Need help finding an exhaust leak

TLDR/cliffs notes version: 02 S10 4cyl 2wd, put new head on, and have a horrid exhaust leak. Any suggestions? Already retorqued/retightened all bolts/studs/nuts.

Long version:

Need the hives help with this one. Working on SWMBO 02 4cyl S10, 2 weeks ago the head gasket let go. So I tore it down, looked over the head, cleaned it the best I could by hand, and decided if I’m going to be cursed with this slow as hell thing it needed some help. After a visual inspection, I decided to do some minor porting, have the head decked and then do a valve job as it has 200k on it.

So I spent a couple of weekend nights playing with the porting, just smoothing everything out, not trying to hog everything out due to the fact this thing is an old pushrod 4 cyl that sounds like it’s going to die if you rev it out to 5k rpm. After getting that done, my old man bailed on running it to the machine shop for me, so took a morning off work and ran it the 30 min down the road to the machine shop. Wanted them to pressure test it, and just do the cut job. I told them I would do the valve job on it. 3 hours later I get a call at work, there’s a crack in one of the water jackets. Little bitty thing, I told the guy I was skeptical, but go ahead and order the reman head as he quoted me a price within 20$ of Rock auto. He was cool enough to tell me to call when I was on my way to pick up the head, and he would throw it back into the pressure tester and show me the crack on the old head. Well it was cracked, and I left with my shiny new UNPORTED aluminum head. CRAP… Oh well. I’m not messing with it again, at this point I just want our car back, as I’ve been stuck with a family owned minivan that my sister has been using with her 3 kids prior to us, and it smells like it. No matter how much Febreze I have been spraying it down with every night.

Since getting the new head, we’ve probably averaged 95+ degree’s a day, humidity as high as 96%. Seriously Saturday morning @ 7am it was 86 out with 96% humidity. WtBERK! The sun’s not even over the tree’s yet! Add to it a vet bill that was more than some cars I’ve owned for our oldest pup, last weekend SUCKED! So I’ve been working on this thing into the wee hours of the morning for the last 4 out of 5 days (we took last night off). Got it 95% of the way back together tonight, decided that before I went through the trouble of refilling the cooling system and putting the fan back on the front of the motor I would test fire it. So we put the serpentine belt back on, set the intake tract in place, turn the key on, and bleed the air out of the fuel rail. Turn the key off and on a few more times to make sure the fuel system is primed, and with a silent prayer twisted it to the start position.

BOOM! She fires right up on the first shot. But now the exhaust leak that we thought we were fixing at the collector is now one loud SOB of a leak. CRAP! After doing a couple of up downs to check if it was the collector or the manifold to head connection we shut it down. Retorque all the manifold bolts, (after re-removing the AC and power steering pump) 1 of them was a little loose. Not badly though. Try again, nothing has changed. Crap, retighten the collector bolts, and still no change. I give up. Calling it a night. Any suggestions on things to try?

Drizzle some M/O in the intake, enough to make smoke. Engine running of course.

Might help pinpoint the location of the leak.

If you can get your hands in there, and you likely cannot get to all of it, one of the easiest ways to find a leak is to just move your hand around the joints and feel for the puff of exhaust.

Another option (likely more practical) is to take a piece of tubing (fuel line etc) and put it to your ear. Move the other end around until you find the loudest point. Plugging the other ear will help.

Agree with the feel around. If you're careful, you can do it without burning yourself. You can also zero in on which cylinder by disconnecting one plug at a time. The disconnected plug that shuts up the noise is the cylinder that is leaking.

Don't just reef down on fasteners in hopes of fixing it. That rarely works and can break things, which leads to tears.

You sorta describe a header being on there. Headers are notorious for being imperfectly made and all but inherently leaking. Especially where they attempt to mate against the head. Some have semi-successfully ground down the face of the header. Others (me included) have had semi-success by slathering copper gasket-goo on both faces of the manifold gasket.

One other thought. If these are headers and you're not used to headers, they are a lot louder than a stock manifold.

In reply to iceracer:

Might try that one.

In reply to aircooled:

I've tried that, no obvious leaks or puffs that I can find. Might try the tubing trick this evening.

In reply to foxtrapper:

Nah, it's the stock cast iron manifold. I wire wheeled 13 years of crud and rust off of it while it was out. Didn't see any cracks in it, gave it a shot of high temp header paint, and dropped a new O2 sensor in while it was out. Also chased every thread on the collector. Knew it was going to be a royal PITA to get it in much less squared and cinched up. Looks like this:

Also the spark plug idea might work. but my money is on the collector. I hated doing them when I worked as a mechanic, but at least it's not a damn doughnut gasket.

Heres an idea that popped in my head, tape a shop vac to the tail pipe and maybe tape over the intake and turn on the vac, you will hear the massive leak cause the engine is off. Otherwise the method ive always used is taken from ed china, hold the engine fan still while the engine runs and hold a piece of tissue, feater, whatever light around the exhaust and you will see it flutter from the leak

In reply to chiodos:

I like it!

Well... I found it. I'll post pics tomorrow while I'm in town. Shop vac did it, just set to blow vs suck. While you could hear the massive leaks on suction. It was hard to locate. Set on blow it was almost instantly able to be found. Plus side of no fear of instantly burning yourself with the vac.

Wherever it is, this will probably fix it. I don't really buy exhaust gaskets anymore (unless they alter some critical dimension), just use ultra copper.

chiodos wrote: Heres an idea that popped in my head, tape a shop vac to the tail pipe and maybe tape over the intake and turn on the vac, you will hear the massive leak cause the engine is off.

Clever! And obviously effective, as the OP has stated it worked.

Cudo's to you!!!

I'm not sure the copper stuff would have fixed this one. Though if the gasket the parts store has "ordered" for me is the same thing as the one I was sent from Rockauto. I might give it a go. Personally if I have to look under the hood again to take something apart in the next year on this truck I'm going to be highly pissed.

Here's what mine looks like on the manifold itself. I didn't even think about the crossover tubes when I posted the above picture yesterday.

I wonder why it leaked?

Oops, yeah, that would do it, never seen one like that before. That said, you could put that together with no gasket, just a thin coat of high temp RTV on the manifold flange, and it would hold up. Stuff is magic, I've even used it on diesel exhaust manifolds. Though the old gasket pictured looks like a steel shim and those are generally reusable.

Yeah I'm thinking that's what is going to happen. The local advance hasn't called yet, but the "parts will be here before noon". I busted my rear with this thing getting all the mating surfaces clean. I would hate to have to goop it up now.

Did you check to see if the manifold was warped? Also if memory serves me those have a very specific torque pattern.

I also seem to remember that those are a SOB to get sealed with the rest of the exhaust system attached.