Full throttle, N18 engine, It hasn't thrown any codes. Seems to go away above 5000 RPM. It is similar to the miss when I had a bad coil. I replaced coils and plugs about 8000 miles ago. I pulled the plugs and no unusual discoloration, all 4 where burning correct, no fouling etc.

I haven't logged any data but I have Torque Pro or BimmerLink to do so with. When I have my Torque gauges up I can view boost, AFR and fuel pressure, none of these appear to be doing anything out of the ordinary. Any other suggestions on what to watch/log?

Also, I have a JB+ on it. My boost maxes out at 19.5 when getting on it hard. I have the new style style diverter valve installed same time as coils/plugs. Could this be an issue? I found this thread https://www.northamericanmotoring.co...under-wot.html. When increasing boost, a lot of people talk about 1 stage colder plugs. Try that?

It is getting ready to turn 75,000 miles (owned since 38,800) in the next couple weeks, I am concerned perhaps some slack in the timing chain could be causing it. I am ordering a new chain, guide and cam lock tool and putting it on my to do list.

1st thing I am going to try this weekend is taking the JB+ out. That is a simple thing to do and see if it changes anything.

 

It wouldn't be out of the ordinary to have a bad coil. Start by removing the JB+. If nothing changes, and it still misses, I would pick up a new set of coils.

 

Not sure if your diag tools can do this, but with ISTA/INPA you can live stream "roughness" measurements on each cylinder. This is what the DME monitors for detecting misfires. If one cylinder is measuring higher than the others, swap coils between that and another cylinder to see if the problem follows it.

 

I am not sure if BimmerLink can do "roughness" or not, I will have to investigate this. I do have ISTA/INPA on my laptop with NCS Expert. I would have to add one of my 110 power inverters as my laptops battery isn't what it used to be.

njaremka, as bad as it it bucks or kicks, if it were a coil or plug I think I would get a misfire code. That is what happened when my coil went bad before. After about 3 or 4 misfires, it shot a code and went into safe mode. Yesterday, I had the pedal down and let it buck about 8 times, no code. I might get another set and try it. If it solves the issue great, if not I have a set for the next time.

 

With 19.5 psi you're in the Stage 1 boost area. I'd suggest NGK 1422 plugs and keep the 0.024" gap they come with. Something else to check is the coil ground wire where it attaches to the ground stud on the forward center valve cover bolt. Look for loose nut, corrosion and also check the wire itself to make sure it's not fraying where it's crimped into the terminal.

 

I was wondering if the stock plugs might be part of the issue. I have read about 1 step cooler plugs with stage 1, and boost numbers are similar. That is something easy and less than $50 to check as well. I am going to be working on him Saturday. I will take out the JB+ first see if it still has issues. If eliminates it, I will get some1422's and try that the following weekend. There is a dial in the JB+ to "turn up/down" the tune. I might try decreasing it and see if that has an effect also. Hate to do that as it is set at 100%, I only use 93 Octane fuel and you can definitely feel a difference with it on there over stock.

Thanks for chiming in Lou!

 

I buy my NGK plugs directly from ngk.com, too many fakes out there to buy elsewhere. Their check compatibility function states they are not compatible. Would this be due to being colder?

Any ill effects from a colder plug? I need him to start rain or shine, hot or cold.

 

The 1422 are actually 2-steps colder than OEM S plugs. JCW are 1 step colder.

 

There is a ton of information on the web and even threads here on NAM with conflicting info. If you search the BMW part number for the N18 S and N18 JCW they both come up as 12122293697.
This crosses to NGK ILZKBR7B-8G. For standard plugs the first number in the NGK part number is the heat range and the second number is the gap. So stock plugs are a heat range of 7 with a gap of 0.8mm.
What is commonly referred to as NGK 1422's are NGK ILKR8E6 which means a heat range of 8 with a gap of 0.6mm.

Both have the same specs otherwise as far as thread pitch and length (1.25mm pitch and 26.5mm reach). The other difference besides heat range is the socket used to R&R them. The stock plugs use a 14mm 12 point socket while the 1422's use a 5/8" / 16mm hex socket. The 1422's are fine to around 320 hp.



Going beyond that you should use a race plug plug such as NGK R2556G-9 which are around $35-$40 each. Same thread pitch, reach and socket size at the 1422's but a heat range of 9 and a gap of 0.7mm.

 

Great information! Thanks Lou!

Those race plugs have an interesting tip design:
https://www.ngk.com/ngk-93253-r2556g-9-racing-plug

 

Lou is a wealth of information! If I were going with a tune, he would be the guy no doubt.

njaremka, I have also seen a lot of your answers and appreciate the input as well.

I have a couple things to try before the plugs but I now have a work flow to try and resolve the issue.

Frustrating when this happens and no codes. Hunting and pecking to try and figure out what is up. I hate just throwing parts at it hoping it will stick.

 

Colder plugs might be called for but you would see signs of plugs running too hot. You don't report seeing that.

Had another brand of car that out of the blue manifested some hesitation at mid RPMs. Long story short I had had the car in for a bad radiator which was replaced and while the car was in for service had the plugs replaced. The tech failed to properly connect all the plug wires to their plugs. One was loose. Over the approx. 500 miles since the service the loose coil wire spark eroded the plug tip enough that the miss developed. A temp fix was to using pliers squeeze the plug wire connector to the point when I put in on the plug it "snapped" into place. Miss gone.

Oh, no CEL. But the hesitation was real enough.

The behavior you describe doesn't have to be plugs or coils. It seems it never is due to these things but check them over carefully just to be sure.

Probably repeating what has been already posted but you need to be sure all the coils have a good connection to their plug and to the engine wiring harness. The plugs should be fresh and gapped correctly.

The behavior could arise from a fuel supply problem, which of course includes the fuel pumps. With other brands of cars a sign the low pressure fuel pump was acting up was the loss of power at higher RPMs.

 

I pulled the plugs and checked them, they looked fine. Made sure the coils seated properly on the plug. I didn't look at the actual coil wire or as stated above the ground wire. I do have a stock set of plugs on the shelf, I might try them this weekend also and make sure there isn't any issue there.

I don't think it is a fuel issue, I think I would have seen some fluctuation on the high pressure side if that was the issue.

As an update, it might need the colder plugs. Today to test things out without changing anything I wrapped it tight 1st through 4th. It didn't start to sputter till in 4th. In conjunction1st through 3rd boost never got higher than 16, 4 it was at 19 when it started sputtering. 19.7 is the highest I have ever seen, 16 to 18 is real common in 4-6th without hammering on it. 19+ if WOT tacking to 6000 and shifting.

 

Thanks for the idea. Bimmerlink does have the misfire in the sensor values. I enabled it and found cylinder 3 misfired 5 times while testing it and logging it. Only issue now is I don't know where Bimmerlink saves them.

 

I found where they are saved but it is a real PIA to get them off my head unit. I went out for another run with Bimmerlink on my tablet connected via a K+DCAN cable and got the data.

Cylinder 3 is the biggest culprit but I did have one misfire on cylinder 4. I was also surprised, boost hit 20.24

I might try a coil and or a plug change and see if that does anything. The colder plugs might be the route to go.

 

Okay, now I am a little perplexed. I let it cool down so I could swap coils on 2 and 3 and took it for a test drive. Figuring either the miss continues on 3 if it is something else or moves to 2 if it is a coil. NO MISSFIRES AT ALL!

Wiring harness maybe? I pulled the coils and plugs a couple weeks ago to check the spark plug condition and made sure I seated both the coil and the wire properly. I still haven't looked at the ground strap.

 

So possible wires? Thoughts?

 

It wasn't missing till just the other day. This time it was cylinder #4. Still no rhyme or reason for coils, originally #2, swapped coils on 2 & 3 and the miss went away for a couple weeks.

I finally had time to change the plugs as I needed to do an oil change as well. Attached is a picture of my old plugs from left to right 1/2/3/4. #1 shows a little heat on the ground electrode but #4 definately shows some heat.

Took it out and ran him hard and no miss currently.

 

With higher boost pressures, there is much greater combustion chamber pressure and heat; so yes, you need to run a cooler plug with a smaller gap. You also need to change the plugs more frequently. I've got a BMW (54 twin turbo) with Stage 2 maps (19 PSI boost max) and water/methanol injection. The plugs are shot by 18,000 miles. When I pull them, they look fine, but a visual inspection doesn't let you know what's going on with the plug when it's stressed.

Also, engine smoothness (roughness) values only work at idle when the engine isn't stressed.

What I would suggest is to put the car on a dyno and connect a lab scope to the secondary ignition of the misfiring cylinder. Run the car on the dyno under your high boost scenario and have someone who knows how to analyze a secondary ignition wave form tell you what type of misfire you have. I'll be it's going to be a secondary ignition misfire.

Also, keep in mind BMW/MINI DMEs may cut the fuel injectors if it detects a misfire (it depends on the severity of the misfire); this is done to save the catalytic converter; so the temporary misfires becomes a hard misfire because the DME had inhibited the fuel injector from firing. Sometimes, a key off/key on/engine start will enable the injector to start firing again; sometimes, you have to clear the misfire DTC with a scan tool and the misfire will go away ... that is until you stress that plug again.