m20 engine wiring

[Finny]

As many of you probably already know i have recently put an M20 in my 316i touring and i am having a problem with the engine only firing on five pots, the other day i removed the -ve connection from the battery whilst the engine was running and the engine died straight away.

I can remember that the car it was in before carried on running when -ve connection was removed and i checked this on my mates 2.5 and his did carry on running too.

Im thinking that i may have the wiring slightly wrong, firstly does anyone know if this is the case and if so what lead would be wrong?

Seccondly could this be causing poor ignition leading to my car only firing on five? The pot which is not firing is the one with the longest HT lead, could it be that the strength of the spark is reduced leading to non ignition in this cylinder?

There is a spark but not sure how i couldmeasure the strength.

Any help or suggestions greatly appriciated.

Cheers

[Brianmoooore]

First of all, NEVER disconnect the battery on an engine that is running. You run a very real risk of spiking every bit of electronics on the car.
If your car dies when the battery is disconnected, it suggests a problem with the altenator, which could cause problems when the battery gets low, but this would cause starting problems.
Length of the lead no 6 is not relevant, although it could be faulty of course.

[gcorky]

cap ok ,not cracked on install?

[Finny]

Leads are definetly in working order as i swaped them with my mates which are known to be working ok.

By cap do you mean the distributor? If so this is in working order bought recently and installed after the engine was put into the new car when i had to replace the damaged water pump.

Any other ideas guys?

Is there possibly any wiring that could be wrong causing this problem?

Cheers

[Brianmoooore]

There's no wiring error that could specifically affect No. 6.
Measure the voltage across the battery when the engine is running at about 2000 RPM.

[Finny]

Iv just had a thought

Could a bad engine earth be causing the poor ignition?

I am currently in sheffield finishing off my degree and havent got time at the minute to go back home to play about with my BM but this problem is really playing on my mind.

Please help!!!

Cheers

[Brianmoooore]

If the engine cranks OK then all earth straps are in order.
What makes you think the problem is electrical?
If the problem is definitely No 6 and only No 6, then I would check that the inlet manifold gasket on 6 is OK, and then suspect the injector.

[gcorky]

daft one try changing that plug.

[Brianmoooore]

daft one try changing that plug.

He's changed dis cap and leads. I was kind of assuming he's changed the plug as well.

[gcorky]

well the plug is the only part of ht left,(is cap ok -look inside,i know its new),injector wiring to no 6....!

is the plug wet when removed?

[Finny]

Dont worry i have replaced the plugs and it made no difference. Yes the plug is wet black and smells of petrol when removed.

Its annoying to have to remove the dizzy again but i guess il have to do it. rotor arm should be ok as it fires ok on all the others.

So it looks like im looking at the injector or inlet manifold gasket then i guess!

I would susspect that the injector is working ok as there is obviously fuel getting to the cylinder.

cheers

[Brianmoooore]

I would susspect that the injector is working ok as there is obviously fuel getting to the cylinder.

?? You have six injectors - one per cylinder!

[Finny]

Yes i am aware that there are 6 injectors but there is only a problem on one cylinder, and the plug in that cylinderf is wet with fuel so i assume that the injector is working ok on this cylinder.

And all of the others are ok because they all work fine.

[Brianmoooore]

There's a bit more to injector design and operation than just letting fuel in.

[Finny]

Yeh i will admit that i dont know anything about injector operation to be honest.

What should i do then?

Il take it out and clean it next time im back home, is there any way can tell or test to see if its working ok?

So i dont have to remove it again if it aint working?

Cheers

[Brianmoooore]

You can't test it yourself, without making up a test rig because of the way it gets its fuel supply.
You can't clean it either - needs ultrasonic cleaning
You could swap it with another and see if the problem moves with it.

[Finny]

Ok i get ya.

Im sure iv seen an article somewhere about how to clean your injectors.

Think it was using brake cleaner and an air line, does that sound a bit dodgey?

Il have a go at swapping it and see if i can move the problem then at least i will know it is that then eh!

Cheers

[stevetigger]

Thats the plan!

Good Luck

[Templ8e30]

Im sure iv seen an article somewhere about how to clean your injectors.

Think it was using brake cleaner and an air line, does that sound a bit dodgey?

Il have a go at swapping it and see if i can move the problem then at least i will know it is that then eh!

Cheers

Very ropey mate !, the injectors clog up inside at the valve seat and the pintle area which are impossible to get at and clean by hand. As Brian said the only way is to get them ultrasonically cleaned.

Have you treble checked the valve clearances ? My 320i ran like a bag of sh!te when I got it, it had low compression and no power from no1 cylinder which turned out to be an exhaust valve clearance slightly too tight. I re-adjusted the lot and it was sweet as a nut.

Cheers,

Iain T

[Jamesy]

I would carry out a compression test on the faulty cylinder? before going any further.

[Templ8e30]

I would carry out a compression test on the faulty cylinder? before going any further.

Yes, or just check all the clearances again anyway as per this article http://www.e30zone.co.uk/modules.php?na ... echnva.htm

Best of luck,

Iain T

[Finny]

Il give that a go, one of the ideas running around in my head was a sticking valve or something similar.

Its a shame the pics arent workin on that article.

Never mind i think i get how to do it anyway.

cheers