Injector Question/Theory

[Ferret]

Guys,

I started a thread about my 525i with one dodgy cylender a a day or two ago, and have thought about the problem so far:

I have one cylender: #3 that's repeatedly carbonising spark plugs and misfiring. This is a non-standard high compression engine...

I just need to tell me what this is more likely to be. Bear in mind here that during the rebuild, the petrol tank was run dry.

Would a compression problem (low ie busted rings) cause the cylender to run overly rich?

Or is it more likely that the problem is a stuck/leaking injector from crap come outta the dry tank?

Thoughts would be appreciated as I'm thinking about pulling it apart today.

[DaveVoorhis]

In the absence of a compression tester to verify the integrity of the rings, I'd yank the injector rail, power up the ignition, and see if the injectors drip. They shouldn't.

[pingu]

Maybe you could try swapping the coil pack and the injector for cylinder #3 with those of another cylinder and see if anything changes?

[Ferret]

Maybe you could try swapping the coil pack and the injector for cylinder #3 with those of another cylinder and see if anything changes?


Coil packs 3 & 4 are brand spanking new - eurocarparts.com have currenty got a couple to be sold off, they're going at like £18 or something near at the moment.

I might try bumping the injectors around, but last time I did something like this on my last M5, I ended up having to wait and get a complete new O ring set as they'd all expanded... took the car out of service for a couple of days... might try it though.

[stu1]

Sooner or later (preferably sooner) your gonna have to do the compression test - it'll save you a lot of fu*king around.

Stu.

[gale]

Ditto, do a compression test. Do it after the engine has warmed up. Take all the plugs out at once & make sure the throttle is wide open & let it crank at least 5 full strokes per cyl. Take note of the numbers and repeat the test with a few squirts of motor oil directly into the cylinders down the spark plug hole, appox. 1 tsp. per cyl. If the numbers jump up the 2nd time, it's bad rings. If they are bad but stay the same, it's a burned valve or cracked head or leaky head gasket.

[Ferret]

Over the weekend I've checked a few things:

Injectors are not leaking
No air leaks

... however ...

Cylender 3's injector has carbon deposits on the nose where the other 5 are spotless clean. I gotta run the compression test now, but it's now looking like the valve is shot at :/

Hopefully it's only the valve and not the valve+rings. If it is, I'm ebaying the car off quicker than you can say 'borked'

I do actually remember thinking one of the cyl 3 valves looked tarnished through it's port, and idiot here didnt think to check. I'm prepared to take the head off one last time, regrind the valves and do the valve stem seals... if the compression test shows the cyl to have a busted valve rather than rings.

Question1 ! Would this also explain why the cylender is running rich as it's pushing fuel back up the manifold before re-entering on the next cycle?

Question2 ! How easy is it to get a piston out if the heads already off, I'd refer to my chiltons manual, but it's at home atm.

P.S. Injectors make fantastic fountains :)

[neil_004]

to get the piston out you need the head and oil pan off. Then the cap comes off the bottom and piston and rod come out the top. Need a ring compressor to put it back in. If you need the car dont try it if you have never done it before and be carefull not to scratch anything while taking it out.

[SnakeyesTx]

I'm about to have a WHOLE bunch of cleaned and prepped for re-assembly valves from my old head. You're welcome to a few if it turns out you have a bad one :D

Also, I've been meaning to ask. Is it possible your injector is just stuck wide open?

[Ferret]

I'm about to have a WHOLE bunch of cleaned and prepped for re-assembly valves from my old head. You're welcome to a few if it turns out you have a bad one :D

Also, I've been meaning to ask. Is it possible your injector is just stuck wide open?

Unfortunately I'm going to need 520 valves, not 525 valves as the head is the 2.0 with smaller bore valves lol.

Also I've had the fuel rail out and turned the car over on the starter with them pointing in the air... just to check. It's producing good spray patterns.