[Kelly_H]

Hey guys,

Jane's running great now with the new EFI, but seems to be determined to kill me through CO2 poisoning. I'm trying to figure out what the source of my exhaust leak is.

Symptoms:
-Excessively strong exhaust smell in car while driving (goes away somewhat with higher speeds, but is very strong at speeds around 45mph or less)
-Smells more up in the front than the rear of the interior
-With the car idling, the engine bay has no exhaust smell anywhere I can find
-Driver's side fender at the cowl is especially strong smelling
-Passenger side tailpipe smells more of exhaust at the rear than driver side tailpipe (driver side tailpipe has no odor at all that I can discern)

What it's NOT:
-Header leak (replaced gaskets today, no change)
-Cowl to hood seal (replaced a few months ago, in great shape)

Things to take note of:
-O2 sensor is installed in driver's side header. Bung is welded in so leak seems unlikely?
-Driver's side header has been removed recently, but passenger side has not
-No previous issues prior to bringing her home from the shop

So, with all of those symptoms, what would you guys think that the exhaust smell is coming from? My best guess is the driver side exhaust pipe flange (where header and exhaust pipe meet) - maybe all the exhaust is leaking out there, which is why it doesn't smell at the rear? I'd just like to know if you think it could be anything else, as Advance Auto apparently does not carry the gaskets I need (3-bolt) so I'd have to special order it from... somewhere :shrug: Up until now, I was not aware that 3-bolt is an unusual pattern for exhaust flanges!

Thanks for the help guys

 

[sdmustangrider]

It's an old trick and I still use it from time to time. But, you need to be pretty careful. What I usually do is stick my hand about 3-4 inches away from all the welds and places bolted on and feel if any warm air is being put out. Sometimes you can see if it's black in the area as well. If you do this, just be careful. I think I have exhaust leaks myself.

 

[HenryJ]

An exhaust leak at the header collector is pretty common. You can get a spray bottle of soapy water and spray it around the collector to see if it bubbles up from a leak. You only have a couple of minutes to try this when you first start her up, before things start getting to hot.
If that quick test doesn't find the leak then I would just take it to a local muffler shop... they should put it on the rack and check for leaks at no cost.

 

[bryancobb]

I have a mechanic friend that finds leaks with pressurized smoke but I can't remember for the life of me, what he uses. I remember it was butt-simple.

Snap-On has a "smoke machine" to do this with that pressurizes whatever you're working on to 1psi but it is expensive.

 

[Mikegh]

Have a friend hold their hand over the tail pipe with a rag and listen under the car for the leak.

 

[Dave DeAre]

Start the car in the dark, shine a flashlight sequentially over the entire exhaust system. A leak should be easily seen.

If no leaks are detected, I would suspect the rear hatch weatherstrip/seal. I believe your car was disassembled for paint; the weatherstrip/seal may be leaking. Hatch/trunk seal leaks are common on Mustangs. I struggled exhaust smell inside my car until I found that the PO had installed the trunk seal incorrectly. NPD has the correct US made weatherstrip. Search this forum for instructions/correct adhesive. It worked for me.

 

[jtfx6552]

Start the car in the dark, shine a flashlight sequentially over the entire exhaust system. A leak should be easily seen.

If no leaks are detected, I would suspect the rear hatch weatherstrip/seal. I believe your car was disassembled for paint; the weatherstrip/seal may be leaking. Hatch/trunk seal leaks are common on Mustangs. I struggled exhaust smell inside my car until I found that the PO had installed the trunk seal incorrectly. NPD has the correct US made weatherstrip. Search this forum for instructions/correct adhesive. It worked for me.

I was going to say something similar. I've had many an exhaust leak, but they always resulted in annoying sounds. They didn't seem to cause any additional exhaust smell in the car.

A leak in a "low pressure" area in the back of the car will pull the exhaust right into the car. I'd check the rear deck lid seal, and the rear window seal.

 

[Kelly_H]

Hmm, you guys might be onto something! I have no decklid weatherstripping installed whatsoever right now Still is kind of strange though that the trunk does not smell like gas, and neither does the rear of the interior...

 

[tx65coupe]

I'm with the others about the trunk seal.

 

[My427stang]

Do you have a PCV valve on the motor after the EFI install? Could be blow by coming out of the breathers as well

Also, do you have full exhaust including tailpipes?

 

[Kelly_H]

Yep, full exhaust and the PCV is installed. Tailpipes come out a couple of inches from beneath the tail panel.

 

[Roddster]

Mustangs are notorious for sucking exhaust in through any hole in the rear of the car. And, while you are going forward in the car, there is a suction that starts at the cowl, this is why you smell it in the car.

So, put on the trunk gasket, make sure the hole for the license plate wire is sealed. Make sure the holes for the bumper and nerf bars are sealed

 

[Woodchuck]

Yep, I think you hit the nail on the head. It is usually PARTICULARLY noxious with the window cracked open just a bit.

 

[Kelly_H]

Will do, thanks!

In the meantime, any ideas as to why one tailpipe smells like exhaust and the other doesn't?

 

[StrokerDude]

I've used the smoke-machine trick too several times over the years. A cheap(er) way is to find one of those smoke machines at the costume stores for dances/halloween. You put a solution in the machine with a little bit of water. I found a cracked header on a late-model V-6 Mustang one time using it.

 

[1-18-68]

Kelly,
regarding your question on one bank "smelling" like exhaust and the other not, I presume you mean it smells rich. This might possibly be caused by the rich side having a plug or wire that's not healthy or if the valves are adjusted too tight (I can't recall if you have mechanical or hydraulics) effectively that will increase the lift and duration of your cam lobes. It is pretty much anything that would cause incomplete combustion or an enrichment on that one bank.
This is also a way to tame a somewhat too agressive cam. By increasing a valve setting (mechanical lifters) by .007" I have helped two folks who by mistake put in cams that were far too hot for their street setup. These were not Mustangs but British sportscars. By increasing the gap, you have effectively reduced the lift and duration.

As far as finding an exhaust leak, when I was a 16 year old kid, an old timer in Vermont helped me by using a length of hose in his ear and the other end used as a crude stethescope. I still use that method to this day. He started doing it on Model Ts so there's a history. It works, try it.
best regards
Russ

 

[Greg'66 5.0]

A rich mixture definitely will affect the smell of the exhaust. The mixture on an EFI engine is directly adjusted based on what the oxygen sensor is sensing in the exhaust, so you might have a bad O2 sensor.

 

[Kelly_H]

I would agree with that, except that my EFI should send an equal amount of fuel to both sides (it's really more of a smart carb). So, one side should equal the other assuming that all other things are good.

Russ, thanks for the list of things to check. Plugs are new Autolites, but the wires are known to be cheapo from Walmart... wondering if they're the culprits. I wouldn't imagine it's the valves, since the problem did not exist prior to the EFI install and we haven't messed with the engine.

 

[slim]

Walmart plug wires? Shame shame shame!!! JKLMNOP!


Slim

 

[Kelly_H]

Hey, not mine, the PO's shame! Obviously, new wires are on the Christmas list this year