XUD knocking intermittently

cox377 · Unread post by **cox377** » 31 May 2011, 08:38

XUD knocking intermittently

Hello guys,

I recently did the fuel pump seals on my 406. there was a co ck up when removing the cam belt and the crank was turned whilst trying to undo the crank pulley bolt. The belt was already off at this time.

upon putting the new belt on and doing two turns of the engine by hand it stopped, assuming maybe pump problem but found the crank was out of sync. Set it all back up and all was well. The car infact seemed to go like stink. Ive done 250 miles in the last few days and as of this morning something on the engine is making that noisy diesel knock/rattle. the rev counter also stopped. I turned the engine off and bumped it going down a hill. The engine went back to normal as did the rev counter.

Could I have bent a valve when doing doing two turns by hand? I thought maybe an injector?

The pump was removed from the engine whilst seals were replaced, immobilizer was also removed and hardwired.

Any thoughts would be greatly appreciated

James

Unread post by **CitroJim** » 31 May 2011, 08:58

Nope,

Rest happy James.

The rev counter gives it away.. You lost the signal either from your Needle Lift Sensor or your TDC Sensor, more likely the former... Loss of the signal will upset the timing control and lead to knocking...

Check the security of the Needle Lift Sensor plug as a fiirst start.

If there was any valve damage, the knock would be constant...

cox377 · Unread post by **cox377** » 31 May 2011, 09:57

Hello Citrojim

I must admit, after the stress of changing the seals the thought I might have damaged something made me feel sick.

Shall i check the plug with a multimeter?

I did check the plug and all seemed fine, traced it back to the loom.

Where is the TDC sensor?

Thank you

James

dieselnutjob · Unread post by **dieselnutjob** » 31 May 2011, 10:03

^^^ As Jim says
A colleagues Xantia became intermittently very knocky. That was due to a failed needle lift sensor.

It's probably not related, but years ago my wife's Audi 80 TDI started suffering from fuel starvation. It was fine around town but on the motorway it would cut out and then run again.

It turned out that one of the overflow pipes had split (the small rubber ones that run between the injectors and back to the pump). Then the needle lift sensor packed up as well. I assume that the lack of diesel intermittently caused the needle lift sensor to fail.

cox377 · Unread post by **cox377** » 31 May 2011, 10:12

If the sensor is actually replaced, does this mean replacing the whole injector?

I did jet wash the engine after doing all the works, but that was like 250 miles ago.

Unread post by **Peter.N.** » 31 May 2011, 12:36

Unfortunately, yes. The TDC sensor is on the n/s end of the engine just below the head and above the flywheel, not very easy to get at, you should be able to see the connector though, a small two or three pin plug, these can cause intermittent signal, take it apart and squirt some WD40 into it.

Peter

cox377 · Unread post by **cox377** » 31 May 2011, 13:59

I shall checked the connections tonight with a multimeter. I shall also give them some WD40. Could I do any damage driving it around when its clattery?

Thanks

James

Unread post by **Peter.N.** » 31 May 2011, 18:05

Probably not although Perkins 4/108 engines used to break the crankshaft by running over advanced, but they only had three bearings as opposed to five.

Peter

cox377 · Unread post by **cox377** » 10 Jun 2011, 11:22

Right guys,

I sprayed WD40 into all the connectors the night before last. I did it to all the ones connected to the fuel pump, the lift sensor and what I thought was the TDC sensor. I checked the connector on the sensor above the clutch bell housing, which I thought was the TDC sensor and realised it wasnt a sensor just a blank with the connector plugged into it. Checked the other 406 and it looked the same.

I unplugged the needle lift sensor when it was running well and nothing happened, the rev counter stayed working ?!?!

Thanks

J

Unread post by **Peter.N.** » 10 Jun 2011, 12:06

The injector sensor won't affect the rev counter only the pump timing, the rev counter gets its signal from the TDC sensor. Its not very easy to get at there are usually wires and pipes in the way but if you can see the bottom of the cylinder head, the join where it fits on the block, the sensor is just below in the top of the gearbox housing.

Peter