Bad idle and missing - e34 540i - BMW Forum - BimmerWerkz.com
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#1 (permalink) Old 07-28-2008, 04:44 PM
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Angry Bad idle and missing - e34 540i

Hi all

I have a 1993 e34 540i auto which I have had now for about 6 months, I havent driven it properly yet as I had to fix most of the suspension, anyway I just MOT'd it last week and it passed. The mechanic told me it sounds like its missing a cylinder. Anyway the car is a rocket and i never noticed it. When warm the car idles at just under 500 which I know is not right. I recently had my mate plug his computer into it and no faults reported. Although he did say the Idle valve could be faulty as the revs wasnt registering on his computer.

Long story short, saturday past I took the covers off it and took all the old plugs out. One of the plugs was filled with oil as the round rubber washers were leaking oil into the plugs. So I fixed the leak dried out all the oil and put new NGK plugs in. NOW everything is worse. Idles worse and when I put it into DRIVE the car drops and drops and eventually stalls. The engine sounds like its missing worse now. This is totally unexplainable. One minute its all ok now its really bad. Does anyone know what is happening here. I took out all plugs and 1 by 1 they sparked brightly against the head. So this must eliminate any problem with the plugs and coils.

Please help this is really frustrating
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#2 (permalink) Old 07-28-2008, 07:59 PM
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Hi, did you get the right plugs? Where they gapped correctly? Check for vacuum leaks. Also, when was the last time the fuel filter was changed. You might not be getting enough fuel.
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#3 (permalink) Old 07-29-2008, 12:11 AM
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why are you using Japanese plugs on a German car???

...hahaha... that wasn't meant to have any racial implications, ok

anyway:
1) what was the model # on the old plugs and what was the NGK model # u used to replace with?
2) are you sure your firing order is correct?
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#4 (permalink) Old 07-29-2008, 12:00 PM
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Thanks for replies, the plugs are bkr6ek which are correct for the m60 engine. The gaps are correct same as the old. The plugs I took out were down by BMW 1000k miles ago which were also NGK. The petrol filter was also done then..When u say is the firing order correct....how do i know if it is???
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#5 (permalink) Old 07-29-2008, 12:24 PM
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This engine is full electronic ignition and the firing order can not be messed up as the correct coils can only be in one location. Spark plug gap will only make a difference if one of the plug electrodes has been smashed in some way. With the car running try removing the coil connectors (three wire connector under a metal bracket) for each cylinder one at a time. Carefully notice which cylinders show no effect and those will be the ones to further diagnose. Wait for a few seconds immediately after disconnecting to wait for the engine computer to catch up.

With the cylinders determined, you may have a split rubber spark plug boot on one of the coils (very common). Replace or wrap up with electrical tape.

Also, another idle issue that happens that is very odd. Check to see if all your plastic fan blades are there. If just one is missing the idle will be messed up.
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#6 (permalink) Old 07-29-2008, 03:03 PM
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Thanks enginesavers,

a bit of new info finally ...thanks. 2morrow im going to do as u said. I did notice last time that the spark plug that was filled with oil, the rubber boot from the coil is split at the bottom!! would this cause a very bad missing in the engine?

When u say remove the coil connectors, what kind are u referring to in this post? I have the m60 ones which are individual and u cannot mix up as they are individual.

Thanks

p.s That is a good tip about the broken fan blades causing a bad idle!
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#7 (permalink) Old 07-29-2008, 03:34 PM
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M60 engine idle

I have had all the idle problems we are talking about. Each cylinder has its own coil connected to the spark plug with a rubber boot and a three wire connector with a metal retaining clip for each. You have probably noticed these very easily if you have replaced your plugs and you have already disconected the connectors. Without removing the coil or anything else, one at a time disconnect the connector just enough to break the contact inside is fine. On properly working cylinders you will notice an increase in rough idle while the connector is disconnected as power from the cylinder is no longer functioning. When you come to a cylinder that is having issues you will see no change in the rough idle. Disconnecting a non-working cylinder won't make it work any less. Get it.

Now to the boot. Small cracks at the end are no problem. A split that runs along the side can very easily ground the sparks to engine and bybass the plug making no spark in the cylinder. Oil or water in the boot or area around the boot (can collect liquids here easily) should be removed. You may want to look into doing a "leak down" test if you decide to take out the coils. You can find the device at Harbor Freight or online for around $50. It will tell you the exact mechanical condition of each cylinder without taking anything apart. It helps to have someone who knows how to do it to show you, then you can do again on your own. Works with any vehicle. Important to do before buying a used car.

The only other problem is if you have a Nickasil coated engine block. They are very susceptible to hi sulfur gas made in the 90s and subsequently phased out everywhere in 2007. Some states like Colorado had really "bad" gas and ruined these blocks easily. BMW replaced these with Alumisil block under warranty on many M60 engines, but not everyone bothered. My 540 is a Nickasil block but the previous owner used premium gas and the standards in California were much higher on sulfur and mine engine does not seem to be effected. You no longer need to use premium, it is mostly a myth for the gas companies to make more money.

Hope this helps.
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#8 (permalink) Old 08-02-2008, 01:33 PM
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540 Firing On All 8 Again

Thanks for all the replies,

Just to let you all know i have sorted it, and by god this 540 goes.

Where I was changing the plugs, i knocked out the connector to the
injector. THAT WAS IT. all that drama and heartache for nothing!!!

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