cdi intermittent surging

[robmc52]

Evening all, just looking through for previous posts about this, but can't find anything. My new to me S320 CDI is misfiring/surging occasionally on part throttle openings. It doesn't seem to be doing it when ticking over, at least, I can't see the tacho needle moving, but pulling away and then at steady revs when on the move it is noticeable.
If I stop the car and turn the engine off for a moment, it then runs fine, and can do so for a day or two before reappearing again.
I'm not sure where to start looking to be honest, if it was there constantly then I might be able to get an idea of what is happening, but the random nature of it is mystifying me.

 

[Paul1948]

If it is purely surging occasionally when cold, it could be the same as mine had, agearbox oil change cured the problem.

 

[robmc52]

That;s a good point, although the previous owner has had a gearbox service within the last year or so. It does happen when the engine has warmed through though.

 

[malcolm E53 AMG]

I’d start by putting a dose of injector cleaner through it and giving it a good run followed by using a premium brand fuel BP or equivalent which will help clean-up the induction side. My E350cdi is running much better than when I bought it especially at lower revs and I attribute this to my recommendations above plus using a premium fuel over the last 7k miles

 

[robmc52]

Yes, that had crossed my mind, the injector cleaner that is. Will stick some in tomorrow and see how it goes. I've got a 200 mile journey on Thursday so it'll get a chance to warm up properly.

 

[malcolm E53 AMG]

If the car is new to you I would check the condition of the air filters and change the fuel filter which are often neglected

 

[Steve@Avantgarde]

Worn subframe bushes or a failing Tc lock up valve can cause surging.

 

[om613]

Fuel filter. Yes.
Air filter. No.
Any fix in a bottle or premium wonder fuel. Another NO.

 

[Steve@Avantgarde]

Fuel can’t surge on a CDI either. It has to maintain a constant 300 bar rail pressure or it will cut out on throttle.

So waste of time even doing the fuel filter.

 

[robmc52]

Thanks for all the interesting replies. I took it out for a 30 mile run last night and it ran as smooth as silk, the whole drivetrain felt completely rattle free and tight. The Mrs is taking it out today, so I'll await her, no doubt highly technical, report when she returns. Out of interest, Steve, where is the lockup valve for the TC? Is it the sort of symptom that would be intermittent?

 

[Steve@Avantgarde]

The lock up valve is in the valve chest inside the gearbox. The valves can chatter causing the gearbox to surge. Mainly felt when cold but it can happen when warm too.

 

[robmc52]

The lock up valve is in the valve chest inside the gearbox. The valves can chatter causing the gearbox to surge. Mainly felt when cold but it can happen when warm too.

Cheers, I'm veering towards having the gearbox serviced anyway. looking through the pile of invoices I got with the car, there's one for an oil and filter change about 3 years ago, although there's no mention of the pilot bush being renewed, which I'd get them to do, would the valve you mention be accessible during a gearbox service?
I'm in East Kent by the way, so the car would be going to Class Cars in Wingham.

 

[Wighty]

Thanks for all the interesting replies. I took it out for a 30 mile run last night and it ran as smooth as silk, the whole drivetrain felt completely rattle free and tight. The Mrs is taking it out today, so I'll await her, no doubt highly technical, report when she returns. Out of interest, Steve, where is the lockup valve for the TC? Is it the sort of symptom that would be intermittent?

The old "Italian tune up " , always improves things , especially if the car has done a lot of short runs .

 

[Steve@Avantgarde]

Cheers, I'm veering towards having the gearbox serviced anyway. looking through the pile of invoices I got with the car, there's one for an oil and filter change about 3 years ago, although there's no mention of the pilot bush being renewed, which I'd get them to do, would the valve you mention be accessible during a gearbox service?
I'm in East Kent by the way, so the car would be going to Class Cars in Wingham.

It would be the best time to change one, but the valve body would have to be removed.