1995 540i Compression Test

[Clarksonvalley]

What kind of numbers has anyone come up with on a 1995 540i compression test?

Tom

[scooter]

Originally Posted by Clarksonvalley

What kind of numbers has anyone come up with on a 1995 540i compression test?

Tom

your numbers should be in the 200-220.
more important then the numbers is the consistency of the numbers, they shouldnt vary more the 5%.

[Clarksonvalley]

Compression check as follows:

Left bank, front to rear = 200, 200, 202, 222

Right bank, front to rear = 200, 210, 204, 212

Engine was up to temp when I did the compression check, throttle was wide open, cycled each cylinder thru 12 compression cycles.

I did a leakdown test on the 222 psi cylinder - with 98 psi reference pressure, leakdown pressure was 97.5 psi.

I think it is an electrical problem - the plug is not firing. Any suggestions on how to check this out?

Tom

[Clarksonvalley]

Compression check as follows:

Left bank, front to rear = 200, 200, 202, 222

Right bank, front to rear = 200, 210, 204, 212

Engine was up to temp when I did the compression check, throttle was wide open, cycled each cylinder thru 12 compression cycles.

I did a leakdown test on the 222 psi cylinder - with 98 psi reference pressure, leakdown pressure was 97.5 psi.

I think it is an electrical problem - the plug is not firing. Any suggestions on how to check this out?

Tom

[scooter]

Originally Posted by Clarksonvalley

Compression check as follows:

Left bank, front to rear = 200, 200, 202, 222

Right bank, front to rear = 200, 210, 204, 212

Engine was up to temp when I did the compression check, throttle was wide open, cycled each cylinder thru 12 compression cycles.

I did a leakdown test on the 222 psi cylinder - with 98 psi reference pressure, leakdown pressure was 97.5 psi.

I think it is an electrical problem - the plug is not firing. Any suggestions on how to check this out?

Tom

the plugs have nothing to do with the compression and as far as electrical issues i fail to see how that can be the case, your engine is wearing and its not wearing evenly as the numbers tell. the leakdown number is good but its only on one cylinder so you cant make too much of it, the 10% difference in compression isnt ideal.
the plug not firing can be an ecu issue or just a bad coil, swap it for another coil and see if the problem stays on the same cylinder or follows the coil.

[Clarksonvalley]

Scooter,

Take a look at my first posting '1995 540i Fouled Plug' dated 8-5-2010.

I've changed all (8) plugs and the #8 (the fouled plug) cylinder ignition coil and still have the 'no-fire on #8' problem. My next step is to put an ohm meter on the wire from the DME to the #8 ignition coil. After that, I'll try to get the DME checked. I'm now about 100% certain the problem is an electrical one - compression is good, leakdown is good, the problem is on the 5-6-7-8 cylinder head as the drivers side O2 sensor is 'faulting'. Have also replaced this O2 sensor. #8 is not firing.

Tom

[scooter]

Originally Posted by Clarksonvalley

Scooter,

Take a look at my first posting '1995 540i Fouled Plug' dated 8-5-2010.

I've changed all (8) plugs and the #8 (the fouled plug) cylinder ignition coil and still have the 'no-fire on #8' problem. My next step is to put an ohm meter on the wire from the DME to the #8 ignition coil. After that, I'll try to get the DME checked. I'm now about 100% certain the problem is an electrical one - compression is good, leakdown is good, the problem is on the 5-6-7-8 cylinder head as the drivers side O2 sensor is 'faulting'. Have also replaced this O2 sensor. #8 is not firing.

Tom

understood and agreed for the most part.
your compression numbers vary by 10% from high to low that is usually not ideal, plug ecu or otherwise.

[Clarksonvalley]

Scotter.

Throw out the 222# on cylinder #8 and the remainder of the figures are within 5% of each other - acceptable values. The 222# figure is probably a result of some carbon buildup due to the fouled plug. Thinking back about 6-8 months, I would occasionally have misses on startup for about 15 seconds, then it would clear up. Now, the plug is just not firing at all. I have verified continuity of the wiring to the #8 ignition coil, so I suspect the DME. Do you have any ideas what might be causing the non-firing on #8 cylinder?

Tom

[scooter]

Originally Posted by Clarksonvalley

Scotter.

Throw out the 222# on cylinder #8 and the remainder of the figures are within 5% of each other - acceptable values. The 222# figure is probably a result of some carbon buildup due to the fouled plug. Thinking back about 6-8 months, I would occasionally have misses on startup for about 15 seconds, then it would clear up. Now, the plug is just not firing at all. I have verified continuity of the wiring to the #8 ignition coil, so I suspect the DME. Do you have any ideas what might be causing the non-firing on #8 cylinder?

Tom

my guess would be the ecu as well as long as everything else has been ruled out.
are you getting any fault codes? misfire on #8 etc?
sometimes a vacuum leak can cause some carnage.

[MarieRian]

Engine was up to temp when I did the compression check, throttle was wide open, cycled each cylinder thru 12 compression cycles.