Misfire on cold start

[Rockhopper]

You left it idling for an hour? is that correct? Not a good plan with a miss fire, excess fuel could cause bore washing and CAT damage.

 

[enuff_zed]

You left it idling for an hour? is that correct? Not a good plan with a miss fire, excess fuel could cause bore washing and CAT damage.

Yes, but he's said all along that the misfire clears once it's warmed up.

 

[Rockhopper]

The plug isn't saying that to me. Thats been miss firing for a long time, not just when cold. Maybe its just more obvious when its cold?

 

[mcbutler]

If diagnosing a leaking injector you need to understand that the injectors typically only leak when fuel pressure is present.

Upon unlocking the car the electronic in-tank fuel pump will pressurise the fuel rail to 72.5PSI. When the engine starts running the high pressure fuel pump will begin to turn and the DME will then modulate the rail pressure.

If you haven't disabled cold start in the engine tune then the DME will ask the high pressure pump to pressurise the rail at 2000PSI for the first 45 seconds of operation and the it will step down back to 700PSI for normal operation. In normal driving the rail pressure will be around 700PSI but once you start loading the engine up it will run around 1500-2000PSI again.

Injectors won't continuously leak as the line pressure falls after you turn the car off. They might not leak at 72.5PSI or only slightly but at 2000PSI they could be leaking like a fountain.

You can verify all this by looking at live engine data with MHD. If you unlock the car and see the fuel pressure reading 72PSI but it quickly drops down then you know there's a leak. If it stays high you are fine at low pressure. If the fuel pressure on startup is violently oscillating the the pump could be weak. If the pressure stays high then the pump is OK and you then need to consider the lambda readings on each bank. If 1 bank is reading a crazy rich value like 10:1 then you know that bank has a leaking injector.

I bought MHD during the recent sale, will have a go at this either later today or tomorrow.
Is it easy to understand the set up of live data? I am presuming I just tick a few boxes - tap record and see what i get....

Yes, fairly easy.

You can customise the data channels that it records but by default it will record everything you are interested in.
Just go to the Mon. menu then press the text that says "Data Logging" and if connected to the car it should display some basic data in the gauge view. These gauges are only live displays, you can set them up however you like but the important thing for you is to record the data so you can review after. You just need to press the green button at the top labelled "start logging" to begin recording the data, then press the button again to stop the logging when you are done.

I would suggest just pressing the ignition button without a foot on the brake to bring on accessory power then connect MHD and begin logging before starting the engine. Let it record until the idle smooths out a bit then upload the csv file here.

Just a Z4 specific note on the logging: The low pressure fuel sensor reading will show 0 as the Z4 doesn't have one. This isn't a problem as we can just observer the rail pressure instead for this test.

Roger that, will get this done tomorrow.
Your experience and time taken to post all this is appreciated, many thanks

 

[Zforbes]

I take it from the fuel pressure investigation the misfire is still on cylinder 6?

The sooty plugs don't look good so something more sinister that a single plug or coil issue.

Out of interest, how does the ECU work with the decat, I'm assuming the remap alters the parameters of the lambda sensors or are they even removed?

 

[mcbutler]

I take it from the fuel pressure investigation the misfire is still on cylinder 6?

The sooty plugs don't look good so something more sinister that a single plug or coil issue.

Out of interest, how does the ECU work with the decat, I'm assuming the remap alters the parameters of the lambda sensors or are they even removed?

Not yet done the FP check, should be today.
You can probably find the answer to teh decat question in MHD literature

 

[mcbutler]

If diagnosing a leaking injector you need to understand that the injectors typically only leak when fuel pressure is present.

Upon unlocking the car the electronic in-tank fuel pump will pressurise the fuel rail to 72.5PSI. When the engine starts running the high pressure fuel pump will begin to turn and the DME will then modulate the rail pressure.

If you haven't disabled cold start in the engine tune then the DME will ask the high pressure pump to pressurise the rail at 2000PSI for the first 45 seconds of operation and the it will step down back to 700PSI for normal operation. In normal driving the rail pressure will be around 700PSI but once you start loading the engine up it will run around 1500-2000PSI again.

Injectors won't continuously leak as the line pressure falls after you turn the car off. They might not leak at 72.5PSI or only slightly but at 2000PSI they could be leaking like a fountain.

You can verify all this by looking at live engine data with MHD. If you unlock the car and see the fuel pressure reading 72PSI but it quickly drops down then you know there's a leak. If it stays high you are fine at low pressure. If the fuel pressure on startup is violently oscillating the the pump could be weak. If the pressure stays high then the pump is OK and you then need to consider the lambda readings on each bank. If 1 bank is reading a crazy rich value like 10:1 then you know that bank has a leaking injector.

I bought MHD during the recent sale, will have a go at this either later today or tomorrow.
Is it easy to understand the set up of live data? I am presuming I just tick a few boxes - tap record and see what i get....

Yes, fairly easy.

You can customise the data channels that it records but by default it will record everything you are interested in.
Just go to the Mon. menu then press the text that says "Data Logging" and if connected to the car it should display some basic data in the gauge view. These gauges are only live displays, you can set them up however you like but the important thing for you is to record the data so you can review after. You just need to press the green button at the top labelled "start logging" to begin recording the data, then press the button again to stop the logging when you are done.

I would suggest just pressing the ignition button without a foot on the brake to bring on accessory power then connect MHD and begin logging before starting the engine. Let it record until the idle smooths out a bit then upload the csv file here.

Just a Z4 specific note on the logging: The low pressure fuel sensor reading will show 0 as the Z4 doesn't have one. This isn't a problem as we can just observer the rail pressure instead for this test.

 

[mcbutler]

Those plugs point to a rich condition. The first two are really bad but all of the are more sooty than they should be.

The cold start this morning was a lot better, strangely.
Car has a huge flat spot when revving the engine through the 2k rpm mark

I did six logging runs and tried attached logs but forum wont allow that, is their a way I can get them to you?

Car currently has MHD stage 2+ with linear throttle selected and VRSF decats fitted

 

[R.E92]

You can upload them using datazap.me and post a link.

Or just upload the raw CSV files to wetransfer.com and give a link

 

[Rockhopper]

Have you done a compression test?

 

[Chippie]

From memory I think Marks car is quit low mileage around the 35000 mark so I wouldn’t have thought there would be a problem with compression, unless having it nuts revved off by an unscrupulous body shop has caused some damage
My money is on a leaking injector due to the high pressures during cold starting

 

[mcbutler]

Have you done a compression test?

Its not compression - its only present during the startup procedure - 40 seconds or so and no smoke

 

[mcbutler]

You can upload them using datazap.me and post a link.

Or just upload the raw CSV files to wetransfer.com and give a link

Sent via PM

 

[Rockhopper]

I had exactly the same symptoms (on a carburated car to be fair), turned out to be a burnt exhaust valve.
It’s always worth doing the simple basic checks first hence my suggestion of a compression check.

 

[Zforbes]

You can upload them using datazap.me and post a link.

Or just upload the raw CSV files to wetransfer.com and give a link

Sent via PM

How did you get on with the cold start issues, would be good to hear the final diagnosis if you have one yet.

 

[mcbutler]

You can upload them using datazap.me and post a link.

Or just upload the raw CSV files to wetransfer.com and give a link

Sent via PM

How did you get on with the cold start issues, would be good to hear the final diagnosis if you have one yet.

Problem solved - Indy diagnosed one of the index 6 injectors as faulty.
Warranty Direct accepted the claim for all 6 injectors to be renewed with index 12 supplied by BMW (BMW give a 2 year warranty on the injectors). So all replaced, coded and an oil/filter change in case of oil dilution.
£1998 paid by Warranty Direct no issues or arguments at all just two short phone calls of around 3 min each.
Car is transformed in all areas, smoothness, response, accelaration, smoothness of tickover and mpg is up a little as well

 

[Zforbes]

Sent via PM

How did you get on with the cold start issues, would be good to hear the final diagnosis if you have one yet.

Problem solved - Indy diagnosed one of the index 6 injectors as faulty.
Warranty Direct accepted the claim for all 6 injectors to be renewed with index 12 supplied by BMW (BMW give a 2 year warranty on the injectors). So all replaced, coded and an oil/filter change in case of oil dilution.
£1998 paid by Warranty Direct no issues or arguments at all just two short phone calls of around 3 min each.
Car is transformed in all areas, smoothness, response, accelaration, smoothness of tickover and mpg is up a little as well

Result!

 

[Chippie]

Sent via PM

How did you get on with the cold start issues, would be good to hear the final diagnosis if you have one yet.

Problem solved - Indy diagnosed one of the index 6 injectors as faulty.
Warranty Direct accepted the claim for all 6 injectors to be renewed with index 12 supplied by BMW (BMW give a 2 year warranty on the injectors). So all replaced, coded and an oil/filter change in case of oil dilution.
£1998 paid by Warranty Direct no issues or arguments at all just two short phone calls of around 3 min each.
Car is transformed in all areas, smoothness, response, accelaration, smoothness of tickover and mpg is up a little as well

That’s great news, you’ve certainly had your monies worth through warranty direct

 

[mcbutler]

How did you get on with the cold start issues, would be good to hear the final diagnosis if you have one yet.

Problem solved - Indy diagnosed one of the index 6 injectors as faulty.
Warranty Direct accepted the claim for all 6 injectors to be renewed with index 12 supplied by BMW (BMW give a 2 year warranty on the injectors). So all replaced, coded and an oil/filter change in case of oil dilution.
£1998 paid by Warranty Direct no issues or arguments at all just two short phone calls of around 3 min each.
Car is transformed in all areas, smoothness, response, accelaration, smoothness of tickover and mpg is up a little as well

That’s great news, you’ve certainly had your monies worth through warranty direct

You're right there bud, my three yr policy expires this june, it cost me £1100 for the three years and I am in to them for nearly £7k. They are an excellent company, they are super fast to sort claims every time..

 

[Pondrew]

Glad you got it sorted Mark