Author Topic: Misfiring m42... trouble shoot? (Read 6419 times)

alpine · « **on:** February 16, 2013, 03:30:27 PM »

Hey guys,

My m42 has finally started after the replacement. Now it is misfiring... just swapped the plugs for brand new ones. I did the intake mess as well. I also put it brand new temp sensors. Checked the timing ticks, they are all straight up.

Here is a video of the horrible noises!

http://www.youtube.com/watch?v=aczKhBD6llk

http://www.youtube.com/watch?v=C1tJBql4mjA

http://www.youtube.com/watch?v=cEx_KMDa8AU

These videos are a bit redundant but you can get a feel of what is happening...
Thanks guys!!

DesktopDave · « **Reply #1 on:** February 16, 2013, 04:22:32 PM »

You don't have any compression numbers on that motor, do you? So static timing is right on...but it's misfiring. New plugs,

Back in the old days that's what a mis-timed distributor sounded like...plugs fire late & backfire into the intake manifold - but those are a relic of the past, aren't they?

Did you test out your cam & crank sensors? Is the car throwing any codes?

romkasponka · « **Reply #2 on:** February 16, 2013, 05:06:06 PM »

Check what high tension leads installed in correct sequence.
Grab you you exhaust pipes and find which cylinder is inop. After you can swap components one by one and check what is happening.

alpine · « **Reply #3 on:** February 16, 2013, 05:37:46 PM »

Checked cam and crank sensors. Swapped them out with others. Look to be working fine. Car has a CEL that comes and goes. Havent checked the codes yet. Dont have a scanner.

Im not sure what a high tension leads is

romkasponka · « **Reply #4 on:** February 17, 2013, 06:37:39 AM »

Quote from: alpine;120182

Im not sure what a high tension leads is

https://www.google.com/search?hl=lt&q=high+tension+leads&ion=1&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.&bvm=bv.42553238,d.bGE&biw=1600&bih=836&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&authuser=0&ei=4c4gUfK4LuWq4ASctIHQCA

DesktopDave · « **Reply #5 on:** February 17, 2013, 09:18:22 AM »

HT leads are what the Europeans call spark plug wires.

Romka is saying if coil 1 is not connected with plug wires 1 to cylinder 1 (and so forth with 2,3 & 4) the motor might run but it'll really be rough. Any 4-cyl engine can run with 1-4 and 2-3 swapped, but it won't run well. If you need to know the coil pack pinout from the computer, LMK. I've confused them myself before - the little labels tend to fall off over the years.

You don't need a scanner to check codes on our amazing cars. Turn the key to position II (run) but don't start the car. Within about ten seconds, stomp the gas pedal to the floor five times or so. The Check Engine light will start to blink. It's called a "stomp test" and it's occasionally worth a check.

You can't use a standard OBD 2 code reader unless it's a '96 or newer BMW, since they have a non-standard barrel diagnostic plug. But you can get a BMW scanner for earlier cars with the appropriate 20-pin round connector to pull error codes. BMW has used code readers since the late 70's. Later BMWs can even send codes for the ABS, SRS, transmission ECU and all the other electronic systems as well, if you can believe it.

alpine · « **Reply #6 on:** February 17, 2013, 11:21:14 AM »

Thank you guys. I checked the coil wires multiple times and they seem to be correct. When I rev up, the car seems fine too I'll try the stomp text later today.

keflaman · « **Reply #7 on:** February 17, 2013, 11:39:20 AM »

Re-check the hoses for the intake mess. When you say it runs fine when revved it makes me think of a gross air leak.

alpine · « **Reply #8 on:** February 17, 2013, 11:56:43 AM »

I'll pop the intake off today and see what I find. This was my first time dealing with this intake mess so I'm worried I left something off. But if there is a huge leak, wouldn't it not start?

DesktopDave · « **Reply #9 on:** February 17, 2013, 12:48:50 PM »

It'll run with a lot of vacuum leaks, just not very well.

IRC you should have three vac lines remaining after the TB heater delete:
The largest one goes from an intake boot elbow to the ICV, then into the intake manifold near the firewall. The ICV arrow points toward the motor, in direction of airflow.
The crank ventilation line goes from the front of the cam cover to the bottom of the TB.
Finally, the little one usually goes from the TB to the FPR.

It's also possible to mount the throttle body crooked. That'd cause some troubles - someone here did it once and posted how they fixed it. Check the lower right corner to see if it's snagged on the stud. You also might have a two-port intake boot, be sure the plug is secure in the one you're not using.

Those metal TB gaskets can also leak.