Diagnose Stubborn Exhaust Leak

The massive fumes seem to be coming from underhood. In 2015, I had both exhaust manifolds replaced. This month, Ford dealer said that left side manifold bolts had backed out. The original tech who did the install said that the bolts were out 1/4 turn,and torqued them back in. I still have massive fumes. I sprayed Windex on the manifolds cold and saw negative results upon starting the engine. I did the same at the back of the manifold (EGR) with no evidence of any exhaust leak. I am having difficulty telling any tech to really chase down and solve the problem. The right side manifold is under the tinware for the hot air to the air cleaner,and the tech said it'd be extra work to get that off and check those bolts. I suppose that where the manifolds connect to the Y-pipe could be problematic as well. It is also noteworthy that there have been fumes previously,but the fumes have gotten
progressively worse,to the point where the car has to be yarded. I am at my wit's end here.

 

Here is the car: 400 V8 w/Motorcraft 2150 2V carb,single exhaust,recent new muffler,C6 trans.,2.75 Trac-Lok axle,etc.

 

Take a long hank of 3/4" heater hose, start and warm up the engine, then put one end of the hose to your ear, and hold the other end out and move it around the places where exhaust could escape, under the EGR spacer, the sides of the intake manifold center, the exhaust manifolds (and it's not hard to remove the TAC heat stove in most cases), and the exhaust pipe donuts. The likely leaks are the EGR plate, the manifold with the loose bolts and the exhaust pipe donuts. Sometimes, it's just a matter of loosening the pipe hardware (don't remove it) then resetting the position of the Y-pipe to get a better seal. Anyway, the hose will amplify the exhaust pulses when you get near the leak source.

 

Usually with an exhaust leak you will hear a ticking noise similar to a lifter tick. You'll also see some burnt or blackened area around the leak from the exhaust gasses escaping.

 

Rev the engine to around 3500 rpm and slowly pour 1/2 cup of Marvel Mystery oil into the carb. White smoke should come out of any leaks. Keep it revved until the exhaust at the rear clears.

 

Nothing audible from this leak. I did do the Marvel Mystery Oil test,and hoo boy,did the left side manifold to Y-pipe junction smoke! The shop I've been going to for years and that did the manifolds refused to look at it,so I am all done with them! Tomorrow early,I am spraying super penetrant on the nuts/bolts. The shop manual seems to say no donuts except for 460 PI,but still I wonder. I plugged up the little holes in the firewall and kept the windows up so the people in the car could breathe,although fumes do seep in waiting at a light. The cowl intake gets fresh air though,so Vent setting on panel,dash vents,blower on high,driver's window open briefly takes fumes out,then button up while in motion. Did I mention,the hot Mustang failed state insp.,so new tie rod end tomorrow,red sticker,can't drive it,so rock & hard place...Anyway, when the penetrant works,maybe I can tighten the pipe to the manifold on the wagon,and be happy again.

 

More delays,but that's life! I had to take the 'Stang to the Ford dealer for the $120 cheaper tie rod end & alignment and back to the shop that did the inspection for the no charge retest--all this while I was at work! So the big car is yarded. Still need to spray super penetrant,wait and attempt to turn those 2 nuts on the LH manifold studs,and hopefully tighten them. The '73 shop manual shows the 460 4V and PI engines getting steel or fiber donuts at the join,and all the other car lines get them,but no mention for the 400 CID full size wagon. Puzzling.
Then I have to fuss with the tune up again,engine idling really rough.

 

There definitely should be a gasket of some type in there. If it's blown out all the tightening in the world won't stop it from leaking. I did have a similar problem when I had a buddy do some work on a car for me. The flange bracket at the manifold managed to get cockeyed and didn't seat even though tight. Loosen off first to see if it's seated properly. I would use Pb blaster or a comparable. It actually dissolves rust as it penetrates.
As for the fumes themselves your engine must really be out of tune to be that bad. A full tuneup and checking your spark plugs would be in order. Plugs should be a nice paper bag colour. Lastly the gasket at the back of your hood or on the cowl that seals both to each other is to prevent the fumes from getting to your fresh air intake. Good luck

 

I'm assuming your exhaust is still 2-into-1, so here's a trick: loosen both sides, then use a floor jack with a wood block to lift the Y-pipe up to put the ends to the manifolds. I honestly cannot remember if the Cleveland and Midland manifolds had conical ends cast into them; but as soon as you loosen the Y-pipe, you should be able to see with a flashlight and mirror, or a flashlight and look through the wheel wells. If they do take donuts, make sure you get the pressed graphite ones (they appear silver), as they do not blow out and last a lot longer than the original Seventies versions.

 

I did get the car up on the ramps today and hit the nuts with PB Blaster. They are tight or frozen,but I did not twist brutally. So far I am only working on the left side where the leak is. I took pix on my old phone of the manifolds before the install. They do have the conical ends. So should the tech have put donuts in there when he replaced the manifolds? If that's the case,I'd think I have to do both sides with donuts. The Mystery Oil smoke only came out of the left side,however. As to the tune up question, I've done that many times,and I checked it today. Timing at 12B,spark plugs the right color,etc. No fumes can get in the cowl,but can through the firewall,because little holes for cables,wires,etc. The only thing with the state of tune of this engine is that the vacuum gauge pointer vibrates while in the normal range. I've checked repeatedly for vacuum leaks and nothing.

 

If the swings are minor, look for internal vacuum leaks. Pull and plug the PCV from its grommet, then fire up and warm up the car. Once at temperature, spray carb cleaner into the PCV grommet hole, and into the crankcase breather hose hole on the opposite side. If a valve guide or an intake runner are leaking inside, you'll pick it up.

 

I still don't know for sure--donuts or no donuts? There is no mention of them on the bill for the manifold install,but the manifold gaskets are shown...or could that gasket line item be a set including donuts? I may have to undo both sides and drop the Y-pipe,but the right side didn't show leakage. So,anyway,conical manifold outlet means utilize donuts? Or???

 

Although it's not impossible, I've just never heard of exhaust joints not having a gasket at the manifold. You will soon find out if you drop both sides and there isn't one on either side. If it's a swedged fit I could see it not needing a gasket.

 

Some are a cast fit when the joint is cast into the manifold. If they are, you can help the seal by coating each cone with anti-seize compound, then attaching the Y-pipe. But, there are some Fords that use a double-conical donut, some that use a single that has an inner steel liner that goes in and holds inside the manifold.