What is Sequential Fuel Injection?
Sequential fuel injection attempts to only spray fuel while the intake valve is open for the cylinder that is about to fire, which in most cases is only possible at low engine speeds between idle and low speed cruising. Benefits can be seen in emissions, drivability, and fuel economy particularly at these low engine speeds and loads.
Batch Fuel Injection
Batch injection (which is what the MegaSquirt-I and and most MegaSquirt-II versions do) does not attempt to spray only when the valve is open. It’s a fact that at higher engine speeds you won’t have enough time to spray all fuel while the valve is open, making this somewhat pointless, particularly for a performance oriented application.
At these higher engine speeds 99% of sequential systems (exceptions being race only systems with super massive injectors) cannot spray all of the fuel needed while the valve is open anyways, and sprays it both while the valve is opened and closed, very much like a batch system such as the MegaSquirt I and II.
Batch versus Sequential — what gives?
Read Chapter 4 in the EFI Tuners Guide for more information on the benefits of sequential versus batch fuel injection. You might enjoy that entire series actually!
We’ve dyno tested several cars with using batch fire and sequential injection on the same motor. Peak power was more or less the same so long as we did not employ individual cylinder tuning on the sequential injection system. Worth noting though, the sequential fuel injection system did fire up a bit smoother/easier, and run a bit more smoothly at idle and at light throttle angles. But for a race car, many would say you’re splitting hairs a bit there. If you want to know where sequential fuel injection systems really shine in getting the MOST out of a motor, read on!
The MegaSquirt III system with the MS3X Expansion board or MS3-Pro will do full 8 cylinder sequential fuel and ignition. If you’re looking for the absolute best possible emissions and fuel economy, as well as the ability to fine tune each cylinder individually, then the MS3 system is the way to go.
As for Plug-N-Play (MSPNP and MSPNP Pro) systems offered by AMPEFI/DIYAutoTune, the MSPNP Gen2 systems support sequential fuel injection for 4 cylinder vehicles so long as the stock ignition system offered up the crankshaft position sensor and camshaft position sensor signals needed for us to be able to do so. MSPNP Pro systems offer the same support of sequential fuel injection for up to 8 cylinders (and more is possible if we were to build an MSPNP Pro for a vehicle with higher cylinder count, the core supports it).
As a general rule, most of the benefits of ‘going sequential’ are in the fuel economy and emissions space– there is generally no significant performance difference with a sequential system over a batch system unless you use individual cylinder tuning. There can be minor emissions and fuel economy benefits particularly at very low speeds though. If your tuning budget allows for individual cylinder tuning, it may be possible to pick up 3-4% more power depending on how much cylinder to cylinder variation your engine has, while also helping to ensure that you can tune your engine to be as safe as possible while still pushing it to the max.
So are there benefits to ‘going sequential’? And are they worth it?
Well, in a word, YES! Automakers would not have made this the standard years ago were there not. That said, they mostly come into play regarding improved emissions and fuel economy, which is obviously a key focus of OE automakers. For a pure race car as we tend to cater to, the answer is closer to…. it depends. If you’re going to take full advantage and tune each individual cylinder like it was it’s own independent engine, and remove the variability of air/fuel ratio per cylinder that is native to ALL engines by dialing each cylinder in to it’s unique airflow characteristics– the by all means, yes!
With a properly setup and tuned sequential fuel injection system using good data and dialed in on a proper dyno, you will be able to make all of the power your engine can SAFELY make by tuning all the cylinders to your target air/fuel ratio, and pushing your ignition timing to the max that you can safely run, knowing now that your AFR is safe, and you won’t have one lean cylinder ruin your day! On the other hand, if you’re going to slap that system on your engine and tune to a single O2 sensor in a combined tailpipe, you’re getting the average of all cylinders in a single reading, and you won’t know which cylinder is contributing most to the mix. This will lead to a need to be just a touch conservative regarding ignition timing, and target air/fuel ratio.
So- give me an example of the difference!
Hypothetical – If you were perfectly tuned with all cylinders balanced for instance using a sequential injection system with individual cylinder tuning, let’s say you should be able to run 15 degrees of timing and 11.5:1 gasoline air/fuel ratio (AFR) under boost… you might instead run 13 degrees and 11:1, using a bit more fuel overall to help ensure that you don’t have a dangerously lean cylinder, and using a bit less ignition advance overall just in case you do!
MS3Pro and MSPNP Pro have you covered!
Check out the MS3Pro and MSPNP Pro systems (which are MS3Pro inside – aka MS3Pro PNP) and their capability to help you, along with the TunerStudio tuning software, to not only tune each cylinder out individually by hand/manually– but also to do so using VE Analyze Live, our version of ‘autotune’, to automatically tune each cylinder of your engine for you!
You can do this with individual wideband o2 sensors on all cylinders… OR… you can do this by moving a single wideband o2 sensor around and letting TunerStudio build a trim table for each cylinder one at a time! We’ve been offering this feature with our sequential fuel injection systems for years now, we’re still waiting for the ‘big name marketing machine ECU made in who-knows-where manufacturers’ to catch up and try to claim they did it first. As usual, they didn’t, we did! And we made them, and continue to make them, right here in the USA!
