Fuel starvation is probably one of our biggest enemies. With a simple fuel pump upgrade, running beneath 1/2 of a tank, making over 350whp with no other resources, it’s a near guarantee to happen, at least briefly.
When air is picked up, while the injection time is met, the fuel just isn’t in the line, available to be injected, so the injector injects whatever is in the line. If there are bubbles, it usually wont be pure air, if it doesn’t misfire altogether, it’s enough to yield a combustion, just typically a much leaner one than intended.
Depending on the scale and frequency of these air-ingestion events and other factors, this can lead to nasty detonation events and parts failures.
So what can we do!? Obviously, a surge tank. Surge tanks are made to solve this. A surge tank is a second, smaller tank that keeps the pump fully submerged, even if fuel level is modest and even if the primary intank pump picks up some air. As long as the surge tank is mostly full, it drastically reduces the chances of sending air to the rail. But there are options before getting this far in also.
For the e46, BMW made a special solution for the M3 that drops into all nonMs.
This will certainly help a bit. It holds return fuel more directly over the pickup.
Then there’s a hydramat. The hydramat is a special sock. It somehow will give fuel preference over air- though honestly I have no clue how it does that. Most importantly is that it does. So if it’s in contact with a relatively small amount of fuel, it can do a very good job of not pulling up air. We carry these for traditional mounting for a e36/e46 fuel pump hanger.
None of these solutions preclude each other. Throwing the kitchen sink at it is a solution. At every step, if air can be prevented from entering the fuel lines, it’s always a win. So even with a surge tank, a hydramat and M3 baffle still help.