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I have a car in my shop that has a nice looking turbo kit on it. The cars owner installed it but he could not get it to run at all. It has a single turbo with a Microtech(mazdaspeed) piggy back ecu on it. The barometric pressure sensor was missing. After retrieving it from the car owner The car would start and stall at idle. If reved up, it would cycle on and off. I found that the bigger fuel pump that was put in the tank was turning on and off and overheating the fuel pump relay. It blew one of the ecu fuses and then would not even recongnize the key to start. After wiring in a relay for the fuel pump and replacing the blown fuse. The car runs and is almost ready to tune. There are two issues that i need to clarify first. The base map for timing that came loaded in the piggyback is 5 degrees at idle and goes straight up to 25 and stays there. I checked the timing with a light to be sure it really was 5 at idle but, here is the question. the trailing plug reads 5 degrees but the leading plug has a lot more. Which should be used for base timing? Should they merge at a higher RPM? Is 25 too much for a boosted motor.
The other issue is it seems that the Original ECU is was trying to control fuel pressure with a duty cycle to the relay. With it wired to battery voltage the fuel pressure is an unsteady 75lbs. It doesnt sound good. I think it needs a return fuel system with a real regulator. Any suggestions will be appreciated. |
You have a very long list of complex and overlapping misunderstandings there that probably need to be addressed.
The OE PCM does not control fuel pressure with duty cycle. It is just a two-step, voltage regulated circuit for the pump that is internally regulated at the pump assembly to 65 PSI or so (58 - 68 PSI, giver or take). If the OE pump motor was replaced with something else that has a higher discharge pressure or flow, the OE regulation system will swamp at 70 PSI or so and the pressure will be up and down at the rail. Without seeing the pump unit, I can't tell you what's in there, but there is a pretty good chance that the installation was botched because there are only a few pump replacement schemes that work and most people get it wrong. The Microtech is not a "MazdaSpeed" piggyback. It is a system that was sold by an outfit in Florida (the now defunct MazSport) called the "Interceptor-X", which was a specially ported version of the Microtech. It is a sub-optimal system at best, but it does utilize the original Microtech ignition timing scheme, which uses a series of overlapping tables to arrive at final timing. That said, if the trailing timing is -5° and the leading is 20° or so, the ignition timing scheme is actually the OE system or the previous programmer of the Interceptor sought to emulate the OE timing. 25° of peak leading timing is too much for this motor, but not by a lot. However, that "flat" timing map is just the base timing and is affected by the "t-MAP" table which will retard the timing based on boost. You need to look there for the math to figure out what the resultant timing will be. Your fuse-blowing situation is also probably the Interceptor - it is notorious for having a serious botch-job going on inside the box with respect to the main power. Tuning the Interceptor-X is a major PITA. Not because it is complicated (it isn't inherently, though tuning a rotary motor is not all that similar to a piston motor, so if you are not familiar with that, you are in for some surprises), but because it does such a horrible job of managing a changing environment. Even the smallest shift in atmospheric conditions will ruin the tune. Having the BARO sensor won't matter to the Int-X because it doesn't use it. In any event, it seems you have your hands full with that project and my advice to you would be to pull in someone who is familiar with tuning the RX-8 as a turbo application. |
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