I got a supercharged 3.8L engine from an '04 Impala SS used from a junkyard for my Fiero.

It's on my engine stand. I wanted to make sure it turned over fine so I pulled the plugs. It spun free so I also did a quick compression test by hand. The center cylinders on each bank completely failed to make any psi. The others were low at around 65 psi but remember this is only turning the engine by hand.

I did a leakdown on the two problem cylinders and they both had 80% leak down. I did head the air leaking out the exhaust manifold.

Giving this, I don't think it can be a head gasket failure. I think it must be the cylinder head. Am I completely wrong? Do 3.8's have a history of failing head gaskets?

Beings it's on a stand, and you probably need new valve cover gaskets anyways, pull the valve covers and rocker arms then redo the leak down test. If you still get large leaks out the exhaust, you probably have burnt exhaust valves. The 3800 have pretty strong and long lasting head gaskets.

[This message has been edited by 1fatcat (edited 04-10-2011).]

LOL. I did have leaking valve cover gaskets. I just replaced them on the engine stand along with a new metal intake gasket.

I'll pull the covers and rockers then recheck leak down. Are the 3800 rockers adjustable or are they just torqued down?

All my other cylinders had between 15-20% leak down so I know I'm testing correctly and the gauge is working fine.

Not only are they torqued down, the bolts are one time use. Are you checking each leakdown AT EXACTLY TDC on the compression stroke? Otherwise you might be lifting a valve slightly, and doing it consistently amongst the cylinders.

Also, there is no way you are strong enough to get full compression on a compression tester turning the engine by hand. You need about 8 complete rotations, at cranking speed. I get the feeling that you are looking for a problem that isn't actually there. The engine is probably just fine.

quote Originally posted by Fierobsessed: Also, there is no way you are strong enough to get full compression on a compression tester turning the engine by hand. You need about 8 complete rotations, at cranking speed. I get the feeling that you are looking for a problem that isn't actually there. The engine is probably just fine.

I agree...
Is your starter still attached? Hook up the battery to it to turn the motor over; I would do this before I start tearing into things... You could remove/loosen the spark plugs from the other cylinders so it will turn over quicker/easier. Just make sure your head is good and clean, you don't want to suck-in any debris into the motor...

I agree I cannot get full compression readings turning the engine over by hand but I know for a fact that I should have some psi reading on a cylinder doing it that way. I have 6 cylinders, 4 of them register almost 65 psi, 2 do not register at all. Zero, nada, nothing. That's why I did a leak down test.

I did the leak down at the top of the compression stroke (with both valves closed). 4 of the cylinders showed 15-20% leak down while my 2 suspect cylinders show 80-95% leak down. I am most positive I definitely have a problem on those 2 cylinders. I can hear air leaking out the exhaust manifold for the respective questionable cylinder under test. I do not hear air leakage out of the normal cylinders.

Yeah, you shouldn't have that much leak down on the two clyinders. As for the others, 15-20% is considered normal...maybe just a tad on the high end, but still good. I usually see 12-15% on a good cylinder, but guage calibration plays into it too. By "clyinder", I'm refering to the pistons, rings and valves. Sounds like you either have burnt exauhst valves or the valve was not fully seated (which can be caused by sticky valve guides). Re test with the valves confimed shut, but I think you need a valve job, possibly more?

Just by chance, did this engine have any mods done at any time that you know of? I've seen chipped pistons from guys running a 3.4 pulley on a bone stock L67.

Update:

I removed the rocker arms on my 2 low reading cylinders (ensuring the valves are truly closed) and repeated the leak down test. Exactly the same 80% reading.

To me that confirms my heads have to be rebuilt. Everyone agree?

Do 3800's have a history of burning valves?

quote Originally posted by sportcoupe: Do 3800's have a history of burning valves?

I don't know about that but they do have a history of developing cracks between the intake and exhaust valves.

I wouldnt worry about it too much. If the motor has been sitting it will probably be leaking around the valves ti some degree.

I would wack the valves with a hammer while you have some air in them to get them seated nicely.

Update #2

I pulled the heads to confirm suspect valve problem while the engine was still easy access on the stand. I found the problem(s). On one of the problem cylinders the exhaust valve was completely white and it had a large hole in it big enough for my pinky finger tip to fit. On the other problem cylinder the exhaust valve didn't have a hole but it was completely white unlike all the normal valves.

I'm glad I did a simple "by hand" compression test or else I wouldn't have found the problem until the swap was in the Fiero.

Interesting.

I could probably supply you with some valves if the seats look good.

Thanks but I have a good friend that owns a cylinder head shop. I'm taking him the heads tomorrow to go over them.

Thanks for all the help. I appreciate it.

quote Originally posted by sportcoupe: I got a supercharged 3.8L engine from an '04 Impala SS used from a junkyard for my Fiero.

Soooo, did they give you a warranty? Exchange for another? If they exchange, take your new gaskets out, you can reuse them.

[This message has been edited by 1fatcat (edited 04-11-2011).]

The engine was shipped. I got it for a very good price so even after new gaskets and a valve job I am still cheaper then they are usually going for and I know it's been gone through well. I'm only slightly disappointed it failed compression and leak down.

I would be a little concerned about how hot the engine must have gotten when the valves burnt. You may have burnt oil in the piston ring grooves. That can cause the rings to stick. Rings stick when oil burns in the grooves, causing the carbon deposits of the burnt oil to hold the rings in the groove. If this happens, the rings no longer hold outward pressure against the cylinder wall and will cause blow-by, oil consumption and power loss.

Going by your leak down test results and assuming your gauge is calibrated, the numbers were just a tad high. You may very well have rings that are starting to stick, and the only way to get to them is with the heads off.

I would also be concerned about the rest of the engine if it got hot. Things like bearings, lifters, pistons, oil pump. If your willing to do the work, now’s the time. If the parts measure in spec, they can be reused. Any burnt oil must be removed.

Well when I said it "failed compression" I meant that in very loosely terms since I only checked rotating the engine by hand. The leak down told me I had the real problem but it doesn't define top or bottom end.
I do agree that I am far enough into it to warrant at least checking the rings and even just replacing them while the piston is out. It would be very easy on the stand.

Edit:

Wow, I just priced rings and they're $141 at Advance Auto. That sounds high. Ouch.

[This message has been edited by sportcoupe (edited 04-12-2011).]

quote Originally posted by sportcoupe: Update #2 On one of the problem cylinders the exhaust valve was completely white and it had a large hole in it big enough for my pinky finger tip to fit..

Can you post a pic of this? Im just curious. I've never run across a burnt valve myself.

Too late for pics, I already dropped off the heads at the shop for valve job. He's getting me a set of piston rings at cost too (very nice).

I have never ran across burnt valves myself either. All I can tell you is one valve had a hole (obvious failure) and the other problem cylinders exhaust valve was distinctly different then a good cylinders exhaust valve.

what cylinder #?

Center cylinder on each head had burnt exhaust valves. I am guessing they are #3 and #4?

Yes, those would be 3 & 4. I didn't mean you necessarily needed new rings, just that you might want to inspect the grooves for carbon build up and clean them out if there is any. Just do one at a time to prevent location mix ups. The rod caps need to stay with the same rod and the same direction on the rod.

Machine shop just called and said both heads are cracked (scrap). I am going to pick them up tomorrow.

Any advice to find a set of good used heads cheap? It's a series II 3800SC. Can I use non SC heads on it or do i have to find SC heads?

Give Andrew a call. https://www.fiero.nl/forum/Forum4/HTML/056346.html

Are all series II 3800 heads the same? Are SC heads different then non SC heads?

Sort of... Same casting, Valves, Springs ect.

But the N/A (non supercharged) heads have no holes drilled in them for injectors. If you can drill and mill N/A Heads, you'll have SC heads. As far as I know, All Series 2 (and 3?) heads are the same, only that SC heads have holes for injectors.