It has been established that Tec jet components on S4000L61/62 Gas engines have a higher-than-expected failure rate.  Branches supporting these installations should review their Tec jet stock levels and consider approaching customers to replace the Tec jet as part of a scheduled maintenance interval at around 15,000 hr life.

The purpose of this Service bulletin is to support troubleshooting and provide a temporary way ahead to prevent out of service scenarios.

The main cause of the failures has been identified as loose bushings failing to keep the housing of the unit secured firmly. This results in the calibration of the unit drifting out of specification until it demonstrates one or more of the below symptoms.

Symptoms of a failed Tecjet include:

·         Failure to start

·         Engine hunting/failure to reach nominal speed

·         Failure to meet load steps

·         Not responding correctly to emissions tune

·         Constant drifting of Tecjet Calibration (0% and 100%)

To confirm diagnosis of a faulty Tecjet a calibration of the unit should be completed. The technician should then apply some pressure to the housing and confirm if the calibrations setpoints move out of the tolerance given in the MTU literature:

·         If calibration is still correct, continue to start and stop the engine and recheck calibration of Tecjet.

·         If setpoints have drifted beyond tolerance the Tecjet is faulty.

Both Tecjet and throttle actuator’s position drifts once the polyurethane rings dry out by aging/heat.

It’s very easy to recognise when the unit is stopped. You can find play at the back end housing of the actuators, which contains the electronics as well as the position feedback sensor.

It has no use tightening the allen key screws, the play remains. We removed the play by placing only some LIGHT pressure on the actuator housing and the position returned to 0. This allowed us to do the calibration inside the MTU ecm’s and we were able to run the unit.

See report. We highly recommend to send the Tecjet or throttles in for overhaul at that point. Re-placement of these polyurethane rings is not a field job.