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timmy.chisholm · 02-09-2010, 06:15 PM

just one quick question, what is the compression supposed to be in the cylinders of a 1.8L m42? Thanks for any help!

**Blackice** · 02-15-2010, 03:34 PM

I think for a older M 42 180 would be a good number. You are looking for pressure difference from 1 cylinder to the next. a big difference of might be a sign of problems.....

What did you get ?

timmy.chisholm · 02-15-2010, 06:31 PM

I got 3 cylinders reading at 180 and a single cylinder reading 170, and i'm not too worried about only a 10 psi difference. Just wondering, would those numbers mean a engine thats in good shape? carbon build up? Thanks alot for the reply!

**Blackice** · 02-15-2010, 07:44 PM

Was that 180 on a cold or warm engine ?

I would say that those are fairly good numbers, only 5 % difference is acceptable ( I think ). The lower number could be from a host of different things, but I would not be too concerned about it. I think you said something about this car sitting of a while ? If so, that compression number could improve with a bit of driving.....

Are you having a problems with the engine ?

timmy.chisholm · 02-15-2010, 07:59 PM

the engine was cold... it currently is running on only three cylinders. (failed on a trip back home) I think i narrowed it down the the fuel injectors so i bought a set of remanufacters ones off ebay. They should be in within 1 or 2 weeks then i'll put them in and hope the engine runs nicely... Its a project car... it's dangerous to drive right now, has a lot of problems but all are fixable with time.

**Blackice** · 02-15-2010, 08:17 PM

Did you pull the fuel rail yet ? You might want to check the fuel injectors for build up first. If the M 42 is dogged around a lot, carbon can build up very quickly..... Maybe clogged up one ????

Have you had the intake apart yet ?

What other problems do you have with the car ??????

Hey show me a photo of the car. I would love to see her.

timmy.chisholm · 02-16-2010, 04:03 PM

Unfortunately I have to keep it out in the snow and it has some surface rust but i'm planning on a new paint job this summer hopefully.

and yes the fuel rail is actually currently out waiting for the new fuel injectors. The injector tips were completely fine but i found the bases were all cracked and they just looked awful. Tried switching two of the fuel injectors to see if the cylinder would work again but they leaked and the cylinder worked but a different cylinder failed which wasn't switched... so i just decided to buy 4 new ones ($90)

As i said this is a project car... completely...
-It also has a problem where the low beams don't work... but on high beams all four work... i'm completely stumped on this problem
-fog lights are cracked (new ones on order)
-brake line needs to be replaced
-need new muffler (broke on the same trip the cylinder failed)

On highway this car drives soo smooth (before the clyinder failing)
hope to make this into a really nice car

**Blackice** · 02-19-2010, 08:58 AM

Originally Posted by timmy.chisholm

-It also has a problem where the low beams don't work... but on high beams all four work... i'm completely stumped on this problem

Could be the high/low beam switch, or the relay. Have you checked the low beam fuses ? There are 2 fuses, one per side.

timmy.chisholm · 02-19-2010, 10:51 AM

high/low beam switch trips the low beam relay, relay was replaced, both fuses are fine and were even swapped just to make sure. weird thing is, when the car is off, the relay is still tripped to be on, but it will untrip when switched to high beams. I completely detached the light switch (not the high/low beam selector one but the one on the dash) and the relay is still tripped to be on. Any thoughts? I hope this won't stump you as bad as me.
any help would be appreciated :P

**Blackice** · 02-19-2010, 01:54 PM

Sounds like the High / Low selector switch is done.

timmy.chisholm · 02-19-2010, 02:34 PM

i broke open the old relay and put it in... when the selector is on "high" the relay is open, when the selector is on "low", the relay changes to closed... so the selector is switching the relay... just absolutely no light on "lows" ever...
So could it really be the selector?

**Blackice** · 02-19-2010, 11:53 PM

Here is a wire diagram, of the relays.

timmy.chisholm · 02-21-2010, 10:37 PM

Thanks for the diagram, i had one already but it must have been the European version or something, it had a few things that were a bit off, this will help me out a lot more. The next time i have some time i'll troubleshoot some more with this, thanks again.

02-09-2010, 06:15 PM	#1 (permalink)
timmy.chisholm newbie Name: Tim Joined: Jan 2010 From: Fredericton Posts: 12 iTrader: 0 Thanks: 0 0 Times in 0 Posts '91 BMW 318IS	M42 compression just one quick question, what is the compression supposed to be in the cylinders of a 1.8L m42? Thanks for any help!

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02-15-2010, 03:34 PM	#2 (permalink)
Blackice Moderator Name: Dave Joined: Oct 2007 From: North Vancouver Posts: 1,088 iTrader: 0 Thanks: 43 47 Times in 46 Posts Blackice's pictures '91 BMW 318i '91 BMW 318IS	I think for a older M 42 180 would be a good number. You are looking for pressure difference from 1 cylinder to the next. a big difference of might be a sign of problems..... What did you get ?

02-15-2010, 06:31 PM	#3 (permalink)
timmy.chisholm newbie Name: Tim Joined: Jan 2010 From: Fredericton Posts: 12 iTrader: 0 Thanks: 0 0 Times in 0 Posts '91 BMW 318IS	I got 3 cylinders reading at 180 and a single cylinder reading 170, and i'm not too worried about only a 10 psi difference. Just wondering, would those numbers mean a engine thats in good shape? carbon build up? Thanks alot for the reply!

02-15-2010, 07:44 PM	#4 (permalink)
Blackice Moderator Name: Dave Joined: Oct 2007 From: North Vancouver Posts: 1,088 iTrader: 0 Thanks: 43 47 Times in 46 Posts Blackice's pictures '91 BMW 318i '91 BMW 318IS	Was that 180 on a cold or warm engine ? I would say that those are fairly good numbers, only 5 % difference is acceptable ( I think ). The lower number could be from a host of different things, but I would not be too concerned about it. I think you said something about this car sitting of a while ? If so, that compression number could improve with a bit of driving..... Are you having a problems with the engine ?

02-15-2010, 07:59 PM	#5 (permalink)
timmy.chisholm newbie Name: Tim Joined: Jan 2010 From: Fredericton Posts: 12 iTrader: 0 Thanks: 0 0 Times in 0 Posts '91 BMW 318IS	the engine was cold... it currently is running on only three cylinders. (failed on a trip back home) I think i narrowed it down the the fuel injectors so i bought a set of remanufacters ones off ebay. They should be in within 1 or 2 weeks then i'll put them in and hope the engine runs nicely... Its a project car... it's dangerous to drive right now, has a lot of problems but all are fixable with time.

02-15-2010, 08:17 PM	#6 (permalink)
Blackice Moderator Name: Dave Joined: Oct 2007 From: North Vancouver Posts: 1,088 iTrader: 0 Thanks: 43 47 Times in 46 Posts Blackice's pictures '91 BMW 318i '91 BMW 318IS	Did you pull the fuel rail yet ? You might want to check the fuel injectors for build up first. If the M 42 is dogged around a lot, carbon can build up very quickly..... Maybe clogged up one ???? Have you had the intake apart yet ? What other problems do you have with the car ?????? Hey show me a photo of the car. I would love to see her.

02-16-2010, 04:03 PM	#7 (permalink)
timmy.chisholm newbie Name: Tim Joined: Jan 2010 From: Fredericton Posts: 12 iTrader: 0 Thanks: 0 0 Times in 0 Posts '91 BMW 318IS	Unfortunately I have to keep it out in the snow and it has some surface rust but i'm planning on a new paint job this summer hopefully. and yes the fuel rail is actually currently out waiting for the new fuel injectors. The injector tips were completely fine but i found the bases were all cracked and they just looked awful. Tried switching two of the fuel injectors to see if the cylinder would work again but they leaked and the cylinder worked but a different cylinder failed which wasn't switched... so i just decided to buy 4 new ones ($90) As i said this is a project car... completely... -It also has a problem where the low beams don't work... but on high beams all four work... i'm completely stumped on this problem -fog lights are cracked (new ones on order) -brake line needs to be replaced -need new muffler (broke on the same trip the cylinder failed) On highway this car drives soo smooth (before the clyinder failing) hope to make this into a really nice car

02-19-2010, 10:51 AM	#9 (permalink)
timmy.chisholm newbie Name: Tim Joined: Jan 2010 From: Fredericton Posts: 12 iTrader: 0 Thanks: 0 0 Times in 0 Posts '91 BMW 318IS	high/low beam switch trips the low beam relay, relay was replaced, both fuses are fine and were even swapped just to make sure. weird thing is, when the car is off, the relay is still tripped to be on, but it will untrip when switched to high beams. I completely detached the light switch (not the high/low beam selector one but the one on the dash) and the relay is still tripped to be on. Any thoughts? I hope this won't stump you as bad as me. any help would be appreciated :P

02-19-2010, 01:54 PM	#10 (permalink)
Blackice Moderator Name: Dave Joined: Oct 2007 From: North Vancouver Posts: 1,088 iTrader: 0 Thanks: 43 47 Times in 46 Posts Blackice's pictures '91 BMW 318i '91 BMW 318IS	Sounds like the High / Low selector switch is done.

02-19-2010, 02:34 PM	#11 (permalink)
timmy.chisholm newbie Name: Tim Joined: Jan 2010 From: Fredericton Posts: 12 iTrader: 0 Thanks: 0 0 Times in 0 Posts '91 BMW 318IS	i broke open the old relay and put it in... when the selector is on "high" the relay is open, when the selector is on "low", the relay changes to closed... so the selector is switching the relay... just absolutely no light on "lows" ever... So could it really be the selector?

02-21-2010, 10:37 PM	#13 (permalink)
timmy.chisholm newbie Name: Tim Joined: Jan 2010 From: Fredericton Posts: 12 iTrader: 0 Thanks: 0 0 Times in 0 Posts '91 BMW 318IS	Thanks for the diagram, i had one already but it must have been the European version or something, it had a few things that were a bit off, this will help me out a lot more. The next time i have some time i'll troubleshoot some more with this, thanks again.

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M42 compression