Compression Test

I'm getting an cylinder 5 misfire check engine light an need to do a compression test on one back of my V6 Tacoma with 240k miles. I've watched a bunch of videos on how to do it but still have a couple questions. Replaced the ignition coil, plugs, and wires so hence the compression test.

1) For the compression test is this the right way to do it: I should disconnect all spark plugs wires, but leave them in the cylinders and only take one plug out at a time (the cylinder I'm testing). Once I test one cylinder I can put the plug back in and take out the next one to test that. Sound right?


2) Someone with an identical problem (cylinder 5 misfire) had deposits on their values and that was causing a problem. They sprayed brake cleaner on the throttle body and that worked. Where/what is the throttle body and is there a reason why this might be a bad idea? Truck is running pretty good besides the check engine light. Some more vibrations and a little more noise but could be unreleated.

 

if you need to ask where and what a throttle body is, you shouldn't do any work on your own truck. Take it to a shop to compression check. should cost about 50-100 bucks. don't go spraying brakelene randomly in your engine bay

 

Well I'm 99.9% sure I know where it is and what it does, just wanted to triple check. It's the air intake with the value that opens when you hit the gas pedal and the value allows more air to enter. Not going to learn more by taking it to the shop.

 

In my humble opinion... take all of the plugs out, open the throttle all the way and crank until the needle on the gauge stops advancing. I use a compression test as a go - no go test. My preferred way is a cylinder leak down... different tool, better result. I will explain. With a compression test the reading is dependent on the speed that the starter can turn the motor over and if the throttle is open. With a leak down test, the cylinder being tested is rotated to TDC and a measured psi of air is put into the cylinder, 100 psi. If the second gauge show 88, you have 12% leakage. Take the oil cap off and listen and watch, if you see oil vapor coming out of the valve cover oil filler, the blowby is past the rings, if you hear it out the tail pipe it is past the exhaust valve(s), if you hear it out of the intake, the intake valve(s). This has to be done on all cylinders.

for carbon deposits to get so thick as to prevent a valve from seating is pretty bad. The motor has large amounts of blow by and or the PCV valve is malfunctioning. Spraying carb cleaner down the throttle body is a patch at best. There are numerous threads in the forum where guys have put a oil catch can in between the PCV valve and the connection on the throttle body to help prevent the blow by oil from ever getting to the intake system.