# Master Fuel question

## Recommended Posts

Hi guys, I'm almost ready to start tuning an M54B30 (Vanos disabled, M50B25 intake, standard B30 injectors, M50B25 sensors) running on an E36 G4+ plugin ecu. The base map is sufficient to start the car, though unsurprisingly it's running pretty rich. The B25 base map runs a 177cc/min injector, whereas the B30 injectors are rated to 282cc. Presently the engine is idling at around 11.7 AFR, and seeing 9s at WOT. The Master Fuel is currently set to 20ms, am I on the right track thinking that the value should be closer to 12ms to allow for the 60% +/- extra flow of the B30 injectors? Fuel table numbers look to be about where I'll want them to be if I'm on the right track.

##### Share on other sites

Yeah about 12 should be approximately correct. Might need to be a few points up or down on that depending on how close the base + current numbers match the real values of the injectors, but your calculations are right.

##### Share on other sites

1 minute ago, cj said:

Yeah about 12 should be approximately correct. Might need to be a few points up or down on that depending on how close the base + current numbers match the real values of the injectors, but your calculations are right.

Brilliant, ta.

##### Share on other sites

I would calculate it like this:

If your measured lambda was 0.61(9:1AFR).  Lets say your target was typical NA target of 0.87.  So 0.61/0.87 = 0.70 (i.e need to remove 30%).

New master fuel = 20 x 0.70 = 14ms.

##### Share on other sites

I would calculate it like this:

If your measured lambda was 0.61(9:1AFR).  Lets say your target was typical NA target of 0.87.  So 0.61/0.87 = 0.70 (i.e need to remove 30%).

New master fuel = 20 x 0.70 = 14ms.

##### Share on other sites

One last thing - I assume I'll need to change the master fuel value before starting the engine? Have spoken to a couple of people about it and I'm not 100% sure if I should change the value before startup or after the engine is at running temp?

##### Share on other sites

1 hour ago, MattR said:

One last thing - I assume I'll need to change the master fuel value before starting the engine? Have spoken to a couple of people about it and I'm not 100% sure if I should change the value before startup or after the engine is at running temp?

You can do either, often easier to change it while it is running - then you can just bump it up or down until it runs best.

##### Share on other sites

• 1 month later...
On 11/6/2018 at 3:36 PM, Adamw said:

You can do either, often easier to change it while it is running - then you can just bump it up or down until it runs best.

After changing Master to 14ms as suggested, I've discovered that the data I had re injector cc rating was incorrect. Instead of the 282cc/min I was told it turns out they're more like 236cc/min @ 3 bar. To get my idle closer to 14.7 the fuel table cells are around the 16% mark, which is leaning the engine out to the point of stalling once all warmup enrichments are removed. From what I can tell from the logs the 16% value puts the injector at or very close to below its minimum injection time - would I be increasing the Master to say 16-17 and continue to lean the cell values out until I get 14.7afr? Or do I need a smaller Master number?

(start the log file at 8:10, I forgot to edit the irrelevant bits sorry)

Thanks again

##### Share on other sites

Looks pretty ok to me towards the end of your log.  Warmup enrichment stops at 90deg ECT so that was already not having any effect from about the 2 minute mark.  Leave the master fuel where it is and start tuning your fuel table now.

## Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

×   Pasted as rich text.   Paste as plain text instead

Only 75 emoji are allowed.

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
• Create New...