?? For Tom Renzo (the GM guru)

Topic: ?? For Tom Renzo (the GM guru) (Read 1875 times) previous topic - next topic

?? For Tom Renzo (the GM guru)

July 05, 2012, 10:28:20 AM

Tom, I know that since you work alot on GM cars that you would be the one to ask.
I'm working on the office girls 07 Impala. It has a 3.9 and according to a numbskull who had just worked on it, it has an extra head bolt per cylinder.
A little history on the car first. Some time before this girls mom passed away, the car had been running warm and shutting itself off, (I was told it's a self-preservation mode) and the same fore-mentioned idiot had disconnected the ECT sensor so that it would stay running. needless to say it ran very very rich, the fans never came on, or the temp gauge never moved. The mother only drove it from her house to the hospital for her kemo and back. After she passed, the girl in the office had that guy repair what was wrong. He replaced the rear head and both head-gaskets. It ran ok for about 30 miles then when the girl drove here to work, it died. I ran a MATCO Determinator scanner on it and it just said "Engine Misses Detected", anyway, she had it towed back to the guys place and after 2 weeks all he could come up with was that the ECU had died. Mind you, it would start up but run real rough and made a horrible noise. She had it towed back here to where we work and I've been trouble shooting it. First thing I did was a compression check. Upon pulling all the plugs, he had reused the old ones one of which the center ceramic piece had broken and was resting on the center electrode, hmmmmmm. Next when I did the actual compression check, all were at between 175 - 180 with the exception of the hole from where the broke plug came from. It had absolutely NO compression. Triple checked myself to ensure that I had the tester screwed in all the way. Still NO COMPRESSION,
so my questions are,
(1) I read that the rocker arm bolts are torque to yield. Is this right?
(2) Do you think that it might have damaged the valves and/or the piston ?? Thanks Any help/ thoughts would be appreciated.

John

I've yet to pull the upper intake and valve cover off. I'm waiting for the older sister to contact me as she is the executor of the estate before proceeding.

?? For Tom Renzo (the GM guru)

Reply #1 – July 06, 2012, 07:10:44 PM

Well, I am not Tom. Nor am I a GM guru. But, I believe the answers to your questions are (1) Yes and (2) Yes. With no compression on that cylinder and visible damage to the spark plug, I would expect damage to piston and or valve.

?? For Tom Renzo (the GM guru)

Reply #2 – July 07, 2012, 10:38:04 AM

John, since you have determined that cylinder has a problem and there is damage to the plug. I would remove the valve cover and take the rocker arms off and perform a cylinder leak down test. By removing the rocker arms you are closing the valves, install the test gauge and then fill the cylinder with air, if the cylinder will not hold air, listen for the air escaping from the exhaust, intake, crank case or the cooling system. That will tell you what part of the engine has damage. If air is escaping from the exhaust system then the exhaust valve has a problem, if its the intake valve then listen for air at the throttle body and so on. If im reading this right and the rear cylinder head and both head gaskets were replaced, it might have warped or even cracked the other head. Good luck and keep us informed, hope this helps you let us know what you find with the tests.

?? For Tom Renzo (the GM guru)

Reply #3 – July 07, 2012, 01:22:07 PM

That engine family (GM 60-degree V6) has different length pushrods for intake & exhaust and is an interference engine. If he mixed up a pair when he replaced the head it is very likely a valve is bent, or a rocker is broken, or a pushrod is bent, or there's a hole in a piston, or all of the above. There's also the possibility that he dropped something (such as a nut or bolt) into the engine or intake and it got past a valve and beat things around in there causing damage just like what I've mentioned. The fact that it drove OK for 30 miles points in this direction.

Can you post a pic of that plug?

?? For Tom Renzo (the GM guru)

Reply #4 – July 07, 2012, 02:24:16 PM

Ya, I can post it Mon night.

?? For Tom Renzo (the GM guru)

Reply #5 – July 07, 2012, 08:37:51 PM

I have also seen the nut/bolt problem before, I would also like too see the plug.

?? For Tom Renzo (the GM guru)

Reply #6 – July 09, 2012, 04:34:49 PM

Ok, here is a pic of the plug. As you can cen, the grounding electrode is fine but that the ceramic insulator has broken deep in the plug and slid down. While cranking the engine over for the compression test in the dead hole. There wasn't any noise to be heard, just as if the tester wasn't in there at all.
Thanks for all the suggestions guys

?? For Tom Renzo (the GM guru)

Reply #7 – July 09, 2012, 04:56:58 PM

Ok, that doesn't look like a plug that was damaged by a foreign object in the cylinder, it looks more like the plug itself broke.

Try squirting a small amount of 5W30 into the cylinder and then run a compression check on it. If compression returns with oil in there the cylinder walls probably washed down from the dead plug not burning the fuel that was injected. If this is the case you can probably get away with a new plug. If compression doesn't come back you've got a valvetrain issue, blown head gasket, or a hole in a piston

?? For Tom Renzo (the GM guru)

Reply #8 – July 10, 2012, 06:05:00 AM

that is strange! I have never seen a plug do that before. This 3900 engine has "Variable Valve Timing" or "Displacement on Demand". This may relate to your problem somehow. I also suggest pulling the valve cover off and seeing what other damage is going on with that cylinder; stuck valve, mangled pushrod, jumped rocker arm, busted valve spring(s) etc.

?? For Tom Renzo (the GM guru)

Reply #9 – July 10, 2012, 07:17:02 AM

Would have been very easy to accidentally mix the pushrods on one hole, only one of the 2 valves involved would bend, and the pushrod would bend, too. That's how my first encounter with a gm 60 degree v6 went way back when. I keep the 3 bent pushrods in my toolbox to remind me to slow down and pay attention. Pull the valve cover on the affected head, pull the rockers, and then pull and inspect the pushrods. If 2 have been swapped, the longer one will be bent and you'll have to pull the head to have at least the one valve replace and the seat inspected.

?? For Tom Renzo (the GM guru)

Reply #10 – July 10, 2012, 10:22:25 PM

OK here is what happens when things are not assembled correctly. With this said it most likely is not a mixed up Push rod. Normally when you do that it is an instantaneous issue if mixed up. But depending on dynamic stacking it may have a mixed up push rod. But with no compression in the cylinder a leak down test is necessary to determine the valve that is most likely BENT. Or a tight guide is my thinking. I think the guide was to tight and the valve seized in it. And the valve hit the piston I have seen this many times in the past. A swapped push rod would have been almost immediate. Guide clearance is critical on these engines and they do have seazing issues if not assembled with the right clearance. The plug does not look like mechanically damaged. But without seeing it in person it is a tuf call. Pull the valve cover and eyeball the retainers after removing the rockers. You will see one that is lower than the others if the giuide and the stem seized.

Typical mixed up rod

?? For Tom Renzo (the GM guru)

Reply #11 – July 11, 2012, 01:41:46 PM

Thanks Tom.
I found that the exhaust valve spring has come undone. The retainer is sitting at the bottom of head and I can't seem to find the keepers. The rocker arm is still in place. Everything is on hold for now due to some conflicts with the brother-in-law, the guy who first worked on it and the sisters who own the car. I didn't get everything completely tore down as I was told to stop. But I was far enough to lift the valve cover and look inside.
Also, taking another (closer) look at the plug, on the other side of what was pictured, was a small some-what shiny mark on the very edge where something may have come into contact with it.

?? For Tom Renzo (the GM guru)

Reply #12 – July 11, 2012, 03:42:26 PM

That would explain it. The keepers might not have been installed correctly and the retainer came out. The keepers are most likely in the pan. If you continue with the repairs you might be able to pull the head and install a new valve and lap it in. Install new keepers and put it back together. The BAD ecm was never an issue and it never crossed my mind. You have to pull the head and fix it properly. Good luck Tom

If you get to finish the job you can drain the oil and poke a magnet in the drain hole and you might be able to retrieve the keepers. Either way the keepers in the pan are a NON ISSUE.

?? For Tom Renzo (the GM guru)

Reply #13 – July 11, 2012, 04:29:44 PM

Thanks alot Tom, and all who have answered in this. It doesn't look like I'll be fixing this.