Not a Super Charger Problem!

[1970 GS]

Last week I wrote to the Forum with what I though was a Super Charger problem. Have a knocking noise from the top of the block on the on my 2000 3.8 Super Charger Grandprix. I just wanted to know if someone could help. I thought that I can eliminate the SC if I remove the belt. And sure enough, the noise was still there. Removed the both valve covers to see if all was working properly. That checked out to be OK. All valves and rocker arms are moving well. Just prior to this we had the computer checked and found that there was a code 304 (cylinder 4 misfire). Checked the coil pack for cylinder #4, but that seem to be OK. We switched two coil packs and didn't seem to be different. At this point I was getting inpatient and finally did a compression check on that cylinder. We got absolutely nothing for compression. Put some oil in the cylinder and nothing changed. So obviously that cylinder is not firing. What do you think that I can check before I tear into this. Here is what I think.
1) Bad/cracked valve or not seating?
2) Piston or piston ring problems (but why the knocking noise)?
3) Cracked head or head gasket (but no antifreeze leaking, yet there was some smoke from the tailpipes reported by the owner right after the loss of power and Check Engine Light went on)?
Not sure what to do next other than pulling off the intake and rear head! Please any suggestions or something else I may have missed.
Thank you.

[tblake]

cylinder leakdown test would be the next diagnostic step. Unfortunatly the average joe shadetree mechanic doesnt have a leakdown tester nor a air compressor.

[tblake]

i myself might remove the spark plug in number 4 and insert maybe a small screwdriver and feel for the piston moving up and down as ou turn the motor over by hand.

Do you have any modificatons to the motor? (smaller pulley?)

[BNaylor]

Maybe check the compression tester to make sure it is working properly since from what you said you only tested compression on cylinder #4. Try it on #2 or #6 just to be sure.

[GTP Version 2.0]

If it is a knocking and rattling noise then take off the supercharger snout. If the supercharger coupler is beat-up (as they often are due to the use of poor materials) buy a new one from ZZP. I replaced my supercharger tensioner and belt, before I found this problem.

[richtazz]

GTP Version 2.0, as the OP mentioned in the first post, he removed the S/C belt and the noise was still there so we can eliminate the S/C as a cause. It sounds like you have a broken piston or ring(s) in #4, and the knock is due to the piston rattling around loose in the cylinder bore.

[GTPpower]

What did your spark plug look like when you pulled it out? Was it all smashed up?

[1970 GS]

The plug was not mashed just wet from not firing. The piston is traveling up/down, I had checked that before I did the compression test. I did check cylinder #6's compression and seemed fine. I think I will do a complete compression test to see if there are any other potential problems. I was told that if I replace this motor, to make sure I get only a 2000 motor. This is because of the way the original engine mounts. I was also told by a GM mechanic that GM had a recall on those SC 3800/3.8 engines for valve problems. He said if the either the piston or the valve(s) are bad for that cylinder, my best bet is to just replace that block all together. A SC puts a lot of exta torque on the engine. Not sure what would rebuilding this block cost or how to trust here in southern Nevada.
Thanks again...........

[GTPpower]

If you do need a new engine, don't rebuild, just get a low mileage engine from Ed Morad ([email protected]) or a local junk yard. It's much cheaper, will last you forever!


I have never heard of there being a recall on these motors because of valve problems. Also, you can put in any other series II or series III. All the mounts are the same, there will be some different wiring/vacuum routing though depending on the year.

This is a strange problem you have. If you would have chipped a piston, or shattered it, your plug would not be intact, unless it got really lucky.

It is possible that there is something wrong with the valves. The only other thing I can think of is a head gasket, but you would probably have a coolant leak if that went bad. Did you check the oil to make sure there is no coolant in it?

[tblake]

Have you got access to an air compressor? is your compression guage the kind that has a sort of air connect fitting on one half and the other half screws into the cylinder head? If you have the expensive type and an air compressor you can take the back valve cover off and loosen the rocker arms for the valves on the bad cylinder. This just closes both valves 100% and allows you to pump air into the cylinder with your compression guage and air compressor. Then listen for where the air is coming out.... Intake, exhaust, dipstick tube, radiator.

[1970 GS]

When I did the compression test, I did what you suggested. I brought the piston to TDC, then forced air into that cylinder. The air seemed to come from the rear/back valve cover, but it's hard to tell. Even if the valve(s) are bad from what I've been hearing, I should just replace the block. Just found a used motor in my local bone-yard yesterday in a 2000 Regal. Waiting on if he wants to sell it.

[tblake]

What you want for the supercharger off the top of yours? couldnt hurt to have a spair laying around.

[tblake]

you did remove the little valve core from the compression tester before attempting the leakdown test didnt you?

And your aware that the piston comes to TDC for the compression stroke and for the exhaust stroke? Like I said, If I were you I would loosen both rocker arms on the defective cylinder just to be 100% posative both valves are closed. If done this way you dont even have to worry about getting the piston TDC.

[blazeracer]

I had this same thing happen. Car ran fine, had a little knock, nothing on cylinder 2 in my case. Pulled the head and it was a broken piston, the result of running regular unleaded under sustained boost. It broke a piece of the top off letting the compression escape from behind the ring. I have the right tools so I pulled the motor and fixed it. One used piston from Morad's a gasket set and some new bearings had me back running in a week. I've put 20,000 on it since then with no mechanical problems.. Plenty of other crap, but no mechanical.