Head gaskets or timing chain?

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golfhack5

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So as soon as I fix one problem another arises. I hadn't started my 02 LS V8 in about a week but when I did it fired right up and ran VERY rough. I turned it off and have not been able to get it to start since.

I checked fuel - approx 40psi at the rail

I checked spark - good to go

Compression test

Cylinder 4 - 140psi Cylinder 8 - 70psi
Cylinder 3 - 150psi Cylinder 7 - 130psi
Cylinder 2 - 125psi Cylinder 6 - 45psi
Cylinder 1 - 52psi Cylinder 5 - 30psi

Since there is decent compression many of the cylinders is it safe to assume the issue is not the timing chains? (Please say yes lol)

So what do you guys think? Timing chains or head gaskets? Am I missing something obvious?

I suppose I would need be able to see if the timing chains are broken while I'm in the process of replacing head gaskets but not sure?

TIA
 
After some more research I found a few different opinions on this question.

Some say that good compression in some cylinders but not in others cannot be caused by a timing chain issue.

Others disagree and say the lack of compression is due to the fact the timing chain has broken and the pistons hit the valves.

Any truth to either of these? Also IF the timing chain is in fact broken wouldn't there be an obvious noise while cranking??

Sorry for rambling just thinking out loud...
 
golfhack5 said:
After some more research I found a few different opinions on this question.

Some say that good compression in some cylinders but not in others cannot be caused by a timing chain issue.

Others disagree and say the lack of compression is due to the fact the timing chain has broken and the pistons hit the valves.

Any truth to either of these? Also IF the timing chain is in fact broken wouldn't there be an obvious noise while cranking??

Sorry for rambling just thinking out loud...
Click to expand...

It's easy to just take off the valve covers and take a look at the chains. Did it sound like something was broke when the car last started? My timing chain broke upon start up so it's possible. You just need to find out if it is a main or secondary chain that is broken.
 
Problems with the timing chain tensioners are far more common than blown head gaskets on the V8.
Either way, you seem to have problems with both banks at once.
 
SlickLS said:
It's easy to just take off the valve covers and take a look at the chains. Did it sound like something was broke when the car last started? My timing chain broke upon start up so it's possible. You just need to find out if it is a main or secondary chain that is broken.
Click to expand...

Yup you're right I'll pop the valve covers off tomorrow night and see what's under there...

And no nothing out of the ordinary when it was running last OR when I was cranking it to check the compression.

Thanks for the response :)
 
Thanks for the advice joegr. Will I be able to tell if the tensioners are broken after I take off the valve covers? Or would the timing cover have to come off?
 
btw: you can only check fuel pressure with the car running - and it should read roughly 30psi at the rail - since it needs to be 40psi at the tip of the injector (with 18-22hg of vacuum). if it's not running - you have not got the right vacuum.
 
Quik you're absolutely right. I guess I was more referring to the fact that the motor is getting fuel. And I know there is plenty because the plugs smell strongly of fuel.
 
no worries. once you have the valve covers off - you'll be able to inspect the guides.
 
When my secondary timing chain was broken, you couldn't tell by the motor turning over while testing for compression. Best way to know for sure is to take the valve covers off. Good luck!! So the car doesn't run and made a loud noise the last time it was running?
 
When my LS started running like crap I immediately figured timing chain, so I did a compression test and got ~150 psi in every cylinder, so it couldn't be the chain, right? WRONG! I tried every test for the better part of a week to track down the mysterious condition, finally in frustration I pulled the valve cover bolts and lo and behold a broken secondary chain. In addition to breaking the chain it also caused bank 2 to jump time.

The moral is simple, pull the valve covers, turn the engine over manually so you have the flats on the cam aligned and see what's lined up and (hopefully not) broken.

Good luck!
 
SlickLS said:
When my secondary timing chain was broken, you couldn't tell by the motor turning over while testing for compression. Best way to know for sure is to take the valve covers off. Good luck!! So the car doesn't run and made a loud noise the last time it was running?
Click to expand...

Correct does not run (which could be partly due to the plugs being flooded)

And nope no unordinary noises whatsoever which has me really confused.

Hauen said:
When my LS started running like crap I immediately figured timing chain, so I did a compression test and got ~150 psi in every cylinder, so it couldn't be the chain, right? WRONG! I tried every test for the better part of a week to track down the mysterious condition, finally in frustration I pulled the valve cover bolts and lo and behold a broken secondary chain. In addition to breaking the chain it also caused bank 2 to jump time.

The moral is simple, pull the valve covers, turn the engine over manually so you have the flats on the cam aligned and see what's lined up and (hopefully not) broken.

Good luck!
Click to expand...

Thanks for the response! So based on your situation the compression wasn't affected by the secondary chain being broken. My situation would then lead me to believe that at bare minimum the primary chain is broken :mad:

But I suppose it's all speculation until I can see the chains. I should be able to get at least the passenger side valve cover pulled off tomorrow night and I'll report back.
 
Chances of a primary chain break are slim. First, you have some kind of compression which indicates at least the intake valves are opening and closing. Second, you don't have odd metallicy thunky noises emanating underhood which would indicate interference of some kind. The low compression in 1,5,6&8 is troubling, since it's not limited to a particular bank or adjacent cylinders it's most likely not jumped time. Perhaps you have burned valves. If you don't find anything wrong with the chains try putting a vacuum gauge on it next (if it will start) and/or get your cooling system leak tested to see if you're head gaskets are shot (though having both fail simultaneously points to a larger underlying problem like detonation)
Sorry for the long-winded post, I try to be reasonably thorough.
 
Pulled both valve covers off last night (F the drivers side one) and the chains look good. I'm going to put it back together and get some new plugs to see if it will start since the old ones are way fouled out. If I can get it running I'll put a vacuum gauge on it and try to test the cooling system.

Thanks again for the replies.
 
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