pressure check

[-eur04lif3-]

I just did a pressure check across all 4 of my cylinders....and i got 90psi for all 4.
I'm fairly knew to cars, only owned this car for 2 months, so i was wondering....it that good or bad? what pressure should i be having?

Also 2 of the 4 spark plugs were oily on the bottom, what can that be?

Any help and advice is appreciated!

Tony

[DesktopDave]

Test should have results above 200psi across all four.  Less is still OK, unless you have one +-15% from the others.  Did you have the throttle wide open when you did the test?  Did the motor run recently?  If not you might need to squirt a wee bit of motor oil into the spark plug ports to get a reliable result.

Oily or black deposits on the plug electrodes aren't usually good.  Wet with a bit of gas is OK (if the car was recently running), but the plug electrodes should have tan/whitish deposits if the car is running well.  If the plug body is oily, that'd be the plug tower seals, they don't seal very well nor for very long.  They're not that expensive to replace.

[-eur04lif3-]

Test should have results above 200psi across all four.  Less is still OK, unless you have one +-15% from the others.  Did you have the throttle wide open when you did the test?  Did the motor run recently?  If not you might need to squirt a wee bit of motor oil into the spark plug ports to get a reliable result.

Oily or black deposits on the plug electrodes aren't usually good.  Wet with a bit of gas is OK (if the car was recently running), but the plug electrodes should have tan/whitish deposits if the car is running well.  If the plug body is oily, that'd be the plug tower seals, they don't seal very well nor for very long.  They're not that expensive to replace.

Thanks for the good info.

No, the car was just idling when doing the check. So, im assuming the reason i got 90psi all across...right?
Yes its my daily driver, it drives fine. I just recently purchased it, so i wanted to do some maintenance on it and discovered this. Would i have to take the engine cover off to replace the tower seals? Sorry if its a dumb question, my mechanic skills are about 2/10.

Heres a picture of my worst spark plug. Sorry for the bad quality, its my phone.

[monko141]

Pressure check 101
1. remove all the spark plugs
2. remove intake boot
3. pin throttle open
4. remove fuse that controls the fuel pump
5. turn over engine allowing the engine to spin several times        5 to 7 times

Make sure you have a well charged battery.  Using jumper cables connected to a running car is even better.
Let the starter "rest" a few minutes between each cylinder test so you don't burn it up.

[DesktopDave]

Yep, take off the cam cover & replace them all at once.  One goes around the cam cover, four seal the spark plug towers.  I think every M42 gets plugs oiled up like that eventually.  Maybe we're looking at it all wrong...it's not an "oil leak" on our cars, it's really a clever BMW system for preventing rust.

Can you post another pic of the plug electrode on the bottom?

[-eur04lif3-]

Yep, take off the cam cover & replace them all at once.  One goes around the cam cover, four seal the spark plug towers.  I think every M42 gets plugs oiled up like that eventually.  Maybe we're looking at it all wrong...it's not an "oil leak" on our cars, it's really a clever BMW system for preventing rust.

Can you post another pic of the plug electrode on the bottom?

I think you might be right about the clever way of preventing rust. Because i remember the bottom was dry. Will post a pic asap.

[-eur04lif3-]

Pressure check 101
1. remove all the spark plugs
2. remove intake boot
3. pin throttle open
4. remove fuse that controls the fuel pump
5. turn over engine allowing the engine to spin several times        5 to 7 times

Make sure you have a well charged battery.  Using jumper cables connected to a running car is even better.
Let the starter "rest" a few minutes between each cylinder test so you don't burn it up.

Thanks a lot for the info. Never knew that.

[DesktopDave]

Add some more steps afterwards, if your readings are low:

A spoonful of oil in each cylinder for the next test...if your readings go up after the oil (a "wet" compression test)...will let you know if the rings are bad instead of the valves.
Another use is to see if readings are low in a pair of cylinders - then you can (of course) assume a head gasket leak.

To test the whole deal you should also think about a "leakdown" test.  You'll need a more experienced mech for this, but basically they use an air compressor to pump 120psi+ (with a spark plug adapter) into each cylinder through a plug adapter, then see how long it takes for the air to leak down into the crankcase.  You can identify all sorts of problems with this...head gasket leaks, bent valves, etc.

All sorts of fun if someone with a lot of experience can show you  their tricks - they can watch the needle on a live test and tell you what  the likely problem is.

[-eur04lif3-]

Add some more steps afterwards, if your readings are low:

A spoonful of oil in each cylinder for the next test...if your readings go up after the oil (a "wet" compression test)...will let you know if the rings are bad instead of the valves.
Another use is to see if readings are low in a pair of cylinders - then you can (of course) assume a head gasket leak.

To test the whole deal you should also think about a "leakdown" test.  You'll need a more experienced mech for this, but basically they use an air compressor to pump 120psi+ (with a spark plug adapter) into each cylinder through a plug adapter, then see how long it takes for the air to leak down into the crankcase.  You can identify all sorts of problems with this...head gasket leaks, bent valves, etc.

All sorts of fun if someone with a lot of experience can show you  their tricks - they can watch the needle on a live test and tell you what  the likely problem is.

Thanks a lot for the help. Right now ive been so busy with school(my last year and a ME), and haven't had any time to look at it. The car runs very well. And im afraid that if ill take the cover off, i wont have enough time to put it back together, since its a daily. Hopefully during the thanksgiving break ill take a crack at it.

Tony

[DesktopDave]

If the car is running OK it might just be that your readings are off or the gauge is inaccurate.  These motors can really rack up the miles.  IMHO get a new gasket set for the cam cover, get a weekend lined up & replace them.  Check the cam chain & cam sprockets while you're in there & post some pictures.  We can advise you on its condition.

If you're feeling ambitious, order a lower oil pan gasket, blue loctite, oil filter & oil as well.  Drain the oil, drop the pan and check for bits of cam chain & loose bolts.

[-eur04lif3-]

Its still alive.

I'm done with school, thankfully i got a job and finally have some money to do some maintenance on the car.

The car hasn't had any preventive maintenance other than religiously having its oil changed with Mobil 1 synthetic.

Recently I've had the washer that holds the shift linkage fall off, car stuck in 3rd gear...lol The nice thing is I've got a friend that knows a friend with a car-jack. So we raised my car up and noticed a small leak from my oil pan gasket, also my diff.

That being said...i'm gathering parts now to get my whole car up to date on maintenance.

Any help, suggestions and part numbers or locations that i could get parts...please fire them away.



To do list:

-coil pack
-magnetic oil plug
-new oil pan gasket
-diff seals
-new radiator (pipe cracked, no AC)


Excuse my ranting....i'm just freaking exited to get my car to a better state, i simply love the m42's.

[-eur04lif3-]

If the car is running OK it might just be that your readings are off or the gauge is inaccurate.  These motors can really rack up the miles.  IMHO get a new gasket set for the cam cover, get a weekend lined up & replace them.  Check the cam chain & cam sprockets while you're in there & post some pictures.  We can advise you on its condition.

If you're feeling ambitious, order a lower oil pan gasket, blue loctite, oil filter & oil as well.  Drain the oil, drop the pan and check for bits of cam chain & loose bolts.

Dave,

Whats this "blue loctite" you talking about? Is that like a paste that would be placed between the gasket and the pan on both sides?

Thanks,

Tony

[-eur04lif3-]

Pressure check 101
1. remove all the spark plugs
2. remove intake boot
3. pin throttle open
4. remove fuse that controls the fuel pump
5. turn over engine allowing the engine to spin several times        5 to 7 times

Make sure you have a well charged battery.  Using jumper cables connected to a running car is even better.
Let the starter "rest" a few minutes between each cylinder test so you don't burn it up.

My engine really runs well now. I know this is a very old post.

Do you suggest i still do this test? I guess what i'm asking is that when its the best to do such a test? Is this a regular test, or when you might feel power loss...

Which btw, i dont really rev my engine that often. But once in awhile i do...and when i go though my gears up to redline, between 5500-6000 RPM, i feel a loss...any idea what that would be?

Thanks for all the input!

[-eur04lif3-]

any thoughts about this item?

http://cgi.ebay.com/ebaymotors/94-95-1-8L-BMW-318-SERIES-DOHC-16V-M42-FULL-GASKET-SET-/200613147203?pt=Motors_Car_Truck_Parts_Accessories&hash=item2eb579b243#ht_2287wt_939

[-eur04lif3-]

Anyone have any input on the mentioned above?