Hello All:

Last month, I spent a lot of time replacing the head gasket in my MC motored urq. Thanks for all the tips!

I ended up pulling out the manifolds and head separatly, but dropped the whole mess back in as one piece. WAY easier...

Now Mr. Bill pointed out that there was a good chance that my head gasket failure was from 'pinging', and that I had to fix that, or I'd have the problem again..

THat man is a genius, because unknown to him, I HAD been hearing light pinging before the head gasket failure. Now that I have replace the head gasket, I've been really listening for pinging. I find if I drive near concrete walls or guard rails, I can hear the pinging if I'm on it fairly hard in mid range revs (3500 to maybe 5000).

SO the next thing is, how do you get pinging, if the computer adjusts everything?

Martin P tells me about the known 'pressure transducer failure'.

So today I wired up some leads to the transducer, so I could measure it's output while driving.

Surprisingly enough, there was no output. I assume that means the ECU thinks it's seeing full vaccum all the time.

That cold explain the pinging..!

So my questions are:
1) What's the chance that replacement transducers are available?
(Probably unobtanium, so I may as well go to a MAC 11 ECU and harness, as I already have the block, head and turbo..?)

2) I'm sure I've seen a spreadsheet somewhere, that shows transducer output vs transducer pressure. Anyone else know where to find that?

I could then substitute the pressure transducer output with a fixed voltage, closer to what the ECU would want to see for near full boost. At least then, It won't ping so much (But have other side effects of never changing value either).

3) Or any other ideas?

It's the MAC 02 with the 'yellow' label, if that makes any difference?

Regards,

 

I repaired mine when I first bought my ur q nine years ago, and have done a few more since.

1. Yes, the exact part is loooong gone and there is no plug-in replacement.

2. It has a pretty linear output from ~0 (<~.1bar) to 5V (2 bar). I don't have the offset handy.

3. Yes, you have several options. First, if you have a MAC-07 to MAC-14 (any ECU inbetween), you can steal the MAP sensor and the fittings from the case out of it and wire it up. This is what I originally did on my car. The output is pretty much the same as the original. The later sensor is powered by 5VDC instead of 8VDC like the original, but you can just tap into the 5V supply in the ECU for this.

You can also use Motorola or Bosch 2 bar MAP sensors (I happen to have a bunch of those), but you will need to add some vacuum fittings to the ECU (not a big deal).

 

Hi Frank - the transducer is inside the MAC-02 right. so you took the cover off the ECU?

For a wimp like myself - I could probably test this by pressurizing the hose into the ECU and looking for the timing to retard.

steve

 

<center><img src="http://audiquattro.org/misc/rdh/mac02.gif"></center><p>Yes, just pulled off the cover, and soldered onto the leads going to the transducer. No big deal. Besides, it doesn't really work very well anyway, and I have a whole MAC 11 setup readyto go.

Now when you pull apart the ECU for an AAN motor, that got a bit more going on inside!

But doesn't bother me, as I've been messing with electronics for years...

Martin P also put me onto the above diagram , which is of a bit of help.<ul><li><a href="http://ECU%20Info">http://audiquattro.org/misc/rdh/index.html</a></li></ul>

 

If pressure transducer fails or any none vital sensors Hitachi ECU switches to default or defense mode,3500 RPM max. Take vacumm/pressure hose from ECU and start the car. If changes idle this is indication that transducer is working.
It looks to me like you have fuel delivery problem
or air/vacuum leak some place.

 

The ECU has no such fault mode for the MAP sensor. The only "limp" mode occurs if the IAT sensor or idle switch circuits have faults, in which case the fuel pump is cut off at 4k RPM. The ECU will also disable the fuel pump in overboost conditions no matter the RPM. If a MAP sensor fails with the output stuck at 5V (max output - overboost), the engine will not start. BTDT.

The BEST test for a fault with the MAP sensor is to check its output after verifying that the vacuum/pressure line to the MAP sensor is intact. A quick check should show about 2.5 VDC (~1 bar atmospheric) at the signal line (it is marked on the PCB) to ground with the ignition on, but the engine not running. If you are at high altitude this reading will obviously be lower.

IME, the sensors almost always fail with a 0 VDC output. This tells the processor that the engine is under full vacuum, so the timing is advanced per the timing map in the EPROM. This results in pinging under moderate boost levels.

IME2, the sensor is either good or bad, the voltage test is much easier than to try to check ignition timing as per the tables in the IST manuals. Those tests are great if you can't open the ECU, but a waste of time IMHO, as you just have to remove a few screws to get at the source.

Just my .02

 

The BEST test for a fault with the MAP sensor is to check its output after verifying that the vacuum/pressure line to the MAP sensor is intact.

&gt;That's working fine.

A quick check should show about 2.5 VDC (~1 bar atmospheric) at the signal line (it is marked on the PCB) to ground with the ignition on, but the engine not running. If you are at high altitude this reading will obviously be lower.

IME, the sensors almost always fail with a 0 VDC output.

&gt;WHich is what I'm getting. Nothing at all, and no change when giving it a good run.

This tells the processor that the engine is under full vacuum, so the timing is advanced per the timing map in the EPROM. This results in pinging under moderate boost levels.

&gt;Again, exactly what I'm getting. But pulls right to the rev limit at 6000+ rpm!




I think my way to resolve the problem will to be (short term) fool the ECu with a false 2.5 volt signal. Maybe as high as I can get away with, and still stay under the level that the ECU will still start at, or not shut down at, at lower revs.

Long term (Like: When I get time to do it!) I'm thinking that I'll switch to the MC harness &amp; MAC 11 ECU and associated bits.


It's been mentioned that the two ECUs have the flywheel reference pin in different places. But as best as I can find, that the difference is only 2 degrees.

Seeing that I already have an MC motor in the car, and I have no idea if it has the original flywheel, or a MC flywheel (Because everything else on the car has been messed. Why stop with the flywheel?), I think I'll be ok with a possibility of the timing being out by 2 degrees?

Thoughts?

 

The timing gets pulled back alot as the boost increases, so I think you will still get pinging. If you set the voltage higher, like 4.5 V, you will be safe under boost, but it will run poorly off boost.

I would recommend replacing the MAP sensor, or doing the MAC-11 swap.

Remember that when you do the swap, you also need the idle stabiliser with its harness and ECU. This also means getting it all plumbed in.

 

The timing gets pulled back alot as the boost increases, so I think you will still get pinging. If you set the voltage higher, like 4.5 V, you will be safe under boost, but it will run poorly off boost.

&gt; I'm looking at it as VERY short term solution. ANd *any* fake boost signal has to be better than the 'no' boost signal it's had for the last year or two!

I would recommend replacing the MAP sensor, or doing the MAC-11 swap.

&gt;I'm going to go to the MAC 11 route, as I have everything to do the swap. I have no source for a new transducer anyway.


Remember that when you do the swap, you also need the idle stabiliser with its harness and ECU. This also means getting it all plumbed in.

&gt;Yes, I have everything that hangs off the red harness. Also the wastegate freq valve, the different coil &amp; coil driver, and some other stuff that escapes me at the moment.

&gt;But what about the possiblity that the timing pin is in the 'wrong' place on the flywheel? Is the two degrees really enough to worry about between the WX &amp; MC flywheels?

&gt;Thanks for all the thoughts!