compression test low
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Fleet Mechanic
Joined: Jul 2004
Posts: 1,552
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From: va
compression test low
2005 neon 2.0 100,000 miles
Hi, ran the test while engine was hot, removed one spark plug at a time. I unplugged the coil, and removed the fuel relay. I depressed the accelerator for each compression test. Each cylinder I cranked the engine for about 5 seconds. I then repeated the whole test. Both times I got
#1 160 psi,
#2 90 psi,
#3 170 psi,
#4 165 psi.
Wet test, I used two cap full of motor oil. I got the same readings.My manual says readings should be between 170 and 210 with 25% difference.
It has a PO302 misfire code. Engine doesn't smoke, or burn (use) any oil. It just idles a little bad. So do the results say it may need a valve job ( bad exhaust valve) on #2. Could adding Seafoam cause this problem? It's the first time adding Seafoam. I had the same thing happen on my caravan at 150,000 miles, seems after adding Seafoam too.
Thanks
Hi, ran the test while engine was hot, removed one spark plug at a time. I unplugged the coil, and removed the fuel relay. I depressed the accelerator for each compression test. Each cylinder I cranked the engine for about 5 seconds. I then repeated the whole test. Both times I got
#1 160 psi,
#2 90 psi,
#3 170 psi,
#4 165 psi.
Wet test, I used two cap full of motor oil. I got the same readings.My manual says readings should be between 170 and 210 with 25% difference.
It has a PO302 misfire code. Engine doesn't smoke, or burn (use) any oil. It just idles a little bad. So do the results say it may need a valve job ( bad exhaust valve) on #2. Could adding Seafoam cause this problem? It's the first time adding Seafoam. I had the same thing happen on my caravan at 150,000 miles, seems after adding Seafoam too.
Thanks
Post Fiend
Joined: Jun 2001
Posts: 5,228
Likes: 5
From: Running Springs CA
Ive stopped doing this type of compression test and now to an aircraft style differential compression test with a setup from Harbor Freight. That way, you can use your ears to tell exactly what is leaking, intake valve, exhaust valve or rings.
Having said that, adding a cleaner causing a sudden drop in compression is puzzling. The only two possibilities I can think of is that intake valve deposits were partially removed and are hanging the valve slightly open, highly unlikely, or the upper compression ring was being so worn that the deposits were helping hold compression and got cleaned away, also hard to imagine.
Having said that, adding a cleaner causing a sudden drop in compression is puzzling. The only two possibilities I can think of is that intake valve deposits were partially removed and are hanging the valve slightly open, highly unlikely, or the upper compression ring was being so worn that the deposits were helping hold compression and got cleaned away, also hard to imagine.
Posting Guru
Joined: Feb 2004
Posts: 1,388
Likes: 0
From: Saratoga, NY
Not sure why you removed 1 spark plug at a time, you should remove them all, then crank the engine. I don't have any experience with your neon engine but just from engine experience sounds like a burned valve, I'm sure when your on the gas it runs ok, but idles rough. It doesn't sound like your head gasket is the problem because you would prolly be over heating or have oil in your coolant or vice versa. Either way the head has to come off, the way I verify the valves are not sealing is to pour a liquid into the ports and watch for it to leak out.
Post Fiend
Joined: Jun 2001
Posts: 5,228
Likes: 5
From: Running Springs CA
If you install a spark plug adapter that takes an air compressor hose, you can listen. Air coming out the muffler, exhaust valve/seat, the air cleaner, intake, oil filler, rings, radiator cap, head gasket.
Posting Guru
Joined: Feb 2004
Posts: 1,388
Likes: 0
From: Saratoga, NY
Let me add to that, #2 cylinder must be on the compression stroke at TDC for this to work.
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