200tq check engine light, but no codes!?

Ivan Tuma ituma at ix.netcom.com
Wed Feb 18 04:04:46 EST 2004

Hi Ben,

I'm afraid I'm not having much luck with the MAC-14 resistor 
modification.... I got most of my information about this mod from your 
website. Last time we "talked" was around six months ago, so allow me 
give you a rundown, along with some links to pictures of what I've done:

1. Car is running near perfect at this point
     -got the check engine light problem resolved (distributor was out 
of alignment)
     -new throttle position switch
     -new warm-up regulator
     -new cold start temp sensor
     -new knock sensor #2
2. Installed a simple, analog Sun boost gauge that I hooked through the 
speaker grill/heater vent on top of the driver's side dash.
3. Put in a heavier wastegate spring (don't know which type, or weight, 
as my friend pulled it from one of his junk 5000tq cars)
      -I get about 1.4-1.5 bar to show up in the dash boost gauge which 
equates to around 8.5 to 9.0 lbs/sq in on the analog gauge
      -ECU registers occasional over boost condition (2224 fault code I 
      -Of interest; sometimes the analog and digital boost gauges are 
out of sync, i.e.. the digital gauge says 1.3 and the analog (directly 
hooked to
        manifold shows ~9lbs when I think it should show around 7lbs) 
this kind of shows off the tolerances range in the electronics.
4. Clamped the intercooler with clothes dryer clamps
5. Installed resistors into a switch box (see pictures link) and 
soldered them between pins 1 and 10.
      -I can use either 430 Ohms or 750 Ohms depending on the switch 
position (Hi or Low) see pictures.

      Pictures (they are big ... sorry):  

6. Today, I added a 1K Ohm POT in series so my range of adjustment is 
now between 430 Ohm to 1750 Ohm.
7. Running 91 Octane (highest available from pump in Denver) plus a 
little Outlaw octane boost


Two tests performed at each of the following 6 stage.

   -Test #1 = Sudden full throttle in 3rd gear from about 2700 rpm
   -Test #2 = Slow full throttle in 4th gear from about 3200 rpm


Stage 1 - 430 Ohms:

Test #1: Boost goes to about 14lbs followed by a violent jerk (cutout)
Test #2: Did not perform (N/A)

Stage 2 - 800 Ohms:

Test #1: Boost goes to about 12lbs followed by jerk (cutout)
Test #2: Car accelerates but analog boost gauge bounces wildly between 9 
and 11 lbs.

Stage 3 - 1000 Ohms:

Test #1: Boost goes to about 11lbs while gauge shakes between 10 and 11 
lbs (occasional cutout)
               -no difference in the cars acceleration (about the same 
as with no resistor)
Test #2 : Car accelerates but analog boost gauge bounces wildly between 
9 and 11 lbs.

Stage 4 - 1400 Ohms:

Test #1: Boost goes to about 11lbs with some gauge shakes , but then 
falls to about 9.5lbs
               -Acceleration seems to be slightly improved (maybe 
psychological at this point)
Test #2 : Car accelerates slightly better, with the analog boost gauge 
reading about 9.5lbs ... eventually tapering off to about 8.75lbs
               as engine approaches 5000rpm.

Stage 5 - 1700 Ohms:

Test #1: Boost goes to about 10lbs with some gauge shakes , but then 
falls to about 9.0lbs
               -Acceleration is about the same as stock.
Test #2 : Car accelerates about as well as stock

Stage 6 - Resistor System in OFF position

Test #1: Boost goes to about 9.5lbs with minimal guage shake , but then 
falls to about 8.5lbs
             eventually tapering off to the low 8's approaching 5000 rpm.
Test #2 : Car accelerates decently for stock

Hope this helps you narrow down the differences between MAC-14 and the 
older ECUs. For now, I'll probably keep the system turned OFF, or take 
Ti's advice.
I'm almost thinking that my aftermarket wastegate spring isn't strong 
enough to handle more than 9.5lbs/sq inch. It doesn't seem to have 
pressure leaks anywhere. Or do I?
What do you think?



Ben Swann wrote:

> Ivan,
> I'd be interested in knowing what your final value is an to what boost 
> it corresponds.
> You might try an adjustable setup similar to the one I made.  I used a 
> fixed resistor in series with a variable pot - linear taper to around 
> 2.5k ohm in your case may work well with about a 500 ohm resistor in 
> series.  The fixed resistor prevents setting to 0 ohms (dead short) 
> which you would not want.
> I installed a cutoff switch, which you can get to mount right on top 
> of the pot.  That way I could turn the pot up to its highest setting 
> and ultimately switch it off, disabling the entire resistor mod.
> Once you find the ideal setting(s), you can mark the settings.  I 
> actually used an ohmeter to measure resistance and marked a sticker 
> that was pasted over the kick-panel where i had located the variable 
> resistor setup.  I also had a pushbutton switch to leads which ran to 
> the top of the fuel pump relay, so I soulc initiate diagnostics 
> anytime i pleased.
> This setup works well for me, even after the car was totalled, as I 
> still use it after I do a QLCC installation to check ECUs for codes 
> and that things are operating correctly.
> Ben
> [Ti,
> Turns out that the ECU was right .... the "mechanic" who performed the
> last timing belt installation apparently didn't properly allign the
> distributor rotor
> with the notch in the distributor housing (it was about 5 degrees off of
> center). That's why the Hall Sender fault code was being reported.
> I adjusted it today, and no more check engine light ... runs better than
> ever (so far). Now I can continue working on my resistor mod. I got
> 14psi of boost
> today (TOOO MUCH, I hit an overboost fault) I need a bigger resistor
> (around 1.4kOhm) to bring it down to a conservative 12psi. Currently I'm
> at 9 with just a wastegate spring.
> Anyway ... thanks for your advice.
> Tschus,
> Ivan
> Ti Kan wrote:
> >I don't think your car's ECU (MC-2 engine) has permanent fault
> >memory.  If the ignition is shut off, any recorded fault is gone.
> >So, to catch the fault, you should do your blink code check after
> >you encounter the check engine light, but before shutting off the
> >car.
> >
> >-Ti
> >2003 A4 1.8T multitronic
> >2001 S4 biturbo 6-sp
> >1984 5000S turbo
> >1980 4000 2.0 5-sp]

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