90 Comanche 4.0 fuel smell

[comanche32]

Ok guys even after sitting all night. When you walk up to the jeep all you can smell is fuel underneath. There are no wet spots on drive and no visible leaks that I can find. The only thing is when I put my nose to the catalytic convertor I smell gas. Any ideas what could be going on

[Pete M]

how rusty is the truck?  is you charcoal system intact?  how's your fuel economy looking?  4.0 or 2.5?

 

you should put some basic info on your truck in your signature.  

[comanche32]

It's a 4.0 and the truck Is starting to show its age with rust. The charcoal canister is intact. It's a completely stock truck my wife's great grandfather purchased new in 1990

[Pete M]

any evidence of fuel leaking out the fuel pump location?

[comanche32]

No I can't find any signs of a fuel leak. Just a catylitic converter that smells like gas

[comanche32]

I just got it going good running the first tank through. But I know it wasn't getting the best fuel mileage 

[Pete M]

does the exhaust itself smell of gas at all?

[comanche32]

I let it idle in the drive for awhile no fuel smell from exhaust. But I noticed when I put My tachometer on it. It fluctuates between 11and 1300 rpm. Then after driving the truck for awhile it jumps to 1600 rpm idling. If I shut the truck of and let it sit a bit It will idle at 1100 again. I have done all of cruisers renix tips. Nothing seems to help and after driving awhile I start getting a surge feeling at 45 to 55. This truck is a problem child that I can't seem to get figured out 

[Pete M]

tested all sensors?  tested for vacuum leaks?

[cruiser54]

Make sure your intake manifold bolts aren't loose. 

That truck isn't running correctly seeing the symptoms it has. 

[comanche32]

I have tested all sensors and checked for vacuum leaks. I replaced the the tps. I haven't checked the intake manifold bolts

[Ωhm]

Yank your spark plugs and see what story they have to tell.

[Pete M]

41 minutes ago, comanche32 said:

I have tested all sensors and checked for vacuum leaks. I replaced the the tps. I haven't checked the intake manifold bolts

 

which technique did you use for finding vacuum leaks?  I've found sometimes propane works better but other times carb cleaner works better. 

[comanche32]

Plugs wires cap rotor and tps are all new. I found that the front and rear upper intake bolts were finger tight. I tightened then and found a vacuum leak. My idle is back to normal again. Still a bad fuel smell after I drive it awhile. 

[cruiser54]

The hose from the throttle body to MAP?

[comanche32]

No I checked that one when I did all your renix tips. It was one on the back of the airbox lid. Still don't know where the fuel smell is coming from on the passenger side 

[cruiser54]

cannister is the only fuel related component on the passenger side. Those hoses go to crap. 

[comanche32]

Ok I will check the hoses on the canister

[comanche32]

I had time to take the jeep on a pretty long drive. The fuel smell is coming out of the exhaust I believe. I couldn't smell anything by the canister. And I noticed while driving there's a tick coming from the driver's side the engine. Almost like a spark knock sound. The more you get on the gas the louder the tick. I'm wondering of I have a intake gasket bad

[cruiser54]

Likely a cracked exhaust manifold. That would also be a cause of the gas smell.

[comanche32]

I looked the manifold over real good. I couldn't see any cracks. But I did find that the bottom rear bolt of the manifold is gone

[comanche32]

Cruiser could the missing intake bolt be causing all the trouble I'm having

[cruiser54]

spray carb cleaner around suspected area at idle and see what happens.

[rokinn]

If you don't in fact have a cracked exhaust manifold you most certainly have an issue with that rear lower bolt.  You could very likely have a gasket leak there causing an exhaust leak and said ticking.  If indeed the bolt is missing you're lucky.  Mine was broken off at the head.  Make sure that that is not the case, if so, you will need to pull the intake/exhaust manifold.  Also if you're lucky you may be able to extract it with an easy out.  You'll need a right angle drill adapter and a short cobalt bit to do the job. 

 

I was not so lucky.  I ended up pulling the head and having the bolt hole helicoiled after I had it completely buggered.  Take the head to a machine shop and have them pressure test it and if it is good then have it milled.  All in all I suppose the ever increasing immersion into the morass of a broken lower rear manifold bolt was good.  My head had to be taken down 13 thousandths to get it flat.  It also needed extensive cleaning of the hardened remains of having been immersed in the Le Brea tar pit for a decade or two.  Why is everything so dam hard?

 

I wish you luck!

[88towmanche]

On 11/25/2022 at 9:12 AM, comanche32 said:

Ok guys even after sitting all night. When you walk up to the jeep all you can smell is fuel underneath. There are no wet spots on drive and no visible leaks that I can find. The only thing is when I put my nose to the catalytic convertor I smell gas. Any ideas what could be going on

 

If you're smelling fuel with the truck sitting static overnight probably not manifold related.

 

Tank gasket leaking is my bet - mine leaks at the top 1/3 of the gasket - if I fill the tank it stinks like hell until it gets down to 3/4 tank.  

 

Been like that since day 1 - got the replacement gasket but every time I get under there to swap it out I find something else and get sidetracked - last time discovered a frayed ebrake cable and that turned into a bigger project than anticipated.