Pug Partner Combi - rev counter problem

[MH123456]

I'm hoping Wheeler can weigh in on this with their venerable reputation:

The last two hot days I've driven my car home from work - not a long distance, the rev counter is fine to start with but after revs have been up a little the needle drops to around 200 rpm, not representative of the engine speed. It does go up when the revs go up but not as you would expect. Today it seemed to drop lower than yesterday. When I start the car the rev counter sits happily at around 900 rpm until I rev it, then it drops (since March I've adjusted the idle until I can fit the new idle controller, otherwise it would be idling at around 1100rpm).

Firstly this has a VAN bus, with mechanical advance on the pump, so I'm assuming this has a separate TDC and rev sensors, the latter being at the back of the bell-housing.

Secondly, if that is correct, the sensor looks to be covered in oil from a small leak from the valve cover gasket ( I should just need to nip up the bolts on the cover to seal that, I put plenty of sealant on when doing the head gasket and didn't tighten further than to make the sealant spread fully, so it should have a little further to go). Is it likely that the oil has penetrated the sensor and caused the sensor control pin to slip and wear out? Looks like I need to get under the car to get good access to this.

Thirdly, the cluster is second hand after I broke the first one, everything else is working just fine however, I did replace the radio with a cheap Chinese bluetooth, radio, mp3 unit, swapped the red and yellow wires to maintain the memory and inserted the additional antenna amp with blue wire to the unit. Is it possible that this would interfere with the VAN bus? I note that a day or two before the rev counter problem, the radio kept cutting out as if the aerial connection was loose but is working just fine now.

[wheeler]

An incorrectly wired aftermarket radio can certainly cause some strange electrical issues however normally its things like the central display freezing or the BSI shutting down after a few minutes of turning the ignition off until you start it back up again. I've never seen one causing just a rev counter issue but that's not to say it cant happen. Best thing to do for the time being is to disconnect it completley to rule it out.
If you get your live data up in PP2000 is it reading correctly when the rev counter is faulting?
Do you have the VIN or reg so i can get a look at a diagram?

[MH123456]

Thanks Wheeler, I'll disconnect the radio, plug in the lexia and let you know how it goes. Unfortunately my wife's C3 Pic was due MOT today, had it booked in and got Turbo faults yesterday, so had to cancel, replaced the turbo actuator sensor with some fettling. Not solved yet because it got dark. Will reset codes tomorrow and see where we are with that. If it doesn't fix the problem, I've got vacuum lines, solenoids and EGR to check. We're then away for our 19th wedding anniversary at the weekend to might be a little wait for an update on this one, since I can still drive the pug without rev counter, it's still running great.

[MH123456]

Started the car this morning with the radio switched off and after revving the rev counter displayed around 1K above actual for the rest of the trip, so thought I'd isolated the radio as the culprit. I reinstalled the factory radio and it initially appeared to resolve the problem until I'd driven a mile into the trip to pick up the kids. Need to clear the codes on my wife's car this evening so if I have time I'll check the rpm values against the dial in the cluster.

[MH123456]

It's still 1000 rpm out mostly, flitting around the rest of the time. Not causing a problem with driving and I've not done further testing yet. No other problems but hope to give an update soon.

[Rp0thejester]

Is it an electronic dash rev counter?

[MH123456]

It is - only wires from the sensor but is separate from the TDC sensor the mechanical pump uses for timing so purely aesthetic - it's noisy enough with slim power-bands so I know what's happening without it. The dash has two large connectors on the rear, typical of the updated dash which isn't the same as the vans.

On a plus point my wife agreed that buying a MIG welder is a good idea since it needed the sills done for the MOT which my father-in-law kindly sorted with an ARC welder, and has an advisory for rear panel rust, and I like to learn new skills!