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3.0 Hdi 160Psi With Poor Idle


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#1 pikesrelaybus

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Posted 05 June 2018 - 05:24 PM

Hi Guys,

I started a new thread yesterday but ironically as I explained my problem I stumbled across the fault but I thought I'd still post anyway. For months now my relay has intermittent "hunting" engine, especially at tick over. If you engage cruise control you can feel the vehicle surging as the power comes and goes. If you stomp on the accelerator your rewarded with a sooty puff of smoke which means these days a MOT failure. It's like it's running rich and those of you out there, like me, might place blame on the EGR valve since there's so much crap circulating around modern diesels. Sometimes, not always, she was a complete bugger to start and I'd get a engine warning light, more often than not she won't start first turn which is unusual. Yep, she rattles away at 140k miles but this is what I found.

 

As I finished off my original post, post fitting a new EGR valve and then having to refit the thing due to coolant leaks, I noticed a "include file" option at the base of the post and thought a quick video of the thing hunting away might help. Upon switching off the engine I hear the familiar sound of the throttle body closing about 3-4s after ignition off and also a buzzing sound coming from the valve which feeds vacuum to the EGR valve. As the vacuum reduced the buzzing noise faded and went up in frequency. That caught my attention and I pulled off the vacuum hose from the EGR and immediately there was air flowing when it was ticking over, that shouldn't be at tick over. SO... what I'm saying is I was spot on diagnosing the EGR problem, the poor running was due to it sniffing it's own farts but it wasn't the EGR valve, it was the sodding valve. Both items are quite expensive, EGR was £160 (pattern part), £280 for OEM (if memory serves me right) and that valve, which looks like if you open it up it'll be broke forever is £120, on my 2008 it's fitted above the engine behind a metal plate. I've got a 2nd hand one off eBay. After I removed it I could blow/suck air through it, so I guess it's opened and stuck open. Having taken it off I get the engine light but it seems the hunting has gone away, well it did for the 6 mile journey I did this morning. I could of course blank the bloody thing off but then I increase engine temperature, so I'm led to believe. Still, worth checking that valve before you remove the EGR valve, which incidentally is much easier if you remove the heat ex-changer it's bolted onto. The worse part was the lower seal, I opted to leave the lower half bolted to the exhaust where the hex bolts had rusted.


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#2 paul.h

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Posted 05 June 2018 - 11:31 PM

Thankyou for posting this, it might help another member with a similar problem on a petrol C8 who has cleaned the egr valve and done other things but still has similar symptoms to yours.



#3 pikesrelaybus

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Posted 08 June 2018 - 12:38 PM

That's not a problem... however!!!. Having received the new valve which has the part number 46524556, looks like this. I checked it against the old one and it behaved similar. Of course I wrecked the old one to find out why it failed. I fitted the valve along with a pressure meter on it's output. When you switch the engine on I measured -30mBar, most of the vacuum is sucked through the third hole the other side of the valve which has a small boot with a little filter fitted. Moments later, the the engine's note changed (became throatier) and the vacuum was now 700-800mBar so obviously on but why? It's ticking over... Also even without the egr valve hooked up to the vacuum, I'm still get this hunting which has now really confused me. If you disconnect the valve electrically it goes back to running smoothly and the vacuum is -30mBar. So, I can connect all the pipes up and leave the electrical connection loose and all is ok. What I'm worried about now is what controls this valve? or maybe it's getting duff info from another sensor which fools the ECU to operate this valve. And why is it running rough even while the EGR valve is closed.? When the valve is connected it buzzes. You think Citroen will find this?


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#4 paul.h

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Posted 09 June 2018 - 10:50 AM

The sensors involved in getting the air flow right will be the coolant temperature, the inlet air temperature, the air flow meter MAF - this probably also contains the inlet air temperature, the manifold pressure MAP. To check these would need a code reader that gives live data. It is possible these do not give a fault code but could be giving wrong values.






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