Turbo Trouble

Had to fix this one, I bought a vehicle as it had a running problem that couldn't be fixed.

Or so it appeared, it was owned by a mechanic and despite spending a considerable sum of money on the car over the last few months he had given up.

The car in question was a Rover 620 ti, this uses the MEMS engine management system.

It is important to note what system is fitted before diagnosis can take place, different systems handle errors in different ways.

The problem was a starting fault that got worse when the engine was hot.

First things first with any diagnosis, the basics, this includes 10mins of look and feel, making sure the car has fuel in it.

To that end 30 litres of fuel were purchased.

A quick code read showed multiple codes, no doubt due to removing sensors connections and testing by the previous owner. As a starting fault it is possible to clear codes, to eliminate any historic codes and only current codes relevant to the fault will remain.

As the car will not start at all when hot, this will prove beneficial, reducing the number of tests required to prove the diagnosis.

The fault code remaining was Map sensor.

This didn't concern too much, but a look at live data showed a reading of 800-830KPa at idle once it had cooled down and eventually started. The expected value would be 300-350.

Such poor engine vacuum would give the sort of fault I was faced with, but the car drove too well to have a engine problem. plus this MEMS system will use the TPS (throttle position sensor) value as a substitute for MAP values giving engine load information to the ECU.

I tested for coil and injector outputs from the ECU during cranking. All Ok.

But his doesn't prove fuel delivery, so a quick fuel pump test as used on the formula Renault's proved the pumps ability to deliver fuel, and a pressure test showed normal results.

As this left no other explanation for the non/poor start it must be the erroneous MAP reading that is the cause, as the MAP sensor is inside the ECU it normally requires a replacement ECU.

However in the paperwork with the car I noticed a receipt for a Collins power chip.

This 'chip' is a frequency limiter that prevents fuel cut off above a given boost pressure allowing more than standard boost pressure.

It was found that to fit this 'chip' requires soldering a by pass wire in the MAP sensor circuit.

This soldered joint had failed, a quick visit with the soldering iron restored normal starting and improved performance from the increased levels of boost.

Word of caution do not increase boost levels above 12psi on this engine without internal modifications as piston failure will result.