basic compression test question

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Mar 13, 2008 | 09:16 AM

StangVT66

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basic compression test question

I did a little searching but I didn't find the answer to this. I have a 2000 ranger, 4.0, 5-speed. Last week it started missing and threw a code, "#4 cylinder misfire detected."

I looked at the plug and that looked good, so I'm going to check timing and compression now. My question is, how do I keep the engine from running when I crank it? There is a small connector on the front of the coil packs, should I just pull that off? I'm used to older cars with distributors. And just to make sure, #4 is the front of the driver's side bank, right?

Thanks.

Mar 13, 2008 | 11:27 AM

jason867

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From: East Central Indiana

I'm no expert, but I believe that to do a proper compression test to get accurate results, you're supposed to cut the fuel supply to the engine, and pull out all of the spark plugs so that the engine can turn over freely.

You might want to wait for someone else to answer to make sure you're getting correct information.

Mar 13, 2008 | 11:28 AM

Flexfuel-Dave

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From: Central, MA

Quote:

Originally Posted by StangVT66

Last week it started missing and threw a code, "#4 cylinder misfire detected."

I looked at the plug and that looked good, so I'm going to check timing and compression now. My question is, how do I keep the engine from running when I crank it?

And just to make sure, #4 is the front of the driver's side bank, right?

Thanks.

I wouldn’t go that deep yet. Check the #4 ignition wire first.

Your #4 spark plug wire could be the problem. How old are the plugs and wires.

If you are going to do a compression test the ignition has to be completely disconnected. You don’t want the engine to fire. Not 100% sure how to do this on our Rangers. You only want to have someone swing the starter over a few turns while you keep an eye on what the gage does on that cylinder.

Yeah, #4 should be the front driver’s side cylinder on a V6 motor.

Keep us posted!

Mar 13, 2008 | 12:44 PM

StangVT66

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OK, checked the plug and wire last week, both seemed fine, but then today I pulled the plug and looked again and the insulator was cracked all the way down both sides. $1.50 later, works fine. Incidentally the compression was low in that cylinder (150 psi), but that's a worry for another day.

I just pulled the wiring harness off the side of the coil pack and it didn't run, did inject fuel though. There's probably an easy way to fix that but I didn't do it.

Mar 13, 2008 | 02:13 PM

Bear River

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From: Salt Lake City, Utah

The proper way to do any compression test is to disconnect and remove all the spark plugs. That way, the engine can turn over freely and at a higher speed, ensuring complete compression. I'm pretty sure you open the throttle too, which ensures that plenty of air is available to compress, and in most setups, is also cuts out the injectors, or reduces their flow. To stop the fuel from injecting, unplug the fuel pump relay.

Mar 13, 2008 | 04:21 PM

bluedevil3758

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From: nj

150 seems fine its based on % but thats deff not a low reading

Mar 13, 2008 | 08:10 PM

mfp4073

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From: down south

for others reading this and in the future, try swapping plug wires with another cylinder. If the problem follows it you know what you are dealing with. Wires will sometimes fail and look completely fine on the surface.