created all sorts of starting and misfires.
Mercedes supply a very handy loom kit,all fitted,good as gold ever since.
There is a poster on the Mercedes section on this forum called R129,he knows everything about this model.

The 300 had a dizzy not HFM. I know what you mean though, my 3.2 had good LT wiring, spliced into a dodgy loom.

[del mar]

Morning,

With more than 1/4 of a tank it fires first time.

Just to clarify it is a petrol - M103 engine (I think).

So if as pointed out fuel is draining back to the tank when the level is low, what is the first culprit to check ?

Thanks

[paintman]

I'd start by looking at the fuel pickup in the tank as suspicion would be that there might be a hole in it allowing air in when the fuel drops below a certain level.