when i did compresion test one of my cylinders came up about 5-8 psi lower than other cylinders.
and also was around 6-7% for leakdown test.

should that be adjusted by individual fuel trim in neptune or small deviation like that would not make a difference for the engine.

 

i honestly dont think thats a big enough difference to matter.

is it cyl #3?
does the spark plug look visibly different from the others that it may have a slight lean condition?

 

Run a wideband on each runner.

 

You could try it and check plugs, probably the easiest way. I usually add a few percent more to cyl 3 to help possibly cool it down, but I have never really seen anything noticable on the plug before compared to others. But this is only a quick eyeball, not checking further down on the porcelain base color.

 

I was just thinkin about that.
Is there a minimum distance from exhaust port for wideband install.

I think 4 bungs are cheaper than buying an egt setup
It is cyl 3 because rings disnt seal as good as other cylinders
Other 3 cylimders have about 2-3 % leakdown if i remember correctly.

 

Neptune is not able to change the parameter which "needs" to be changed in this situation although, honestly, just because your static compression test shows you low in that cylinder that may change in a dynamic situation when the ring expands from the higher cylinder pressure. what you would need to change to "fix" this void would be ignition timing and injector phasing. However, changing cylinder ignition timing (on a capable system which is able to do it without blending these changes to other cylinders)and injector phasing (given the system has these parameters) can be done on cylinders that are perfect because each cylinder will be different. Not every cylinder will induct the same air, not every cylinder will reach the same peak cylinder pressure....etc.

 

Why can't the Individual Cylinder Trims under Fuel/Ignition Corrections be used? What parameter would need to be changed if this does not suffice?


I am in the very, very early stages of learning about Neptune and tuning so I am learning what does what in this program.

 

neptune can change fueling for each cylinder, it is something you need to be careful with. And if you dont know what you are doing, i would leave it alone until you understand more of the basics of the software as there are more important aspects of tuning than learning that right off the bat.

Thats the only parameter which can change per cylinder. I would not try and judge a cylinder fueling/ignition offset based off of a low rpm compression test. To really see whats going on, you would need a cylinder pressure gauge with an external logger to see it graphically based on RPM which you can then cross with your timing and fuel table. But i wouldnt be able to justify doing all that for a street car. Great data and a great way to understand combustion but for your average street car, no worth the money when following standard guidelines when tuning can yield great results.