Hi All,

Has anyone had any experience with spurious RPM readings in Live Data on an ECU?

I have been trying to get to the bottom of a problem on my 2007 Vauxhal Vivaro for some time (2 years) and despite having got to extremes have so far failed to find and fix the issue. It's had a complete fuel system change from the tank to the injectors. All the fueling sensors have been replaced with both new and/or known working. The Crank and Cam sensors have been replaced similarly. Engine Wiring Harness, EGR, Throttlebody & 3 x ECU's too. The van starts, runs at idle and will rev perfectly and be fine all day for as long as it is not moving. No errors, no faults logged and no apprent engine problems at all. It sounds great, better than I have ever heard it but, it still wont drive. Get it in to second gear and put some load on the engine with the throttle and "bang", it's off and a full turn off and key restart is required to get it going again. It's been a long journey (of going nowhere) but I think I may have now found the issue.

Using my Launch Diagnostics, I decided to monitor the RPM & Fuel Rail Pressure using the Live Data of the OBDII diagnostic system. Normally I would just watch other stuff because there is a rev-counter on the dashboard but, this time I chose to watch the RPM on the Launch. At first, while at idle, nothing was apparent but, when revving the engine to beyond 2600, I noticed a very strange and intermittend anomaly. Every so often the
live data for RPM will read 1053.5 for less than a second and then jump back to what the engine is really running at. I thought it may be a quirk of the launch but have now tested the same on a second van and found that the second van does not do it at all. It therfore make sense to me that if this anomaly becomes present at the ECU while it is trying to calculate fuel requirement from load, rail pressure, air pressure, etc. the ECU will take steps to dump rail pressure and then when the anomaly goes away again, the ECU will be unable to recover at the speed that it sees the revs change at. A fuelling failure will be assumed and the ECU will shut the engine down.

I have looked very cloesly at the loom and found no entry point for this spurious signal and wondered if anyone else had experienced and cured anything similar and/or may have something for me to try.

Thanks for reading