Turbo buick tuning

[Vrturbo]

Id say its trending rich mostly but can be either way depending on rpm, the afrs arent steady ever like they will jump around a little bit all throughout the rev range fluctuating mostly between 13 and 15 sort of range but very quick jumps like will go 15 then half a second later at 13 and reduce timing as in lower or raise the number in the spark table?

[immortality]

Keep the timing stable and at nice and conservative number and work on cleaning up the fuelling. Once that is sorted than you can chase the timing looking for power.

[Vrturbo]

So you think it could be the timing making it backfire once it gets into the boost spark table? Its not just the odd backfire its like 2 step limiter wont let me rev past around 3k revs

[antus]

check the fuel first, more likely that, or ignition problems (trigger or insufficient spark or wrong plug gap).

[Vrturbo]

yes antus you were correct it ended up being my coil packs werent bolted down correctly so their ground to the engine wasnt good enough resulting in bad spark at high rpm i fixed that and now its going really well no issues at all just some light tuning to do and it will be golden thanks

[vlad01]

I was going to say most likely a coil or module connection issue.

Many years ago when I first got into these cars, I had the exact same issue. Turned out that I forgot to tighten the 7mm bolt on the DFI plug, so it was only lightly seated in, ran ok for a few days before it was backfiring under load and more than around 3-4k rpm. I was an hour from home and pulled over next to a bus depot where I found the issue, I went over to the depot and they let me quickly borrow a 7mm, tightened that bolt and the issue went away. I had done an engine swap and forgot to tighten than one bolt.

[Vrturbo]

Yeah very easy to forget little things like that that make all the difference, another question i had is when tuning my ve table should the numbers be close to 100 before boost or a lot lower its around 50 ve at idle currently. I read the advanced tuning guide and in that the ve table only got close to 100 when it was on boost but didnt explain why, my engine is leaning out under boost so i raised the numbers so theyre sitting around 120-130 ve at 130kpa not sure if this is the wrong way to go about it or not

[immortality]

It all has to do with (or rather centres around) atmospheric pressure.

See https://en.wikipedia.org/wiki/Atmospheric_pressure

Basically put, atmospheric pressure at sea level on a standard day is 1 bar or ~101kpa. So on a n/a engine with the throttle wide open you should see about 100kpa pressure inside the intake manifold (assuming everything flows perfectly which it doesn't).

At idle, with the throttle closed (on a stock style motor) you would expect to see somewhere in the range of 30-40kpa manifold pressure.

When you get into boost you are creating pressure over and above atmospheric pressure inside the intake manifold so you will see readings over 100kpa

Anything under 100kpa is vacuum, everything over 100kpa is pressure (boost).


VE is volumetric efficiency. A good n/a engine would be 100 volumetrically efficient (in a small rpm window), most OEM's are probably in at around the 80% efficiency. When you add boost you are artificially increasing VE in excess of 100% so yes, you need to increase the VE numbers in the map (table).

[vlad01]

Pretty sure the VE for each range in 12P has only a 0-100%, it is the calculated efficiency of the engine's ability to ingest air regardless of the available air pressure, so it doesn't care if it's boost or NA. So there will be a VE for 0-100 kpa and one for 100-200kpa for example from what I recall last time I tuned a boosted engine, the addition of boost basically just extents the kpa range while VE % range remains the same, but of course the way the code and map sensors work, they are split into seprate tables, but you can just look at it as the same table longer sideways, split into two down the middle. The tracer moves along this as if it's one table if you watch it. You physically can't go past 100 VE in any of the tables, it will clip at 100%, much like trying to overdrive an amp, it will clip at the voltage rails as a good analogy.

Good practice is to aim for a max of 85-95% VE so there is a buffer and a lot of the internal code models are built on the assumption of the VE being around that at max. The number is somewhat arbitrary anyway as you can adjust the injector flow value to scale the VE as needed to get into that ideal range. So if the injector flow scalar is increased by 10%, the VE can be scaled down 10% for example. This also allows one to readjust the entire map when one realizes their VE is calculating past 100% which as mentioned just clips back to 100% as that is the max.

[immortality]

AHh yes, that's correct. (I've been looking at MAF tunes for too long).

Have a look through the tune repositories and find something similar to what you are doing and have a good look at the tune, it will give you a idea of what you are aiming for.