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!

*** NEW *** Diagnostics Manual Now online

The NEW Diagnostics Manual is now on-line!

See the link in the pages section on the right

OR click the link here

http://t2bay.blogspot.co.uk/p/blog-page.html

Its a very early draft and is to help out some the Brazilian Air-Cooled owners to resolve some issues.

Please contact me if you need any help or more information.

As always I do this for FREE so please, please click the donate button if you use this and wish to support me further.

Running Rich - Exhaust Investigation

As part of the investigation into the apparent running rich mixture and higher fuel consumption I have started working on looking at the last piece of the "jigsaw" The exhaust.

I have been thinking that the exhaust system could be partially blocked or  restricted either by the CAT or the two exhaust boxes.

This would lead to back pressure where CO etc in the exhaust was coming back towards the lambda sensor causing the typical 0.8 to 0.9 readings. Also this would also cause the exhaust analyser to try to suck air during the MOT sampling causing the over Lambda (o2) reading

So I managed to find a second hand CAT from e-bay and some new gaskets. Plan was to remove CAT inspect and run diagnostics to see what Lambda sensor reads without CAT or any exhaust restriction. Then try "new" CAT to see if anything changes.


1. Removal of the CAT involved soaking the bolts in penetrating fluid over night.
2. Bolts where not that bad to remove. CAT came out - noticed that a gasket was missing from the CAT out side.

3. Inspected both ends - Both looked like running a rich mixture. Lots of black soot on both ends.

4. There is no sign of blockage of any of the honeycomb inside the CAT. Seems not to be blocked but unsure of any catalyst material or function. 

5. Ran the engine without CAT It was very very noisy sounded great but I am not sure the neighbours where too impressed!

Captured a diagnostic log of the usual functions (rpm, coolant, injector, engine load).

   
From the graph you can see that sensor warms up quickly dropping down to a lean level of 0.1 / 0.2 engine does richer upon acceleration. I would expect the engine to run lean as the lambda sensor is fitted just before the CAT so would be quite lean exposed so close to air.

If I compare this to a typical run with full exhaust fitted it normally goes straight to rich 0.8 / 0.9. Did not dare take it for a drive but would have been interested in knowing if any changes to injector timings would happen.

Removing CAT and having an unrestricted exhaust does improve mixture (all be it a little too lean)

6. While I was under the van working on the exhaust I thought I would treat my van to some new exhaust hangers.

7. Carried on not sure if to put on new CAT but decided if I did not change anything then I would just get the same result again. New CAT was similar but looks like to be a different shape. Maybe a replacement from the original Brazilian one.

8. Once new CAT was fitted took the van for a drive along my "typical" A6 drive which gives two dual carriageway constant speed sections.

Logged the data as before.

Did not manage to capture the initial warm up but still the two humps at the start are the same sections as other logs.

As before there seems to be running yet again as constantly rich (0.8/0.9)

Changing the CAT has seemed to have no effect on Lambda levels. So I suspect its running the same as before

so what I have learnt? I think the following:

1. CAT does not look restricted but running rich for so long will reduce effectiveness.
2. Running free non restricted exhaust does not show a rich mixture.
3. If exhaust is restricted then it must be CAT or two boxes further.
4. To confirm I will remove the CAT to BOX 1 connection and re-test and remove connection from BOX 1 to BOX 2 and re-test.
5. Try the back pressure measurement. No idea of how much back pressure is acceptable.

I think there is a possibility of a restricted exhaust. so will need a new exhaust but the choices are:

1. Stock steel - VW heritage sell Box 1 / Box 2 for approx £250
2. Longlife Stainless - £359 for stock but stainless.
3. Remove all including the CAT and opt for a S/S vintage with Lambda port £410

I am tempted by the vintage speed BUT concerned without a CAT it could fail. I think Stainless Steel Longlife is good BUT expensive £££ but at least will last and an investment.


UPDATE - Did the back pressure measurement - Connecting into Lambda port.

NO BACK PRESSURE AT ALL - ZERO PSI at idle and only 1-2 PSI on acceleration etc. SO no back pressure.

Still Running Rich?

So I have gone back through diagnostic log files from over 2 years now in order to work out why my engine is running rich (Failed emissions and also poor fuel economy) and also black exhaust.

Following graphs taken at different date intervals

RPM, Lambda Regulation, Engine load and injector pulse widths

06/07/14 - Runs at around 0.8-0.9 except when de-accelerating. Still looks like its running rich but plenty of lean.

14/10/14 - Runs at around 0.8-0.9 except when de-accelerating. Still looking rich but again some lean.

05/08/15 - After fitting in March new "universal" sensor. Not really sure what's going on could be "normal" but no real regulation.

12/12/15 - Lambda Runs most of the time at 0.45v. Signal very poor stuck around 0.45v little response.

At this time the "universal" sensor response was stuck at 0.45v confirmed by unplugging and it stays at 0.45v

Decided to fit OEM Bosch Sesnor.

20/12/15 - Fitted new Lambda Sensor. Improved over previous BUT only a very few lean points.

UPDATE:

Changed FPR regulator after issues seen with Fuel Pressure tests. Re run the same trip:

No to confirm the lambda signal I removed it. Fixed it out of the way. Rerun the same drive. Very noisy from the hole left behind.

From the above graphs 2014 was before last MOT and engine seems to be have high Lambda except during de-acceleration

2015 March (03) time fitted "universal" lambda sensor due to emissions failure. at some point from then on sensor started to run constantly 0.45v

Fitting the OEM Bosch sensor on 20/12/15 the sensor has started to indicate rich at around 0.8 / 0.9v similar to 2014 at the later parts of the graph but still with not much rich / lean switching going on here.

SO in summary:

At the first traces some rich / lean cycling fitting universal sensor failed within 6-8 months.

Fitting OEM Bosch sensor improves response BUT still looking rich with little rich / lean.

I have then proceeded in using my USB oscilloscope to check the actual sensor response.

As you can see it is actually rich at 0.8v. Blipped the throttle a few times and saw the response drop from rich / lean BUT not switching enough only on de-accelerating.

So in conclusion:

Diagnostics logs & Scope of OEM sensor show rich.
Unsure if ECU actually switches rich / lean in response to o2

Things to yet to confirm / check:

1. Fuel Pressure Test - Too much fuel-Fuel Pressure regulator / Stuck Injectors - Completed - Fuel pressure decay at full vacuum - Replaced FPR - No difference. Still could be injectors. Repeat tests with FPR.
2. All Cylinders firing - One not firing - Incomplete fuel burnt
3. Find more info on ECU - Does it switch (need another Kombi / Info) - Looks like artificial lean (removed) makes no difference to Injection on time. I am suspecting that this MP9 ECU does not operate a closed loop so the Lambda is just for indication or base level of injection timing.
4. Lambda Sensor - New OEM sensor works fine out of exhaust (Lean) and Rich when in exhaust.
5. Blocked Exhaust - Still could be block CAT or exhaust - Plan is remove the CAT with Lambda in place and check signal. Inspect CAT.
6. TPS - Maybe TPS showing 6.7 degrees at Idle is causing the lack of lean at idle due to the ECU still thinking its open (foot on throttle) - Will need to reset the TPS by checking that Butterfly is actually closed and ECU detects no throttle.