Reducing the number of DNFs in GTR2 championships

Not sure if I should post here or GTR2 Misc but here goes.

I am getting very high levels of DNFs in some races. For example, I did a 30 lap race on Virginia Raceway, Grand East Course, and by around lap twenty five all 12 cars (including myself) were DNFS. I am not sure if this is due to mechanical failures or not. I know you can turn off mechanical failures in the standalone races, and I think it is possible to turn them off in the championship via editing stuff in the userdata folder, but I still seem to get the same DNFs.

Any ideas? I have not yet observed this happen in any of the original tracks, and it only occurs in some user made tracks, so I am wondering if each track has code controlling this.

The fuel lap estimate for this track is wrong. Too low. I'm not an expert but the problem should be in the .AIW file.
There is a line "fuelEstimate" or something like this. You have to raise this value.

Thanks for the suggestion. Alas, it does not solve the problem, it seems not related to fuel use as such but rather rather any pitting will make the cars DNF on this track. The race runs fine if I turn off fuel use and tyre wear, having run a three hour race without any DNFs in a 24 car field. Also, I read that DNFs can be caused by too few pitboxes but I get all DNFs with just two cars running.

I might have a play around in the awi file (I was wondering how to modify this sort of thing, being new to the game, so finding out about the awi file is very helpful).