really really low compression

[Drexer13]

OK so here’s what happened. When I bought my car it was throwing a bunch of codes among them was p0301-p0304. After a little work and a lot of help from you guys I managed to get them all cleared up and the car runs and drives really well. Aside from the cold weather fuel leak in the fuel rail the car has been great. Then a few weeks ago the light came back on. When I pulled the code it was P0302, a misfire in cylinder 2. I changed the fuel filter, the clip on the coil was broken anyway so I just replaced the coil and I replaced my spark plugs, the CEL is still there. I just got done checking the compression in that cylinder and it read 30 psi not 300 not 130, but 30. Is that even possible? The car runs and drives great. I haven’t noticed any loss of power and it only misses when its idling.
The car is a 02 wrx with 30k a cat back exhaust and an aftermarket turbo inlet ducting. So what do you guys think I kind of think that my gauge is broken. Has anyone else had a car that still ran with only 30 psi in one cylinder? If so is any one looking to sell a good or rebuildable EJ205 long block, because I think I might be needing one.

[jdowrx]

Maybe you should check the other cylinders to determine if youre gauge is really broken or not.

[Kjott21]

What were the other cylinders? Was the engine hot or cold? Were you at TDC when you did it? If the compression is really that low you have a problem.

[LiL Shoaf]

Kjott21 is correct. Also are you sure that your nipple was sealed and not leading?

[Drexer13]

Sorry I haven’t had a chance to post any updates. The engine was hot when I tested it. I’m not sure what you mean when you ask if it was at top dead center I’m assuming that you are talking about a leak down test. I don’t have a leak down tester but I am going to order one today. As far the other cylinders I don’t know how they were I broke the hose on my compression tester trying to unscrew it from the cylinder.
So Im just waiting for the leak down tester
I did notice yesterday that the car smelled like gas after I filled it up. I pulled the back seat and took off the fuel pump access door and noticed that the tank is leaking there pretty bad. I know that sometimes when you don’t put the gas cap back on tight it can cause problems. Could the leak be causing my misfire?

[LiL Shoaf]

Top Dead Center means that the piton is at it's "hightest" point on the "Compression" stroke. Do you understand how the combustion chamber works?? How the valves, piston and ect all work and when?? It's important that the piston is at Top Dead Center so that all the valves are fully closed or else the air can leak out of a valve and create a false low compression reading.. I say false becuase the combustion chamber can't build pressure is a valve is slightly open.

[Drexer13]

I do have a pretty good idea about how an engine works I’ve rebuilt many including a few Subaru’s I was asking about top dead center because its impassible to keep the cylinder at tdc when performing a compression test. I think that the test you are referring to is a cylinder leak down test. A compression test measures the amount of pressure the engine builds while it’s turning over. Correct me if I’m wrong.

[LiL Shoaf]

I was not trying to be a jerk, just have to ask, you never know ones abilities..

As for TDC. LOL, you got me, I was focussed on Leak down after reading your post about getting a testor.. LOL. You mentioned that you broke your test line for your gauge, were you able to get a new one yet?. Did you retest?

[Drexer13]

I wasn’t trying to be a jerk either I was just trying to be clear. Your right you do need to know about people’s ability before you know how to help them. I’m now exactly a novice when it comes to the mechanical side but I am pretty new to anything obd2 related. I haven’t had a chance to get a new tester yet but soon. In the mean time I’m going to fix the leak in the gas tank and see if that helps.
If the motor is blown I have a friend that is building an sti and will be pulling his stock motor to put in the one he’s building. He offered to sell me his stock motor for pretty cheap. What would I need to get to run that in a wrx, and would my 5 speed hold out?

[newtothegame]

Just do the hybrid build. Use his short block, or you will have to get his ECU or splice wires to make it work. Search around about the hybrid build, many people are running it now and love it.

[dumdum]

Also remeber when doing a compression test to hold the throttle 100% open when cranking the motor. I do agree the next step is a leakdown test.

[Drexer13]

Just a little update. I'm still waiting for my leak down tester and my new compression tester to come so I haven’t done either of those tests yet. But I did drive the car today and noticed that it only misfires at idle and at normal operating temperature. I’m starting to think ( or hope ) that it might be a cat. I also found that the fuel tank is leaking where you access the fuel pump.
I ordered a new seal for the gas tank and am still going to test the compression and do a leak down when the tools get here.

[03 CrazyTaxi]

Umm, couldn't you have just gone to some auto parts store and picked up a compression tester? Seriously, they are only like $20

[Drexer13]

Ya I could have. But I had the cash on my Paypal account. It was just easier to order one then request the funds and then go to the auto parts store.


The results are in

Cylinder 3. 4% loss Cylinder 4. 6% loss

Cylinder 1 4% loss Cylinder 2. 85% loss Threw the piston and or rings.

The rest of the engine seems to be in pretty good shape I don’t think I’m even going to take apart the passenger side bank of the engine unless the cylinder wall in number 2 is really bad. Then Ill either bore out all four or do a hybrid swap. If I can get a hone down far enough with just the #2 piston out I might just do the one cylinder.
Well I just hate it when threads End without an ending

Thanks for everyones help