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Re: 86 5kTQ breakup/tuning problems

Earlier, Robert D. Houk wrote:
>    I've got a 86 5kTQ that has a computer modified by Total Audi Performance,
>    or maybe I should say screwed up by TAP.
> The one time I talked to those folks (looking for help with a different
> computer problem), the guy there said they replace the 28-pin 6840 chip,
> and not the 24-pin 2532 EPROM. When I sputtered in disbelief, he double
> checked and confirmed the 6840 -- "that 28-pin chip to the left of the
> cpu". While it's possible that they indeed do perform some serious Black
> Magic, I kinda concluded that they were full of bovine excrement . . .
> (personal hypothesis not backed up by any solid facts one way or the ot-
> her)

Both the MAC-10 (035-905-383S) and the MAC-11C (035-905-383T) are made by
Hitachi.  The internal circuit boards, top and bottom, are different in 
both.  The only large chips in either one, are on the 'top' board, the "L"
shaped one that does NOT have the pressure transducer on it.  There are 
three large chips in each box, as follows:

        |                                 |
        |    XXXXXXXXXX (#1)              |
        |                                 |
        |                                 |
        |                        ---------
        |    XXXXXXX (#2)        |
        |                        |
        |  XXXXXXXXXXXXX (#3)    |
        |                        |

		#1 (42 pins)	#2 (28 pins)	#3 (64 pins)
MAC-10		8451PY		HN482764G *	HD63A03XP
MAC-11C		8648P9		HN61364P	HD6303XP

* original chip in MAC-10, an EPROM with UV erase window.

When TAP sent the MAC-10 back the first time, they had replaced chip #2 with
another soldered in EPROM, and returned my original chip.  During one of the
times I returned the MAC-10, they socketed their chip so I could exchange
it with the stock one for diagnosis.  

The MAC-11C has the original soldered-in chip, with a TAP sticker on it.
It doesn't look like it has ever been desoldered, and it is not an EPROM,
at least there is no UV erase window.

On the 'bottom' board, there are no 'large' chips, and the only 
daughterboard is the one with the pressure sensor unit.  Interestingly
enough, the pressure sensor daughter board in BOTH ECU's looks like it has
been modified by the addition of a 3.3K resistor and (I think) a diode,
brace yourselves for another ascii drawing  :-)

      | 1      XXUUUXX A |
      | 2      X P   X B |   PS being the pressure sensor
      | 3      X  S  X C |
      | 4      XXXXXXX D |
      | 5      | | | | E |
      | 6              F |
      | 7 XXXX         G |
      | 8 XXXX         H |
      | 9              I |
      | 0              J |

Connections 1-0, and A-J are standoff leads 3/8" long, between the daughter
board and the bottom main board.  On both ECU's, the standoff lead #1 has 
been cut and replaced by the 3.3K resistor, and there is what looks like a 
diode added between connection points #1 and #7 on the MAC-10 - and between
points #1 and #8 on the MAC-11C.  And, no ... connecting the diode to point
#8 on the MAC-10 didn't make it work.

> You might be able to tell something by pulling the plugs right (as soon
> as safely practical) after a high-speed run.
> Or stick a voltmeter on the O2 sensor and see if it just pegs at +1 or so
> volts (running rich) or near 0 volts (running lean) [if it's bouncing a-
> round inbetween and you can't get a reading, that means the computer is
> properly maintaining "ideal" mixture]. Typical ECU usage is to force the
> mixture rich under max boost/rpm.

These sound like the next two things to try.  I had the plug check on as 
something to do, but your O2 sensor check is a good idea.
>    To make a real long story shorter, the MAC-10 computer had a bad pressure
>    sensor - whether caused by the high boost from the wrong spring, or whether
>    caused by their mods - I don't know.  It worked before I sent it to them.
> My (limited) experience says anything Audi Electrical is very fragile and
> will break given the slightest opportunity. I find it easy to believe that
> your original ECU did break all by itself.

I'm certain the check engine light phenomena started with the modified ECU.

> I'm curious -- is your MAC-10/11 ECU made by Hitachi? If so, and it's handy
> can you pop the cover (5 screws on my MAC-02 unit) and tell me if there is
> a xxx6802 (e.g., HD46802 P) chip in "upper right" corner, and an HD46506 chip
> (squarish, not long rectangle like the 6802, if any) chip on a big squarish
> daughter card sitting just "below" the 6802 (and just "above" the big air-
> pressure transducer assembly mounted in the "front" of the ECU with the
> nipple for the manifold vacuum/pressure line sticking out the front of the
> box). [Be careful not to touch anything inside, as static electricity loves
> to zap (very expen$ively!!) these chips!] How many "pins" in the klunking
> wiring harness connector?
> Also, when you have the cover off -- are there three wires running out of
> the air pressure sensor box (green, and I think white and ???)? Do these
> wires run "cleanly" and directly to the circuit board, or do they connect
> up to some "stuff" that looks "after-the-fact" like resistor/capacitor/
> potentiometer *not* mounted onto the circuit board but just soldered to
> something on the circuit board on one end, and to one or more of the air
> pressure transducer wires on the other. (E.g., has someone "hacked" into
> the sensor directly, rather than actually modifying the EPROM program...)
> Did they actually replace the EPROM (xxx2532-yy chip)? Does the soldering
> look "different" for that chip and the other chips of similar construction
> on the board? Is it in a socket? Did they return the original EPROM chip?

I think your ECU is altogether different than the 10/11C.  See discussion
above.  The resistor and diode on the pressure sensor board sounds like
they are dorking with the sensor output!

I've got a copy of the original EPROM contents, and the TAP EPROM contents.
I'll do some binary comparisons later and see if anything is really 
different.  I've fooled around with the Weber F.I. EPROM's on the Ducati
851 motorcycle, and have a disassembler for those chips.  Maybe ...

>    Does anybody have any ideas?  Is the MAC-11 computer likely to be 
>    different enough from the MAC-10 to be causing this?  
> Insufficient data...
> What are the "part numbers" of the ECUs (as in 035 905 383F)?

Again, see above.

>    I've thought of buying another MAC-10 computer and installing the TAP 
>    MAC-10 chip myself (I've got a copy of that EPROM and can burn another
>    chip for the new MAC-10).  I hate the thought of what that will cost,
>    even used.
> My guess - $500 used (hopefully less, as 5KTQs are more "common"), and
> around $1100 new [my '83 UrQ's MAC-02 ECU], from Linda@Carlson, or $1500
> new (and up) from most other Audi vendors.

Shocan Audi wants $525 + $50 core deposit for a used, guaranteed MAC-10.

> Are you in the New England area?

Columbus, Ohio.  If there were someone within a few hours driving range,
who has a stock MAC-10 that I could install for a 10 minute test drive
it might be the quickest way out of the woods.

And, thanks to the other folks who have posted thoughts and suggestions.
I'll update this as things progress.

Charlie Smith   charlie@elektro.cmhnet.org  614-471-1418  
Columbus, Ohio USA 

 4 wheeled fleet:			 2 wheeled fleet:
_________________________               _________________________
86 5kTQ      				92 Ducati 851SP     851cc
69 Porsche 911S   3,200cc		95 BMW R100-RT    1,000cc
81 VW Diesel Pickup  			62 BMW R27          250cc