Running Rich - Replacement ECU - Solved!

Running Rich - Solved!

Background

For those that have been following this blog for the last 2 years my Brazilian Kombi has been struggling to get through the yearly MOT.

The issue has always been High CO emissions coming at idle and also at fast RPMs.

After investigating the Lambda sensor is always running at about a constant 0.9v which indicates rich levels. The Lambda sensor should run rich / lean (0.1 to 0.9v) averaging out at about stoichiometric of 0.45v (Lambda=1)

I have checked every sensor and actuator and ran many diagnostic logs all without finding anything wrong. 

I finally concluded that the ECU system was not responding to the rich levels and not adjusting. If you inject more fuel (Propane) or ristrict air the ECU should detect this and adjust its fuel (trim) to aim for 0.45v stoichiometric.

At this level the CO emissions should be at the lowest levels.

My original ECU showed NO SIGNS of attempting to correct anything.

So I have now secured another (used) ECU...... It has travelled a 6800 Mile journey to my Kombi (contact me if you need supplier details)

It an earlier version of the original ECU but its basically the same version.

The Swap

The swap over took half a day. Removal of the old ECU was simple enough (battery & wiring disconnecting and one nut)

I then spent a few hours checking all the 25 connections from the ECU ensuring that each Pin went to the correct place compared to the wiring diagram and that all sensors and actuators where correct.

Then came the replacement ECU which was a simple plug in and secure and then reconnecting the battery.

First Start

Then came the moment of truth. First turn of the key the engine fired up first time and sat at Idle with only a little hunting.

After a few minutes everything settled down. Struggled to restart a 2nd time for unknown reason but after that it was fine.

Hooked up the VCDS Diagnostics (see Diagnostics Guide page on the right) and cleared some old fault codes.

Everything ran fine and the drive was improved. A few fault codes came up about Fuel trims but I assume that this was the ECU "Learning" the engine set-up.

The Results

So after a few longer drives I captured some log files and this is the result:

You can now see the Lambda response switching lean / rich during running.

Also of note is the Fuel Injectors switching basically off during letting off the throttle.This is what I would expect to see from a fully working ECU.

During long periods of idle the injectors period are low and the engine is running rich to lean consistently

RESULT!

Follow Up.

Now I have a functioning spare ECU to use on the bus I can now turn my thought to the orginal ECU. I have been starting an ECU repair manual detailing as much little information on the Bosch Motronic MP9 used on the air-cooled Kombi.

I have been speaking to a ECU repair company and will plan to send of the ECU to them to see what they can find.

I suspect from the repair information I suspect it could be an issue with the supply ground of the Sensor inputs not connecting or floating so it does record the right values BUT not be able to respond. Will keep you all updated on the repair.

I suspect the ECU was always faulty and even more damaged when the Engine Earth lead was found disconnected (see hot start issue)

I am SO happy to have finally resolved the issue. I always suspected it was the engine, timing or sensor wiring issue BUT never suspected the ECU to be at fault. 

I did not want to be a typical parts swapper mechanic condemning ECUs but in this case it was the ECU!

More details and information to follow!