35i 'surging' under power with no error codes!

[mcbutler]

Hello all,
Ok, my 35i with 34k on it and running on Vmax has developed a bad habit of surging on hard accelaration. You cant really feel it in the car but you can hear it.
Another possibly related symptom is warm starting has changed as well. Before when warm it would just jump into life, nice growl and into tickover. Now it starts like its rolling over in bed with a hangover, no growl just a bit of a sputter and into tickover.
Indy said something about an airpump or something, didnt understand that really!

Had it to my indy who have been through it, no codes and could not replicate the issue.

I have managed to catch it briefly on dashcam, audio isnt great but at the 18 - 20 sec mark you can just make it out. If someone has sound editing software they might be able to clean it up?

Any ideas please let me know.

https://youtu.be/5qDMLscN-zg

[Pbondar]

Plugs, coils, injectors, HPFP for cost reasons…

Probably injectors or HPFP

All IMHO

As I’ve learned..with these turbo engines you can get nebulous ‘soft fails’ that don’t flag any error codes…

You’ve already had it walnut blasted?

[mcbutler]

Plugs, coils, injectors, HPFP for cost reasons…

Probably injectors or HPFP

All IMHO

As I’ve learned..with these turbo engines you can get nebulous ‘soft fails’ that don’t flag any error codes…

You’ve already had it walnut blasted?

Hey Peter,

Its only done 34k last 10k with an oil catch can, its all clean on the inlet side, plugs are all new.
We share the same thoughts on possible culprits, its just the odd start behaviour changes that bug me.
Cold start was alway immediate and smooth into fast idle, slow idle after a minute or so - now it sometimes stutters on cold start but after that its good.
Warm start sounds like a wet fart whereas it was an instant 'leap into action'.

I will try and get some recordings if it ever stops fekin rainig lol.

[Jembo]

Pbondar certainly has most bases covered, where my suggestions are

- replace fuel filter
- could be some dirt has contaminated /blocked injectors… where maybe a good excuse for a long italien tuneup could be in order… with a fresh fill halfway round

[Pbondar]

From my experience and research age and the number of hot/cold cycles seems to figure as much or more than pure mileage…IMHO…

It could be something obscure like a cam box leak slowly filling a plug recess..I’ve seen that reported on those engines..

Have you had a proper diagnostic like ISTA attached to it?

[R.E92]

The poor starting is usually fuel pressure related. That kind of lacklustre startup is usually a sign of a failing HPFP.

Surging can be caused by a lot of different things so I would focus on the HPFP first. You could scan for error codes, sometimes a failing HPFP will leave some error codes. Otherwise you would need to use something like ProTool or MHD to log the fuel rail pressure during startup.

[ori]

I know exactly what you mean about a warm start up. It growls beautifully.

HP Pump sounds plausible for all your symptoms.
Car with such low miles is a prime candidate for a bmw warrantee. Do you have one?

[mcbutler]

From my experience and research age and the number of hot/cold cycles seems to figure as much or more than pure mileage…IMHO…

It could be something obscure like a cam box leak slowly filling a plug recess..I’ve seen that reported on those engines..

Have you had a proper diagnostic like ISTA attached to it?

Yeah as i stated its been to my indy and hooked up for a deep scan, nothing showing and they could niot recreate it on the road either.

[mcbutler]

The poor starting is usually fuel pressure related. That kind of lacklustre startup is usually a sign of a failing HPFP.

Surging can be caused by a lot of different things so I would focus on the HPFP first. You could scan for error codes, sometimes a failing HPFP will leave some error codes. Otherwise you would need to use something like ProTool or MHD to log the fuel rail pressure during startup.

Echoing my primary suspicion here - i think its time to return to my indy for mpre investigations. I have heard about HPFP leaking fuel into the crankcase and then that fuel getting into the induction system via crankcase breathers, sesnors seeing this extra fuel as overfuelling and causing all sorts of problems. Have you ever seen this?

[craig3.2]

The poor starting is usually fuel pressure related. That kind of lacklustre startup is usually a sign of a failing HPFP.

Surging can be caused by a lot of different things so I would focus on the HPFP first. You could scan for error codes, sometimes a failing HPFP will leave some error codes. Otherwise you would need to use something like ProTool or MHD to log the fuel rail pressure during startup.

Echoing my primary suspicion here - i think its time to return to my indy for mpre investigations. I have heard about HPFP leaking fuel into the crankcase and then that fuel getting into the induction system via crankcase breathers, sesnors seeing this extra fuel as overfuelling and causing all sorts of problems. Have you ever seen this?

Yeah,had read similar about these engines,Mark.
Worth a look into that,or coil packs/leads being shot.
The hpfp has been an issue with these cars since the early days,when the cars were new/nearly new,but I don't think it's as widespread as may be it's made out to be,who knows.
Inevitably,as time goes on, regardless of mileage ,often,the z4m's and 35i/is have these kind of issues more and more, given the type of cars they are.

Hopefully your Indy gets to the bottom of it soon mate
Keep us posted.

[R.E92]

The poor starting is usually fuel pressure related. That kind of lacklustre startup is usually a sign of a failing HPFP.

Surging can be caused by a lot of different things so I would focus on the HPFP first. You could scan for error codes, sometimes a failing HPFP will leave some error codes. Otherwise you would need to use something like ProTool or MHD to log the fuel rail pressure during startup.

Echoing my primary suspicion here - i think its time to return to my indy for mpre investigations. I have heard about HPFP leaking fuel into the crankcase and then that fuel getting into the induction system via crankcase breathers, sesnors seeing this extra fuel as overfuelling and causing all sorts of problems. Have you ever seen this?

It's the injectors that leak into cylinder which then gets into the crankcase. Leaking injectors manifest in long cranking when warm and rough running.

HPFP doesn't cause leaks, it just gets lazy so injectors get starved of fuel. The symtoms of this are poor starting as described, long cranks and misfires/cutting up at high rpm and load.

[mcbutler]

Car has 34k on it and already had one new HPFP at 18K!!!!!!

Thinking of fitting this coil kit, thoughts anyone (R.E92)

https://www.mlperformance.co.uk/collect ... system-n54

[mcbutler]

I know exactly what you mean about a warm start up. It growls beautifully.

HP Pump sounds plausible for all your symptoms.
Car with such low miles is a prime candidate for a bmw warrantee. Do you have one?

I am on Warranty Direct, brilliant company covers everything £1100 for three years, paid out £2600 for my new Idrive screen a few weeks back, DCT sump leak with all new filters, gaskets and oil and zero excess....
I will go to BMW product when mine expires as most warranties only run to ten years....

[Pbondar]

I know exactly what you mean about a warm start up. It growls beautifully.

HP Pump sounds plausible for all your symptoms.
Car with such low miles is a prime candidate for a bmw warrantee. Do you have one?

I am on Warranty Direct, brilliant company covers everything £1100 for three years, paid out £2600 for my new Idrive screen a few weeks back, DCT sump leak with all new filters, gaskets and oil and zero excess....
I will go to BMW product when mine expires as most warranties only run to ten years....

No mods allowed under the BMW policy ie no DCIs /exhausts etc...

[R.E92]

Car has 34k on it and already had one new HPFP at 18K!!!!!!

Thinking of fitting this coil kit, thoughts anyone (R.E92)

https://www.mlperformance.co.uk/collect ... system-n54

It would be a waste of money unless you are pushing 650hp+. Those coils are an upgrade for people that are going beyond the capabilities of their stock coils. You would also need MHD to run that kit as the dwell times of the coils would need changing in the DME, none of the UK dyno style tuners will be capable of doing that.

If you want more power then get MHD. With a larger intercooler and catless downpipes you would see about 410hp (£120 total). With a custom MHD tune pushing the limits of the stock turbos you could get maybe 430hp (extra £250 for a custom tune). Then if you still want more then you need to upgrade to some larger turbos (an extra £3000 including upgraded inlets and outlets) which would probably top out at 600hp on 99RON fuel.