Technical Another little niggle to diagnose please!

[Bonefish Blues]

We're on a good run with the (113K) 4x4 Multijet at the moment and it's running really nicely but there is one thing that's niggling at the moment that I'd appreciate thoughts/advice on. As with the last one (smoke in specific circumstance) it's very particular to a certain action. To explain:

My regular run involves a stretch of dual carriageway with a roundabout at each end, so to get on at either end it's a slow RH turn round the roundabout and then straight into acceleration up to NSL. The issue is that I don't get clean acceleration, I get a slight judder, associated with a mild metallic noise. I can make it stop and resume smooth acceleration by just a momentary lift of the throttle. Alternatively I can come off the roundabout and maintain my speed for a little while, and then acceleration will be smooth.

Welcome your thoughts, knowledgeable comrades - failing front LH driveshaft maybe? Wheel bearing? Something else?

 

[Herts Hillhopper]

Sounds more like a turbo lag/waste gate issue? Mine very occasionally will do the same thing ('only' 48k miles). I think lifting off lets the waste gate shut so then the turbo can do its thing.

Oddly, you can also force this symptom by momentarily catching the brake pedal with your left foot while trying to accelerate...

 

[Greasytrucker]

We're on a good run with the (113K) 4x4 Multijet at the moment and it's running really nicely but there is one thing that's niggling at the moment that I'd appreciate thoughts/advice on. As with the last one (smoke in specific circumstance) it's very particular to a certain action. To explain:

My regular run involves a stretch of dual carriageway with a roundabout at each end, so to get on at either end it's a slow RH turn round the roundabout and then straight into acceleration up to NSL. The issue is that I don't get clean acceleration, I get a slight judder, associated with a mild metallic noise. I can make it stop and resume smooth acceleration by just a momentary lift of the throttle. Alternatively I can come off the roundabout and maintain my speed for a little while, and then acceleration will be smooth.

Welcome your thoughts, knowledgeable comrades - failing front LH driveshaft maybe? Wheel bearing? Something else?

Hesitation with a metallic sort of noise could be pinking (pre ignition) so could be a timing issue maybe?

 

[Greasytrucker]

Sorry ignore that, missed the multijet bit lol!

 

[Bonefish Blues]

Sounds more like a turbo lag/waste gate issue? Mine very occasionally will do the same thing ('only' 48k miles). I think lifting off lets the waste gate shut so then the turbo can do its thing.

Oddly, you can also force this symptom by momentarily catching the brake pedal with your left foot while trying to accelerate...

Hadn't thought about that - at all. If the boost is not at spec., wouldn't I get an engine warning light though - no sign of one at the moment?

 

[Jamie KC]

Do you always approach this in the same gear at a similar speed? Sounds like a second gear type manoeuvre, but would it be possible to try in first? May help point to a rev related issue indicating engine based problem, or a mechanical issue related to wheel speed.

 

[Bonefish Blues]

Do you always approach this in the same gear at a similar speed? Sounds like a second gear type manoeuvre, but would it be possible to try in first? May help point to a rev related issue indicating engine based problem, or a mechanical issue related to wheel speed.

It'd be quite difficult to hold first around a couple of quite major roundabouts I'm afraid. This is the only circumstance in which I can provoke this behaviour - I'm sure if I had a wander over to MK I'd get much the same though!

 

[Herts Hillhopper]

Hadn't thought about that - at all. If the boost is not at spec., wouldn't I get an engine warning light though - no sign of one at the moment?

I get no warning light - just a moment of hesitation and a distant rattle. I don't think it would show as a fault light - that would only happen if the car thought the turbo pressure was less than expected, whereas here I think its simply that the turbo doesn't spin up. As well as very briefly easing back then reapplying teh throttle to 'cure it', I can simply be less 'heavy footed' when pulling away then it's all fine. I get this effect on a roundabout on the A10 near Puckeridge in Hertfordshire: the exit is at about 1 o'clock but with quite a tight left as you leave the roundabout... I did wonder if its the ESC but never see a dash light for that here (do in other places!)

 

[Bonefish Blues]

I get no warning light - just a moment of hesitation and a distant rattle. I don't think it would show as a fault light - that would only happen if the car thought the turbo pressure was less than expected, whereas here I think its simply that the turbo doesn't spin up. As well as very briefly easing back then reapplying teh throttle to 'cure it', I can simply be less 'heavy footed' when pulling away then it's all fine. I get this effect on a roundabout on the A10 near Puckeridge in Hertfordshire: the exit is at about 1 o'clock but with quite a tight left as you leave the roundabout... I did wonder if its the ESC but never see a dash light for that here (do in other places!)

Does yours sort of 'throb' like mine - that is pulsed acceleration, not clean, almost like a misfire? (Innuendo intended!)

 

[Herts Hillhopper]

Does yours sort of 'throb' like mine - that is pulsed acceleration, not clean, almost like a misfire? (Innuendo intended!)

Ooh er, and no

 

[Bonefish Blues]

I'm thinking we have different symptoms

 

[Greasytrucker]

My Sedici Multijet had a bit of a hesitation sometimes and a bit of a clatter and that was when the EGR needed a clean

 

[Herts Hillhopper]

My Sedici Multijet had a bit of a hesitation sometimes and a bit of a clatter and that was when the EGR needed a clean

Good shout - and with a particulate trap you (shouldn't) see the 'tell-tale' cloud of black smoke from a stuck EGR as that gets caught in the trap.

(The EGR is a bugger to get to on the Panda...)

 

[Greasytrucker]

If you were sitting at a constant speed 70 or so with your foot in the same place it used to fluctuate or “throb” . You could always try a bottle of EGR cleaner in the tank and see if it helps

 

[Bonefish Blues]

My throbbing was upon acceleration. Mechanical sympathy meant I've never got anywhere near 70 mph with this happening, I've backed off, then resumed clean, unthrobby acceleration. Could an EGR system produce those symptoms which were so easily overcome, do you think?

 

[Greasytrucker]

Could be fuel starvation like a dirty fuel filter or something. My first port of call on any car if it’s not throwing up codes when hesitating is EGR valve. Work of the devil they are