Tech query two: Valver having a funny 5.....

[Kitch]

Second issue regards the valver, which is displaying an rare moment of engine issues!
Nothing major, it starts and stops fine. Still operates fine under 'heavier driving conditions' but when you're at lower revs in the operating gears, say approaching a junction or gradually accelarating, it misses a bit. Not like missing on a certain cylinder, but like a total cut-out very briefly, like when my dizzy cap expired. Also when it does this, the rev counter bounces around everywhere.
Only thing I've thought of are coil and TDC sensor. It seems to be throttle related, as when you push slightly harder it goes away, but I can't work out how the coil is throttle related. I'd have thought it'd have more chance of failure at high revs, not low. And the TDC sensor....well if that had gone I'd have thought it'd just die full stop.

So again, I'm a bit stumped! I guess whatever it is must somehow be connected in with the rev counter for it to play up at the same time, but I'm not sure what sends the signal for that?

So, help...again??!

[CitroXim]

Faults like those Kitch are often caused by a vacuum leak on the inlet somewhere. One common problem used to be a perished vacuum advance pipe to the distributor or a duff vacuum advance capsule but I'm not at all sure if the valver has a vacuum advance distributor.

Air leaks anywhere on the inlet tract can cause it and the tacho bouncing around can be a bit of a red herring as my old 205GTi tacho would bounce around a bit during misfires, however caused.

I too cannot see how it could be the coil, ignition amp or TDC sensor. You'd either not go, have starting issues or experience it worse under power.

[Kitch]

Yeah thats what I thought ref the coil etc.

Valver has no distributor, so no vacuum advance. Last time I had this problem it was at high revs and it was the fact a bolt had come out of the rotor arm and gone through the dizzy cap!

Might be worth checking all the vacuum lines then. Sadly, I think they're all going to be fine as they've only just gone back on, but not before a thousand miles or so. So they've had long enough to fail if I put them on wrong, but not long enough if the pipe has perished.

First port of call though, thanks!

[prm]

Kitch,

You’re right about CAS/TDC sensor. When this fails – nothing, as the ECU needs to see an AC signal to operate the fuel pump relay. Maybe intermittent?? This would show up on the rev counter. The block cable connections may be under the battery tray

The ignition module,?? if breaking down usually gives an increasing duration/intensity, as revs increase, found most, faulty at around 3500rpm and above, due to insufficient heat transfer to the ali heat sink, attached to the bulkhead. Remaking the block connection to this unit might be worth a look.

Can you check to see if there is any alteration in richness/weakening on exhaust emission whilst misfiring. Just see you cycling behind your 16v!!!

The reason I mention this, as the ATS on the AFM can cause a similar fault, pronounced in colder weather, by dropping out, fluctuating the mixture.

Might be worth initially inspecting the connections on the AFM multi-pin plug. These can be closed up slightly with a thin bladed instrument screwdriver, also the cable crimp connection under the rubber boot.

Main AFM valve sticking???

Regards

[Mike E (uk)]

The ignition module can give intermittant running, I had this once.

You say you have no distributer- has it been replaced with a solid state system as found on the xm?

or did you mean the ignition advance is only controlled by the ECU?

I have not seen an unmodified BX16V with no rotor arm/cap

Mike

[Kitch]

Pete (I think?!): I did wonder about the AFM. I do have another which I could try in it's place to see if the problem goes. The car is also chipped, and the signal from the AFM had to be altered (mixture screw tinkering) as with the OE setting it wasn't happy.

Mike: I mean the engine has no distributor itself; the cap and arm are bolted directly to the end of the cam.

[prm]

I would have thought, with the rev counter isolating I would go for ignition circuits intermittent, somewhere?? but these type of faults can be right sods to track down with ageing French wiring.

The CAS/TDC cables and block connectors are extremely susceptible to any leakage of the AC current generated, as with any increase in speed, the variable voltage is monitored by the ECU.

The cable crimp connections under the rubber boot on the ignition module can be quite brittle and cause intermittent faults at low revs due to engine vibration.
Tie down any free floating cables and block connectors with ties, one at a time to see if there is any improvement.

The ATS on the AFM and the CTS on the engine block might be worth testing, they have approximately the same resistance, cold, stationary. About 3.5 – 4.5k? this weather. Have found very few failures with these units, just incorrect readings due to age.

Sorry, I’m not to familiar with ECU chipping on 16v’s.

Can you identify if the misfire occurs at the same revs or, almost identical throttle position, regardless of gear selection. AFM faulty??

With the AFM, you can remove the square cover on top, to clean the contact tracking inside, by using a thin blade, ran around the silicone type sealer/adhesive, and gently prise off. Caution with the brass wiper arms, as these are quite delicate

Best of luck.

Pete