Number of cylinders?

**Aberk** · 09-01-2009, 01:18 PM

Is there a reliable way to determine the number of cylinders in a car using only OBD II data? I am thinking of using the number of O2 sensors, but that doesn't seem reliable on some older models as they may not have as many.

**p2psmurf** · 09-01-2009, 02:17 PM

4-cylinder BMW's have 2 O2-sensors in front of the cat.
Older 6-cylinder BMW's only have 1 O2-sensor in front of the cat.
Some V12's have 2 O2-sensors in front of the cat, others have 4.
How do you think you can determine the number of cylinder's?

Diesels (4, 6, 8 cyl) have none, 1 or 2 O2 sensors.
Again, how do you think you can determine the number of cylinder's?

**Aberk** · 09-01-2009, 03:04 PM

Originally Posted by p2psmurf

4-cylinder BMW's have 2 O2-sensors in front of the cat.
Older 6-cylinder BMW's only have 1 O2-sensor in front of the cat.
Some V12's have 2 O2-sensors in front of the cat, others have 4.
How do you think you can determine the number of cylinder's?

Diesels (4, 6, 8 cyl) have none, 1 or 2 O2 sensors.
Again, how do you think you can determine the number of cylinder's?

I thought this would be the case with O2 sensors. That's why I asked if there was any other thoughts.

**Curiosity** · 09-01-2009, 04:47 PM

The best method would be decoding the VIN, but it's manufacturer specific so would take a bit of work. Fuel trim could give you a hint but it's a lot like the O2 issue.

**DarquePervert** · 09-01-2009, 08:46 PM

Why don't you just open the hood and count the number of spark plugs or spark plug wires?

**Tidder** · 09-01-2009, 08:51 PM

Seems the most logical to me.

**bratnetwork** · 09-01-2009, 10:13 PM

use the streaming obdII data to see how many injectors are firing, or how many cylinders it is monitoring for misfire. you will obviously need obd software that can monitor live data and not just read codes.

**soundman98** · 09-02-2009, 10:05 AM

Originally Posted by DarquePervert

Why don't you just open the hood and count the number of spark plugs or spark plug wires?

this method has worked flawlessly for me, though, i think desiels use glow plugs(no spark plug wire?), so you might need to count fuel lines, or something.

**DarquePervert** · 09-02-2009, 10:10 AM

Originally Posted by soundman98

this method has worked flawlessly for me, though, i think desiels use glow plugs(no spark plug wire?), so you might need to count fuel lines, or something.

Good point about the diesel. I didn't think about that at all, obviously....

Of course my method of counting plug wires would be inaccurate if a motor happens to be missing a plug or plug wire for some reason, such as removing them due to a problem in a certain cylinder, possibly.

**soundman98** · 09-02-2009, 11:13 AM

Originally Posted by DarquePervert

Good point about the diesel. I didn't think about that at all, obviously....

Of course my method of counting plug wires would be inaccurate if a motor happens to be missing a plug or plug wire for some reason, such as removing them due to a problem in a certain cylinder, possibly.

after you said that, i remembered that in at least the mid 90's--i am not a engine guy, so it could have been earlier/later, ford had a inline 4 cylinder motor that actually had 8 spark plugs, so counting the wires might not always be the best option either...

i guess the only reliable way would be to decode the vin, or, in case the engine was swapped to a different one at some point, learn your motor good enough to just know what it has.