Lumpy running at constant speed...

[bsa77]

Hi All,

My 2002 TD4 developed a fault the other day which it has decided to keep...

When driving at constant speeds (i.e. on a motorway) randomly it starts to run roughly, if I accelerate hard it pulls smoothly and as quickly as normal but after a while once at constant speed it randomly reverts to rough running.

Then last night in traffic on the M25 it started doing it at idle/low revs, clear traffic and the issue vanished - a bit later at 70 ish it started again.

Has not repeated the rough running at idle since and always starts perfectly.

100 miles before this first happened I filled up with fuel from Sainsburys and after ~ 450 miles I filled up again, this time at ESSO. After the issues on the M25 I bought a bottle of injector cleaner and have added that to the tank - however I have only driven 20 miles since that so not enough time to do anything I suspect.

For some reason I couldn't log on here yesterday so I looked elsewhere and hence deduced dirty fuel/injector - anything else I have missed - moth of the rough running probllems on here tend to be either poor startign/idle or lack of power - which I don't think is the main issue.

Car has Synergy 2 fitted but Bosch MAF.

Cheers!

 

[teddywood1]

it could be dirt on your filter in the tank? or main fuel filter

 

[angeloc]

What number is the synergy set at?

 

[bsa77]

Set at 5 - I am suspecting dirt as the tank was quite low (cost £87 to fill) when I filled at sainburys.

Forgot to say that when it is in lumpy mode I can hear a pinking type noise from the engine.

Is it worth pulling the main pump out and giving the filter a clean?

Cheers!

 

[nickcc]

Probably worth changing the fuel filter first, as the cheaper option, especially if yours is still the original as it should be changed every 60,000 miles (presuming a 10 year old car has covered in excess of 60,000 miles)

 

[angeloc]

Try dropping the synergy down to 1 or 2 - you may have an Injector going down and the extra rail pressure caused by the synergy is too much for it.

 

[bsa77]

Will do, fitting new fuel filter tomorrow too. Did the gatwick run today (120 mles or so) and seemed pretty smooth, doing a variety of speeds between 50 and 85.

Will report back!

 

[angeloc]

Any update?

 

[bsa77]

Right, its been a couple of months and the car has had a full service inc. fuel filter. I dropped the synergy down to 1 for a while but it made no difference.

So, logically it has to be an injector? But I was reading about a wiring harness issue on the TD4 engine - could this be causing this rough constant throttle running? Also it has become more noticeable that I randomly get uneven idle too.

Seems to accelerate as well as normal.

Is it possible to interrogate the ECU to see if an injector faul has been logged?

 

[bsa77]

Any one got any advice on this? Just been in for its MOT and passed with no advisories so quite chuffed, now just want it running properly.

Is there any point totally removing the synergy box or am I right in thinking this couldn't cause this problem?

 

[mjrimmer]

Check the high pressure fuel sensor plug/socket that the synergy attatches to, make sure all the contacts are clean.
If it still does it try running with the synergy disconnected (not just switched off). Failing that it could be an injector on it's way or even the low pressure fuel pump

 

[bsa77]

Will do, hope not the LP fuel pump as that is only 8 or 9 months old!

Assuming it isn't I will have to get it plugged in - any one got a diagnostic puter in the Farnborough (Hampshire) area?

 

[mjrimmer]

Did you replace the low pressure pump with a genuine one or an aftermarket copy?

 

[bsa77]

Genuine (with receipt in case it goes wrong)!

But when that went the car randomly wouldn't start - very different to this!

 

[mjrimmer]

I take it you changed the fuel filter?

When one of my injectors was on its way at times the engine would be very rhaspy until you reved it.....that would normally get rid of the noise. But every now and then driving at a constant speed it would feel as though the car would momenterally loose power and then pick up again giving a slight surging feel.

 

[nickcc]

Rover Ron (synergy) recommends reducing the setting if you experience lumpy running/tickover, worth a try before you start changing anything else.

 

[Vertuas]

Hi,

This sounds like the issue that I just had, but not the same.

With the car in neutral and running, slow increase the revs to about 1250rpm.

does the car run roughly and lumpy between 1000 and 2000 rpm?

Does it hold 1250 rpm or hunt up and down?

Mine would not hold the revs and ran roughly. It was caused by the crap in the EGR stopping it from closing. The PCV was also cleaned but I thing that the EGR was the culpret.

Thanks

 

[john t]

i have had a similar issue, i found the synergy connection to the fuel sensor faulty,
also have had failed injectors in the past similar symptoms ,

try disconnecting the synergy, also be aware if you have fitted the pierberg maff with the synergy unit may be running issued if the synergy unit is not connected ?

 

[mjrimmer]

Another thought....try running it with the synergy disconnected and also unplug your maf. It should then run on default maf values and will prove if the maf is ok.

 

[bsa77]

Hi,

This sounds like the issue that I just had, but not the same.

With the car in neutral and running, slow increase the revs to about 1250rpm.

does the car run roughly and lumpy between 1000 and 2000 rpm?

Does it hold 1250 rpm or hunt up and down?

Mine would not hold the revs and ran roughly. It was caused by the crap in the EGR stopping it from closing. The PCV was also cleaned but I thing that the EGR was the culpret.

Thanks

It idles at around 700-800 and sometimes bounces around a bit between the two, then the worst bit is just over 2000 RPM at constant throttle.

No EGR valve, was removed but I had this problem before and after!