Weird BMW engine! Please help.

[Jezz_S13]

Still struggling with my beemer.

See what you think of this.

I set the timing on No1 to 25deg BTDC at 2900 rpm as per book, easy off and it idles reaaly bad, timing is now about 10deg after TDC. Anyway i disconnet the advance vacuum and it about right now. About 28deg at 2900 and 13deg at 900rpm

However there is more, much more.

While it is idling really badly I try unplugging a spark lead to see if a cylinder is out, take No1 off and makes absolutely no difference, take No2 lead off, still no difference in engine note what so ever. Both 1 and 2 out!!!

So i pull No 3, now it judders like a bitch, put it back on, pull number 4, judders again. I now pull No3 too, so all four off and it stalls.

Took No1 plug out to check for a spark and there is.

Here wha seems to me to be the really weird bit, I unplug 3 and 4, and connect 1 and 2 and start the car, it runs the same as before. i plug in 3 and then 4 and makes no difference.

What is going on? Stuffed coil perhaps?

All of the leads are connected correctly in the right order etc, got a nasty shock or two in the process of jiggling them. Hurts doesn't it. :-(

This is really spooky. Or is there something I'm missing!
Any help will be gratefully recieved.

Cheers,
Jezz.

[Chris]

what is the firing order on the engine (prob ably1342) has the vacuum advance pipe been disturbed recently (could be in wrong place engine end? not all vacuum conections give same levels!) probably in swansea on saturday anyway (seen a nice pub/restaurant in mumbles recently, gorra try it)

[Leon]

What manual are you using?
If haynes - don't trust em - the often tell you to wire engines in reverse order...
OR their favourite is instead of 1342 - 1423!!!

[Jezz_S13]

Originally posted by Starionman
What manual are you using?
If haynes - don't trust em - the often tell you to wire engines in reverse order...
OR their favourite is instead of 1342 - 1423!!!

Firing order is on the top of the cam cover, that is right.
Using preoper BMW and haynes, but only for finding out timing angles etc.

[Clong]

On my beemer i had a similar problem. The cause was down to the rockers being broken in half, so the vavles wouldn't open. In addtion to that, one of the plugs self destructed so it was only running on four cylinders. Doubt it is the same in your case mate, but might be worth looking at.

[Jezz_S13]

Cheers Clong,

Unfortunately it's not that obvious, the plugs and rockers are fine.
Just damned weird.

Gonna try some new leads and rotor arm. The rotor arm is new, but it's a rev limiting one, don't need that now do I. :)

[Clong]

Dizzy cap? Carbon pin wore out on mine which buggered things up nicely. Sounds like it is more electrical than any thing. What i used to do was take the plug out, connect it to the HT lead, then use a jump lead to earth the body of the plug. Start the engine and check for spark at the tip.

Broken pin on one of the injectors meant that one cylinder ran permanelty rich, didn't cause problems but it did flame on every now and then. Bit of hassle to check these and it ain't likely to cause bad misfire but it may be worth checking.

[Jezz_S13]

I have the broked dizzy cap thing before, must have been arcing over the plug and the 5mm in the cap, amazing.

It's a carb version so not an injector thing.

When I took the plug out to test the spark, it was wet with fuel, yet it still sparked. FFS baking my noodle somewhat!

[Clong]

Originally posted by Jezz_S13

Here wha seems to me to be the really weird bit, I unplug 3 and 4, and connect 1 and 2 and start the car, it runs the same as before. i plug in 3 and then 4 and makes no difference.

What is going on? Stuffed coil perhaps?

All of the leads are connected correctly in the right order etc, got a nasty shock or two in the process of jiggling them. Hurts doesn't it. :-(

This is really spooky. Or is there something I'm missing!
Any help will be gratefully recieved.

Cheers,
Jezz.

This is the bit that is doing my head in, mate. As far as i can see if the coil was going it would just die, not this half arsed stuff. Check the air intake (grabbing at straws now), defo worth checking the dipstick and oilfiller are seated properly (or anything else connected to the oilways, i.e. breathers) , beemers run like pigs when the dipstick is left out.

And yep, it does bloody hurt when the HT gives you a belt. Disconnected the coil lead once to stop the engine to save me the long walk:rolleyes: to turn the ignition off once. Lesson learned and all that.

[Jezz_S13]

LOL, doing your noodle in!! Tell me about it.

Gonna get a new rotor and leads to see if that makes any difference. I'm sure I'll have more to say tomorrow.

The cam cover breather is disconnected, but still doesn't explain this weirdness!

30,000 volts hurts yes, should have twigged when it started arcing as I was trying to plut the HT lead in. What a twat! :rolleyes:

[Clong]

Was it doing this before the cam cover breather was disconnected? My beemer would throw an wobbler if you took the dipstick out or the oil filler cap out while it was running. Didn't look at what it did to the sparks, just put the dip stick back in back in and the engine ran fine. With them removed it would shake the engine all over the place, very lumpy idle, to point where it would almost stall.

[Jezz_S13]

Sussed it!

After your comments I've done some scouring around Carl.

There is a air hose that goes from the plenum (near No1 & No2) to the air filter thing, now I don't fully understand why this is there but basically it sucks loads of air in making these 2 cylinders run VERY lean, so lean that they don't fire. Plugged it up and hey-presto, running 316.

Thing that baffles me is why the **** this thing is there full stop, why would you want to pull air in and bypass the carb, it's a pretty bit hose too, I used an 300zx brake caliper - upright bolt to plug it, they are 11 or 12mm I think!

However I'm But back to my initial problem of it overheating though, also the timing is a bit odd. very odd.

at 900rmp its about 11deg, then at 2900 it's 29deg, this is without the vacuum attached? Uh? With the vacuum it's about 40deg at 2900. It should actually be 25deg, I don't know what the idle andgle should be but I'm guessing at about 12-15.

Just can't undrestand why the compression is so sodding high, it is 13bar. Should be 10-11 bar. I reckon this is why it over heats.

At least I can get around in it if needs be while doing S13 HG.

Cheers,
Jezz.