Almost jacked up my world doing a compression test on my 2.7L and some quesitions.

This will sound stupid, but this is how I learn:

So I had a compression test kit in the back of the truck that I picked up months ago at Harbor Freight. I've never done a compression test before on any motor, although I knew the basics of the process: disable fuel injection by pulling the fuse, remove plugs, screw in gauge, open throttle, crank 5-8 times, record number.

When I went to screw in the compression guage, I figured I needed one of the fittings to properly screw into the spark plug hole. I compared the spark plug to the four fittings provided in the kit (M10, M12, M14, and M18) and went with the M14 as it was the same size as the plug. This is the photo of the kit:



I used the third one down from the top - screwed it on the compression gauge tube and screwed the assembly into the #1 spark plug hole. Got in the truck and cranked it over, read the reading (175 psi) and unscrewed the tube (thinking the extension had come out with the tube) and went on to take the readings on cylinders 2,3, and 4. What I hadnt realized is that the extension had remained in cylinder #1 and I had just screwed the naked hose into cylinders 2,3, and 4. The readings were (125, 155, and 155).

When I went to put the plugs back in, I noticed that the extension for the compression tester was still screwed in to cylinder #1 and had on of those "Oh Shit" moments. It was not possible to screw the compression tube in to the extension and unscrew the whole thing out as the tube would unscrew itself from the extension inside the spark plug well.

I tried puting a magnetic wand in there but the fittings are not magnetic. I tried a long socket with an extension but they were too thick for the spark plug well. With images of me having to remove the head incuding panic in my mind, I decided to try a different approach: I put a light coat of Blue Loctite #243 on the threads of the compression hose, put it down in the spark plug well and screwed it into the fitting. I sprayed some Ford penetrating lubricant in there and gave it 10 minutes. Holding my breath, I unscrewed the the compression hose and THANKFULLY the fitting came out with the hose and I was able to put the spark plug back in.

So I have a few questions regarding the process:

I.) how do I know if I need to use a compression fitting. Is it always necessary or is the hose itself sufficient?

II.) if you do use a fitting, how do you keep it from getting stuck in the spark plug well?

III.) becuase my #1 cylinder reading was done by with the fitting, did it change the reading? My #1 had 175 psi which was significantly higher than 2,3 and 4 (125, 155, 155).

Anyway, to get the fitting off the compression hose, I had to hold it over a flame to heat it up enough to loosen the locatite and remove using vise grips.

 

If the hose only fits in the spark plug hole then you are good. There really isn't a set number of times to crank the engine over. You just crank it until the number stops going up on the gauge. If those are true readings you have some problems. I would try it again with just the tube, if that fits ok.
How many miles are on this engine?

 

Thanks for the reply.

There's 186K on the motor. I have no problems with it - I was just running the check just to mess with the truck and out of curiosity.

The only issue I see with the compression #'s is cylinder #2. I actually took 3 readings on that one and they went up each time: 115, 125, and 135. So I averaged out to 125. The 155 psi cylinders are not a worry as they look to be in spec and if the 175 is right, it looks like a great cylinder. The motor runs fine and burns no oil (knock on wood). That rules out in my mind a bad ring in #2. Perhaps some the valves on #2 are no longer sealing completely allowing some leakage?

Either way, Im not planning on a rebuid based on this just yet. Im going to repeat the test and have a helper so that I can get a more accurate read on the gauge.

 

Just because you have bad rings does not mean that it will necessarily burn oil. The cyl with 155 is right on the edge of being worn out if the 175 is true. The 125-135 is a tired ass cyl. Use a teaspoon of oil and put in in the 125 cyl through the spark plug hole. Then re-test that cyl. If the compression goes up you have a bad rings. If it stays the same you have valve sticking more than likely. It could also be a head gasket or small crack in the head. There would be other stuff going on then too. If you have a buddy help you, get a leak down tester as well. This can aid in further diagnosis. You can rent them from Autozone or those other stores.

 

Good reply, thanks again. Before I get carried away - I will double check my readings again with the same setup for each cylinder and someone to monitor the readings at the gauge immediately.

 

Just to answer the fitting question…


If you do get a fitting stuck, you have a couple of options. The first is what you did. I've used that trick before with other fasteners and fittings and it does work well, as you discovered.


The other option (plumber background here) is to get a nipple extractor. There are a few types. Some are reverse threaded fittings that look almost like reamers. They'll kill the threads on brass, since they are designed for the smooth I.D. of a pipe, but they do work. Some are the T-handle type, often used to remove sprinkler system risers. Both of those tools tend to leave shavings when used on soft metals, so coat the end with grease to capture those shavings. Another type of extractor has a pawl that kicks out when turned counter-clockwise. These tend to create the fewest shavings, but I've never seen them in a size smaller than 3/8" I.D. If that's your I.D., then a set of those will work too. Whatever you do, don't get cheap ones.


And yes, I've used all of the above on things other than plumbing work. Very handy tools to have around.

 

There is a bit on contention there. I have always, for the past 30 years, done compression tests where you only allow the engine to turn over 5-7 times. Here is the reason:
If a valve is sticking, but not every time, turning the engine until the gauge stops climbing can mask a sticking valve. Also some cylinder with burnt valves, or worm camshafts can eventually build up enough pressure to show good if you crank it over enough times.
I always recommend only cranking the engine over 5-7 times, AND to watch the gauge each time to see if the pressure builds up fast, or builds up slow.

VERY important part when running a compression test! Spot on there.

 

This info is gold. Thank you.

 

I should have went a little further in that comment. I didn't mean it to read like you should crank the engine over for 2 minutes. 5-7 is a good rule of thumb. I was trying to convey that a couple more would not hurt to make sure you get a good reading.

 

Ahhh...cool. I was worried there for a second with the initial post. hahaha.

 

Crank Crank Crank...oh wait should I keep cranking????

 

I would be sceptical of the extension hose's fitting making a good seal. Working with one variable at a time is always best. I would suggest you try again using the proper fitting on the extension hose on all cylinders before getting to excited about your results.

 

So I dont know how this happened, but I did another compression test over the weekend - this time with my girlfriend in the cab, cranking the motor and me observing at the gauge. Wouldnt you know it, these are the reading I got:

#1 ~175 psi
#2 ~170 psi
#3 ~170 psi
#4 ~175 psi

Im clueless as to what I could've done wrong the first time. Although this time I just screwed the hose without any fittings into the plug hole and made sure to twist to hand tight and double check for a good firm fit. I had her crank 6 times for each cylinder and every cylinder popped up to no less than 170 psi.

Im guessing the first time I did this, I limp wristed the hose and didnt have a good seal in the plug hole??? Im guessing that the first time around, I either didnt seal up the hose well in the plug hole and/or compression was dropping before I could get out of the cab and check the gauge.

Anyway, Im OK with the above numbers. Like I said before, the motor seems to run well and I had no significant issues.