E34 535i - misfiring and now cut out altogether; help please

[mat1227]

Guys - can I ask for your collective BMW wisdom?

The car is a 1990 535i (M30 six). I am trying to sort out a major misfire that appears on full throttle openings. It's not a minor hesitation, more a full scalle 'dugga dugga' miss and massive drop in power. The car was pulling cleanly on part throttle.

When it happened we pulled the car over and it cut out, tried to restart five or six times with no joy (with a pause in case it was flooded). On the final try, it backfired so hard it blew the backbox into pieces scared the hell out of me...!

Checked all the plug leads and they were all connected, no obvious loose connections in engine bay, no obvious problems with dizzy.

Any suggestions? How can I work out what I need to replace? Are there regular problems with M30s that anyone knows of that could cause this?

- dizzy?
- rotor arm?
- king lead?
- coil?
- ignition relay?
- others?

It's a lovely 1 owner FSH 1990 535i, had a fortune spent on it and is otherwise nearly perfect so very keen indeed to get it behaving again.

Thanks!

Mat

[mat1227]

Can anyone help? Have tried the BMW5 forum too, with limited joy, was hoping this might be something someone has had experience of?

Much obliged

[Vixpy1]

MAF or Coil

[bob1179]

I agree with Vixpy, have a look at the MAF as if it's buggered it will be sending the wrong information to the ECU causing the engine to run incorrectly.

The M30 in your 535i is the later version with a more advanced version of Motronic fuel injection, you may be able to plug a fault code reader into the diagnostic socket and get some information that way.

Have the plugs and leads been changed recently?

Edited by bob1179 on Monday 8th December 14:55

[Vixpy1]

bob1179 said:

I agree with Vixpy, have a look at the MAF as if it's buggered it will be sending the wrong information to the ECU causing the engine to run incorrectly.

The M30 in your 535i is the later version with a more advanced version of Motronic fuel injection, you may be able to plug a fault code reader into the diagnostic socket and get some information that way.

Have the plugs and leads been changed recently?

Edited by bob1179 on Monday 8th December 14:55

Bob is the later version 6 individual coils, or coil and dizzy?

[mat1227]

bob1179 said:

I agree with Vixpy, have a look at the MAF as if it's buggered it will be sending the wrong information to the ECU.

The M30 in your 535i is the later version with a more advanced version of Motronic fuel injection, you may be able to plug a fault code reader into the diagnostic socket and get some information that way.

Have the plugs and leads been changed recently?

Thanks Bob & Vixpy much appreciated (Vixpy it appears to have a dizzy).

Is a fault code reader something I can get access to as Joe Bloggs or is that something I need a dealer for?

No idea on last service as have just brought the car, but the leads look fairly recent with no visible damage.

Only other thing that occured to me is that when it misfired it literally burst the backbox like a baloon (!) - is this going to complicate things due to lambda sensor or similar? ie. will an M30 run with a hole in the backbox?

Thanks chaps, Mat

[Vixpy1]

Hole in backbox should be fine, the lambda is much further up the exhaust

[bob1179]

Vixpy1 said:

bob1179 said:

I agree with Vixpy, have a look at the MAF as if it's buggered it will be sending the wrong information to the ECU causing the engine to run incorrectly.

The M30 in your 535i is the later version with a more advanced version of Motronic fuel injection, you may be able to plug a fault code reader into the diagnostic socket and get some information that way.

Have the plugs and leads been changed recently?

Edited by bob1179 on Monday 8th December 14:55

Bob is the later version 6 individual coils, or coil and dizzy?

My E28 is fitted with a dizzy and single coil. I am sure the set up is similar on the later cars. I could be wrong but I am sure it wasn't until the M50 engine came out that they replaced the old fashioned dizzy with seperate coils.

Edited by bob1179 on Monday 8th December 15:06

[mat1227]

Thanks alot - so, first I will try and source a known good MAF to stick on.

If that doesn't work, will get a new coil from GSF.

Anything I'm missing?

[Vixpy1]

bob1179 said:

Vixpy1 said:

bob1179 said:

I agree with Vixpy, have a look at the MAF as if it's buggered it will be sending the wrong information to the ECU causing the engine to run incorrectly.

The M30 in your 535i is the later version with a more advanced version of Motronic fuel injection, you may be able to plug a fault code reader into the diagnostic socket and get some information that way.

Have the plugs and leads been changed recently?

Edited by bob1179 on Monday 8th December 14:55

Bob is the later version 6 individual coils, or coil and dizzy?

My E28 is fitted with a dizzy and single coil. I am sure the set up is similar on the later cars. I could be wrong but I am sure it wasn't until the M50 engine came out that they replaced the old fashioned dizzy with seperate coils.

Edited by bob1179 on Monday 8th December 15:06

Think your right, My 3.8 is individual coil, the 3.6 was dizzy

[bob1179]

[quote]Thanks Bob & Vixpy much appreciated (Vixpy it appears to have a dizzy).

Is a fault code reader something I can get access to as Joe Bloggs or is that something I need a dealer for?

No idea on last service as have just brought the car, but the leads look fairly recent with no visible damage.

Only other thing that occured to me is that when it misfired it literally burst the backbox like a baloon (!) - is this going to complicate things due to lambda sensor or similar? ie. will an M30 run with a hole in the backbox?

Thanks chaps, Mat
[/quote]

If you have a local BMW specialist they should be able to read of any fault codes that appear for a nominal fee (or sometimes even for free if you talk to them nicely). German and Swedish sell the service light resetting tool, they may be able to supply the tool to read the fault codes too (no idea how much it would be mind!)

You could try replacing the leads and dizzy as a matter of course.

Edited by bob1179 on Monday 8th December 15:21

[mat1227]

bob1179 said:

If you have a local BMW specialist they should be able to read of any fault codes that appear for a nominal fee (or sometimes even for free if you talk to them nicely). German and Swedish sell the service light resetting tool, they may be able to supply the tool to read the fault codes too (no idea how much it would be mind!)

You could try replacing the leads and dizzy as a matter of course.

Ok thanks Bob.

Only thing with leads is that the misfire isn't just one cylinder hesitating, it's the whole engine and completely dependent on throttle position (behaved fine on light openings) - so I'd assume this would suggest leads are ok, unless it's the king lead? I maybe talking rubbish though..

I'd read elsewhere online that moisture gets in behind the dizzy, so as this is only £34 from GSF think I'll have a go.

Having tried to fix a similar misfire on my pug and spent a fortune before doing so, I'm keen to do my research before I start, and replace suspect components in an informed and orderly manner this time

Edited by mat1227 on Monday 8th December 15:25

[bob1179]

mat1227 said:

bob1179 said:

If you have a local BMW specialist they should be able to read of any fault codes that appear for a nominal fee (or sometimes even for free if you talk to them nicely). German and Swedish sell the service light resetting tool, they may be able to supply the tool to read the fault codes too (no idea how much it would be mind!)

You could try replacing the leads and dizzy as a matter of course.

Ok thanks Bob.

Only thing with leads is that the misfire isn't just one cylinder hesitating, it's the whole engine and completely dependent on throttle position (behaved fine on light openings) - so I'd assume this would suggest leads are ok, unless it's the king lead? I maybe talking rubbish though..

I'd read elsewhere online that moisture gets in behind the dizzy, so as this is only £34 from GSF think I'll have a go.

Having tried to fix a similar misfire on my pug and spent a fortune before doing so, I'm keen to do my research before I start, and replace suspect components in an informed and orderly manner this time

Edited by mat1227 on Monday 8th December 15:25

If it is moisture inside the dizzy cap, you could just remove it for a while and allow it to dry off. I had a similar problem with my old 309 after I hit a rather deep puddle at speed, a couple of days to dry and the car was right as rain (as well as dousing the all the bits with WD40!) Check the cap isn't cracked as well as this can cause problems.

Hopefully it will be something simple rather than an expensive bit like the MAF sensor!

[Boulder]

My old beast used to misfire after it had stood for a few days in the winter but soon dried out-usually damp that causes it.
How is it with the Airflow meter disconnected?

[bob1179]

Boulder said:

My old beast used to misfire after it had stood for a few days in the winter but soon dried out-usually damp that causes it.
How is it with the Airflow meter disconnected?

It's dead easy to remove the airflow meter, just unplug the socket in the side (it should have a little wire spring type thing that you can prize out, it does tend to 'ping' away so you have to be careful you don't lose it), undo the the big jubilee clip that connects the unit to the intake and thats basically it. You can undo the three bolts that attach the airflow meter/air filter assembly to the inner wing of the car and lift out the job lot.

[mat1227]

bob1179 said:

Boulder said:

My old beast used to misfire after it had stood for a few days in the winter but soon dried out-usually damp that causes it.
How is it with the Airflow meter disconnected?

It's dead easy to remove the airflow meter, just unplug the socket in the side (it should have a little wire spring type thing that you can prize out, it does tend to 'ping' away so you have to be careful you don't lose it), undo the the big jubilee clip that connects the unit to the intake and thats basically it. You can undo the three bolts that attach the airflow meter/air filter assembly to the inner wing of the car and lift out the job lot.

Excellent stuff Bob thanks alot. I'll have a play at the weekend.

One thing to add is that when cold, it just wont take full throttle. When up to temp, it won't even idle, and won't restart once stalled. So, applying my limited knowledge I think this adds ecu temp sensor to my list? At least this is what it was when the 205 was doing the same thing..

[roofer]

M30 six misfiring? First port should be the cap, the blowback is where it fired when flooded. Its a big flat cap, known for cracking and drawing damp.

[mat1227]

roofer said:

M30 six misfiring? First port should be the cap, the blowback is where it fired when flooded. Its a big flat cap, known for cracking and drawing damp.

Ok thanks for that Roofer - edit because I now understand that blowback = misfire, having re-read it

Sounding like list of suspects in order of replacement is now dizzy; maf; coil (dizzy being cheapest and easiest to source)?

Edited by mat1227 on Tuesday 9th December 07:56

[podman]

When the backbox blew on my 535 the car lost a shat load of power and ran awful...On that note, a genuine BMW backbox was cheaper than a copy from the likes of QuickFit or similar so ring around a bit for prices.

Good luck and any pics of the car?

[mat1227]

podman said:

When the backbox blew on my 535 the car lost a shat load of power and ran awful...On that note, a genuine BMW backbox was cheaper than a copy from the likes of QuickFit or similar so ring around a bit for prices.

Good luck and any pics of the car?

The plot thickens (as it often does with these things..). I was hoping the exhaust could be isolated as a contributing factor for the time being as it was behind the lambda (sic?!), but that suggests otherwise.

In two minds now, whether to start replacing stuff as above and hope for a result, or take it to local garage who are quoting £60ish for an hours labour on the diagnostic machine. Hmmmm

Pic is here. It's immaculate, drove lovely before the problem, completely standard down to original tape headunit - like £7k of receipts in last three years - hence worth the effort: