Running Rough and Misfires
 

My '07 x5 4.8i has been running terribly with a misfire in cylinders 4, 5, and 8. The misfires start when I decelerate, and sometimes when I accelerate. My father wants to change the mass air flow sensor, but I don't believe that is the problem. My reasoning for this is I have cleaned the MAF and it hasn't had any change in the way it runs. I want to change my spark plugs and ignition coils because they have never been changed in the 137 thousand miles that are on the engine, but my father says I should be looking to change my crankshaft/camshaft sensor, or my throttle position sensor. What should I do?

Listen to your father after you change out the sparkplugs with OEM equivalents. Plug change cycle on this engine is every 100k miles, any recommend at the 80k mark. If no other codes exist, you did use a BMW capable scanner didn't you, Just check the coils before reinstallation if you can.

An acting up O2 sensor, or a vacuum leak, or sticky cam adjustor can cause one bank to misbehave as well.

Run a can of tectron or equivilant fuel system cleaner through it to help the injectors.


Good luck, always obey your dad till you are 23 and in the military.

Sent from my SM-T377V using Tapatalk

I used the Carly scanner for codes and consistently got the misfire codes, I haven't gotten any other codes like camshaft and such. Thanks for the advice.

A little back ground,

I am a:
Military brad (US Navy Chief's son)
Father of 2 plus one bonus daughters
73 years old
Lets me get away with my openiing and closing statements. Lots of vacuum lines that like to leak at most inappropriate locations and times. And it is good that the Vanos is not showing any alarms//codes.

Did not always follow dad's advice, daughters almost never followed mine.

As the signature does not show up from the tablet

2007 e70 4.8l 142k miles
1988 e24 M6 178k miles
94 Jeep Grand Cherokee
84 Chevy S10
Prior: 88 535is, 87 635csiA, 00 528t, 02 e53 4.4l


Sent from my SM-T377V using Tapatalk

You do not need to premptive replace coils.

Every BMW I've worked on has needed Cam position sensors replaced by 130k mi.

Almost never see an error related to CPS always just random misfire.

Since they are overdue;

Plugs, CPS, chain tensioner (only OEM for any of those).

Techron or Lucas injector cleaner.

Oil and filter with 5w30 I believe is factory spec (wrong weight will throw off vanos).

If after that you get misfires, swap coils to determine coil or fuel problem.

Never a good idea to chase a problem with new parts regardless of when parts are estimated to wear out. I would not move forward based on assumptions. Troubleshoot, troubleshoot, troubleshoot. Find the core issue first. That's something Dads know from experience.

You mentioned that it starts with deceleration and only sometimes happens (starts) during acceleration. Do you mean it sometimes doesn't miss at all, that the missing is intermittent? Does it happen whether the engine is at operating temp or cold starts? Most of the most likely 'common' problems would be associated with acceleration when the engine is under most load so would like to learn more details about severity, conditions, and frequency.

Cleaning the MAF doesn't always work. However, if the MAF is bad the misfires would normally be all cylinders rather than just 3.

To troubleshoot for vacuum leak the best method is a smoke tester. IMO it is a must have tool for every DIYer. There are several videos on youTube showing how to make one for about $20.

If you want to find out if the problem is a coil, move one of the coils from a cylinder not showing a code to one that does, swap them. Clear the codes and see if same codes return or misfire moves to the other cylinder. You can verify if it is a spark plug in the same manner.

If you don't use a premium brand fuel that usually have cleaners in them do so for next fill up. Gas I use already has Techron in it. Otherwise, as mentioned, add a can of Techron to the next 1-2 tanks of gas.

There is a test for a bad MAF: tap with the handle of a screwdriver while the engine is idling; it should not cause and change in RPM. If it changes the MAF is shot