Fuel smell from engine bay
 

Posting this in its own separate thread instead of the "What have you done to your Mustang today" one to make it a little easier for the next guy to find. Long story short, I started smelling gas inside the car, but only when stopped in traffic or at a light. As soon as I started moving again, it dissipated. I started sniffing around in the engine bay and after several minutes and several brain cells, I narrowed it down to the front of the driver's side fuel rail. Based on some searches and some tips, I suspected the fuel injector O-rings. The car's 13 years old and there's a lot more heat in the engine bay since I did long tube headers in 2015, so seemed reasonable. Ordered 2 replacement sets (AC Delco) from Rock Auto.
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Installing wasn't too bad, just have to take off a few 8mm bolts that hold the fuel rails down, disconnect the pigtail for the fuel pressure sensor, all the injectors (duh), a couple vent hoses, and the fuel line. The fuel line will require a quick disconnect tool to do. Have lots of rags handy. I will say, you can do it with the strut tower brace in place, but it was always kind of in the way. Next time I'll remove it. American Muscle has a great video on how to do it, here:


They're working on a S550, but the basics are the same for the S197.

The original O-rings were starting to break down for sure. I wiped each of the new O-rings with silicone spray to let them slip on easier. I don't think that was enough. Everything smelled OK at first, but after the first couple lights, the smell was back. I went sniffing in the engine bay and couldn't narrow it down any further than the front driver's side fuel rail area again. I started suspecting the O-ring around the fuel pressure sensor since I pulled it off and later re-used it. And when I pulled it back off to check, I had sure mashed it putting it back in. No one sells the o-ring by itself, you need to buy a new fuel pressure sensor. My dealer wanted $160 for one (:wtf:), but I found the same one on RockAuto for $35. Both are identical Bosche's. Ordered up. To try to prove it was the o-ring on the FPS, I bagged it.

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I let the engine run for a while, but still smelled gas. Just in case the bag was leaking, I cut it open expecting to smell stronger fumes, but got nothing. Guess that's not my culprit.


I started searching online for some sort of electronic sniffer, and I found this:


It's not explicitly for gasoline, but works for heavier than air gasses, and it does work. I took off the gas cap and the thing went crazy. So, I saved some brain cells and used the sniffer:


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I probed around and it showed no reading from the FPS. No reading on the rear of the engine. Strongest readings from the area around the spark plugs - which scared me at first, but remember that fuel vapors are heavier than air, so they'll settle there. I blew into the area to dissipate the fumes and started probing. Strongest reading came from the front driver's fuel injector. But I also got a weaker reading from the next one back and some weaker readings on the passenger side. I think I need to re-seat them. Reading some threads on another forum, I think I need to use something like vasoline to really lube them up <jokes go here> so they don't pinch or bind. And I'll definitely be using this combustible gas detector. Definitely worth the $30!

When replacing the injector O rings.Lubed with motor oil will do the job and you can feel when they seat just slowly work the injector back into the fuel rail or intake. You will know if the O ring seats it just sort of pops into place and the injector will turn freely side to side.

Interesting idea, I'm sure the o rings are nitrile if they're supposed to stand up to gas, so they should theoretically stand up to motor oil just fine. I gave it a shot, and they did seat MUCH easier than last time. I think I damaged the rings (maybe putting them in last time w/o enough lube) because more of them are leaking now. I picked up a new set from the dealer the other day, I'll try motor oil on those when I install.

Sub'd. This is interesting. @Cavero you always have the really good threads! :)

Thanks man, I don't post much anymore but when I do I try to make it worth a read.

Verdict today -- inconclusive. I put in the new Motorcraft o-rings and used oil to lubricate them (MUCH easier), and everything seemed to pop into place nice. Driving around I got the faintest wiff of gas when stopped. I'm thinking its residual spill. It doesn't smell like fresh gas, if you know what I mean. The yellow sniff-o-meter is definitely reading lower from the front driver's side of the engine, but it's reading a lot higher on the passenger side - conveniently where the fuel rails leaked all over when I was pulling them off. I'm going to try to drive it around a few days to see if it gets better or stays the same. If it stays the same, I have a new idea. I'll use a spray bottle of soapy water to see if I can spot anything. I don't know about that though...the intake pulls a vacuum, so it might suck the water in. :dunno:

seriously? You'd figure the engine would run rough if the plugs weren't sealing. I did just change the plugs a few weeks ago but the meter is showing higher readings in a different area now.

Still, definitely going check my plugs again

I would have thought so too. I even went as far as putting a stethoscope on the boot of that cylinder and nothing sounded out of the ordinary. It wasn't until I set the gas detector on a very high sensitivity that I was able to narrow it down to that plug.

I'm assuming you have a GT. The way the plugs seal is a silly design. Most plugs seal with a washer just below the threads, but these plugs seal with with a tapered edge farther down. After this whole odyssey I did some research and this is a fairly common problem on F150s after plug changes.

Best advice on these Deep Well spark plugs is to clean out the" well area" with compressed air BEFORE removing the plugs. This way the new plugs will properly seat in a clean well area. As a side note I always apply a bit of never seize on the lead spark plug threads.

I always do, I'm paranoid about crap falling down into the cylinders. I use nickel anti-seize on the threads and the barrel. Although the stuff I put on the barrel usually burns off.


Yep GT. Interesting, this is my 4th set of plugs on this car (100k mi, but I change early and often to keep them from seizing) and I've never had that problem, until maybe now. I've been dropping the sensitivity on the smell-o-matic because I was trying to get it to ignore all the background fumes. I didn't torque them to spec a couple weeks ago, I tightened by feel. And the 2nd plug on the driver's side (#6) I'd not tightened down as much as the others because it felt weird when I was tightening it down, like I was starting to strip the threads :eek:. That was the original area the leak was coming from. I went back tonight and pulled all the plugs and re-torqued to spec. Even that #6 plug that felt weird. I checked the threads and it didn't look like it was stripping or cross threading at all. It felt better tightening down too, I think it was just my socket extensions binding the first time.

Also went back and re-seated the fuel rail on the passenger side because I was getting high readings between #3 and #4 cylinders. I had loosened the hose clamp on the fuel rail cross tube to move the rail around the other day, so I re-tightened that down extra.

We'll see how the test drive goes on all this.

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Still smelling it...WTH? :wtf:

Cavero, Just a thought you may want to change your cabin air filter. Good luck.

According to Ford TSB 08-7-6, they recommend only applying nickel anti-seize on the ground electrode shields (barrels) Also, IIRC, using anti-seize on the plug threads can result in over torquing beyond the required 25 ft lbs.

If you use Motorcraft high-temp nickel anti-seize as recommended by Ford? the compound will not burn off!

I used Permatex version. I bought a bottle of the stuff 10 years ago and I still have probably a quarter of the bottle left! I've used on everything from spark plugs to brake jobs and it just keeps going and going.

I took the car to my speed shop the other day, all they smelled was "normal engine smell", but I'm still smelling it building inside the cabin when I'm stopped. I made an appt with the stealership for Monday morning. They charge a lot $$$ but their troubleshooting is pretty decent. If they can't figure it out, well I guess I'm going to have to do a Coyote swap :devil:

Hope this doesn't come across a dumb question, but when was the last time you changed your cabin air filter? If you haven't changed the filter in quite a while, that could possibly be your reason for the excessive engine smells you're getting inside the cabin. If you know for certain it's the Permatex you're smelling? I really wouldn't be very concerned over it, as any access that would make its way into the combustion chamber will just end up burning off anyhow. But If it's something other than Permatex you're smelling? Hopefully, the stealership will find that it's nothing serious through their diagnostic troubleshooting equipment :yup:

yeah I still haven't had the chance to change it yet, but if the filter were saturated, why would the smell go away when I'm moving?

You're right and I totally agree, If the filter were saturated? the smell would still be there when moving as well. Only other scenario I could possibly think of, other than a small piece of O ring which you already brought up dropping inside the head, is check your entire exhaust system for possible leaks :dunno:

:doh: :doh: :doh:

Dealer said multiple spark plugs were loose and the compression was bypassing the plug. I torqued them down to 25 ft lbs, but I'm guessing the torque wrench is a piece of **** in that range. It's rated for 10-75 ft lbs so I figured that'd be better than my 10-120 or 250 ft-lb wrenches. Normally I tighten the plugs by feel (as hard as I can go without feeling I'm going to strip it out) but with the weirdness I felt on that 2nd plug, I decided to use the torque wrench. Lesson learned.

I got stuck in traffic in the way home and sure enough no more gas smell

Surprised that didn't cause her to throw a code, but glad you figured it out!

I would tend to agree that something is definitely wrong with the torque wrench in the 25 ft-lbs range, being that several of your spark plugs were loose. I'm also very surprised that you didn't encounter any malfunction codes with the compression bypassing the spark plugs from being loose. You would also think a torque wrench that's rated for 10-75 ft lbs should be more than sufficient enough to handle 25 ft-lbs torque with no problem? Anyhow glad the dealer was able to troubleshoot and correct your issues and found that nothing fell into your heads/combustion chamber as you had originally suspected.