Speedometer and compression test??

[Lacross]

First off , my speedometer doesnt work. So today i replaced the speed sensor, and still, nothing. I have the Torque android app, and it shows me that the ECU reads random speeds while im driving, such as 0-3-64-19-126-0-0-192 , just all over the place...

Any ideas?


Also i did a compression test today
1-170 2-200 3-200 4-200

Any ideas why 1 is so low, or 2-4 are so high?

 

[2gnt99]

Not sure about your speedometer problem.

But your compression on cylinder 1 is exactly 15% from the other cylinders.
Pour a cap of oil in cylinder 1 and redo the compression test.

If you get a higher reading you need to do a leak down test.

 

[Lacross]

thanks for the response! I dont have any oil on hand at the moment, but what exactly is a leak down test?

EDIT: also, doesnt a 200 psi compression seem a bit high? i know the engine was rebuilt but that seems kind of extreme

 

[2gnt99]

Basically, a leak down test pumps air into the engine to find bad seals.

It does seem to be high, but other threads I've found on here say that anywhere between 170 and 225 are fine.

Note: If after you add oil and do another test, if your compression rises, you may have a worn (or damaged) ring or cylinder wall. If the compression does not rise, you may have a leaky valve seat or leaky head gasket

Edit: Here's more information on leak down tests:
http://www.dsmtuners.com/forums/articles-engine-fuel/338152-compression-leak-down-testing.html

 

[Lacross]

Wait so, if it rises its bad, and if it doesnt its bad? Whats SUPPOSED to happen?

 

[B1ackout]

you want compression to rise because the oil makes a good seal and increases compression

 

[Joethefallen23]

you want compression to rise because the oil makes a good seal and increases compression

No you don't. The oil doesn't permanently seal the cylinder, it just lets you know that you likely have a ring/bore problem. Honestly, I'd rather the compressor not move knowing I only have to worry about fixing a leaky valve. Much less of a hassle than ring work.

 

[Lacross]

So, what would be a good thing to see?

 

[2gnt99]

So, what would be a good thing to see?

The oil to not change the compression, as that would rule out a few things.