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Matt
Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 22000
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Golf 1.6 Mk VI Match TDI DSG Intermittent Starting Problem In

Resolved Question:

Golf 1.6 Mk VI Match TDI DSG Intermittent Starting Problem

In Mar 2013, I bought a used Golf 1.6 Mk VI Match TDI DSG on 11 plate.
It has done only 10,000 miles and has been fully serviced.

Since I have bought this Car, it has a completely random issue when I try to start it.

One day it will start straight away, another it will turn over anywhere between 3 or five times to more than 10. There is no pattern. It almost happens during the first start in the morning on cold start, and the problem also happens randomly other times. Some morning starts will be perfect.
When I get it going eventually, there is no smoke from the Exhaust but the engine is erratic in the beginning but smoothes out farly shortly.

The Car has been to two VW authorised service centres several times but the diagnostics tests have not shown any fault. The Battery, Glow Plugs and Starter Motor are all fine.

I took the Car to a private Garage who is expert in VW's. The diagnostic test showed nothing, he checked the Electrical Fuel Pump in the Fuel Tank which was building good pressure and Fuel Lines were ok. He then checked the fuel pressures between the Main Engine driven Fuel Pump and Injectors and found the pressure was low on 1, 3 and 4 Fuel Pipes when checked on cold engine. The pressure was fine once the got going and after the first start. This cost me €100.

Any ideas??
Submitted: 4 years ago.
Category: Car
Expert:  Matt replied 4 years 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

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.

Customer: replied 4 years ago.


Can you please let me know if the private VW expert is correct in saying that the Main Engine Dirven Pump is defective?


On a cold start he found low fuel flow coming out of 1, 3, 4 Fuel Lines when he checked the fuel pressures between the Main Engine driven Fuel Pump and Injectors on cold engine?


The car only two years with 16,000 km done and the Pump replacement will be fairly painfull?

Expert:  Matt replied 4 years ago.

Hello

OK if the main pressure is slow to build then yes its possible the pump is damaged

however I really would replace the filter before anything else as this is pretty fundemental to the main pump working properly plus its cheap and easy to do

if its still slow to build then before jumping into a pump replacement ( as yes this is expensive at about £800 for parts and a few hours labour) ask about the 'run back' test I mentioned above as a set of injectors are cheaper than a pump

 

if this shows the injectors are OK then sadly yes its then time to replace the pump

Customer: replied 4 years ago.

 


Thanks, someone had mentioned that leaky Injector Seal may intermittently allow air into Fuel lines when cold.


 


Is this a possibility?

Expert:  Matt replied 4 years ago.
Hello

typically any leaks on the high pressure / injector side will show up as lots of fuel everywhere

however it may have developed an air leak on the fuel supply pipe from the tank to the engine. If a leak has developed on the fuel suction pipe then air entering the system will air lock the pump.
The problem will be cured by checking the supply pipe along its length for signs of leakage and repairing any you find.
If you daub each pipe joint with heavy grease and the issue goes away then wipe the grease away one at a time to highlight the problem joint
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