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Idle misfiring

Road Tuning

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Discussion and questions related to the course Road Tuning

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I have started my engine using information in this training

but after engine starts, I have tried to do some coarse adjustment but it won't stabilize with regular lambda only get a bit stable with rich lambda (around 0.78 to 0.8)

and after a while car start misfiring and get leaner then engine stall,

checking spark plugs I have noticed that ceramic insulator and plugs head get a bit yellow, even with new set of spark plugs I got the same problem after idling for a while attached is a picture for some new plugs used for only few minutes.

Can anyone please advise as I need to get the car moving and tune it.

Attached Files

What ecu and lambda are you using?

They look like they've been running lean


I am using a LINK extreme ECU

and yes it looks running lean but car isn't idling at correct lambda of 0.85 to 0.95 it misfiring and I should go around 0.75 to get it stabilize and this couldn't be normal

What are you using to measure your AFRs? When was it last calibrated?

I'm with Chris on this - Given the information you have posted so far I'd be very suspicious of your lambda meters accuracy. If the engine was idling at 0.78-0.80 I'd expect the plugs to be looking quite black and sooty. Of course this assumes that there are no basic mechanical issues or ECU configuration issues first and foremost.

Thanks for your feedback Ben

actually I am using a well calibrated LC-2 device that is connected to my Link extreme ECU and was calibrated before my start and I have also checked using my LM1 device and found the same readings.

but I have found a leak in the vacuum line of my fuel pressure regulator and get it idling smoother and with more reliable lambda numbers of around 0.96-1,

the only problem I am facing now is tipping throttle body where car goes extremely lean even with acceleration enrichment activated.

I have built my map based on this training and only have small adjustment at idle area to have in the correct lambda area.

attached is a log where I am trying to freely rev my engine (car is stop) hope it will show something.

Attached Files

sorry just need to highlight on something I have noticed while checking my log where ignition stay at 15.3 degrees when I have pressed throttle body as per attached screen shot,

could it be the reason Ben? does the car need some advance to rev the engine smoothly

Attached Files

What engine is this on?

What are you using for load in the fuel table?

It does look like it's adding 60% during throttle but it's hard to tell with how quick your snapping open and closed the throttle, you need to think when testing if there is any real world time you're going to need to rev a car like you have in the log

Hi Chris

my engine is a lowered compression BMW M52,

as for snapping throttle I agree that there is a very wired sharp snapping but if you look at the first 9 seconds you will notice that I was only trying to press it less than 10 percent like what when you need to start driving any car from idle,

Can we just clarify where you have got to in the tuning process? Have you properly calibrated the fuel table yet? If you haven't done this, you need to do so before you start trying to tune accel enrichment.

There are a couple of good webinars also that I'd urge you to watch about accel enrichment tuning - One is specifically on the Link platform - https://www.hpacademy.com/previous-webinars/038-configuring-and-tuning-acceleration-enrichment-on-a-link-g4/

Hi Andre

I have started my engine using the base fuel map from the course,

while reviewing my data logs I have noticed a very rich start so I am waiting for the cold start webinar,

it will be appreciated if you could check the attached log and advise about any coarse adjustment needed as I am afraid an extreme rich start is affecting my fuel map tune.

Attached Files

Can you post your current tune file too please?

Just to confirm, accel and cold start tuning are basically the very last part of the tuning process. Unless you have already accurately tuned the main fuel table then don't worry about these two aspects just yet.

Hi Andre

attached is my current tune where I only have small adjustment in the idle/idle off area based on lambda reading

Attached Files

It looks like you still have quite a lot of work to do to get the fuel table optimised so I'd suggest working through this as discussed in the course. In particular with regard to your idle misfire issue you have quite a dramatic change up and down in the fuel table in the idle area that may be causing unstable or erratic AFR. I've attached this via screenshot. In general I would expect the fuel table to have a relatively smooth and consistent shape where the numbers increase as load goes up. You have a large hump in the idle area and if the MAP input has the engine moving in and out of this hump, it will cause poor control of AFR.

Attached Files
  • Screen-Shot-2015-10-20-at-11.08.02-AM.png
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