M47 Diesel Engine Whine / Whistle On The Overun
 

M47 DIESEL ENGINE WHINE / WHISTLE ON THE OVERUN REVISITED

I am re-kindling this problem as its really niggling with some M47 Diesels out there! Some owners can't hear it but when I point it out to them, they are sorry I did!!!

Always on the face lift 75 or ZT's and affects about 2 in 10 cars I've had.
I agree with various findings of others on this subject

ie High pressure Fuel line resonance in the form of a 1Kz tone between approx 1500 RPM & 3000

Put the engine under load and whine disappears so we can rule out belts, bearings, turbos etc. Also mileage is not a factor either as we've had Brand new stock with this noise !

Electronic fuel regulation is from the ECU and is a PWM waveform and guess what it's I believe from memory a 1Khz waveform!! But why would it only seem to effect later diesels? a mystery to me for the last 3 years.

Here are some old threads on the subject from the other side

Hi everyone, about six weeks ago I bought a 135 diesel ZT-T (registered Aug 2004 ). The car developed an annoying whinning sound that is present on engine overun and can be heard everytime the cluth is depressed to change gear and the engine revs drop. I thought it sounded like an air leak.
I took the car into the local Rover dealer in Basingsoke after work for them to have a listen. A mechanic came out and promptly ran the car into the workshop for further investigation. A hour later I was still sat in their reception area and they were now putting the car back together. I was informend that noise was being transmitted from the high pressure fuel line under the inlet manifold but they could not trace what was causing it. They suggested I book the car in for a full days investigation.

Before I was due to take the car in the Service Manager contacted me to say that he had been in contact with Rover Technical and that it was a known problem but at the present moment it was being investigated and there was no fix. I could not get a time scale for the fix but he assured me it was being given a high priority.
Not being able to do anything else I waited unaware of the impending doom faceing MG-Rover.
I recently have been in contact with the Sevice Manager and the news is not good. He has been working for Rover for 18 years and he has built up a lot of contacts but has been unable to contact anyone - he said basically he knows as much as what people read in the paper - we're all in the dark.
Now faced with no warranty and no technical support I am left with a great car but a very annoying noise.
Does anyone have any ideas on a fix? Cheers Nick


Thanks for the input.
I managed to get a copy of the original work sheet from my Rover dealer that was completed for their investigation. It refers to a "resonance narrowed down to the low pressure/high pressure joint pipe under the inlet manifold". It also mentions that BMW are looking into the problem - maybe I'll try speaking to them.
Somebody else said to me other manufacturers have run into these problems, especially on common rail diesels running very high fuel pressures. Noises from the fuel lines/pumps which have been cured by the fitting of a relief valve - I think they may have metioned Ford.
Cheers Nick.


The specs are for the Rover 75 2.0 CDT classic....

Again the scan is not so hot, but here goes:-Well actually the scan failed, but as it is a public document that anyone
can check on the diesel car site, I'll type the relevant bits....

"One of the best things BMW left behind when it fled Longbridge was its superb 2.0litre M47R for the 75. It is unique to Rover: The 320d uses the
same block, but with high pressure rotary pump instead of common-rail to achieve more power." The facts reveal 116bhp, 192ft/lbs of torque.

If it is a resonance you should be able to affect it by damping the pipe.

Try few hose clips clamped around the pipe to add mass in case it is just the pipe length and method of attachment that is the cause.
Or try some rubber strips under the mounting bracket.
Or cable tie some lead strips to it (lead roof flashing)

It is plausible that the modulation of hp regulator is the root cause but is should be possible to locate exactly where the noise is being produced and damp it.

Ron

Thanks Ron I was thinking along those "lines" !
It may even be a pipe that needs slightly bending a different way so the tension is different.

It's got to be an assembly issue as it only affects approx 2 in 10 cars

I would like to spray that expanding foam around but that would be an awful mess!

Last year I took a CDTi up to Frank Massey in Preston who specialises in diagnostics & PWM's etc. He even runs Diagnostic courses for garage techs.
He thought it was regulation but we ran out of time to look further.

I would like to swap a high pressure pump assembly from an CDT that doesn't have the Whine to a CDTi ??
Any differences as far as you know. Rail pressure's same as its just a remap?

I'm going to do a visual now on a CDT & CDTi to see if I spot any differences.

If it only affects 20% of facelfited models, maybe its because this 20% are using new parts (different supplier?), whereas the others are assembled from the parts used on the prefacelift cars. Or maybe only 20% of facelfited models have only one low pressure pump and the associated piping.

Ron

Think your right again Ron....
Bit like the duff batch of squealing clutch plates on 04 plates.
Have you seen any of those? many were replaced under warranty.

Its almost certainly to do with the use of one pump on the later models.

Thanks for that but what is the cure?
Also it doesn't explain why only affects 20% of the single pump versions!

I have this problem on my facelifted 2004 ZT-T and I've been trying to find the time to sort the problem. In a few weekends time, my wife is going down to her sisters so I can spend some time working on the problem withhout hearing "what you doing?" every 5 minutes, and concentrate on it!

I'm going to start with the cable tie route to see if I can break the wave form up and reduce or get rid of the whine. I'm working out in Italy at the moment with a diesel manufacturer and I'm going to see if they can suggest anything before I leave or have anything that I could try in my system to damp, or remove the wave form.

Would be interested to hear how people progress with their investigations.

Nic

Glad I'm not alone Nick!
Another observation is, at first start up of the day, there is less or no resonance for the first minute or so
ie when the diesel fuel is cold and at it's most dense.

Yup, will totally agree with that one!

On very cold days it doesn't seem to happen for (me anyway) until I've driven for a couple of minutes. However, in warmer weather, it starts after the 2nd gear change.

You're far from alone matey, far from alone. There are many of us out there, but in the big picture, not that many (if that makes any sense at all!?) I've been under the car and you can feel it in the grey fuel lines as the start their climb up into the engine bay. Someone was kind enough to be in the car with a light throttle application - say round 1500 to 2000 rpm and you can hear it outside of the car.

After a bit of poking and prodding and the use of a electronic "hearing" device that you clamp or touch on parts that you're concerned about, you can hear it and feel it as clear as day.

Crunch is I've never got round to sorting it - I just turn the radio up! However, I now have a stack of tie wraps that I'm going to try before trying to make anything more permenant (well, professional in appearance!).

We shall prevail and sort this problem!!!!!

Nic