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This article’s purpose is to educate individuals who may be attempting to tune their cars with open source, or other consumer products. The intention is not to point out any inadequacies or call any particular tuning style wrong, I’m writing this in an effort to spare a blown motor or two. This article will go over the top mistakes I commonly hear from new do-it-yourselfers.

Making changes to a car and assuming that fuel as already ‘dialed in’.

The number one mistake I generally run into its changing one variable and not expecting it to impact other parts of the tune. An example of this would be “I’ve got my fuel dialed in, I think I’ll sell my wideband”. This is making the assumption that it wont change over time or in other conditions. When tuning a car many things will impact how the car reacts to fueling changes. Cam angle(AVCS), boost, head volumetric efficiency, etc. I’ve seen adding a header to a car lean a mixture out over .25 AFR. If a tune was already knocking this may be enough to detonate and destroy ring lands or crack a piston.

Riding the Stock Knock Sensor

This is an issue I commonly see with off the shelf maps. The ECU does a pretty good job of protecting the motor from knock as long as its given a chance to learn before too much load is applied. The issue with some maps is since they are designed for the one size fits all mentality - there is no way it could possible be close to the timing that would be able to make good power without knocking. Bottom line is all motors knock - OTC maps often knock frequently. Since most of the time OTC maps make alot of assumptions and run lower than max boost(thinking this is safer), they add a ton of timing in - especially in the higher rpm’s. So if the car may only be able to run 19 degrees advance at 6500 rpms, the ecu will pull timing until knock subsides. I commonly see over 34 degrees advance on OTC maps in that same region. That would mean you may suffer up to 3 knock events before the ECU learns how much timing to apply in one rev to redline. While the ECU will generally save the motor from detonating - I find the practice very bad and so does your motor.

Intake Diameter and the Mass Air Flow Sensor

Another very common mistake is bolting up an aftermarket intake with out making the necessary adjustments to run correctly. Even on cars with the stock airbox I’ve seen AFR trims that are significant enough to impact the way a car would run, on an aftermarket intake they are not even in the ballpark. When I tune a car my goal is to get the trims as close to as 0% as possible - these will change some with climate but should always be within 5%/-5% or less. These trims are eventually applied to your fuel table and will make the car run more lean or rich than before. If its too lean, this is a much bigger issue and is putting your motor at risk. If its too rich the car will run poorly and rob most of your power.

Choosing Small Injectors for Big Power

Frequently, alot of people have already purchased injectors before locating someone to tune their car. I see this alot, “I have an 18g, 650cc injectors”. There is some myth out there that large injectors are difficult to dial in and run properly. This simply is not true - just like any electrically driven component, it is controllable. I would much rather have 200cc’s of unused bandwidth than be in the middle of a tune on an 18g and say well, your at 95% injector duty cycle at 18psi - come back when you have larger injectors and we can make about 50 more horses.

Well - that is all I have for now, I’ll probably have some more info published in a few more weeks. If you have any questions feel free to shoot me an email at keith_fields@awdtuning.com

Thanks!

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