In tune with engine tapping from behind dash board when vehicle is cold ?

[anorakmark]

Time to scratch ones head for another P38 brain Teaser
Does anybody else suffer from this weird one as I do as does my work colleague and we have identical RR, P38's 1998, 2.5 DSE
Here we go.
When starting the vehicle from cold when I accelerate I get a weird tapping noise which seems to run in tune with engine speed revolutions. This tapping seems to be coming from behind the dashboard speedo somewhere between the bulk head and dash board. this tapping only happens when cold and as soon as the heaters are warm and the engine is at normal tempreture the tapping noise fades. It seems the colder the outside tempreture the louder the tap? My work colleague complained to me about his RR making weird noises from cold so last night whilst at work we put both vehicles to the test and they both made the same identical tap, tap from cold. we are both 100% sure this is not coming from the engine, the noise is coming from behind the bulk head on the off side somewhere near the brake booster, as soon as they are both warmed up the noise fades away, the tapping can only be heard on acceleration and the harsher the acceleration the louder the tapping noise. Anybody got a clue on this Gremlin

 

[dave4x4]

Glow plug relay?

Or maybe not. Mine clicks very loud.
Leave ignition on for a while (2 or 3 minutes) and see if it starts to click with the engine off.

 

[Saint.V8]

Why would a Glow Plug Relay continuously tap in time with Revs....until it gets warm??

 

[Datatek]

Glow plug relay.

That's in the ECU box by the battery, doubt you'd hear that in the car.
I was thinking blend motor jammed, mine makes a tapping noise from time to time and it's definitely the temperature blend motor.

 

[dave4x4]

Just that my relay clicks really loud. I can hear it inside the car with the doors shut. It starts after 2 or 3 mins when I leave the ignition on. Just a suggestion anyway.
If it increases exactly in time with the engine revs it won't be that but OP said definitely not the engine. That rules out blend flaps as well.

Not sure where the crankcase PCV valve is on '98 cars. Mine is in the cam cover. Can it click?
Further suggestion - select some fuses to take out to pinpoint the problem

addendum: my glow plug relay is outside the ECU box because I have had the engine ECU in and out a lot.

 

[stopover]

Gear lever, cam till warm, maybe cats? You could also try an old days method!!!! get the wife, girlfriend or mother in law to wedge under the bonnet and see if they can trace the noise - you might get another noise to deal with whilst doing this experiment though!! Oh and watch out for the fan! My son tells me he has heard of someone who strapped their smartphone under the bonnet to record a noise only he didn't do it very well and is now claiming for a new one on his insurance!!!!!!!!

 

[Blackader]

I have a 2.5 dhse with the very same tap tap tap or more of a light nock nock in time will engine revs when cold for about 1 to 2 minutes depending on going up or down hill in cold weather not warm , I think it's the cat being restrictive and not let's all the exhaust gases through (pressurising the exhaust before the cat) when cold and beeing less restrictive when hot , the tapping or nocking is the flexy joint on the exhaust before the cat (which is right behind where you mentioned behind bulk head by your right knee cap) sort off blowing up (exspanding)or poping in time with valve timing ?
This is my penny's worth don't know how possible it is but that's all I can think of without decating the exhaust to try the theory !!

 

[Saint.V8]

I have a 2.5 dhse with the very same tap tap tap or more of a light nock nock in time will engine revs when cold for about 1 to 2 minutes depending on going up or down hill in cold weather not warm , I think it's the cat being restrictive and not let's all the exhaust gases through (pressurising the exhaust before the cat) when cold and beeing less restrictive when hot , the tapping or nocking is the flexy joint on the exhaust before the cat (which is right behind where you mentioned behind bulk head by your right knee cap) sort off blowing up (exspanding)or poping in time with valve timing ?
This is my penny's worth don't know how possible it is but that's all I can think of without decating the exhaust to try the theory !!

Why would a Cat be more restrictive when cold??

All it is, is a filter made of various expensive metals to assist in remove nasties from the exhaust....

 

[Blackader]

Diesel cats are slightly different to petrol cats I've been told , diesels are more like fine filters made of theses expensive metals which build up an amount of particles which then get released in a cloud of soot when enough pressure is built up, given the heavy right foot (all brand new diesels do this at a drag start)
Or
This could be as far fetched as the Virgin Mary ?

 

[Saint.V8]

Diesel cats are slightly different to petrol cats I've been told , diesels are more like fine filters made of theses expensive metals which build up an amount of particles which then get released in a cloud of soot when enough pressure is built up, given the heavy right foot (all brand new diesels do this at a drag start)
Or
This could be as far fetched as the Virgin Mary ?

True, but I would think if there is that much soot and ****e going through the Cats, there is something afoot somewhere else i.e. Over Fuelling etc...

 

[Blackader]

That's where my idea gets a slap down to the kerb ,it's only taps or knocks when very cold and the engine is choking or over fuelling till the ecu temp sensor says ok that's enough cold mixture now and starts to run leaner on a hot engine fuel mix
Or my theory when the cat is warm enough a starts letting gases though faster (possibly a damp cat ,condensation mixed with soot)

 

[Saint.V8]

Stranger things have happened at sea!!

 

[Grit Valve]

Sound like bell housing area to me I'd start in that area .

 

[wammers]

Diesel cats are slightly different to petrol cats I've been told , diesels are more like fine filters made of theses expensive metals which build up an amount of particles which then get released in a cloud of soot when enough pressure is built up, given the heavy right foot (all brand new diesels do this at a drag start)
Or
This could be as far fetched as the Virgin Mary ?

The thing on a P38 is a cat. Maybe slightly different to a petrol in construction but a cat never the less. Particle filters are a different kettle of fish. They store soot from the engine generated at low speeds before the engine warms up usually made by the action of EGR unit. If the EGR is faulty it can generate lots of soot. Then when the car is driven over say 40 mph for any period of time the filter heats up and burns off the soot. If the car is driven around at low speeds the particle filter can block and have an effect on performance. The cat fitted to the P38 does a bit of both but neither very well to be honest.

 

[Blackader]

It's is definitely behind the speedo not central (off side) it's just for a minute so haven't been bothered by it , its always done it and you wouldn't here it with radio on , its that quiet but I can get a little paranoid with noises I haven't herd before (like most p38 owners) . I was just wondering today cause two other DHSE owners on here had the very same noise , which could be that they always done it on warm up but non of us have ever owned one from brand spanking new ?(I presume).

 

[anorakmark]

It's is definitely behind the speedo not central (off side) it's just for a minute so haven't been bothered by it , its always done it and you wouldn't here it with radio on , its that quiet but I can get a little paranoid with noises I haven't herd before (like most p38 owners) . I was just wondering today cause two other DHSE owners on here had the very same noise , which could be that they always done it on warm up but non of us have ever owned one from brand spanking new ?(I presume).

Yep deffo behind speedo area more to the lower where your right knee would be. And yes turn the radio up and you can drown it out LOL. can only be heard when accelerating under load when cold only?

 

[anorakmark]

A big thank you to you all, there has been some very interesting suggestions regarding this post. I'm not gonna worry my ass off on this one as it does seem more common than I thought. On reading the posts I think I may be looking down the road of Datatek's suggestion.

 

[clarkie]

mine does this also,but it only started after i did the heater o rings,i put it down to when i put the car back together i gaffer taped all the joints of the heater ducting so maybe its this expanding as the car heats up,maybe, maybe not, its been 2 years since i did them.

 

[anorakmark]

mine does this also,but it only started after i did the heater o rings,i put it down to when i put the car back together i gaffer taped all the joints of the heater ducting so maybe its this expanding as the car heats up,maybe, maybe not, its been 2 years since i did them.

Now theres a good answer Clarkie, Hmmm I have also had my O rings done. could well be the heatter ducting expanding. At least I know it's deffo not engine ot transmission.