Join Date: Aug 2003
Location: Torrance LA, Camp Patriot Kuwait
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So OP, you need to decide on EMS? Its a big one.
Tuning a piggyback is like having to work with two parties/groups of people to get a project done. Imagine your in a meeting and you have one group- say the engineers (the piggyback) with a design goal in mind (boost- fuel, timing, power), and at the other end of the table there are program people/bean counters with the goals from corporate that common sense from the engineers is not allowed to trump (OE ECU)- its march or die. Your in the middle trying to make the overall goal (say making a new model of smart phone) work out, both parties getting their goals met (say engineers want X speed and performance, removable memory, Y battery life etc) and bean counters want it done with only a certain SOC supplier, costs below what supports X speed and memory options etc. IMO it gets into a game of trickery and compromise that requires a thorough understanding of both parties- where they are coming from, whats reasonably possible.
Put this analogy into the Piggy and standalone conversation, and with the piggy- a) you need to know what are normal signals-- get an OBDII logger and get to know your car before even modding it. Understand that our ECU is more like two ECUs, Siamese twins of ECUs if you will- when manipulating exhaust streams, o2 sensor locations and count, etc, it can get really messy when the o2 reports things that make either ECU change things per their programming and it starts to seem un-tuneable. b) the OE ECU is on your side, it wants to run good N/A timing, it watches the OE knock sensors, it wants to run good air fuels for an N/A setup. Help it do it's job and it won't throw much of a fuss- compensate for larger injectors correctly, put the MAF in an optimal location, plumb things with sensor performance in mind, don't use 20 year old nasty a$$ injectors that have a piss stream for atomization etc.
It can be really hard, but tuning a standalone can be really hard too, its a very relative term. IMO I can take off tuning a piggy faster than a standalone, as IMO a standalone requires a lot of attention to operate as if you have an OE ECU. In fact IMO there should be two types of people you take your standalone to, a calibrator, then a tuner-- or a tuner that clearly demonstrates a strength in calibration. I think the ease people find in standalones is the brute force of it-- you don't have to worry about the OE ECU- just brute force ignition and fuel control and for many (the many that do not continue to refine their setup, just slap a standalone on and throw it at some hack tuner in their town), live with odd idles, weird VVTi powerbands, inconsistent tune with weather changes etc- which is far more liveable and likely more reliable than a badly tuned piggy setup.
I'll concede I ran into a 2001 EMU setup that somehow, someway, had a "slippery" tune that the band-aid was the all famous reset relay. In my defense I didn't get to spend more time on it to play with some more ideas.
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