All,

I bought my V8 petrol FFRR about three years ago. It has always had a what can only be described as a slight misfire/hesitation at around 50MPH -55MPH at around 2000RPM, mostly going up hill, kick it down a gear and when the revs and speed increase it dissapears. Never really bothered me as its was only ever at that speed going up hill.

A couple of weeks ago the fuel pump in the sender unit packed in. I had that replaced and now that hesitation seems to be worse, might be coincidental with the fuel pump failure maybe not. i did not replace the entire assembly, only the pump itself.

Again it only happens at around 50MPH, but will now also happens on a level road surface, any speed below that and its fine, any speed above and its fine. Its only in that small window between 50MPH and 55MPH. By the time you reach 60MPH its gone, all the way to 90MPH and beyond it fine.

I have done some research on here and the only real topic that I can find with similar symptoms is gearbox related. The 'box in mine was replaced just before i bought the car and has done around 70k miles, also if it was the TC going I would have expected it to have failed a long time ago, or exaggerated when towing the tin tent.

I have a loss of coolant, but not enough to indicate a failed head gasket, I only need to top it up once month, no masses of white smoke or steam on start up, in fact the Subaru we have put out more exhaust fumes! No oil/coolant mix either.

So I am stumped, it idles fine, revs dip slightly for less a second when the air conditioning compressor kicks in but returns to normal again. I am thinking MAF or possible dodgy ignition pack, possibly a position related sensor, camshaft or crankshaft? However RSW does not show any codes or errors for any sensors.

Anyone else have any ideas?

TIA

Ken You are either at Le Mans or waiting for Le Mans

RSW MKIII V2 All Comms in Central Scotland

I can think of two things,

First, clean the entire fuel system, pump, lines, filter (on the intank pump). Clean the injectors, inlet tract, MAF sensor. This is quite a job but worked wonders on my 4.2 SC (new pump as well).

Second, have the ECU of the motor management updated with the latest software. I did that at the same time as the fuel system was cleaned.

After the above the car ran absolutely brilliantly !!! MY 2010 5.0 SC Galway green and sand interior!!
Have the Faultmate MSV2 Extreme to be tinkering with the settings etc. !!

Does it do it at the same speed in 4th ?? if it does it's not likely to be the engine... or does it do it at the same revs in forth ?? in which case it might be the engine, if it doesn't do it at all in forth then it's more than likely the gearbox or other drivetrain issue...

Your water loss could be a small leak in the gearbox oil cooler between the matrix, this allows a small quantity of water into the oil and over time will get slowly worse...

If you don't want to drain the gearbox you could go through the checking level procedure and see if there is too much in there, if some comes out then you should be able to see if there is water mixed with it... Pete

__________________________________________________
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2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
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Hi Pete,

That's an interesting take on it.

I wouldn't have described it as a judder in the way other posts have described it.
However it worth considering. In response to your question, no idea

I will take it for a drive later and let you know.

Thanks

ken You are either at Le Mans or waiting for Le Mans

RSW MKIII V2 All Comms in Central Scotland

I once had a similar sounding problem on a Fiat Coupe - slight misfire at a specific rpm, only happened on very light throttle, turned out to be a coil pack problem

I'd go with the suggestions above and if it's still not cured, perhaps something to consider - good luck! 2007 Zermatt Silver TDV8 Vogue SE - now sold but was a great car!

Thanks to all those that have answered.

So I have been away for a couple of days and traveled around 600 miles mostly motorway.
There is a vibration, however its intermittent, almost like unbalanced rear wheels.
Last time I had that the bearing on the front prop-shaft was worn.

I tried Pete's idea of seeing if the vibration/hesitation was present in fourth at the same speed/revs.
it is, but not as pronounced, and again not consistent, I cant get it to do it every time.

I have the RSW ALL comms and there are no errors for the gearbox. the only error found was this one

P0000 ECM/PCM processor

Not sure if this is related to the recent fuel pump failure or just a red herring as P0000 is a no diagnostic code found. I have cleared the code but not had chance yet to see if it has returned. You are either at Le Mans or waiting for Le Mans

RSW MKIII V2 All Comms in Central Scotland