Drivbiwire
Zehntes Jahr der Veteran
- Joined
- Oct 13, 1998
- Location
- Boise, Idaho
- TDI
- 2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
Welcome, obviously you have an issue with "hard starting your car when cold" if you are reading this thread, don't worry becuase its an easy fix.
Basic background: "Pre-Glow" occurs when the temperatures drop below 40F. This means the glow-plugs activate to speed up starting due to lower temperatures and slower cranking speeds of a cold engine. Injection timing plays a VERY significant role here becuase injection must occur at the precise time of maximum compression to use the heat of the compressed air mass in the cylinder. If injection occurs after this point then you will have an engine that is very hard to start.
Injection timing tends to slowly retard as your timing belt gets some miles on it. Generally once a year before winter (August) get the injection timing checked and have it set around 70/110 in basic settings mode. What this means is that the mechanical timing will inject the fuel at the point in time where compression pressure and temperature are the highest. If your timing is below 50/110 the timing is retarded to the point that you are missing peak pressure and temperature and the car will become harder to start requiring longer cranking periods.
Back to "Pre-glow" if your timing is retarded the car will become harder and harder to start as the temperatures drop off closer to 40F then all of a sudden the car starts normally as you get below 40F due to the glow-plugs being activated by the ECU to assist in starting. Glow-plugs create a very hot point within the cylinder that helps to set off the chain reaction that causes the hundreds of thousands of fuel droplets to ignite. If the temperature during compression is so much as 1 degree below the auto-ignition temperature of the fuel... a no start of the engine will occur. Adding the Glow-Plug provides a hot spot that will set off the chain of ignition causing the fuel droplets to burn. Despite the rest of the cylinder being below the auto-ignition temperature to ignite the fuel the glow-plug compensates for this and helps to get the motor running soley using compression.
As a rule once the first cylinder fires this increases the speed of compression resulting in less time for the rapidly compressed air to lose it's heat and the engine begins to run relying on compression rather than relying on the glow-plug.
Advancing the injection timing allows your motor to start easier in all seasons but mostly you will see the greatest improvement as the temperatures drop below 60F.
Even when the temperatures are at 41F you should have a very fast start requiring only 1 or 2 cylinders to run through their compression stroke before the engine starts and runs. If it takes more than 1 second you have an issue with any one of the following in order of importance:
#1 Check injection timing, below 70/110 ADJUST it and advance the timing.
#2 Timing is at 70/110 yet the motor is still hard to start when the engine is cold:
-Check your glow-plugs for proper resistance, they should all read around .8 - 1.4 ohms. If you get no resistance or a short you have a bad plug... it happens! Change out the one bad plug and press on.
-Check the battery, VW batteries are often not "Maintenance Free" meaning you need to check the water levels! Check that all the cells are properly filled with water and consider putting the battery on a charger for 24-48 hours on a 10amp charge.
Diesels are simple,
* heat/compression + fuel injected at the right time = a running engine
* heat/compression + fuel injected too late = No running engine or at least one that does not want to start
Before getting worried GET YOUR TIMING CHECKED every year before winter sets in.
DB
Basic background: "Pre-Glow" occurs when the temperatures drop below 40F. This means the glow-plugs activate to speed up starting due to lower temperatures and slower cranking speeds of a cold engine. Injection timing plays a VERY significant role here becuase injection must occur at the precise time of maximum compression to use the heat of the compressed air mass in the cylinder. If injection occurs after this point then you will have an engine that is very hard to start.
Injection timing tends to slowly retard as your timing belt gets some miles on it. Generally once a year before winter (August) get the injection timing checked and have it set around 70/110 in basic settings mode. What this means is that the mechanical timing will inject the fuel at the point in time where compression pressure and temperature are the highest. If your timing is below 50/110 the timing is retarded to the point that you are missing peak pressure and temperature and the car will become harder to start requiring longer cranking periods.
Back to "Pre-glow" if your timing is retarded the car will become harder and harder to start as the temperatures drop off closer to 40F then all of a sudden the car starts normally as you get below 40F due to the glow-plugs being activated by the ECU to assist in starting. Glow-plugs create a very hot point within the cylinder that helps to set off the chain reaction that causes the hundreds of thousands of fuel droplets to ignite. If the temperature during compression is so much as 1 degree below the auto-ignition temperature of the fuel... a no start of the engine will occur. Adding the Glow-Plug provides a hot spot that will set off the chain of ignition causing the fuel droplets to burn. Despite the rest of the cylinder being below the auto-ignition temperature to ignite the fuel the glow-plug compensates for this and helps to get the motor running soley using compression.
As a rule once the first cylinder fires this increases the speed of compression resulting in less time for the rapidly compressed air to lose it's heat and the engine begins to run relying on compression rather than relying on the glow-plug.
Advancing the injection timing allows your motor to start easier in all seasons but mostly you will see the greatest improvement as the temperatures drop below 60F.
Even when the temperatures are at 41F you should have a very fast start requiring only 1 or 2 cylinders to run through their compression stroke before the engine starts and runs. If it takes more than 1 second you have an issue with any one of the following in order of importance:
#1 Check injection timing, below 70/110 ADJUST it and advance the timing.
#2 Timing is at 70/110 yet the motor is still hard to start when the engine is cold:
-Check your glow-plugs for proper resistance, they should all read around .8 - 1.4 ohms. If you get no resistance or a short you have a bad plug... it happens! Change out the one bad plug and press on.
-Check the battery, VW batteries are often not "Maintenance Free" meaning you need to check the water levels! Check that all the cells are properly filled with water and consider putting the battery on a charger for 24-48 hours on a 10amp charge.
Diesels are simple,
* heat/compression + fuel injected at the right time = a running engine
* heat/compression + fuel injected too late = No running engine or at least one that does not want to start
Before getting worried GET YOUR TIMING CHECKED every year before winter sets in.
DB