Misfire on cold start

[mcbutler]

Hi all,
Hope you are all well.
My car 35i has developed (overnight) a severe misfire on cold start.
I will do a video tomorrow if I get the chance and post a link.
Misfire lasts about as long as the cold start cycle and then disappears with only a slight 'hiccup' every now and then.
Full set of new Bosch coils and new plugs fitted 300 miles ago, car has MHD stage 2+ map with decats.

I am guessing injector but no fault codes are shown.
I have checked for codes after turning the engine off and also without turning it off but nothing at all.

Your thoughts chaps

 

[Zforbes]

I'd start by removing the new coils and plugs, make sure no moisture is getting in somewhere.
Why did you change them, did you have a problem before?
If not I'd be trying them to eliminate this as your issue. If you didn't have a similar problem before it wouldn't be my first call to blame the injectors although I am aware of potential issues these can cause. I'd say your map hasn't anything to do with it on tick over.

 

[Pondrew]

Are you sure it's a misfire and not a fuel problem? You know what these N54's fuel pumps are like. :roll:
I am in no way an expert as you know (quite the opposite) but would check all the plugs for oiling or carbon even though they are new.

Out of interest; what sort of bhp/ torque figures does the map you have give with decats? What sort of boost pressure does it run? Not related to the problem, just interested.

 

[B21]

Looks like injectors..coils n plugs tend to misfire under load not start..HPFP again tends to show strain under load.

A dibbling injector won’t flag itself up as a fault.

What gaps are on the plugs?

 

[Pondrew]

N54 Fuel Injectors Failure Symptoms

Hard time cold starting the engine
Misfires (especially upon a cold start)
Excess oil and gas on the spark plugs
Rough engine idle

Copy and pasted from the "8 most common N54 problems site". HTH

Edit: posted same time as Peter

 

[richg]

Hi,

Suggest leaving car overnight and removing each spark plug, nd if moist from fuel you have leaky injector(s).

I had similar startup issue and garage diagnosed as injectors. Mine was intermittent. I had no fault codes. Fixed with new injectors.

I do believe the failure mode of the HPFP is similar.

Rich

 

[Jollyjoiner]

My 35i had been doing this for the past 18 months on very cold days on cold start and only slightly noticeable on warm summer days. Not a severe miss fire though, more of a fluffing miss fire. If I left the car ticking over for 5 minutes then drove it it would be fine. If I started the car and drove it down the road straight away then you could feel the miss fire for about half a mile then it would be fine after that.

I first went for walnut blasting of the inlet valves as car was on 52k miles and is a known problem but this didn't sort it. I was hoping it wasn't the injectors just because of the price of them at the moment.

So about a month ago I took a deep breath and ordered a set of 6 index 12 injectors and swapped them out and coded them to the car and its been perfect ever since and I've cold started it from say 10 degrees temp outside down to minus 3

 

[mcbutler]

Are you sure it's a misfire and not a fuel problem? You know what these N54's fuel pumps are like. :roll:
I am in no way an expert as you know (quite the opposite) but would check all the plugs for oiling or carbon even though they are new.

Out of interest; what sort of bhp/ torque figures does the map you have give with decats? What sort of boost pressure does it run? Not related to the problem, just interested.

its not a fuel pump related problem as its only during the cold start cycle!
The map with decats gives around 420 BHP running 18psi, not sure what the torque is (more important than BHP I know) - All the details on the MHD maps can be found on their website if you're interested.

 

[mcbutler]

Looks like injectors..coils n plugs tend to misfire under load not start..HPFP again tends to show strain under load.

A dibbling injector won’t flag itself up as a fault.

What gaps are on the plugs?

I bought the OEM plugs with the 4 electrodes, they came pre-gapped.
Its been running great for 300 miles, not missed a beat, then yesterday after a week sat in the garage it is missing badly - but only for the cold start period - approx 45 sec!!
All info I can find points to injectors

 

[Pondrew]

The map with decats gives around 420 BHP running 18psi, not sure what the torque is (more important than BHP I know) - All the details on the MHD maps can be found on their website if you're interested.

MHD website quotes 650nm on the stage 2+
That is a lot of torque for the N54 from just a remap. Most Artics have less

 

[Zforbes]

Did you have the problem before changing the coils?

Injectors are notorious for issues like this but before spending a major amount of money I'd be checking the coils first regardless of being brand new, always check the last thing that has changed first

 

[B21]

Looks like injectors..coils n plugs tend to misfire under load not start..HPFP again tends to show strain under load.

A dibbling injector won’t flag itself up as a fault.

What gaps are on the plugs?

I bought the OEM plugs with the 4 electrodes, they came pre-gapped.
Its been running great for 300 miles, not missed a beat, then yesterday after a week sat in the garage it is missing badly - but only for the cold start period - approx 45 sec!!
All info I can find points to injectors

Yes, swingometer points to injectors ..do you know what the index number is ? You can read it in situ.

General advice seems to run one stage cooler plugs on the more aggressive MHD maps?

Also plug gap often needs narrowing on higher tunes…

Mine misfired on stage 2+..on stage 2 no misfire.

Will fit my B58 high energy coil packs later this weekend then I’ll put the stage 2+ back with probably 25 thou gaps (29-30 thou stock)

Then I’ll take it back to the dyno boys.

 

[mcbutler]

Looks like injectors..coils n plugs tend to misfire under load not start..HPFP again tends to show strain under load.

A dibbling injector won’t flag itself up as a fault.

What gaps are on the plugs?

I bought the OEM plugs with the 4 electrodes, they came pre-gapped.
Its been running great for 300 miles, not missed a beat, then yesterday after a week sat in the garage it is missing badly - but only for the cold start period - approx 45 sec!!
All info I can find points to injectors

Yes, swingometer points to injectors ..do you know what the index number is ? You can read it in situ.

General advice seems to run one stage cooler plugs on the more aggressive MHD maps?

Also plug gap often needs narrowing on higher tunes…

Mine misfired on stage 2+..on stage 2 no misfire.

Will fit my B58 high energy coil packs later this weekend then I’ll put the stage 2+ back with probably 25 thou gaps (29-30 thou stock)

Then I’ll take it back to the dyno boys.

Index 6 so OLD.
Car only has 34k on it FSH and on its secong HPFP already.
With regard to the plugs, its been driven faultlessly for around 300 miles since the new plugs and around 150 since the MHD remap.
Last week I started it to get it out of the garage, absolutely fine, no issues at all. After the weekend and it starts like an old diesel truck.
I am swinging towards injectors as well.
Coils dont seem relevant as the problem quickly disappears after the cold start cycle and coil snags are generally load related.

I will make a video later and post it to youtube with a link in this thread.

 

[Jollyjoiner]

Yep I'd go with injectors like I said, mine was index 7 what I took out

 

[mcbutler]

Heres the video fellas.

Cars in a garage so it sounds loud and harsh but you get the idea.

Interesting how it settles down after the initial cold start cycle, flashes an error light (no code recorded) then its all over, although the car still 'feels' lumpy.
Its booked into my indy for next monday so they can do a live data cold start on Tuesday morning.

Any thoughts/comparisons with your own experiences??

https://youtu.be/uO6vutTfQwM

 

[N4LLY]

Ouch

 

[Jollyjoiner]

Mine wasn't like that at all. Mine was just a very slight lumpy idle nothing like what you have going on there. Nothing to say it's still not a few injectors out though. Hope your indy can find something with the live data on cold start up.

 

[Zforbes]

Sounds like it's not attempting to fire on one cylinder to me, I would've thought an injector would get gradually worse over time and not fail all of a sudden, there are folk on here that know better than me but I'd still be trying to rule out the electrical side before fuel.

Sure your indy will find the cause quickly, swapping plugs coils or injectors from one cylinder to another should pin point it easy enough

Keeping an eye on this thread as you never know when you need this knowledge in future

 

[mcbutler]

Sounds like it's not attempting to fire on one cylinder to me, I would've thought an injector would get gradually worse over time and not fail all of a sudden, there are folk on here that know better than me but I'd still be trying to rule out the electrical side before fuel.

Sure your indy will find the cause quickly, swapping plugs coils or injectors from one cylinder to another should pin point it easy enough

Keeping an eye on this thread as you never know when you need this knowledge in future

Problem with the electrical theory is why does it only happen during the cold start prodcedure !!??

 

[craig3.2]

Sounds like it's not attempting to fire on one cylinder to me, I would've thought an injector would get gradually worse over time and not fail all of a sudden, there are folk on here that know better than me but I'd still be trying to rule out the electrical side before fuel.

Sure your indy will find the cause quickly, swapping plugs coils or injectors from one cylinder to another should pin point it easy enough

Keeping an eye on this thread as you never know when you need this knowledge in future

Problem with the electrical theory is why does it only happen during the cold start prodcedure !!??

Hope you get it fixed soon, Mark