PD cold timing?

nokivasara · Feb 3, 2019

Is timing the only "cold enrichement" system on the PD, or does it inject more fuel too when the engine is cold?

When is the timing returned to that of a hot engine? At which temperature?

The reason for these thoughts is that I monitored the engine temps on my commute to work this week via the hidden meny's in the climatronic display and was surprised of how much longer the engine needs to get up to temp even in moderate cold weather. I wonder if the mileage takes a hit even if it isn't that cold...
At -14C I was up to about 66C efter 12km and it took another 10km to get up to 84C and that's where it parked for a while.
At -6C the engine was at normal operating temp (87) at that 12km mark.

This is with a 550W coolant heater that was on about 1,5hrs before I took off, I think the engine temp was about 30C before I started the car.

Time to put a piece of cardboard in front of the radiator, I usually only do that when it gets really cold.

JB05 · Feb 4, 2019

Did you check the t-stat to see if it is not stuck open?

k_pt · Feb 4, 2019

JB05 said:
Did you check the t-stat to see if it is not stuck open?

x2, check the thermostat.

nokivasara · Feb 4, 2019

I'll check the t-stat but I'd still like to know how the ecu controls timing and perhaps the quantity of fuel injected while the engine warms up to normal operating temperature.

ejoskf · Feb 5, 2019

I've had problem with my 1.9 TDI PD, after 10 miles temperature would rise to 75 and stopped never reaching 90. I've changed thermostat and removed temperature sensor at the bottom of the radiator it had some dirt stuck to it. Now temperature is 90. Tstat wasn't stuck open but upon testing it open too quickly before water reached 87'C. They do fail over time and opening too early. Change it and clean sensor too. Have a lot of coolant ready and drip pan under the car. You'll need 10mm long extension and ratchet. Tstat first into the block followed by new gasket.

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Giberish33 · Feb 5, 2019

nokivasara said:
I'll check the t-stat but I'd still like to know how the ecu controls timing and perhaps the quantity of fuel injected while the engine warms up to normal operating temperature.

You would think there should be increased fueling when the engine is cold but it is actually the opposite. Injection quantity will be higher mg/st (less fuel) when cold and will gradually come down a few points (more fuel), the reasoning being that a cold diesel engine has a hard time combusting fuel until cyl temps come up and fuel temp also comes up a little so to not stall out, fuel is reduced. I have seen this happen when watching IQ in vagcom as my car warms up.

As for timing, it is increased when cold to again aid in allowing the fuel to have as much time to get compressed and create the best combustion possible when cold. Timing like IQ will also come down as the engine reaches operating temp.

I can't say exactly at what temp IQ and timing are "normal" as I haven't watched the entire time but generally its around 80c. That is the minimum temp to check the timing graph in vagcom so I'm going to assume thats also when other things equalize. Operating temp should be 87c -/+5c.

If your saying it takes an additional 10+kms to only go up a few degrees when the engine is already fairly warm, it all pretty much points to thermostat getting very weak and opening up too soon (allowing coolant to pass through the radiator too soon). Fuel economy will be affected for sure because its going to take longer to get up to that point when the ecu values reach normal. What you can do for the moment to help is use some foam pipe insulation and cover up the upper grill vents and the lower grill to block as much air from the radiator as possible.

Some people will also block the side openings but one is for the intercooler and the other is where fresh air enters the fender to be sucked in by the airbox so cover the side ones if you want but I wouldn't.

nokivasara · Feb 5, 2019

Giberish33 said:
You would think there should be increased fueling when the engine is cold but it is actually the opposite. Injection quantity will be higher mg/st (less fuel) when cold and will gradually come down a few points (more fuel), the reasoning being that a cold diesel engine has a hard time combusting fuel until cyl temps come up and fuel temp also comes up a little so to not stall out, fuel is reduced. I have seen this happen when watching IQ in vagcom as my car warms up.
As for timing, it is increased when cold to again aid in allowing the fuel to have as much time to get compressed and create the best combustion possible when cold. Timing like IQ will also come down as the engine reaches operating temp.
I can't say exactly at what temp IQ and timing are "normal" as I haven't watched the entire time but generally its around 80c. That is the minimum temp to check the timing graph in vagcom so I'm going to assume thats also when other things equalize. Operating temp should be 87c -/+5c.
If your saying it takes an additional 10+kms to only go up a few degrees when the engine is already fairly warm, it all pretty much points to thermostat getting very weak and opening up too soon (allowing coolant to pass through the radiator too soon). Fuel economy will be affected for sure because its going to take longer to get up to that point when the ecu values reach normal. What you can do for the moment to help is use some foam pipe insulation and cover up the upper grill vents and the lower grill to block as much air from the radiator as possible.
Some people will also block the side openings but one is for the intercooler and the other is where fresh air enters the fender to be sucked in by the airbox so cover the side ones if you want but I wouldn't.

Thanks a lot, this all makes sense to me. The 80C minimum for testing is probably set for a reason

I just came to think of this because when I had VW IDI's they had that cold start lever that advanced the injection timing a bit and I always pushed that back in as soon as the engine ran well. But on a computer controlled car it probably is done in small steps until the timing is where it needs to be @ normal operating temperature.

JB05 · Feb 5, 2019

The fuel temperature sensor also affects the timing/torsion value on a PD, but I don't know just how.

k_pt · Feb 5, 2019

JB05 said:
The fuel temperature sensor also affects the timing/torsion value on a PD, but I don't know just how.

Really doubt that, torsion value is just angle diference between crank and cam sensor.

Fuel temperature affects start of inject angle, inject duration and quantity.

PD cold timing?

nokivasara

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JB05

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k_pt

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nokivasara

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ejoskf

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Giberish33

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nokivasara

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JB05

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k_pt

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