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Matt
Matt, Mechanical Engineer
Category: Volvo
Satisfied Customers: 23083
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a 2008 Diesel Jetta VW. Although there is no

Customer Question

I have a 2008 Diesel Jetta VW. Although there is no difficulty in relation to the engine being turned over, it often won't start when the weather is wet.For example if it rains overnight. There is no problem if the weather is cold or frosty it starts without a problem.
I have just had new glow plugs fitted and an engine decarb, plus full service. the problem appears to arise if and when the vehicle has been standing overnight and only during wet weather. It has quite a high mileage (170000) but has been regularly serviced from new.
It has been a very good vehicle. so we don't want to scrap it, we hope to be able to keep it as a second car, Can you help,
Submitted: 4 months ago.
Category: Volvo
Expert:  Matt replied 4 months ago.

Hello

I'd check that you're getting full power to the glow-plugs, they pull a lot of current so take care when checking but see if the relay is clicking when the ignition is turned on first and also check the fuse if this is OK check to see if the engine earth strap is also OK.

You can test the glow-plugs with a multimeter by measuring the resistance across the plug ( between the power connection and the body) it should be around 4-8ohms if its tending to infinity / open circuit the plug is faulty or by using a clip on current clamp, either on the supply wire to glow plugs or onto engine earth, with glow plug light on you should see 15-20amps for each glow plug fitted, 4 cylinders would be approximately 60-80amps.
Also if its not injecting at all then check the connections to the crankshaft sensor, unplug it and check for corroded contacts and broken wiring, and consider fitting a new sensor - do the same for the cam position sensor
If the EGR valve is stuck open then this too can effect starting so try disconnecting it to see if this helps or changes anything
Could also be an injector leaking fuel back through the overspill pipe, so not getting enough fuel pressure to tell ECU to fire the injectors, this is trickier to find and you’ll need the garage to do a ‘run back’ test to identify which one is the issue
you can also do a reasonable run-back test yourself by disconnecting the electrical plug on the injectors and the downstream pipe of the leak off, crank the engine over and if you see a noticable difference if the flow in the leak off then that the likely problem injector.
Lastly it’s also worth considering fitting a new fuel filter as if only slightly blocked this can lower fuel supply pressure and choke the main pump, the pump will be more sensitive to this when its cold as diesel thickens considerably with low temperatures.

Expert:  Matt replied 4 months ago.

Hi
do you still need help?
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Thanks Matt