Desperate help/ only vehicle

[Don S]

2007 Tahoe 5.3 engine is perfect and so quiet you can’t hear it. Oil sending unit leaking oil so I decided to change it today. Valve cover drivers side leaking so pull it off and laid T shirt over the head to make more room to change sending unit. It was very easy job. Started up, oil pressure came up to 50 but heard a ticking so shut it off. When I hit the key to restart I heard a loud smack. Since I had coil packs unhooked on drivers side could timing of gotten off or what? Totally baffled by what this sound was. I haven’t dared to hit the key again. Makes no sense it could be running perfect and changed oil sending unit and now some major knock happened unless it’s computer timing off because I unhooked coil packs? Thanks for help.

 

[OR VietVet]

Sounds like you may have plugged the coil packs in out of order. Or you have something loose under the valve cover or something fell in there that you did not see. I would pull the valve cover and look.

Supply pics when you do and pics of the coils plugged in now as they sit.

 

[rdezs]

Agreed, most likely something got left under the valve cover.

I would think it's pretty difficult to connect the coils out of order.... They're pretty much lined up on the harness where they need to be, I would think if you got one plugged in out of order another one would be unable to be plugged in?

 

[Don S]

Sounds like you may have plugged the coil packs in out of order. Or you have something loose under the valve cover or something fell in there that you did not see. I would pull the valve cover and look.

Supply pics when you do and pics of the coils plugged in now as they sit.

You can’t mess up plug arrangement, the cords are very short that go to each one.

 

[Don S]

Agreed, most likely something got left under the valve cover.

I would think it's pretty difficult to connect the coils out of order.... They're pretty much lined up on the harness where they need to be, I would think if you got one plugged in out of order another one would be unable to be plugged in?

Removed cover again. Nothing inside. I’m more careful than that. I also had a t shirt covering the rockers the whole time so no dirt would get in there. Somehow it lost oil pressure. Can the screen I replaced be put in wrong and be blocking off an oil passage but still read at the gauge but oil not get to the lifters?

 

[rdezs]

Wondering if the screen had caught some debris, that may have dropped into the oil galley when removed. (And then sent it on its' way to your lifters?) I can't see installing the screen wrong, it just drops in...

 

[mikez71]

Somehow it lost oil pressure.

You mean before changing your sensor?

And you are at 300k+ miles?
I wonder if something else broke coincidentally, like your timing jumping teeth due to worn tensioner?

Haven't tried bumping it again?
'Smack' wasn't your loose coil pack plug terminals getting tapped by cranking motor over?

 

[strutaeng]

That's weird.

Mechanically jumping time is almost impossible. If that happens, you have much bigger problems. Think bent pushrods, piston to valve smacking, catastrophic failure...can't see how that happened by simply describing what you did...

Out of abundance of caution, I would remove all the spark plugs, and try spinning the engine over. If that's good, get a mechanical pressure guage and hook it up and fire up the engine. With a helper, kill the engine immediately if you don't see any oil pressure...

Hopefully it's nothing major.

 

[Don S]

You mean before changing your sensor?

And you are at 300k+ miles?
I wonder if something else broke coincidentally, like your timing jumping teeth due to worn tensioner?

Haven't tried bumping it again?
'Smack' wasn't your loose coil pack plug terminals getting tapped by cranking motor over?

Ran like a dream until I shut it off to change oil sending unit. I have valve covers off now and plugs out, going to cycle motor through by hand. Just absolutely totally weird.

 

[Don S]

That's weird.

Mechanically jumping time is almost impossible. If that happens, you have much bigger problems. Think bent pushrods, piston to valve smacking, catastrophic failure...can't see how that happened by simply describing what you did...

Out of abundance of caution, I would remove all the spark plugs, and try spinning the engine over. If that's good, get a mechanical pressure guage and hook it up and fire up the engine. With a helper, kill the engine immediately if you don't see any oil pressure...

Hopefully it's nothing major.

Valve covers off, one more plug to get out number 8 so I can turn it over by hand. This is absolutely goofy. It ran so perfect and just simply changed the oil sending unit then this random freak thing that makes no sense. I used a bolt jack to remove old screen. No way anything could have went down the tall stand the oil sending unit mounts on top of. I’m lost, my brain is tired on this one.

 

[OR VietVet]

You can turn it over with #8 plug in it.

 

[Don S]

Ran like a dream until I shut it off to change oil sending unit. I have valve covers off now and plugs out, going to cycle motor through by hand. Just absolutely totally weird.

No interference at all when cycle motor through by hand. Smooth as can be and all I hear is oil inside the block gurgling around. All the rockers are rocking as the should too. No dead ones.

 

[Don S]

You can turn it over with #8 plug in it.

Just turned the motor over by hand about 20 revolutions and it feels perfect. No noises except for oil gurgling sounds. Smooth as butter. All rockers moving and no dead ones. All the more info to make me confused what the loud smack was when I hit the key. But didn’t let it start up. It was ticking til I tuned it off and loud but shut it off real quick because it’s never made any sound. It’s always super quiet. I think I’m going to take screen out of oil sending unit even though supposedly they can’t be out in wrong. Maybe somehow blocking oil passage to get to lifters. I checked the old one with the new one before I installed it and it was exactly the same.

 

[Chris2144]

Well if all rockers are moving and nothing appears out of place I would start it and run it.
Verify you have good oil pressure.
If the sound is still there then you can tray to isolate which cylinder is the culprit.

 

[Don S]

That's weird.

Mechanically jumping time is almost impossible. If that happens, you have much bigger problems. Think bent pushrods, piston to valve smacking, catastrophic failure...can't see how that happened by simply describing what you did...

Out of abundance of caution, I would remove all the spark plugs, and try spinning the engine over. If that's good, get a mechanical pressure guage and hook it up and fire up the engine. With a helper, kill the engine immediately if you don't see any oil pressure...

Hopefully it's nothing major.

Removed valve covers both sides, pulled plugs. Rotated engine by hand about 20 revolutions. No noise except for oil gurgling in block. Smooth as butter. All rockers are moving full rocking motion, no dead ones.
I’m going to remove screen I guess. I compared it to old one and they were the same but since it started ticking start up and I shut it down then hit the key and heard a loud smack, it makes me think it’s not getting oil to lifters. Maybe the screen is blocking a passage way. Engine is very very clean inside.

 

[Don S]

Well if all rockers are moving and nothing appears out of place I would start it and run it.
Verify you have good oil pressure.
If the sound is still there then you can tray to isolate which cylinder is the culprit.

Just ordered new plugs and wires but I think I’m going to remove the screen on the sensor in case it’s blocking an oil passage somehow. The ticking that started after I replaced the sending unit made me shut it off but pressure went up to 50. Then I hit the key and heard the loud smack so
Never tried to crank it again with that bad of a noise. Makes me think lifters are not getting oil due to screen?

 

[Don S]

Valve covers off, one more plug to get out number 8 so I can turn it over by hand. This is absolutely goofy. It ran so perfect and just simply changed the oil sending unit then this random freak thing that makes no sense. I used a bolt jack to remove old screen. No way anything could have went down the tall stand the oil sending unit mounts on top of. I’m lost, my brain is tired on this one.

 

[MrMonte]

What is the condition of the flexplate(flywheel) & starter?

Since engine rotation is fine I would put back together & try starting it. The sound could be a mismatch between flexplate & starter with maybe a gear??

 

[mikez71]

Some times it's a total coincidence, completely unrelated. Some times..
Fingers crossed it's something minor..

Agree on checking starter/flexplate..
I don't imagine no oil to top end causing a smack and not starting...

Could the ticking been the starter not retracting and starter gear got wedged at engine stop? (or next crank)

IF your starter is original, you'll want a new one. Mine sounded like a case with loose bits at 200k..
(still worked, but once I felt it in my hand, I was unwilling to re-install it..)

 

[Don S]

What is the condition of the flexplate(flywheel) & starter?

Since engine rotation is fine I would put back together & try starting it. The sound could be a mismatch between flexplate & starter with maybe a gear??

I just tried to crank it over with key and I hear fuel and smell it but it didn’t crank over any. Is it possible that since I have everything unhooked like airflow tube, ignition packs, etc that it wont crank or would that matter?