2003 mp5 alternator modification

ok so ive been wanting to swap out my alternator. I know people are going to say it isnt possible :( and i have already talked to shops and read the posts

my question is a little different

the mp5 uses a ecu regulated alternator this i know and this is the cause of much frustration. Does anyone know what the wires going from the alternator actually do and how does the ecu control the alternator or vise versa. 

"Computer games don't affect kids, I mean if Pac Man affected us as kids, we'd

all run around in a darkened room munching pills and listening to repetitive

music."-Kristian Wilson, Nintendo Inc.

Not sure about Mazda mp5? But I recently dropped in a Fitzall 220 in my Corolla (1990). I was told by Fitzall and a good friend who runs a shop that I may need to apply 12v to one of the legs. ?? My alty harness had 3 wires. White - Ignition switch Yellow - Chg. warning to Inst. cluster Blk/yel - Eng. Fuse I have not done anything with this harness, it's just unplugged. I don't have any alarms or dash warning light coming on. So far, so good. I was still not 100% comfortable so I took my electrical schematic to a local Alternator shop. The guys there told me that without the plug being in, I should at least get a charge warning indicator when first turning my key to the ON position. Maybe my cluster light is out? You can have your original alternator rebuilt for higher output but may or may not be adequate for your system. The best my OE would do is 165a. (so I was told) I am sure there are some old-school pros here that can elaborate on details of your car. This was my personal experience on a 1990 Corolla. Best of luck to you, they really do make all the difference in the world. Still learning

Kraco

Can work one of two ways that I have encountered. There is a feedback terminal that tells the ECU the alternator demand or load, this can be used to compensate for engine idle speed control. When large electrical consumers get switched on, headlights, blower, then idle speed can be compensated to prevent or limit the sag in engine speed from the increased electrical load. These types can be both fixed voltage regulator or also have ECU controlled charging. The second type is a commanded terminal where the ECU controls the voltage regulator, these can get into fuel economy gain strategies, something like charging the battery when the engine is in decel fuel cutoff or reducing charging load during WOT. Things of that nature. Some alternators can have both feedback and control, some only feedback. I have not seen an alternator with control and no feedback (doesn't seem feasible but doesn't mean it doesn't exist) In regards to nodiggie's response regarding applying 12v to one of the legs: If the alternator doesn't receive 12v on the appropriate terminal it may start off in "limp-home" mode and not have any charging output. That is until it reaches a certain alternator RPM. It will then switch on internally and then start to self regulate again. That might be why you aren't seeing any difficulty in your setup without applying 12v to that wire. (Again, manufacturer specific) For the charging lamp not working, its most likely because you don't have the other side of the bulb connected. Usually their is 12v on one side of the alternator/charging lamp and the other side hooks up to the L or Lamp terminal on the alternator. When at rest, there is no voltage or ground at this terminal making the lamp light. When the alternator is producing voltage, the terminal will show positive voltage = to the voltage on the other side of the lamp/bulb and no voltage drop means no illuminated light.

Most alternators must have the charge lamp to guarantee charging. If there is no residual magnetism in the rotor, it doesn't matter how fast it spins, it will not excite and hence not charge. Only if it is just below threshold residual (or remnant) magnetism will increased RPM allow self-excitation. However this does not mean the unit will charge - some alternators MUST have external voltage applied to the D+ or L (charge lamp) circuit to work. F.ex - the Bosch S&L must have ~12V applied to both S & L terminals else the regulator will not operate and hence will not pass rotor current. (I read elsewhere where someone claimed otherwise and even posted the Bosch schematic "to prove it" - except that it didn't prove it, and his claim was simply wrong - at least for the Bosch alternators I used until I returned to the faithful Jap brands.) As to ECU & alternators, when I first heard that, I thought crap. However it does apparently exist and though I question its interpretation, I certainly question its function.... (Not for combined starter motors & alternators - just the dedicated alternators.) But it is interesting hearing the reasons etc. There are 2 load parameters - voltage and current. Traditional alternators never regulated current - they merely regulated voltage. And during acceleration, if an ECU wants to reduce the load of an "up to" 2HP alternator and thereby drop the voltage from 14.4V to 12.7V or lower, I guess these days it can since CDI ignition is common (hence you don't lose 40% spark energy etc), and likewise HIDs don't dim. But at first I thought I was hearing a repeat of racers that wanted to disconnect the alternator (using an air-con clutch!!) during racing. Surely they'd dump the alternator and use CDI and a full-loss system, else (with non-CDI etc) reduce their battery size and keep the alternator?

does anyone know specifics about the mp5 what each wire does perhaps

how does the computer and the alternator comunicate i guess is what i am trying to figure out

is it done by resistance on the wire?  voltage differences perhaps?

does the alternator need computer feedback? or can the plug simply be disconected or modified?

will it only lose the rpm increase under load or are there any other negative effects to this idea.

i have a hard time believing that a car like this would have such a sophisticated electrical charging system that cant be figured out and modified

thanks for any help in this matter

"Computer games don't affect kids, I mean if Pac Man affected us as kids, we'd

all run around in a darkened room munching pills and listening to repetitive

music."-Kristian Wilson, Nintendo Inc.

The alternators that I have worked with that provide feedback/control with the ECU communicate via LIN bus. I do not know the specifics of your vehicle. Trying to track down a spec for your stock alternator would be a good starting point. I forgot to mention in my previous reply that your alternator is going to be diagnosed too (Good old OBDII) and in addition to the charging lamp you will most likely set the MIL if you just leave it disconnected. Without a spec for your particular alternator its hard to say what the ECU needs to see or how its diagnosed. oldspark, In regards to the Bosch alternator: The last one I worked with behaved the way you described, it needs to have 12v applied to the L-Terminal in order to function or the alternator is left in limp-home state. That is until it reaches a certain speed and then it would switch itself on. (4000 RPM alt. speed for this particular case) So in theory, you could start and idle the car and be running off the battery only not charging the system. Until you drove away and the alternator reached its turn-on speed and then it would begin to regulate voltage. This was a low feature, feedback only model btw.

Thanks for that info.... Mind you, with alternator RPM typically being similar to crank (at least for my 0-6500RPM engines, namely 1.05:1 gearing), that means breaking the speed limit for a charge. (And yes, I have been charged enough thank you!) I only tested my Bosch to 2,000RPM. And I also noted that without the L circuit, the regulator would also stop. (Some alternators will continue charging even if the L or D+ circuit is disconnected AFTER initial charging commences. Those that do must switch off the regulator after the alternator ceases output - ie, engine stall or off.) Since the Bosch S terminal is connected direct to the battery, it is the L circuit that tells it that Ignition is on (since it obviously isn't using RPM sensing). I understand its off operation when the S terminal is disconnected. BTW - I have recently seen mentioned an alternator's limp home state. For non-ECU connected alternators, isn't this simply a dead alternator? (Limp-mode EFI and ignition I well understand, but a simple alternator? It's either charging or not (or partially due to internal faults).) Is this something I have missed?

Newer BOSCH alternators I've worked with have an ASIC in them so they are not so "dumb" anymore. Even the economy models. While it is either charging or not, limp-home may not necessarily correspond to a dead alternator. In some cases it is just not initialized due to an incorrect/broken L-Terminal connection and it does not regulate voltage until it reaches the turn on speed, also referred to as cut-in speed. I don't want to get side tracked on pulley size and gearing, but i typically see around 3:1 ratio from crankshaft to alternator pulley for the OE work that I am involved with. Ensuring under normal conditions the cut-in speed would be reached while driving but not necessarily at idle after a start.

The Bosch is academic for me - I tried them and they failed (weak stator diodes - a bullsh spousetale about leaving the jumper battery connected proved to be true after all! ). I'm using Hitachi and NDs which are different in behavior (not that I have investigated yet). But as I said, that extra bit about exceeding a certain RPM is well worth knowing (for others). Thanks! But I assume that requires residual rotor magnetism unless some of the the (typical) 12uA S current goes through the rotor. And there is the blown L lamp issue - but that is almost impossible in post 1970 vehicles - it is usually due to a disconnected L circuit. But such issues are no priority for me.... Enough butts, as you indicated, we shouldn't hi-jack. I too would like to find out more about ECU-alternator interactions. I have heard some explanations to do with voltage regulation and I find them flawed - or rather - a bad and unreliable design. (A self-contained alternator that sensed the battery is best and all that is required. Load prediction for regulation should be irrelevant!) But as a way of increased acceleration etc, I can see merits, though I question the resource - especially if still using a separate starter motor etc (ie, save weight by combining alternator and starter - that may effect acceleration more(?) and certainly improves fuel economy more).