Off a cylinder or 2!! any ideas??

Post Mon Sep 17, 2012 11:21 am

hi guys, would appiciate any help. heres the story i picked up a tech 2 sport recently for parts or repair. Originaly was going to use for parts to restore my tech 1 but she was in too good of order to break. Owner had said head gasket problem. Car was stored in garage for 10 years. replaced tank, pump an filter as both were in bad condition. Put a battery in and bang she fired up. Straight away when givin a gentle rev could tell she was of a pot. the mates a mechanic he was giving me a hand. We think it is pot 1 and 3. when pulling the lead of the plugs 1 & 3 when ticking over the car doesnt seem to really respond dying or anything. there seems to be plenty of spark although the plug seems to be a bit wet with petrol. we changed over all leads etc of another engine i have to no effect. Left the car ticking over for a while no signs of overheating the coolant isnt bubbling it a bit strange really. Going to do a pressure test before taking the head off. Any ideas??

Post Mon Sep 17, 2012 12:12 pm

These engines don't have head gasket problems, they have head cracking problems; they really don't like overheating. So if the previous owner said there's a head issue, you really need to get the head off and pressure tested.

Before you do, get the rocker cover off and make sure there are no snapped rocker arms. You can't check for bent valves, but consider it a possibility.

Post Mon Sep 17, 2012 1:24 pm

You say 1 and 3 are off. How about 5? The injectors for these three cylinders are fed by the same wire, and it is very common for this wire to corrode through at the plug and socket where the injector loom connects to the main engine loom, under the inlet manifold. The rubber cover on the lower half of this connector tends to trap any moisture that enters higher up, instead of protecting the joint, so BMW issued a TIS some years ago that a hole should be made in the rubber at the lowest point.
The signal from the coolant temperature sensor also passes through this plug and socket, and if the corrosion spreads to this wire, severe running problems can occur.

Post Mon Sep 24, 2012 1:34 pm

Okay, the mate done a compression test on eact pot, all are at around 10 bar apart from number 4 which gets up to about 7 bar approx. He says this could poss be head are rings?! I hope its not the rings, going to take the head off and hopefully it will explain itself! any more advice guys?

Post Wed Sep 26, 2012 12:18 pm

Any ideas?? when i say pot 4 i am talking about forth from bulkhead. The mate thinks this is very strange as the coolant isnt bubbling no oil blowing out through dip stick when out. No real signs of over heating, also when i take out the spark plugs the one in pot 4 always seems to be soakin. Going to take the head off tonight for a look but just looking any any ideas before doing so. Some one also mentioned that the injector could be fu@ked and spraying too much petrol?? when turning the car over it was mentioned about a sticky valve or a fu@ked valve. Any knowledge appiceated!!thanks!!

Post Wed Sep 26, 2012 12:45 pm

A way to check if it's piston rings is to pour a thimble full of engine oil in through the spark plug hole, and repeat the compression test. If it goes up, then it's stuck or worn rings or bore wear. If it doesn't, then you probably have worn valves.