2006 SS (LSJ) won't start; thinking bent valves?
 

Hi all, I'm new here. Just unloaded a 2006 SS into the garage earlier today, that I picked up yesterday. Long story short, it's gonna be used as a donor for a DF Goblin kit car, but my intention is to get it running and drive the Cobalt for now, and likely until Fall.

So I traded for the car, it was a great deal, and I knew it wasn't running. According to the previous owner, it died on him one day and he couldn't get it back started. Got it home, looked, and saw that the timing chain was loose. Suspected the timing chain tensioner broke, so he had all the timing and balance shaft components replaced. Also replaced the water pump, fresh oil, and new plugs, while he was at it. After this, the car would crank, but wouldn't start. He did a compression test and tells me that he got 180, 180, 145, and 150. Frankly, 180 seems quite high, but maybe that's normal on these LSJ's. Regardless, something is going on. But, that's where I am today.

Previous owner believes it has a couple bent valves, and that's why the compress is lower on 2 cylinders and it won't fire. I suspect, and could be wrong, that maybe one of the cams are off time by a link, which might explain the timing.

Anyway, thoughts? Where should I go from here? I assume a leak down test might be a good start, but I don't have the tool. I mean, only like $30 from Amazon, and I can start there if that's the best thing to do. Or should I pull the timing cover and inspect that? Previous owner (and his buddy) are confident the timing is right, but I can't confirm that obviously. So buy leak down tool and test? Pull the timing cover and check timing? Or should I just go ahead and pull the head?

If I pull the head, I want to go ahead and beef it up a bit. Performance valves, heavier springs. Besides there, is there a benefit to swapping cams? What about port and polish? my intention is to keep this engine supercharged, but I would like to get around 300 WHP from it. I have no experience tuning, but that's something I plan to learn with this car.

Any advice is appreciate!

I appreciate the super quick replies!

So yes, piston rings could be bad. Engine has 134k miles, and I'm not sure how it was drive for those miles. I mean, it's a clear car so I feel it was taken care of, but never know. To be honest, I've not tried starting the car myself (battery is charging up right now and I will try it later), but I also assumed it should have started if the timing was just a tad off. I have a scanner and will be scanning it for any codes this evening as well.

I can test for spark, but I don't think that's the issue. I've ordered a leak down tool...the more I thought about it, the more I decided I should have one in the garage anyway. Also ordered a compression tester, same reason.

I guess from here I probably need to attempt starting, check for codes, and go from there.

Thanks for confirming the compression numbers. Also good to hear the stock valves are plenty capable. I've read that 82# springs are recommended for stage 3 kits, so I was thinking I should just replace the valves too. Trying to avoid having to pull the head more than once if that's what I'm gonna have to do.

Thanks!

You're right I need to check fuel pressure. I got the battery charged enough to start, but it died a few seconds later. Also dies sooner if I hit the throttle.

Video if curious:
https://youtu.be/DD9X2QcmM0A

I don't hear the fuel pump, assuming it should be audible. Haven't check the fuel pump relay, but plan to once I get a chance to head back to the garage.
Do these Cobalt's have inertia switches? Just want to eliminate that if so.

Thanks!

EDIT: Also, P0135 was the only code. With the exhaust on this car, that may be the cause of that.

Tested fuel pressure earlier, came back with 50psi...almost exactly on the money. I do in fact he's the fuel pump, so no concerns there. Battery is also fully charged, but still acting the same way after several attempts. Cranks, starts, and dies 2-3 seconds later. Sounds smooth while it's running, though though.

Compression and leakdown tests will happen tomorrow, assuming Amazon delivers my new testers.

Regarding the P0135 code, I've discovered there is no o2 sensor installed, so that code makes sense.

So any more ideas what I can check? I talked to the previous owner who said he replaced the Crank sensor twice. Honestly not sure why, but he said something about the dealer having to do a relearn after replacing the crank sensor? Does this make sense at all?

Thanks!

according to gm service manuals you have to do a case relearn whenever you do anything that could affect the crank or cam sensor (anything with cams, timing components, crank, sensors, etc). most dont bother as its not really an issue, and the only time it must be done is when your replacing the ecm/pcm. the relearn involves the car running at operating temp, you put into the relearn mode and rev the engine slowly from idle to redline. but the key thing here is the engine has to be running with no codes to do it. this isnt your issue, 100% sure on that.

so is it like you start the car, it runs perfect for 2-3 seconds and it dies in a manner similar to if you turned the key off? if so, that could be the anti theft system. is there a light on the dash that looks like a lock?

Good to know; thanks for confirming.

So yes, when I crank the car, it turns 3-4 times and starts as expected. Runs great for 2-3 seconds, doesn't sound sloppy or like it's missing, and then it just dies just like if you turned the car off. I've seen the lock icon once or twice, but it's not been on since I first tried starting it (when the battery was really weak/dead). Now that the battery is charged, I've tried starting it 6-7 times, no lock icon, and it's consistently doing the exact same thing. Only code is P0135, and that's for the missing o2 sensor. I wouldn't think that could cause this, unless the ECU sees the sensor is missing and decides to kill the engine? That even make sense? I'm not just not sure else it could be at this point, and I don't want to start tearing into it without really knowing why. Compression and leakdown test to come later today, and hopefully I can get a decent video of the behavior.

It wouldn't hurt to try a security relearn. as long as you have somewhere warm to do it lol, takes a while. i don't remember the exact procedure off the top of my head but it should be easy to find.

I found THIS post about doing a security relearn, and while it seems simple enough, I don't quite think that's the issue here. This assumes I have the security lock dash light coming on which prevents then engine from starting at all, even though mine does start. Thoughts?

So I attempted the security/theft relearn procedure, but I don't think it helped anything. Interestingly, now I can't get the car to start even though I did several times yesterday. It's noticeably colder today, but the car is in the garage. It also threw a P0336 DTC, for the crank sensor (which was recently replaced by the previous owner). Now I'm wondering if timing is off, or if something is wrong with the crank sensor connector. It's like hitting a moving target. :(

If the timing is off enough, the car won't start at all. I think it's a safety feature from blowing up the engine but I could be wrong on that secondary fact.

So I did a compression test yesterday, and got 133,146,154,146. Completely different from what the previous owner claims he got.

I'm also wondering if he removed the cam position sensor housing and didn't re-time it properly, even though he said he didn't replace the cam position sensor. I'm kinda getting an itch and start tearing into it this weekend, though. Pull the valve cover, timing cover, cam position sensor housing, crank sensor, and retime everything, clean connectors, pull and clean the throttle body, run through all the fuses/relays, etc.

Any benefit to doing a leakdown test at this point? I mean, clearly something is going on with cylinder 1, hopefully just the head gasket, or maybe timing is off, but I would the car should still start and run with those kinda of numbers. There will be a time I pull the head for some upgrades, but I would like to avoid that at this time and just get the car running as is. I want to see ~300WHP with this engine before it goes in a kit car I hope to get started on later this year.

Thoughts? Other things to check for?

Thanks!

Those are low numbers for a compression test. They should but 180+. I would try the compression test again with a bit of oil in the cylinder and see if you don't have another problem.

So literally put a little bit of oil in through the spark plug hole and run the compression tests again? What exactly will this tell me? If air is getting past the rings, valves, or head gasket, wouldn't that be better found with a leak down test?

Yep, just checking o-rings on the pistons. If no change, then at least the walls/pistons/o-rings are still good.

Ah, didn't realize I could rule out piston/rings that easily. Will definitely give that a go tomorrow, as well as a leakdown test.

Thanks!

So today I pulled the throttle body, gave it a good cleaning, and put in some new NGK spark plugs. For the first time, I got it to start and run! However, it acts like it maybe is starving for air?

Here's a video of the first start up today:
https://youtu.be/8ly8vXjBFLE

After it died, I started it back up and this is what it sounds like under the hood:
https://youtu.be/ZlmZRjomHk8

And a third video after the previous one:
https://youtu.be/TYyToe29uI0

The tach kinda jumped around some, and I have no idea what to make of that. If I hit the throttle, it sounds fine until I let off...like it starves for air and sputters out and dies. Idle sounds smooth, so I don't think I have a timing problem.

I did pull codes while it was first running, and this is what I got:
https://cimg8.ibsrv.net/gimg/www.cob...ea6f7f866a.png


I cleared the codes, and they never came back. The crank sensor has already been replaced twice by the ordvipre owner, so I don't there is a problem with the crank sensor itself.

Thoughts?

Thanks!

After the previous videos, I couldn't get the car to start back up last night. Just cranks.

But today, went out to the garage on my lunch break and tried something. I pulled the coil and plug from cylinder #1, threw in a little bit of oil, put plug and coil back and was able to get it to start back up. This makes me think, along with previous compression test results, that I have a blown head gasket or piston rings have gone bad.

Thoughts? How difficult is it to replace piston rings without pulling the engine?

That's how my valves got bent
 

My timing chain got slack broke the guilders valves hit the pistons and bent to shit. Obviously engine didn't wanna start. Time for a salvaged engine.
Found a low km one with transmission and supercharger attached for way less then the cost of repairs to my damaged engine.

Just to post an update, I'm up and running with this car. I ended up pulling the head and sending it off for a little love (valve job, resurfaced, pressure tested, etc) and they found no bent valve, but did find some slight damaged valve seats. They fixed that.
While the head was off, I replaced piston rings, gave the pistons a good cleaning, replaced rod bearings (stock bearings looked fine...but replacements are cheap and I was in there), and got it all back together with a few upgrades. TVS 1320 w/ 2.9" pulley installed, Siemens 80# injectors, dual pass endplate, ZZP shorty headers, retimed, and a tank of E85. Just dialing in the tune right now, but otherwise she's feeling strong.

@deviantgoblin on IG, if anyone is interested.