Desperately hoping for some expert advice on engine fault R320

[joeysnowey]

Hi all, I am at the end of my tether with my R320. I love it, it's beautiful and I have enjoyed it since buying it around 6 months ago, except for one fault I just can't seem to get diagnosed.

The fault is very intermittent, just happens occasionally. What happens is the car will stutter under acceleration. It's usually minor, just a few seconds where the throttle doesn't work and then the acceleration kicks in and you are going strong again. But it's disconcerting and worrying, and obviously I am not sure what the problem is so I assume I could break down any time.

I have had it looked at by a Merc indie and he changed fuel filter, glow plugs (they reported one faulty), and nothing has cured the problem. Last resort is fuel pump, but it's pricey and I just can't afford to buy one of those if it won't definitely sort the problem. When the car does the bunny hopping it flashes a warning triangle and writes a fault into memory. When having it read the fault reads as "low fuel pressure". therefore I am advised it's probably the fuel pump but no way to know without changing it, and I have a funny feeling it may not be this, and certainly can't afford to fit a new pump just to suck it and see!

Has anyone ever heard of this problem before? Its much like in the old days when a car was missing on 1 or 2 cylinders, you stick your boot down and nothing happens, then you feel a bit of a kick and stutter a few times, almost like there is an intermittent fuel blockage, but garage says the fuel lines look fine.

Any ideas very much appreciated.

 

[whitenemesis]

Were the codes read using STAR/XENTRY?
Are you accelerating when the fault happens and the triangle flashes up? Does the triangle have an exclamation mark in the middle?

 

[joeysnowey]

Pretty sure it was Star, its a decent garage who did it and they seem to have all the decent gear. They work mainly on Mercs and Range Rovers.
Yes I am accelerating when it happens, its like what happens if you bounce your foot on and off the throttle.
Yes I think the triangle is a yellow warning triangle with exclamation mark in the middle, inside the rev counter.

 

[whitenemesis]

That sounds like the traction control (ESP) indicator.
I had similar in my CLS55, only rarely but found out it was actually the tires breaking traction and the car cutting fuel to regain traction.

 

[joeysnowey]

Thanks for your input. Funnily enough the garage said that warning means I "lost traction", wondering if I was pushing it a bit in the car! It happens when going VERY slow on a straight road in dry conditions, no way it's actual loss of traction, but maybe if the car THINKS it is, that could be the answer. How easy would it be to check if that's the problem do you know?
thanks again, much appreciated

 

[whitenemesis]

Could be an issue with one of the ABS reluctor(?) rings, the car erroneously thinks one wheel is spinning faster than the others.
I would have thought there should be error codes stored, which STAR would report.

 

[joeysnowey]

Yes, i have had it read several times in past 6 months and the only error reported is "low fuel pressure" hence why the garage says its probably the pump, but could so easily be other things!

 

[MercedesDriver]

I had exactly the same problem you’ve described with Volvo V70. On acceleration, always while overtaking on motorway, it would stutter for a moment and the EML would come on. After it would run normally till it happens again. The error code was described exactly as yours “low fuel pressure”.
Different engines, I know, but in my case the problem was with faulty fuel rail pressure sensor.

 

[joeysnowey]

Hi, thanks for posting and that's interesting. I assume that would be cheaper to replace than the pump so if I am going to start guessing I will start with the cheaper guesses first!

 

[philt32]

I had a similar fault on my vw caddy van, it kept doing the hesitation type fault you describe then went into runsafe mode, I pulled into a garage and they said the fault was reading low fuel pressure

I had a diesel heater fitted a couple of weeks earlier and this was the first proper run out....long story short...back to the installers....apologies “we kinked a fuel hose when putting the tank back”

Might be worth checking fuel hoses / loose unions / splits ?


Sent from my iPhone using Tapatalk

 

[BTB 500]

I have a Vito with the same engine, and also had a low fuel pressure error. The start point is to replace the fuel filter (as you've had done) and fuel pressure sensor as those are relatively cheap and easy to do. Glowplugs are a complete red herring as they're only used at startup (mine needs plugs replacing fairly regularly - IIRC the first one went at about 30k miles).

But I learned the hard way not to use my local (good) independent garage for work like this. After successfully clearing the fuel pressure error another one came up for the EGR valve. After replacing this they were unable to clear the error on the system they had ... they had the van for 2 weeks, after which I ended up having to take it to a dealer anyway. A couple of weeks later it went into limp mode again ... the dealer found a fault associated with the mass airflow sensor, but this was traced to an outstanding software update on the vehicle (the sensor itself was fine). This was applied and (fingers crossed) it was OK. An indie would never have been able to fix that (actually the garage who worked on the EGR valve did find a MAS fault then, but couldn't identify what the problem was and it 'went away' so they didn't think it was significant).

Modern turbodiesels are highly complex computerised things and non-franchised garages can really struggle to work on them now. Our van has also had the crankshaft position sensor fail (engine completely dead) and differential pressure sensor go (limp mode). Those both happened under 60k miles ... it's only on 90k now, which should be nothing for a Merc. diesel.

 

[alecmascot]

Thanks for your input. Funnily enough the garage said that warning means I "lost traction", wondering if I was pushing it a bit in the car! It happens when going VERY slow on a straight road in dry conditions, no way it's actual loss of traction, but maybe if the car THINKS it is, that could be the answer. How easy would it be to check if that's the problem do you know?
thanks again, much appreciated

Traction control looks at the rotational speeds of the front and rear wheels.
Are you running different tyre sizes front/rear (staggered) ?

 

[joeysnowey]

Nope, tyres are all the same. Thanks Bill - I am not sure if he replaced the fuel pressure sensor but will ask, thanks