3.9 engine ?

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Bossed

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As some of you may remember, I've had trouble trying to diagnose a #3 cylinder misfire issue. I took it to the dealership to see if they could figure out what was going on. The technician did a compression check, checked the PCM, tried different coils, swapped injectors, all the electrical stuff checked good as well as the other things he checked. He said theres one more thing he can try, but he's starting to think it could be a valve spring or maybe a camshaft. I replaced the secondary timing chains and tensioners before the engine was installed in the car, when doing so I did'nt have any trouble. I was wondering if any of you had seen this before? Any help would be appreciated!

Bossed
 
Yes, before I swapped the tensioners and chains I rotated the engine so that I could see the flats on the camshafts, that way it would be easy to keep the cams in time. I know anything is possible, but I sure felt like the swap went without a hitch.

Bossed
 
I would tend to think that it would be more the spring than the cam.. But that is an educated guess with his diagnosis.. Good luck
 
Anyone had a broke valve spring, or bad cam lobe? Any 3.9 engine gurus have an opinion as to whats causing the misfire condition?
 
Bossed said:
Anyone had a broke valve spring, or bad cam lobe? Any 3.9 engine gurus have an opinion as to whats causing the misfire condition?
Click to expand...

I've heard of a single valve being bent when the tensioners fail or a chain jumps.
 
Bossed said:
Anyone had a broke valve spring, or bad cam lobe? Any 3.9 engine gurus have an opinion as to whats causing the misfire condition?
Click to expand...

I highly doubt a bad cam lobe..

joegr said:
I've heard of a single valve being bent when the tensioners fail or a chain jumps.
Click to expand...

I would agree with Joe.. Either broken spring or bent valve.. Probably the later.. You said they pressure tested the cylinder? I wonder what kind of pressure they got
 
joegr said:
I've heard of a single valve being bent when the tensioners fail or a chain jumps.
Click to expand...


Joe, when I replaced the tensioners they looked to be in great condition, motor supposedly has 60,000 miles on it. Before I took anything off I rotated the engine around to align the flats on the cams, I laid a steel rule across them and they were in line. After swapping chains and tensioners I checked the flats again to make sure they were aligned as before,then I rotated the engine by hand and everyting seemed good to go. In fact I remember looking at the sprocket and thinking it would be easy to tell if it was off a notch either way because the flats on the cams would not line up.

Bossed
 
Bossed said:
Joe, when I replaced the tensioners they looked to be in great condition, motor supposedly has 60,000 miles on it. Before I took anything off I rotated the engine around to align the flats on the cams, I laid a steel rule across them and they were in line. After swapping chains and tensioners I checked the flats again to make sure they were aligned as before,then I rotated the engine by hand and everyting seemed good to go. In fact I remember looking at the sprocket and thinking it would be easy to tell if it was off a notch either way because the flats on the cams would not line up.







You said they pressure tested the cylinder? I wonder what kind of pressure they got
Click to expand...

He did'nt give a number but said all cylinders looked good.

Bossed
 
Any special tools required to change the valve spring? Anyone done it on an LS with the motor in the car? Thanks

Brian
 
it could be done if you have a cyl. leakdown tester, just take off the oil cap and pressurize the cyl from an air compressor. But it you lose that air in there and drop the valve, off goes the head.
 
I finally got time to take the valve cover off the passenger side. I rotated the motor by hand, and the flats on the camshafts are in line, so it has'nt jumped time. I checked the valve lash clearance and they were in tolerance by factory specs. The cams looked fine, did'nt notice anything unusual about them. It seems unlikely to me that it would have a bent valve if the cams are in time. Please help!?:confused:
 
3.9 LS engine Misfiring due to oil soaked spark plug and boots.

I own a 2002 LS, bought it new for wife. It now has 112000 miles on it. The 3.9 engines has lots of problems with the valve cover gaskets, leaking oil into the spark plug wells, thereby shorting out because of being oil soaked. Today I removed the right front valve cover from the LS because the valve covers are leaking again for the third time. Manufacturers claim to have "a fix" for this problem. They are manufacturing the seals, from totally different materials and are colored blue, so they can be easily identified from the original black ones. I guess time will tell. The symptoms initially start with a spark plug misfiring, occasionally. You can feel car jerk pretty hard when it does misfire. It may run a week or longer and it will do it again. This sequence continues, until the spark plug gets so oil soaked, it will not fire at all. I have seen lots of people, posting about the same problems they are having with their LS engines. You may have discovered a fix for this particular problem by now, If not hope this helps somewhat. If I can help any further, just let me know. Good Luck with your LS. -Tnman
 
Tnman said:
I own a 2002 LS, bought it new for wife. It now has 112000 miles on it. The 3.9 engines has lots of problems with the valve cover gaskets, leaking oil into the spark plug wells, thereby shorting out because of being oil soaked. Today I removed the right front valve cover from the LS because the valve covers are leaking again for the third time. Manufacturers claim to have "a fix" for this problem. They are manufacturing the seals, from totally different materials and are colored blue, so they can be easily identified from the original black ones. I guess time will tell. The symptoms initially start with a spark plug misfiring, occasionally. You can feel car jerk pretty hard when it does misfire. It may run a week or longer and it will do it again. This sequence continues, until the spark plug gets so oil soaked, it will not fire at all. I have seen lots of people, posting about the same problems they are having with their LS engines. You may have discovered a fix for this particular problem by now, If not hope this helps somewhat. If I can help any further, just let me know. Good Luck with your LS. -Tnman
Click to expand...

Tnman,

Thanks for your help, very nice of you to try and offer some friendly advice. It's appreciated, and welcome to LVC.

Bossed
 
Well folks I finally found the culprit to the #3 cylinder misfire. After checking about everything I could think of, then having the dealership check the things I could'nt, I brought the car back home. I pulled the valve cover, everything checked good, so the only thing left that I had'nt done was a running compression check. That cylinder was down at idle and snap, about 30psi @ idle, and the snap only increased to about 60psi, while the others were around 65psi @ idle and the snap test averaged around 125. This told me something was restricting the intake air entering the cylinder. After much thinking, I remembered when I bought this engine, the throttle body was not on the engine, so I placed a towel in the hole to keep trash out. I never dreamed the mechanic would leave the towel in the intake?!! So after thinking about this "restriction" I pulled the throttle body off, shine a flashlight into the hole and I'll be DAMNNED theres a 2x1 ft. towel just dying to get out!!!!!!!:eek::eek::mad::mad::):):D:D UN:q:q:q:qINGBELIEVABLE

Bossed
 
So you're going to make the mechanic pay for your time and the dealership fees right? I sure as hell would try it. I mean he left a towel in there!
 
Im sorry Im not laughing (Ok a Lil) I feel the pain. But I have never heard of a story quite like that before! We need an archives to save this in lol.

Glad she is running!
 
Add this to the owner's manual thread:

"Causes for misfire:
1) leaky VCG, causing coil and plug failure
2) towel in intake"
 
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