Piggyback ECUs are Bad for Your Health

I took apart an engine last weekend from an IS300 that literally torched a piston. It had a turbo on a stock engine (2JZ) with a piggyback ecu (engine control unit). No names, but it starts with a big “E” and it can’t really manage. If you haven’t figured it out, the brand starts with a big “G”. If you still can’t figure it out, then just add “reddy” to the end. I usually define a piggyback ecu as anything that does not control ALL fuel and timing outputs.

Piggyback ecus (SHIT) by nature are incapable of controlling a modern day OBD2 ecu with highly adaptive fuel and ignition correction routines. SHIT ecus generally attempt to enrich or enlean the final fuel output by tricking the stock ecu’s air flow meter or pressure sensor voltage. This is fine and dandy, but if you tweak your air flow setting, you are also tweaking the timing at the same time (not good). To make things worse, the stock ecu takes readings from your O2 sensors and slowly trims the fuel map to change the fuel output to match what it is SUPPOSED to be. To make things even more worse, many of the newer engines come with wideband O2s so now the correction ranges are much broader and corrections occur even faster. What does this mean to you? It means that you should unplug that SHIT ecu and sell it to some cheap fuck on Ebay. Are you a cheap fuck? No? Then take that piece of SHIT piggyback out of your car.

Some SHIT ecus actually control your coils/ignitors which is a general step in the right direction. However, some of the shittier piggybacks just trick the stock ecu by retarding or advancing the cam/crank triggers to retard or advance timing. Newer OBD2 ecus are highly adaptive with ignition too. The stock ecu takes a knock count from the knock sensor and continually retards timing until there is no knock. It then continually tries to advance the timing to optimize emissions and power. Over time, if the stock ecu senses that it cannot advance the timing, a long term trim value is “remembered” and the ecu will attempt to advance the timing less often and in smaller increments. This is great feature in a bone stock car and can save an engine. It sucks ass when you bolt a turbo on to your non turbo car. Why? Because chances are if you’re running a SHIT ecu, the A/F ratio is lean. When the fuel is lean the knock count goes up. Sure, the engine no longer knocks with the stock ecu retarding timing, but with the ignition super retarded, the exhaust gas temperatures skyrocket. When that happens, you crack a piston, torch a piston, torch a valve, destroy the head, destroy the block, break/melt a spark plug or any combination of these.

For those piggybacks that control timing independently of the stock ecu, guess what? Those are fucked too. When on the dyno or initially tuning a SHIT ecu, there are no long term fuel corrections in “memory”. But after your tuning session, you’ll start driving around on the street and putting miles on the car. Since I doubt your so called tuner spent 15 hours mapping, chances are he did not match the factory ecu’s air fuel ratios exactly and the stock ecu will develop a long term fuel trim that globally affects the overall fuel output. At the same time, every time you floor the engine and the O2 sensors are reading pig rich, the stock ecu is also attempting to lean out the A/F ratio and will also add to the long term fuel corrections. Over time, your engine will be running leaner than crap. And what about your timing map? You bet your ass you didn’t trim it at the same time the A/F ratio was going leaner and leaner. You will more than likely break your engine in the ways I mentioned above.

When you get serious about horsepower and reliability, stick to these options with PROFESSIONAL tuning. Stay away from those internet tuners who do not have a place of business. Why? Because when he leaves town and something is not right with your car – you’re fucked.

Standalone ECU (Apex Power FC, HKS V-Pro, Motec, Haltech, Hydra, etc.)

Factory ECU with reflash (by a professional)

Factory ECU with reflash module (Cobb, Diablo, Sniper, etc.)

If you have a normally aspirated engine, then a piggyback is OK. Or if you have a turbo and are running like 2-3psi, then you’re probably OK too, but who does this anymore? The bottom line is that the only correct way to control your engine is with ABSOLUTE control. That simply is not possible with any piggyback (SHIT) ecu.

AEM has taken a step in the right direction with their piggyback where you can send a mappable dummy output signal to the factory ecu’s O2 sensor inputs. This definitely helps to prevent the short/long term fuel trims from getting too out of hand, but why not just spend the extra money and do it right? Your engine and wallet will appreciate it in the long run.

Lexus IS300 2JZ-GE torched piston.

The piston was literally torched and here you can see the molten aluminum along the beam of the rod. This guy will spend $15k on a built engine and another $5k on an HKS V-Pro to do it right this time. He only needed to spend $5k in the beginning and he would have saved $15k. Relatively speaking, that’s cheap insurance. Nobody said playing with cars was cheap!

1 comment

  1. I have the jb4 tune, and works well, although have not loaded the app to control chip, i get asplit second jerk or hesitation while normal driving. Do not think nothing but a remap problem as it seems its not getting rid of the exhaust gas quick enough. Could this be just a to upgrade to better bov. 2014 ford f150 3.5 eco with some exhaust/ intake upgrades.

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