Hi all,

I'm still fairly new to this forum but not to forums in general. Before the Z, I had a 94 325i. Needless to say, I spent a lot of time on forums because a lot of things went wrong with that car.

As far as my issue, I've searched every possible thing I could think and haven't found my answer. My car has a "jerk", but only around 1700-1800 rooms and generally only in first gear. I've noticed that it also only does it when the car is warmed up. I'll take off (6mt) and as soon as I get to that rpm, it feels like I let off of the gas for a split second, enough to make the slightest jerk.

103k miles. No lack of power elsewhere. Only mod is K&n drop-ins, and it did this before I switched them. I just cleaned the maf sensor and throttle body cause I thought that may be it, but no. I had my buddy, who also has an 07 6mt Z drive it on Sunday, and he didn't have the slightest clue, but assured me that his clutch and mine felt exactly the same. Also, no CEL on or detected. He has a scanner.

Any ideas??

 

What year is the car?

Does the jerk happen during light, moderate, WOT acceleration, or all three?

 

If you haven't done spark plugs, I'd start there.

 

I have an 07. I notice it at all levels of acceleration, but it's a lot more noticeable in the medium to WOT acceleration.

The only reason I haven't thrown plugs at it yet is because at idle, I don't hear any sort of a misfire.

 

drive about 20 mph in 4th gear, floor the throttle. do the rpms jump up but you barely accelerate. the csc could be starting to fail on you

 

Just because it is not misfiring at idle does not mean that the plugs are fine. At those miles I highly recommend changing the plugs.

If it is engine related, it can only be a few things since you aren't modded. It is either spark, air, or fuel. If your sensors are fine and the correct amount of airflow is occurring, I would think spark or fuel. Typically spark would be the first thing I would look at.

I had a similar issue with my B13 where it would bog at certain rpms at higher throttle and it ended up being a clogged injector. It also had over 200k miles so it happens with age.

I agree, also try this.

 

Going out of town today and taking my fiancées car, but I'll check this when I get back. Thanks.

From taking a quick look around, the OEM plugs are Denso FXE20HR11, right? I don't plan to stray away from OEM. Tried to get the more expensive plugs for the BMW before (I was young and dumb - hadn't done research), and it wasn't having it.

 

I am always a big fan of NGK. I haven't changed my OEM plugs yet so I am unsure on what is stock.

 

denso. i changed mine at like 50k miles

https://conceptzperformance.com/Cart...on.php?II=5426

 

If it was plugs it would be global. Sounds like a lean spot as a result of the increased airflow. Look into a tune. 1800 is where it happens every time I make a change and need a tune.

I have heard of the iridium plugs literally breaking off and destroying turbocharged engines, food for thought... I'm sticking with the PLFR series by NGK to avoid that headache. The PLFR5a plugs are OEM for the G35's unless your Z's run on magic they should specify the same plugs...

 

iridium are oem for the hr motors, de are different, just changing the air filter wouldnt lean him out enough to do what he is saying. i had intakes, high flow cats and exhaust and i never experienced what he has

 

Just to reiterate, it did this before ever doing any mods, still had stock paper filters. And I've only changed filters to k&n drop-ins.

I could see this being more of a spark plug issue, as I read up more on them in our cars and stealerships say they'll last 100k. I hate throwing parts at my car without knowing the true issue, but again, without a CEL, I'm sorta shooting in the dark. If nothing else, changing them will be maintenance that I would have needed to do sooner than later.

 

plug in a scan tool, see what ur sensors r showing, u can get those 20$ elm adapters and a torque app if u got android, or find somebody with a scan tool. ive got that problem, but only at 1000, and that happens only when i press the gas at 1000, after that its all good. only jerks AT that mark, not past, not below. the only lead i have is that one of my downstream sensors is reading twice the voltage then the other, but this also can be an app error(iphone), thats why i'm waiting for a new phone(android, torque app) to see for sure. otherwise i have :
cleaned the TB
cleaned MAF
cleaned injectors( went to a racing shop, had them do it right)
cleaned the fuel rail
i havent changed the spark plugs bc i only have 22k on my car, and i really dont want just to part change every possibility. right now, its not so much as the jerk concerns me,but the different voltage, so i still in the diagnosing stage, but i hardly have time to mess with my car

edit: forgot to mention, my only does that IF i havent disconnected the battery. so try to disconnect the battery, leave it for a day, and then connect and go drive it, see if that changes things. On mine it does(for the first 50k its runs like it sopose to)

 

A buddy of mine had this issue with a maxima. And at 2700 rpm cleaned everything changed plugs nothing. Turned out there was a broken/ not so well connected ground. Cleaned up and fixed all the grounds and fixed the issue. Something to look at for free

 

Tried this on the way home today, and everything seems to be working fine. I was hoping it would be this easy.

My buddy has the dashcommand app and an OBD II adapter that it connects to. I doubt it reads specific sensor voltage. He might also have a scan tool. I'll look into this.

Would you elaborate? I can only imagine there are so many grounds in this car that could have a relation to this.

Before I go throwing spark plugs at it, does anyone else have ideas? The only new info I have is that it is not directly related to my a/c being on. Windows were down all day and it is still there.

 

I was going to say check your grounds too, but ghost beat me to it.

Stillen makes a decent grounding kit for about $100. Includes instructions.

STILLEN GROUNDING KIT

Otherwise, just check all your ground connections, make sure they're clean, hit them with a spritz of WD-40 and tighten them up.