VEMS cold start issue

[euro_urs4]

Hi, all I have been having trouble starting my car now that it has been getting colder out, last week i was able to start the car after numerous cranks, now the car will just crank over and no start , any tips on which settings I should adjust and in what increments. Attached you will see my cranking enrichment curve, and other charts that may help resolve the problem. Thank you!

[A80Avant]

i have my cranking enrichment to 500% at -40 and going to 400% at 12C
also my cranking VE is at 86%

there is no specific setting here. If it doesnt start when its colder, you need more fuel. So gradually increase everything on the cranking bins, not the afterstart. If it cranks and then stalls, then tamper the afterstart enrichments.

[euro_urs4]

i have my cranking enrichment to 500% at -40 and going to 400% at 12C
also my cranking VE is at 86%

there is no specific setting here. If it doesnt start when its colder, you need more fuel. So gradually increase everything on the cranking bins, not the afterstart. If it cranks and then stalls, then tamper the afterstart enrichments.

thanks for the response, (excuse the simple question most likely), but what does the cranking VE do exactly? and why is yours set so high at 86%, the car started and ran fine for me in the summer (warmer) months.

[Mcstiff]

All VE is dependent on "Req Fuel" in "Engine Setup", if you cut that number in half you need to double VE. So there is really no "right" number and no concrete comparison unless the other person has all the same hardware (fuel pump, lines, injectors, fuel pressure, engine, etc).

One thing I do notice is that your cranking enrichment never hits 100% which suggests that you could increase cranking VE since you are always adding x% to the VE. This can make things easier but IMO does not make a huge difference since you end up with the same final enrichment.

Also, beware that too much fuel can cause similar starting issues as too little so try working your way up from the hot start levels rather than making arbitrary enrichments.

[euro_urs4]

Also, beware that too much fuel can cause similar starting issues as too little so try working your way up from the hot start levels rather than making arbitrary enrichments.

meaning in the cranking enrichment chart? and thanks for the input

[prj]

Also, this might be painfully obvious, but do make sure that VEMS is showing the correct coolant temperature and the sensor is not knackered.
As no amount of tuning the cold weather bins will save you if the sensor is telling the ECU the engine is at 40 degrees, when actually it's freezing outside.

Btw, in case it's useful for someone, stock 2.2T Motronic cranking enrichment, which I've needed to tweak only extremely rarely:

-33C 1800%
-20C 838%
  0C 363%
 10C 238%
 40C 125%
 94C 100%

[prj]

All VE is dependent on "Req Fuel" in "Engine Setup", if you cut that number in half you need to double VE. So there is really no "right" number and no concrete comparison unless the other person has all the same hardware (fuel pump, lines, injectors, fuel pressure, engine, etc).

P.S.
Putting some theory behind it - VE is engine volumetric efficiency, req. fuel is the size of the injectors/FPR.
If req. fuel and injector offset is calibrated 100% correctly, you could theoretically change injectors and only change req. fuel and injector offset (voltage compensation), but in reality all injectors have a little bit of non-linearity, and as VEMS does not have a fuel system linearization map, some of the non-linearity is always inherently encoded into the VE map.

[GazzaG60]

good info prj

[AndyP]

Also, this might be painfully obvious, but do make sure that VEMS is showing the correct coolant temperature and the sensor is not knackered.
As no amount of tuning the cold weather bins will save you if the sensor is telling the ECU the engine is at 40 degrees, when actually it's freezing outside.

Btw, in case it's useful for someone, stock 2.2T Motronic cranking enrichment, which I've needed to tweak only extremely rarely:

-33C 1800%
-20C 838%
  0C 363%
 10C 238%
 40C 125%
 94C 100%

Based on the above, what sort of AFR would you expect to see on a 0°C start?

[prj]

Based on the above, what sort of AFR would you expect to see on a 0°C start?

AFR is completely irrelevant nor measurable during cranking!
This is cranking enrichment, not warmup enrichment. Once the engine is running this map is not used.

You want AFR, which is air-fuel-ratio, but you use a sensor that measures the amount of oxygen in the exhaust, making it an excercise in futility, especially since your exhaust is full of oxygen at this point from having the car stood there for ages.
The reason there is 3-4x more fuel needed for starting at 0C is because only 20-30% of that fuel ever evaporates and gets combusted, the rest just goes into the sump.

The curve is mainly dictated by the scientific property of the fuels ability to atomize at a certain temperature, and then corrected by good old-fashioned testing by the OEM by placing the engine/car into a freezer. Or in this case by the end-user/tuner by placing himself with a laptop into the freezer (erm car) in the morning

That said, the majority can just copy paste that motronic table and it should work fine, I really only altered it on very few occasions. This goes also for the OP, as to reliably start the engine he needs like 2x the amount of fuel, and the curve is wrong too.
Try adjusting the start VE to have the correction have a value of 100% as the starting point at 90C, then it'll be easier to transfer the values over. This can be literally copy pasted since Motronic works identically to the letter in this regard - it has a starting air filling value (start VE in VEMS), injector size (req. fuel in VEMS), injector offset and a correction map.

[Mcstiff]

P.S.
Putting some theory behind it - VE is engine volumetric efficiency, req. fuel is the size of the injectors/FPR.
If req. fuel and injector offset is calibrated 100% correctly, you could theoretically change injectors and only change req. fuel and injector offset (voltage compensation), but in reality all injectors have a little bit of non-linearity, and as VEMS does not have a fuel system linearization map, some of the non-linearity is always inherently encoded into the VE map.

Agreed. I suppose I should have said that VE values are influenced by the req fuel number as, theoretically, req fuel is dependent on injector and engine specs being set correctly for the VE. As you say, if we were all so lucky to have a VE map specific to our configuration and all info necessary to properly calculate req fuel and injector offset we could basically ignore the VE table.

[AndyP]

AFR is completely irrelevant nor measurable during cranking!
This is cranking enrichment, not warmup enrichment. Once the engine is running this map is not used.

Missed the bit about it being cranking enrichment, I meant AFR during warmup enrichment.

[dkw_dude]

I have my cranking VE set to approximately the same value as the VE table @ 100 kPa and 1000 rpm (in my case 150), starts good on that setting. 40 seems very low. Thanks to PRJ for sharing warmup info. Spent some time last winter in the freezer (car) adjusting cold start parameters

[popdemonic]

I have longer cranking when cold start in the morning with E85 fuel too.
during the day she just starts without problem.i have tried to tweak on the crank VE
a bit giving it more gas and result is better.previously,i needed to give 2nd more
times to fire up the engine.I'm going to give it little more gas hopefully,it will be solved.
Just not had a time to get tuning on the car now.normally the coolant temp in the morning
is 29-31c.

[Morris400]

Also, this might be painfully obvious, but do make sure that VEMS is showing the correct coolant temperature and the sensor is not knackered.
As no amount of tuning the cold weather bins will save you if the sensor is telling the ECU the engine is at 40 degrees, when actually it's freezing outside.

Btw, in case it's useful for someone, stock 2.2T Motronic cranking enrichment, which I've needed to tweak only extremely rarely:

-33C 1800%
-20C 838%
0C 363%
10C 238%
40C 125%
94C 100%

Hey so I know it an old post but really looking for some advice her. I'm having issues on cold start taking 2 starts to fire up and keep running. It will start and idle for 4 second then stall. On the next turn it stays running. I'm guessing crank here is good and afterstart ot warmup needs adjusted?

And warm start needs flood clear to start everytime...should I reduce the fuel at 20c and 80c? The coolant temp is at 68c when trying warm start. So I again assume it's taking the 20c values as it's not at 80 yet? On warm start I smell fuel as well.

my current settings are
-33c 500%
0c 375%
20c 200
80c 150

Thanks to everyone and Merry Xmas to all.