VW TDI forum, Audi, Porsche, and Chevy Cruze Diesel forum banner

1 - 2 of 2 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter #1
Hello All,
If any of you have had experience with the diesel engine quick start function I would appreciate your advice. I have been working on this for a few weeks with limited success but not repeatable after the first start of the day. I have replaced the fuel module in the tank (the lift pump and check valve were not working, fuel filter now has a level in it), replaced the camshaft sensor G40 (original sensor was pulsing on from 0 to + 540mV new sensor is 5V negative going pulses), check all of the glow plugs with a Fluke meter and outside of the engine ( ambient temp too high for initial heating, all plugs heat up in the extended glow period of 4 minutes), replaced the check valve located on top of the filter, captured the camshaft/crankshaft sensors with my oscilloscope ( looks just like the signal pattern in the manual), replaced 680 amp VW battery with same. The quick start function is described in the VW manual:
Quick-Start Function
To allow the engine to be started quickly, the Diesel Direct Fuel Injection Engine Control Module J248 evaluates the signals generated by the Camshaft Position Sensor G40 and the Engine Speed Sensor G28. The Diesel Direct Fuel Injection Engine Control Module J248 uses the signal that the Camshaft Position Sensor G40 generates to determine the relative positions of the pistons in the cylinders when starting the engine. Because there are two gaps on the crankshaft sensor wheel, the Diesel Direct Fuel Injection Engine Control Module J248 receives a usable reference signal from the Engine Speed Sensor G28 after only half a turn of the crankshaft. Cylinder 1 Cylinder 3 Cylinder 4 Cylinder 2 By interpreting the signals from these two sensors, the Diesel Direct Fuel Injection Engine Control Module J248 determines the position of the crankshaft in relation to the camshaft and thus the positions of the pistons in the cylinders at an early stage. With this information, it can activate the correct solenoid valve at the proper time to initiate the injection cycle in the next cylinder to reach the compression stage. The quick-start function enables an early engine start because synchronization with the first cylinder is not required.

8835
 

·
Registered
Joined
·
6 Posts
Discussion Starter #2
Well I haven't given up on this, just work on it when I have the time. To date I have replaced these components all from the local VW dealer but still have the same issue:
  • battery
  • lift pump, filter and check valve on the filter
  • cam position sensor
  • coolant temperature sensor,
  • fuel temperature sensor
  • installed a no return check valve in the fuel supply line (2 psi cracking) between the filter and tandem pump
  • checked the fault codes with a VAG my mechanical engineer colleague and good friend (Jim) has, none found. He grew up troubleshooting and rebuilding diesel engines in his dad's big rig shop, he is just as puzzled as I am
  • installed a pushbutton to activate the lift pump for a few seconds before starting, somewhat improved but still a long crank after the engine is hot.
  • measured the tandem pump pressure at the fuel return port, found that the check valve in the return line is bad. Pressure at idle is 50 psi not the 15 psi stated in other posts. Pressure fell off to zero after stopping engine. Installed a hand valve in the return line to trap pressure when the engine is turned off. No difference. Looking at replacing tandem pump, we are both believe it's possible since the cv is bad then the pump vanes and possibly the high pressure cv in the pump may be going out also.
  • Will try recommendation in other posts to unplug the coolant temp sensor after a run to see if it cranks in two strokes. Might indicate a software mistake VW had on earlier models with warm start injection timing when the engine is hot.
  • All advice is welcomed.
 
1 - 2 of 2 Posts
Top