Any help with a bad exhaust smell problem

[PatrickGMC70]

Hey guys. I'm pretty new to this truck, and older cars in general, so I was hoping to get some help here. I'm pretty frustrated with this truck at the moment, but I'm trying to keep my cool.

The symptom is that whenever I'm near this truck when it's running, even for a short time, I reek of exhaust. It gets in your hair, on your clothes, and even gets to your eyes after a bit. It's really intolerable.

I don't know exactly what the problem(s) is/are, but I suspect that my carb is way too rich. I paid to get it rebuilt, but I think they didn't do such a great job. More on that in a bit.

I think the second problem is that I may have an exhaust leak. I haven't seen any visible exhaust smoke, but there is carbon on the manifold. Here's a pic:



Even though there's a lot of carbon, I can't see any visible cracks.

I took it to a local exhaust shop (Meineke) and they told me that there is a crack in the manifold and heat riser. I said that I couldn't see a crack, and they said that the carbon indicates a leak somewhere. They said I have to replace the manifold and heat riser (plus gasket and studs). [I should add that while I am a bit suspicious of their explanation, I'm very reluctant to call anyone a liar, when I know so little myself. I should also say that they were very courteous to me.] They said I can bring in my own parts and they'll put them on for me, but it's 2.5-3 hours of labor per side, which equals about 5-600 bucks (plus parts).

I really don't want to mess with these manifolds because I don't know what I'm doing, and I definitely don't want to mess with a torch or worse, drilling out a broken stud. Actually, I really don't want to replace them at all, but I absolutely have to get rid of this smell because the truck is useless to me now.

As for the carb, I'm really lost. I suppose I can try replacing jets and rods, but well, I don't know what else. I feel like I'm just going to keep throwing money at this thing, but never solving the problem. I guess I'm just fed up and I'm really looking for some guidance here before I just run this thing over a cliff.


P.S. I tried not to make this post too long, but I certainly provide more detail if needed.

P.P.S. The truck is a 1970 GMC 350/3spd with a 1975 Quadrajet (from the casting #s anyway).

[swamp rat]

Well if you reek of exhaust just by driving the truck and your eyes are burning then i'd say you have to have a leak somewhere, manifold or maybe in the exhaust pipe under the cab but i'd lean toward the manifolds. if ya lift the hood most manifold leaks sound almost like a ticking noise and you'd see some black colored build up at the leak, sometimes the leak may be on the underside of the exhaust manifold too. about the only way to find the leak is to fire the truck up and listen and feel around with your fingers while the engine is still cold. but keep in mind sometimes the leak won't occur until the truck fully warms up as heat makes metal expand.

Bottom line here is if your not comfortable doing something then someone else will have to be hired. Did you try going to a different place for another opinion? that may help ya rest easy, eventually you need to trust someone.

[Stocker]

With such a bad odor, you may be right about running too rich... look for any hint of black exhaust smoke as well as black sooty buildup inside the tailpipe. Could the choke possibly be stuck, partially closed?

As to the exhaust leak, I agree with swamp rat -- listen for a ticking sound, and it will be best to feel for hot gases escaping when you first start a cold engine.

[PatrickGMC70]

Thanks for the advice guys. I'll check around the manifold tomorrow to see if I can feel a leak anywhere. If I get the manifolds swapped out, does 2 1/2 hr per side seem reasonable (including replacing the studs)? I know these guys have to make money, I just want to make sure I'm not getting ripped off.

I think if I have them replace the manifolds, I'm going to have them do both sides, even though the driver side is the only one with the carbon on it. It looks like LMC and most of the other online places have the manifolds for about 150 a piece, but I might see if I can get something locally for a little less. I've read that the Dorman manifolds aren't too bad.

As for the carb, the choke is working okay. I think it's running rich because of the smell, plus a little hesitation. The plugs are new, and because of the odor, I haven't driven it enough to see if they're fouled. I think the guys that rebuilt it weren't the greatest, plus with the age, I'm not sure if it has the stock jets and rods in it, so that might also be the cause. I know that if the float isn't right, it might flood out, but an incorrect float wouldn't cause it to run rich, would it?

Thanks again for the suggetions. I'll post up with what I find.

[rsavage]

You can get a set of aftermarket manifolds for under a hundred bucks or a used set from one of the board members. You have 2 wheel drive manifolds and there are a lot out there. 2 1/2 hours per side may or may not be too much time. The bolts are rusty and often twist off, at least that has happened to me on two different occasions and I use a lot of good penetrant over a period of days prior to removal. If one or more break off in the heads, it becomes a more expensive job labor wise. If your manifold is cracked you should be able to hear it as noted above - almost like a lifter tick. Does your firewall have a bunch of holes in it where rubber plugs have been removed? Brake rod boot still whole? If you have holes the exhaust smell is going to draft into the cab. Carb running too rich will also cause some fumes but you should be seeing some black smoke out the tail pipes and it wouldn't be idling too well. The wires for #'s 1 and 3 cylinders look like they will burn through against the manifold in short order - probably the same on the passenger side. Good luck getting it sorted out. If you can't work on it yourself, it will cost you some money, but less than work on a new vehicle.

[sporty1200xlc]

I use about a 3 foot piece of hose. Garden or old heater hose to try and listen for a engine noise when its running. Hold it to your ear and move it around to you find the noise. Really helps narrow it down.

[Zoomin]

A rich carb will smell like gas, not exhaust. I would guess you may be burning oil somewhere. Is there evidence of a leak? Also, do you have functioning pcv valves?

Last, there are a bunch of holes in the firewall. Make sure they are all plugged. Good luck!
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[geezer#99]

Originally Posted by sporty1200xlc

I use about a 3 foot piece of hose. Garden or old heater hose to try and listen for a engine noise when its running. Hold it to your ear and move it around to you find the noise. Really helps narrow it down.

I too use a makeshift stethoscope. I use an old broomstick handle. That way you can put one end on anything and not have a burned 'scope.
And you can hear inside the motor too.
Just watch out for that fan though!!!

[68 IRON]

As for the smell, PCV, air filter, stuck choke, closed/ stuck heat riser. Every one of these has to function properly to vent and "breath" the engine. Check and replace as needed. Maybe even check your plugs to see if they are fouled from carbon (running rich) or oil. Timing could also be a factor. I'm just attacking the smell first because it shouldn't leave a lasting impression by close quarters with your vehicle. Our 69 had a terrible trashy sound to it when we brought it home. The heatriser was stuck partially closed and its gasket was gone....but you couldn't smell any exhaust in the cab a lot of noise but no smell. So check your vents timing and carb settings first. And ya any oil leaks also. Good luck!

[PatrickGMC70]

Well, I found one hole so far - where the fuel line runs through the cab. I have the correct grommet, so I can plug that up pretty easy. I'm glad that problem will be solved, but there is no way all of that stink was coming through that little hole.

Even if it were, there is still a leak somewhere because standing over the engine bay makes you stink, so there is definitely something going on. The PCV valve still rattles when I shake it, but they're cheap enough to just throw a new one on anyway.

The timing is set at 0.

As for the heat riser, they said it was cracked, so I planned to replace it with the manifolds. I don't have it hooked up to anything though (i.e. there's no tube running up to the snorkel). The valve in the snorkel is melted, and in any event, I don't think it's the air cleaner that is orignial to the truck.

I've looked at the local part shops, and the Dorman manifolds are about 300-350 a pair. I'll check the parts section to see if there are any used ones. But my original concern is trying to determine whether the manifolds are junk in the first place. (I should say that the passenger one is allegedly okay - I was just going to replace them in pairs). The shop pointed to the carbon on the manifold as evidence that they had to be replaced. I'm going to try the hose stethoscope tonight and see what I can hear.

Maybe I can try to get a second opinion next week, but finding a competent shop can be difficult.

P.S. I should add that the valve cover gaskets have been replaced, so I don't think there is any oil leaks coming from there, though they had leaked in the past.

[PatrickGMC70]

Okay, well, I found another hole behind the dash that is behind the glove box. When I had my head underneath the dash/below the seat, I definitely smelled some stink, so maybe more was coming through the fuel line hole than I thought.



I also think that there is definitely a ticking sound on the driver's side. I have a video below of the engine running, and it's a night and day difference in the sound between the two sides.

YouTube - VID 20110423 185349

[LandonL]

You say in the first post that whenever your near it while it's running you reek of exhaust, if you mean standing outside of the cab of course you are, but if you mean inside then you may have a problem. My '67 GMC has no sort of smog reduction, no cat no nothing, and if you crank it and stand beside it your gonna smell terrible. It's probably the same thing with all of these old trucks. I wouldn't advise spending all of this money unless your getting to smell bad just from riding in it. (which you may be, didn't look through every line of your other posts. If the heat risers are built in on V8 manifolds LMC's straight six manifold didn't have one cast in like the original when i bought mine. Hope you get this straightened out!

[PatrickGMC70]

Well I don't spend time behind the truck, but my clothes will smell if I'm near the front of the truck (like taking that video tonight) or if I ride in it. I rode in the truck for about 10 minutes tonight to get gas and come back.

As for the heat riser, the exhaust shop told me that I had to put one on, otherwise, there'd be nothing to connect the manifold to the rest of the exhaust.

[Stocker]

If you're referring to the heat riser valve below the exhaust manual, I'd just toss it. They are expensive and not really necessary IMO. I've been running without one for several years and cold starts are the same as when the valve was in place.

Good video clip. Sounds like you have a major leak on the driver's side.

[dadsworktruck]

yep, sounds like an exh leak on the left side to me, but if i were you i would ebay or google search ramhorn manifolds or dorman , or something your posted price was way out there.but first you got to see if it's the manifold or just a donut gasket leaking, simple but aggervating stuff,,,warm up the manifold a bit and use some liquid wrench or pb blaster, on the bolts and remove it for inspection....

[Autoblueprint]

I'd suggest raising the truck up on ramps or jackstands, then have a buddy hold a large wad of damp shop towels over the tailpipe while you crawl underneath and lean inside the engine compartment to see where the leak is in the exhaust system ( have your buddy wear leather gloves when he does this ).

Your buddy will only be able to hold the wad of rags over the tailpipe for 30 seconds or so because of the heat and pressure, so this task will have to be repeated several times.

You should be able to hear and feel where the leak ( or leaks ) are.

Then you can plan for the repair once you know, exactly, where the exhaust is leaking.

It could be as simple as loose bolts on the exhaust manifold or an exhaust donut, regardless, you need to find out where the system is leaking first.

BTW : any wrenching on exhaust components is best done when the system is warm, there is less of a chance then of breaking bolts.

[GASoline71]

So is the choke completely open when the truck is all the way warmed up? If that choke flap is hanging half closed all the time... the truck will run very rich, and hesitate a little. The idle screws need to be turned all the way in, and then out 1 1/2 turns for a baseline.

The PCV valve will rattle when you shake it. That's the way they are. So yours probably isn't bad.

Gary

[PatrickGMC70]

Yeah the choke is completely vertical when warm. I replaced the coil thermostat for the choke, so that's working okay. I set the idle screws earlier, and I didn't see any fuel trickle down the venturi, so I don't think the idle circuit is too rich. I can't be certain that the jets and rods are correct, but I don't want to go tearing into the carb until this exhaust situation is resolved. Thanks Gary.

[PatrickGMC70]

Originally Posted by Autoblueprint

I'd suggest raising the truck up on ramps or jackstands, then have a buddy hold a large wad of damp shop towels over the tailpipe while you crawl underneath and lean inside the engine compartment to see where the leak is in the exhaust system ( have your buddy wear leather gloves when he does this ).

Your buddy will only be able to hold the wad of rags over the tailpipe for 30 seconds or so because of the heat and pressure, so this task will have to be repeated several times.

You should be able to hear and feel where the leak ( or leaks ) are.

Then you can plan for the repair once you know, exactly, where the exhaust is leaking.

It could be as simple as loose bolts on the exhaust manifold or an exhaust donut, regardless, you need to find out where the system is leaking first.

BTW : any wrenching on exhaust components is best done when the system is warm, there is less of a chance then of breaking bolts.

That's a pretty good idea. The only "buddy" I have around this weekend is my pregnant wife, so she won't be getting near the stink-machine truck for now.

I've never taken manifolds or an exhaust apart before, and these bolts look pretty crappy. That's why I was going to let the Meineke people do it - in case a bolt snaps off. I can stomach the labor charge, but I'm concerned about their statments that I have to replace the manifold (when it could only be a gasket) and that I have to put in a new heat riser, because it won't bolt back togther without one. They're not really looking to make money on parts, because they said I can bring in my own.

Maybe someday I'll work up the nerve to put a wrench on those bolts. I just don't want to be halfway in, and find out that I'm totally smurfed.

[Kidd-7]

Being "totally smurfed" is part of the fun of these old trucks.
I had an exhaust leak last year on my drivers side, ended up being the donut; NAPA recommended a good shop and they showed me what the problem was & took care of it right away; really recommend having someone else look at it. See if your local parts store can recommend a shop.

[don t. - 72gmc]

Originally Posted by PatrickGMC70

I'm concerned about their statments that I have to replace the manifold (when it could only be a gasket) and that I have to put in a new heat riser

They're telling you this cuz they do not want a call back. If you don't buy the riser, then they can say we told you so and charge more. I'll defer to those w/more experience if you "need" the riser.

You would be correct to fix the exhaust b/4 you fix other areas of concern. You may find that an exhaust leak is your only problem(fingers crossed for ya).

JMO...If you do have a need, a q-jet carb is one of the easiest to rebuild. Im not a mechanic in any form of the word, and rebuilt my 1st q-jet in the early 80's, way b/4 the advent of the internet, by using the enclosed instruction sheet. Nowadays, there are many sites on the web w/tons of rebuild info.

Good luck..HTH....don t. ...

[zeeklu]

If I can't find an exhaust leak on the engine I take the belt off. It is easier to find without the fan blowing everything around. The only thing blowing will be the exhaust leak. It's quieter also. Chris

[PatrickGMC70]

Well, I ordered the Dorman manifolds from Amazon. $138 for the pair with free shipping.

I also ordered a heat riser delete spacer.




When the manifolds get here, I'll throw some hi-temp paint on them and see if I can't finally get this problem resolved.

I'll let you guys know what happens. Thanks again for all the help.

[cericd]

Did you ever get this problem resolved? I'm tired of my my truck making me stink too.

[PatrickGMC70]

Well, no not really. But two weeks after my last post, my wife and I welcomed our son into the world, and the truck sat untouched for about 18 months.

You must be inside my head though because just about two weeks ago, I took the manifolds off and put the replacement Dorman ones on. Taking the old ones off was actually pretty easy, but the passenger side was a bit of a pain because of the AC and starter (damn that starter was HEAVY!) I got it all back together, but I think there's still an exhaust leak on the passenger side.

I was getting a little frustrated by that point, so I had a shop look at it. They didn't charge me, but they think that the cheap Chinese Dormans (their words) probably aren't smooth and are the cause of the leak. I've only driven it about 2 miles since then, so I don't know yet what I'm going to do.

I did use the gaskets that came with the manifolds (I know there's a big controversy about gaskets v no gaskets), and torqued the bolts to the factory setting (30 inside; 20 outside). Honestly, I just don't feel like jacking up the truck, crawling on the cold concrete in my unheated 30 degree garage, dropping that damn starter on my chest again (with its really short wires), take off the AC bracket to MAYBE fix the problem.

As for the smell, I haven't really driven it much as I said, but I did advance the timing to about 10 degrees from 0. It seems to be running a bit nicer now. Actually, when I advanced the timing, the idle came up about 3-400 rpm, so once I locked in the timing, I lowered that back to 750. I'm sure there's some slack in that timing chain (assuming the marks are even accurate), so the advance may help with any richness in the mixture.

I'm going to give the manifolds a few heat cycles to see what happens, including re-torquing the bolts. Depending on what happens, I may try no gaskets or add a second set. (for some reason the Dorman manifolds came with two sets of gaskets so I have an extra). If I have to take them completely off to get them resurfaced, I may reconsider cleaning up the GM manifolds and putting them back on.

I'm taking it for a bit of a trial run tonight (first real drive in 18 months) so we'll see what happens.