John Speake

Hi Jon,
The LH ECU should recognise there will be no CO pot because of the code plug.

Hi Ken
Try this.....disnnect battery ground strap, disconnect Os sensor. Reconnect battery and then start the car. The LH ECU weill then recognise that an O2 sensor is not fitted and will defualt to a mid range setting.

If still running very rich, then double check that the 8 way coding plug on the LH/EZK mounting plate is not disconnected (flying lead from cable form, coding plug usually mounted on the plate.)

Lorenfb

"Yes, without a signal from the O2 sensor, the fuel mixture goes to FULL rich............." - Gretch -

Not correct! John stated it correctly; "will defualt to a mid range setting".

There're a number of possible issues:

1. fuel pressure
2. water temp sensor
3. grounded O2 sensor input

The LH ECM is the LAST possible source of this problem.
They rarely fail in an overly rich running mode!

Larry928GTS

What year is your S4 and how did you setermine it's running rich?

Gretch

Not always correct. I have tested this with an AFM.........and seen the results I posted. Not saying there are not other factors. For example in John's scenario, resetting the computer is necessary. See what happens if you don't reset the computer. FULL rich, mr know-it-all................

Rich9928p

I'd say 10 - 15% of the LH failures that I see exhibit are overly fuel rich mixuture. It often starts being jut a little rich and over time goes to so rich the engine won't run.

Is this rare? I'd say a little more like "medium well" ...

John Speake

I didn't say it would recognise an open sensor always.....that is why I desribed the reset for default procedure.....

I've seen some cars that do recognise an open O2 sensor without a battery reset, but others that don't.

I didn't note the MY, but it is possible that the software was upgraded over the MY.

In the uk, when a car was supplied non cat, the O2 sensor has a shorting link between the O2 input to the LH and ground. So it would appear that the LH software is better at recognising a short rather than an open circuit.

About the temp senor 2. If the sensor is open circuit, or short circuit the LH always defaults to the hot settings. So a faulty temp 2 sensor will give difficult starting and running until the engine is at normal temperature. Then it will run "normal".

Rich is correct that O2 loop problems are commonly caused by partial LH failure.

Mrmerlin

Hi, not sure if you tried this but, remove the vacuum line from the fuel dampers and FPR one at a time see if they have gas in them then try pulling vacuum with a myti vac any that wont hold vacuum or have gas in them need to be replaced

Lorenfb

"Not always correct. I have tested this with an AFM.........and seen the results I posted." - Gretch -

The LH unit doesn't use a AFM! Do a bench test to really see the effect.

"So it would appear that the LH software is better at recognising a short rather than an open circuit." - John Speake -

It appears that your tester doesn't fully test nor indicate what happens when
the O2 sensor input (pin 24) "sees" a low voltage (ground). This needs to be
checked using a o-scope and this condition WILL be apparent!

Also, using and o-scope, you'll see what occurs with a bad water temp sensor that
reads too high (or open) and how the mixture is affected.

"Rich is correct that O2 loop problems are commonly caused by partial LH failure."

- John Speake -

"It often starts being jut a little rich and over time goes to so rich the engine won't run." - Rich -

Very very rare!!!!!!!!!!! May be less than 1-2%.

Again, let's not SELL parts to Rennlist users when the problem may be elsewhere.

Here's the bottomline: www.systemsc.com/tshoot.htm

Gretch

And you are adding value how?........Do you give a ****e about helping solve this guy's problem or are you here strictly for the ego cookies?

inokiyo

Woah!
What happened here while I was away?
I have to p/up my wife soon, and hopefully after dinner, I can work on the S4 again.
What really puzzles me is why the S4 won't go back to the original state with the old MAF, temp 2 sensor installed, Bty disconnected, O2 sensor disconnected. Maybe I'll try driving it with the old MAF too.
Will keep you posted!
Thanks guys!!
Ken

inokiyo

Just did the tests/checks. Here are the results.
John, I tried what you recommended;
disnnect battery ground strap, disconnect Os sensor. Reconnect battery and then start the car. The LH ECU weill then recognise that an O2 sensor is not fitted and will defualt to a mid range setting.
...started up, idled fine for a few seconds, then went back to idle fluctuating, running rich, black smoke from exhaust.
I double checked the coding plug, it was 12 way, not 8 way, but was connected at 1, 2, 11, 12.
Rich, I checked the WOT Switch signal;
Throttle Idle swithwith no pressure on throttle pedal was at 0 ohms, pedal pressed was at infinite.
Full load throttle switch with no pressure on pedal was infinite, pressed on the throttle and IT STAYED AT INFINITE. did the test 10 times, same results.
These tests were done with the battery hooked up, ignition off.
Is this the problem?
Thanks guys!!
Ken

Rich9928p

Ken,

Sadly, if the WOT switch is always open, it will not affect anything other than reduce your top-end performance (engine stays in closed loop - lambda regulation, rather than going open loop and run a bit more rich). The situation that could affect your situation would be if the WOT switch was closed (low resistance) all the time - thus telling the LH that the throttle is mashed and it is time to go open loop).

I would guess that you did the throttle switch test at the LH connector. The next test would be to do it at the switch itself to determine if it is a switch problem or wiring problem.

But alas, you've done all that is reasonable to find other problem sources than the LH. I'd say it is time to get your LH rebuilt.

Rich9928p

Ken,

This is what the manual shows for coding plug wiring. I'm confused that you found a 12 way plug. Attached are some pictures that may help. Item 1 is a 150 Ohm resister.

Lorenfb

"But alas, you've done all that is reasonable to find other problem sources than the LH. I'd say it is time to get your LH rebuilt."

Please, no guessing allowed, especially on an expensive item as an LH ECU.
Remember, once your potentially good LH unit is gone, it's GONE!
Get a loner and verify the problem completely with another LH unit before
potentially wasting money.

"disnnect battery ground strap, disconnect Os sensor."

Not a good troubleshooting approach! One needs to always check
from the main connector, i.e. the LH ECU connector, and NOT assume
that test results at a sensor are conclusive.

Maybe it's time to have a Porsche shop diagnose it, as it may be less expensive
in the long run versus the "shotgun" approach and following suggestions
on what parts to buy from "vested" parties.

inokiyo

Yep, that is what I found. i will try to post a pic later on. It was 12 point. My S4 is Euro, doe this make a difference?
Ken