520i running rough when warm 1,2,3 cyldrs not firing

[wiggywigton]

OK, Guys need some URGENT help here.

THe line that runs through the temp sensor in the air box to the TB busted the other day and the water pump ended up going out before I noticed it, ran out of water. It pegged out the temp and ran really hot for about 5 mins until I got it home.
I cleaned out the engine compartment before I replaced the water pump. I also replaced the spark plugs. I found oil in the #1 cylinder spark plug hole. I think it is from spill from filling oil.
When the car is cold it runs ok. Has a little bit of hesitation but when it warms up it is noticable that there is something wrong.
I drove it around until it was warm and started taking off the wire to the coil one by one. There is no change in the idle when I remove 1,2.3 but 4,5,6 there is a noticeable difference in the idle. Which lead me to beleive that whatever it is that sends the spark to 1,2,3 is bad.
Any ideas on what it can be?

[nizmainiac]

do a compression test then go from there, what condition are your new plugs in from 1,2 and three, also get the rocker cover off it and check the rockers , on my old engine i had a simalar misfire and the cause was a broken rocker arm , i changed that put a new cam belt on it and it was ok until it broke the next rocker to it , broke the head off the valve and threw the valve seat out into the inlet manifold

[neil_004]

If you fill in your profile you will get more answers.

[wiggywigton]

I filled in my profile. I am going to do a compression check today.
Still think it has something to do with the spark.
Runs fine when cold. Soon as it warms up it is rough. All Spark plugs are new Bosch platnium.

[E34-520iSE]

Have you check and ruled out problems with the spark leads? Rotor arm? Dizzy cap? If you have and your compression readings are cacky then it's time to get your hands dirty!

Best of luck!

Shaun

[wiggywigton]

Nope. I haven't been that far.

Where is the dizzy and rotor? I traced the spark plug lines but it looks like they dissapear into the firewall. There isn't a noticable rotor cap in the engine compartment.

I am new to these German cars. I appreciate the help.

[E34-520iSE]

Ah yeah I forgot you have an M50! Check the coil packs (the block things that plug into the spark plugs). Put a blob of paint on the ones that don't appear to be firing so you don't get them all mixed up, and swap them with the ones that are firing properly. Run the engine and check for misfires again on the 'other' cylinders. If the misfire has simply moved then the coils with the paint on are dead - throw them away and get new ones.

Hope that helps!

Shaun

[wiggywigton]

I swapped out #1 and #3 coil packs with no change in performance.

The car runs perfect when cold. As soon as it hits the middle of the temp guage it runs rough.

#2,4,5,6 run fine. There is no smoke.

I guess I will run a compression check tomorrow but I find it hard to believe that it is something mechanical.

Any other ideas?

[SnakeyesTx]

Try swapping coils that work to the cylinders that don't work.. like 6 to 1 and 5 to 3. Also reset the computer, disconnect the battery for about 15 minutes and put it back to see if the computer had something to do with cutting off the signal to those cylinders. You could also check the wiring going *to* the coil packs in question. On my friends legend, his #2 cylinder wasn't getting a spark (same ignition setup like ours) because his battery terminals weren't getting good connection! (Go figure!)

[wiggywigton]

Well it is fixed! For now. Thanks to all, Snakeyes your suggestion worked. I disconnected the battery for 15 mins and it fixed the problem. So frustrating and embarassing driving through the security check point when it was running bad. Glad it is fixed. Thanks again guys!