patmcg

I'm hoping someone out there can help with this.

Here are the details; 2007 Impala LT 3.9L 128000 miles.

The car broke-down and would not restart so we had it towed to our house. I read the codes immediately, I don’t remember the codes but they referred to the throttle peddle position, & throttle position sensors. I replaced both and was able to start the car but it was smoking making some nasty mechanical noises so I shut it down immediately. I went ahead and checked the codes and came up with ‘multiple misfires’. I removed the sparkplugs and found #1 plug to be damaged so I proceeded to remove the cylinder head for bank #1 and found the intake valve seat in cylinder #1 had dropped out and was destroyed. It damaged the head & piston and debris found it’s way into cyl #3 & #5, damaging those pistons also.

I talked to 2 different Chevy dealer service managers and they said it was a rare mechanic failure and had nothing to do with any other problem. So I pulled the engine and and completely tore it down, replaced the damaged parts , reassembled & reinstalled in the car. It started no problem and ran fine, I took it out for a test drive, about 2mi. and it seemed down on power but was running quiet & smooth. waited about 30 minutes and went for a 2nd test and went about 50 yards and started to hear something, turned around and it got worse to the point that I shut it down and coasted in to the driveway. Thinking for sure that I forgot to tighten something I started to check things. To get to the point I found that the intake valve seat in cylinder #1 had dropped out of the new head and damaged the new piston. Yes the same thing in the same cylinder!!

I told one of the Chevy dealer service managers and he is convinced that it’s just a horrible coincidence. I have also spoken to several other mechanics, one dealer tech from another brand, and they find it hard to believe it’s not caused by something else and gave me some things to check buy are unfamiliar with the motor to give a definitive answer.

I’m ready to reassemble for the 2nd time and I need to know if anything else could cause the problem or is it a part failure.

Thanks for any help with this. We love our Impala and want it back!
Pat

tech2

I've heard of the intake tuning valve bushing going into cyl #1 but never dropping a valve seat.


to have 2 drop would make me go right into an engine swap. Maybe there is a engine rebuilder here who could offer an explanation.

patmcg

I thought of that but how do I know the problem isn't with the ECM or wiring harness, or some other system that I didn't change with the motor swap? Also a reman motor is between $3,000 & $4,000 and is only warranted if it's professionally installed, another $1500. adding up to more then the car is worth.

tech2

with today's diagnostics that the modules run, the likely hood of this being caused by an electronic problem is unlikely. Its a mechanical failure imo. A used motor from a reliable wrecker is under $1000 and they warranty it regardless of who installs it.

sledge.impy

You are not the only one with dropped valve seats on 3.9L motors. And another guy had it happen 2 times.

Look here:

2006 Monte carlo 3.9L dropped valve seat - Topix


-This is probably some what under reported as most people don't tear into their engines

patmcg

If it was purely mechanical and a fantastic coincidence that the seat in the new head was bad in the same cylinder, then i could get a replacement for the defective head at no cost and one piston & ring set, bolts & gaskets for under $100. What sense would it make to buy a used motor?

tech2

if you can explain how a electronic problem can cause a mechanical failure with not one dtc setting; i'd love to hear it.
a manufacturing problem seems more likely to me.
do what you think is best. What's gonna be different this time?

patmcg

The only way it could be a mechanical problem is a improperly installed seat. Installing a new head will solve the problem assuming the seats in the new head where installed properly.


If there was a problem with the #1 injector causing to much fuel to the point that it cools the valve & seat causing it to expand slower then the aluminum head then the seat could become loose and drop. What could cause the injector problem? I don't know. Possibly mechanical, injector stuck open or slow to close completely? I would thing a gas puddle and the smell of raw gas would be noticeable. Besides the chances that injector #1 was returned to #1 spot after reassemble is like 24/1. Is there a way to test the injectors? Can a wiring problem cause the injector to misfire? A short or crossed wire would stay on that cylinder no matter how the injectors where shuffled. Could the ECM cause the problem? can it be tested off the car?


It's still better to install a 3rd head and trash that, or not , then swap the motor out and trash a 2nd motor because the real problem was never found and fixed.


Thanks for your input and please don't take offence if I seem to have an attitude you must understand I've been working on this car since July.


Pat

tech2

[QUOTE=patmcg;287091]The only way it could be a mechanical problem is a improperly installed seat. Installing a new head will solve the problem assuming the seats in the new head where installed properly.


...unless you had a bad production run of valve seats or machining of the head, which is what I was offering up. corvette heads are right now being sent out for head work. Mind you, they are not dropping valves on the 2nd test drive.


I've pulled heads off motors that had injectors stuck open. the cars ran like crap, fuel trim codes would be set, misfire dtc and the cylinder would be washed out by all the fuel. I've even seen raw fuel in the exhaust.


I hope you figure it out.

sledge.impy

2006 Impala blown engine - Engine Troubleshooting