[urq] Mac 02 repair - How to.
seiche at shadetreesoftware.com
Mon Feb 26 13:47:45 EST 2007
FWIW, yes, I used to repair these and still could, but honestly, these
are a PITA. Not because of the ECUs per se, but because I end up being
on the hook for troubleshooting other CIS issues, like vacuum leaks,
pressure issues, sticky metering heads, etc. Soooo, because I really
never want to mess with another MAC-02, here you go:
First off, make sure that you actually have an ECU issue. First make
sure that you have NO vacuum leaks. A pressure test is best, but the
quick test is to pull the dipstick. The engine should stumble, but
continue to run. Then pull the oil filler cap. The engine should die.
If it doesn't you likely have a vacuum leak which MUST be fixed before
you should mess with the mixture setting. Often, a mixture setting that
is not correct will cause the duty cycle of the valve to be out of
range, perhaps because someone compensated for a vacuum leak by
adjusting the mixture, and once the leak was fixed the mixture is too
rich. Sometimes the valve will run when the engine is cold, but once it
goes open loop it will stop. If this happens, your mixture may be out
of range of the control. If EVERYTHING else is OK - no leaks, correct
fuel pressures, good O2 sensor, then you probably have a failed ECU. It
is pretty common.
Parts for MAC-02 ECUs. First off, IME, the actual output driver usually
doesn't fail. The small signal transistors that drive it usually do.
These are components Q8 and Q6 on the board. I believe that one handles
the warm up and the other operates with the Lambda regulation, but I
don't have the schematic in front of me. You should replace both of
them. These are standard NPN transistors, but I bought a bunch of the
actual 2SC458s just because I like to keep it exactly as is was. I
bought them from www.bdent.com years ago, but you could also get them
from matelectronics.com. You can use something like a 2N2222 as long
as you make sure you have the collector, base and emitter in the right
place as the 2N2222 may not have the same pinout as the 2SC458. Note
that the PCB is marked. As for the main driver Q7, which is a 2SD1087,
they are long gone. I have seen a few places that list them, but once
you try to order them they cannot be had. I don't see any reason that
you couldn't substitute another injector driver, like those used in more
modern engine computers, but I haven't had the need. Anyway, with all
of the engine swaps going on, there are a lot of good MAC-02s floating
As for other failure items, #2 on the list is the pressure transducer,
which have been NLA for about 20 years. The most common failure mode is
0V output, in which case the timing is very advanced (the ECU thinks
that the engine is under full vacuum - no load) and will ping badly
under boost. IMO, this is often caused by resistor or diode mods put on
the output of the sensor, which puts too much load on the output, which
eventually fails. They can also fail with a full scale 5V+ output,
which will cause the engine to start but the fuel pump will cut as the
ECU thinks that there is too much MAP (overboost). These are simply 2
bar MAP sensors with a 0-5V output, but an 8V supply. You can
substitute the MAP sensor from a later MAC-1X ECU, just grab 5V for the
supply off the the PCB instead of the original 8V supply. The range,
offset and linearity of these are close enough that you won't notice
operational issues. I think that a 2 bar Bosch MAP, like from '91 200q
which I have a TON of, would also work, but the sensors from the MAC-1X
ECUs are nice because you can use the vacuum lines and fitting from the
MAC-1X box in the MAC-02.
Some tips on soldering on these old boards. Number 1, do NOT use solder
wick to remove components. This puts too much heat onto these delicate
old boards (or ANY PCB IMO), and WILL result in lifted pads, etc. Use a
vacuum type desoldering tool and add new solder and flux before you suck
out the old solder. Wiggle the pins a bit with the tip of the iron as
you heat it to make sure that the pins are free. Number 2, If you don't
get all the solder the first time, add more solder and do it again.
Minimizing the amount of time you heat the PCB is critical. You should
not be touching the PCB with the iron for more than 3-4 seconds. If done
properly, the component will simply lift off of the board without
needing to be pried off. If you are prying any harder than is necessary
to free the chip from the conformal coat, you will likely damage through
EPROMs. The ancient 2532s are long NLA. You can find them from
electronics places that have parts for old video games, but you may need
to buy a few to find one good one. These generally aren't as robust as
new IC designs. If you really want to, you could make an adapter for a
more modern EPROM, like a 2764 fairly easily. The pinouts for both
EPROMs are easy to find on the web.
Sockets. If you don't want problems, use ONLY machined pin sockets with
gold contacts. ZIF sockets are not suitable for vehicles, or any
equipment that vibrates. If I see these in ECUs that I work on, they
are the first things that I remove. Personally, I can't think of
anything other than a programmer that I would use a ZIF socket in.
OK, that is about all there is to tell.
I believe Steve Eiche was at one point and may still be?
I have a Mac 02 that I suspect has issues with the frequency valve
driver circuitry. I have heard of people repairing these in the past;
anybody still doing so?
Anyone have a known good unit they'd care to sell?
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