I have a V6 280CDI which when the engive is cold, particulary at the moment, strugles to start i.e turns over 4 or 5 times before firing up. Drives perfectly once warm.
Does anyone have any ideas what the problem might be?
Ours does this (sometimes) and Olly suggested it might be fuelling that's causing the problem, not glow plugs. As per other suggestions, just leaving the car a few seconds in the ignition position before cranking might make all the difference.
Hi, Not sure about the V6 320 or other models but my C270 had the same problem. The glow plugs were checked and found to be OK. The mechanics suspected a fuel shortage due to a possible airlock in the fuel supply pipe caused by a possible very small leak in the supply pipework causing air to be drawn back into the pipes due to the fuel/gas in the tank sort of shrinking in the freezing conditions and drawing a partial vacume. I first replaced all the cylinder head top flexible pipes and these come as a kit from MB 86.00 + vat. the labour cost me 20-quid. This helped but didn't cure it completely. Next I had all the seals replaced in the rest of the low pressure fuel supply pipes by MB Automotive in Loughborough, an independant MB father and son outfit website at MB Automotive - Independent Mercedes-Benz Servicing | Repairs | Diagnostics based in the East Midlands I found them to be very good and reasonable price wise. This cured the problem but on very cold mornings it still takes around 8 revolutions before it fires up. I found that installing a 60-watt greenhouse type metal tube heater on the bulkhead overnight helps a lot.
The v6 cdi has a different set up to your 612 engine. Earlier cdi's have a fuel feed pump which relies on a vacuum being held once the vehicle is switched off.
Unless there is a noticeable fuel leak from a line, it's unlikely for o rings to be the cause. The piezo injectors which are used are also far less likely to return excess fuel and cause a rail pressure drop on start up.
The om642 engine used in the v6 cdi's has a lower compression ratio than earlier cdi 611,612,613,646,648 engines and does need pre heat to start efficiently.
It was a faulty glow plug control unit - even though the glow plug light was showing on the dash no current was going to the glow plugs. I heard this is a common problem and the new control unit is supposed to have been modified to resolve it reoccurring