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Gm vivaro pt. 2

The first part of our assessment of the vivaro was to say the least a little confusing, not least to us. Several facts were unknown to us and as such had to be factored in to our conclusions. This leaves an element of uncertainty on our part.

The dpf had been removed and modified software installed , I am in no way suggesting any of this previous work was faulty , unfortunately we could not check it as we do not have access to the oe software suite. A replacement volume valve had also been fitted. However curious to resolve the problem we decided to continue knowing our final conclusion may be flawed.

A brief resume of the facts so far
1 high pressure run away
2 dpf removed
3 software validity unknown
4 replacement volume valve

My focus moved away from possible pump internal issues and re focused on what the pcm was trying to achieve.
All programs run on the premise that request control values are received from various sensors, then, compared to the specified values which form the software parameters. When a control value is not reached correction or adaption should attempt to rectify the discrepancy.

So far we had concentrated on the physical aspects of high pressure control, priming, inlet control valve, the high pressure pump, and injector back leakage.

The evidence did show an inability to control rail pressure and especially the curious response of increasing volume when the pressure went too high, but why?

I did previously state this system employed a Bosch cp1h pump, volume not pressure control, had the software been incorrectly installed for a cp1 variant?

I decided to drive the vehicle and monitor live data, I had to ensure no rouge request inputs were causing this strange response.

Focusing on request load values, app input, air mass calculation, rail pressure feedback, brake and clutch input as well as all other possible input variants that had a direct or possible effect on rail pressure control.

Unbelievably if driven on the open road, throughout the entire load and speed range the rail pressure exactly matched specified and actual values? Except, and every time the vehicle reached the idle condition. With experience it was possible to reset the error by prompt cycling the key off, even whilst the engine was still rotating!

What happened at the idle load speed range was even more curious, the pcm changed the initial correct control duty of 43 %, to the inlet metering valve, rapidly reducing it to approx. 30%. Resulting in max system pressure.

At the same time the specified rail value was correctly reported as 300 bar, the actual feedback from the rail pressure sensor was 1350 bar, so basically the pcm was ignoring input request. Our final conclusion was therefore, a programming error or hardware issue. Our advice, to re flash the exact original code, before replacing the pcm. Sadly we will never know, as this little duck is going back to whence it came, the auction, such is life.

To experience and benefit from the unique test methods developed by ads forming part of our training program contact Annette @ ads 01772 201597, ads-global.co.uk,

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Published on: September 14, 2015

Filled Under: Technical Articles

Web site: http://www.autoinform.co.uk

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