SOLVED: Strange exhaust "gargle" noise at 1100 under load

[vegas]

I've been chasing a few errors lately and fixing things. First it was the EGR valve, vacuum modulator and vacuum lines. That fixed the EGR error. But now I'm getting the "coolant temp not high enough for closed loop fuel blah blah blah" error so I'm replacing the coolant temperature sensor, the thermostat, and both O2 sensors. I've noticed that the exhaust has a pretty strong smell which suggests the motor is running at a non-idea mixture probably due to sensor failures. One thing that has me concerned is that my truck has developed an odd exhaust noise that only happens at around 1100 RPM when under any kind of load (e.g. road not flat, starting from a stop, etc). It's a '96 with 180K and it's time I start replacing sensors and tubing a little at a time. I have a recording of the exhaust noise, it's best heard at the 16-18 second mark. I wanted to see if any of you had heard this before. I'm hoping that once I replace the sensors and get the codes staying cleared that this will all go away. I just hope the cats aren't toast.

Recording: Strange Exhaust Gargle Noise

If you turn the bass down on your speakers you can hear it better. It's a "gargling" noise to me. It's much more noticeable from the outside of the truck as I've been told by my buddies.

 

[vegas]

It's funny, looking the other noise diagnosis thread I noticed the same exhaust noise in that truck as well just before the birfs bind up in the video. My truck never had loud exhaust before all of the sensor failures started. After replacing the EGR, vacuum modulator and vacuum lines the idle smoothed out and it started to purr again. It used to purr all the way from idle to 4500. Now it purrs at idle, gargles loudly from idle to 1800 and then is just kind of loud up to 4500. And the exhaust smells. Used to see puffs of white smoke before the ERG/vacuum work but those are gone now.

 

[BILT4ME]

I've been chasing a few errors lately and fixing things. First it was the EGR valve, vacuum modulator and vacuum lines. That fixed the EGR error. But now I'm getting the "coolant temp not high enough for closed loop fuel blah blah blah" error so I'm replacing the coolant temperature sensor, the thermostat, and both O2 sensors. I've noticed that the exhaust has a pretty strong smell which suggests the motor is running at a non-idea mixture probably due to sensor failures. One thing that has me concerned is that my truck has developed an odd exhaust noise that only happens at around 1100 RPM when under any kind of load (e.g. road not flat, starting from a stop, etc). It's a '96 with 180K and it's time I start replacing sensors and tubing a little at a time. I have a recording of the exhaust noise, it's best heard at the 16-18 second mark. I wanted to see if any of you had heard this before. I'm hoping that once I replace the sensors and get the codes staying cleared that this will all go away. I just hope the cats aren't toast.

Recording: Strange Exhaust Gargle Noise

If you turn the bass down on your speakers you can hear it better. It's a "gargling" noise to me. It's much more noticeable from the outside of the truck as I've been told by my buddies.

There are a couple distinct possibilities.

1) There is a crack in the exhaust down pipe where the two come together at the "wye". Common crack requiring welding ($20 at an exhaust shop)
2) One of your O2 sensors had lost the nuts and is starting to push outside the hole.
3) Your catalytic converters are starting to get holes or the plates are starting to come apart internally.

When the engine is cold, start it up and get under there quickly with bare hands and start to feel around the wye, the flanges, and along the pipes to determine if you can feel or hear an exhaust leak. You do this while it's cold so you can find it without getting burned. If it takes you more than 5 minutes, it will get too hot to touch.

 

[vegas]

1) There is a crack in the exhaust down pipe where the two come together at the "wye". Common crack requiring welding ($20 at an exhaust shop)

I started it and was under there in less than 30 seconds. No obvious leaks but I did smell exhaust immediately when I was up under there which suggests there is an exhaust leak somewhere. I'm not 100% sure but probably?

2) One of your O2 sensors had lost the nuts and is starting to push outside the hole.

The downstream O2 sensor is missing a nut and the other one is rusted away down to a smooth tube that is still threaded and rusted to the bolt. That's probably where the error codes are coming from. That will be fun using an extractor to try to get that loose and off to replace the sensor.

3) Your catalytic converters are starting to get holes or the plates are starting to come apart internally.

No way to confirm this. I'll need to fix the O2 sensors first and see if anything changes.

Thanks for the help. I'll add updates over the next couple of days as I make repairs. I need replacement nuts for the O2 sensor, are those 12 mm?

 

[BILT4ME]

I started it and was under there in less than 30 seconds. No obvious leaks but I did smell exhaust immediately when I was up under there which suggests there is an exhaust leak somewhere. I'm not 100% sure but probably?



The downstream O2 sensor is missing a nut and the other one is rusted away down to a smooth tube that is still threaded and rusted to the bolt. That's probably where the error codes are coming from. That will be fun using an extractor to try to get that loose and off to replace the sensor.



No way to confirm this. I'll need to fix the O2 sensors first and see if anything changes.

Thanks for the help. I'll add updates over the next couple of days as I make repairs. I need replacement nuts for the O2 sensor, are those 12 mm?

You don't go by the head size. You go by the thread size.

I'll find the info and post it in a minute.

With then nuts rusted away like that, you can use a pair of small vise grips to remove the remaining shell of a nut. After you get them off, use a die to clean up the threads on the studs. Make sure to get a new gasket (local FLAPS carry them) and use COPPER anti-seize on the studs to reassemble. Torque to 15 LB-FT max.

I've had this exact thing happen on mine. My O2 sensor would pop out when I would accelerate, then drop back in when I let off the gas. I had little noise at idle, but when hard accelerate, it made noise.

Complete list of exhaust parts:

Bosal , your $200 cat-back option

I wanted to put this here for anybody thinking of re-doing there exhaust. When I started this project my exhaust was bad, really bad. It was leaking at the seal between the rear cat and the cat-back. Only one of the exhaust hangers had not rusted off and it was being held by some pipe strap...

forum.ih8mud.com

 

[BILT4ME]

These are the nuts I installed on mine to reinstall the O2 sensors. Along with copper anti-seize.

M8-1.25 Flanged Hex Nuts
Dorman P/N 982-008D from O'Reilly Auto Parts

 

[vegas]

Thanks. I was able to get nuts, copper anti-seize, a die for cleaning the threads and all new mounting flanges, gaskets and denso O2 sensors for upstream and downstream. I've got a tiny pair of vice grips, free-all and some nut extractors just in case. Wish me luck. I'm hoping the exhaust noise goes away once the new O2 sensors are down snug.

 

[vegas]

Update time. I was able to replace the O2 sensors. Free-all and nut extractor sockets were required. I also used a die to clean up the threads. Put the new gaskets, sensors, copper anti-seize, and flanged nuts on.

I took it for a drive and noticed a few things:

1. The smelly exhaust is gone.
2. Throttle response is much better and there is more power.
3. I was able to clear the check engine codes and they haven't come back (yet).
4. The exhaust noise is still there but less gargly.

I think I have an exhaust leak somewhere between the cats and the motor. It's probably at the wye but I didn't feel any exhaust air at idle. It could be the cats failing too.

 

[ppc]

Have you checked valve clearances and the condition of the lobes on the camshafts? A partially open valve can cause that type of sound.

 

[vegas]

Have you checked valve clearances and the condition of the lobes on the camshafts? A partially open valve can cause that type of sound.

I have not. I'm a little nervous to go that deep into this motor because I'm not sure I have 1) all of the tools needed and 2) all of the money needed to repair and put it all back together properly. I have been learning auto maintenance on my cruisers for the past 5 years and I'm confident in most things. I've replaced bearings and birfs, brake rotors, water pump, sensors, tubing, fixed the fan clutch properly for the 115 degree heat here in Vegas, on and on. The one thing I have *not* ever done is taken the valve cover off and and done anything inside the motor.

For me to do this check and repair, if needed, is a good idea of the parts I'll need and what to do if I find the valve clearances are off or if the lobes on the camshaft are messed up. I have no idea how to know if either of those things is bad. I have no idea how to fix any badness if either is bad.

 

[BILT4ME]

I have not. I'm a little nervous to go that deep into this motor because I'm not sure I have 1) all of the tools needed and 2) all of the money needed to repair and put it all back together properly. I have been learning auto maintenance on my cruisers for the past 5 years and I'm confident in most things. I've replaced bearings and birfs, brake rotors, water pump, sensors, tubing, fixed the fan clutch properly for the 115 degree heat here in Vegas, on and on. The one thing I have *not* ever done is taken the valve cover off and and done anything inside the motor.

For me to do this check and repair, if needed, is a good idea of the parts I'll need and what to do if I find the valve clearances are off or if the lobes on the camshaft are messed up. I have no idea how to know if either of those things is bad. I have no idea how to fix any badness if either is bad.

I don't think your issues are the valve clearances at this time, but that's IMO.

If you've done bearings and birfs, you can do a VC and Spark Plug Tube replacement easily enough. There's nothing technical about it. Just read up on it, then buy the right replacement seals, and you're golden.

 

[vegas]

Cool, thanks. Looking at the other recent ticking noise thread (mine ticks very slightly as well and that started before the gargling) I think I'm going to try running it briefly without the A/C and power steering pumps going to see if the ticking goes away. I'll have to read up on doing valve clearance checking and get ready to do that soon.

What's the best way to check for exhaust manifold leaks and/or exhaust pipe leaks? I'd like to eliminate that as a variable. I'm afraid to take it to an exhaust shop to check because I'm pretty sure no matter what the condition of my exhaust is, they're going to tell me I need a whole new exhaust.

BTW, the toughest thing to fix was overheating in August in Vegas. Especially on the uphill climb out of Mesquite, NV going south on the I-15. I tried all kinds of things including an extra electric fan in front of the radiator but I eventually worked out the magic formula. I used 30,000 CST silicone oil (it's $15 from the river) in the fan clutch and adjusted the ports so they are a tiny bit open at cold (room temp)--by a tiny bit, I mean the smallest opening your eyes can see. That makes them go full open when the engine is at 190. The OEM set up I think has 10,000 CST oil and the ports never open fully, even at high temps. I used a toaster oven and infrared thermometer to determine this for sure. Even when the clutch is heat soaked at 300 degrees, the ports are only about 75% open with OEM settings.

The result of the using the heavier oil and adjusted ports is that the fan spins freely and barely pulls air from November until April. Then I start noticing a little fan noise in the afternoons (90-100 degrees) in May-June and the month of October. July-September the fan is running all of the time because the temperature rarely drops below 90, even at night. Last August when the DOT was doing work on I-15 around Mesquite, I was fully loaded with fuel and gear and got stuck in traffic forcing me to slow-crawl up the longest hill heading south--that hill that once sent my coolant temps to 223 briefly and that was at highway speeds. With my current setup, the engine temp only hit 198 in 118 degree heat. My coolant temps never go above 200 anymore. I have a tablet giving me realtime numbers from the sensors via a bluetooth ODB adapter and it keeps histories for me. Once I got this dialed in, I no longer worry about taking this thing up hills in August down here anymore. It took me all of last summer doing different experiments to dial it in.

EDIT: to be perfectly clear, I tried just the 30,000 CST oil first without adjusting the ports and it was only a marginal improvement. I saw my coolant temp hit 212 in 115 degree heat going up the Mesquite hill at highway speeds. After adjusting the ports, the coolant temp stayed within normal range, maybe even a little low, while going up the same hill in similar heat and at all speeds. I did it several times over subsequent weeks. Some slow due to traffic and some at highway speeds.

EDIT 2: I tried other oils in this process. I tried 15,000 CST and 20,000 CST with almost no change in heat management. It took 30,000 CST oil to make a noticeable change, but like I said, things didn't really get better until the ports were properly adjusted for the conditions. For somebody in a similar situation, I'd first try adjusting the ports. Then, if that doesn't work, I'd try going to higher CST oils in a few steps (20,000 CST, then 30,000 CST) until you see the change you want. The goal is to find the lightest oil that makes the darn clutch work in your situation. Maybe 20,000 CST works for you, maybe it doesn't. Here where I live on the surface of the sun, it took 30,000 CST. YMMV.

 

[vegas]

I think I earned the Fan Clutch Merit Badge.

 

[vegas]

So I've made all of the repairs, EGR valve, vacuum modulator, vacuum lines, both O2 sensors and the coolant temp sensor. I cleared the engine faults and the catalytic converter test completes green, the O2 sensor and heater tests both complete green, but the EGR test still comes back saying insufficient exhaust recirculation. I'm thinking that the temp sensor in the EGR tunnel in the intake manifold is bad. Anyway, it is running better and I took it out wheeling this weekend.

The gargling noise is less noisy but still present. I finally got a really good recording of the noise.

What do you think it is? It sounds like an exhaust leak. But it could be timing. It could be valves. Not quite sure.

 

[vegas]

So I've been going through the FSM and testing sensors. The exhaust gas temp sensor appears to be working. I was getting the correct resistance readings at the correct temperatures. Here it is reading 14.4 KOhms at 100 C which is smack in the middle of the range of correct readings at that temp. Same thing happened when the temp was 50 C.

 

[vegas]

I think maybe the problem is just an exhaust gas leak somewhere between the engine and the first cat. That's what is causing the noise I'm hearing. Do exhaust manifold gaskets fail all on their own? Could it be something that simple? Or is it likely the manifold has a crack or the exhaust has a crack. I guess I'll just take it to an exhaust shop for an inspection and see if they can find any leaks. It definitely starts out not very audible when the engine is cold and it gets louder as the engine warms up. This suggests to me that as the engine warms up, the metal expands in the exhaust manifold or exhaust pipes and the crack opens up. Maybe it is at the wye after all. Is there any other sure fire way to find a crack like this other than visual inspection? I didn't feel exhaust blowing out of the wye right after starting the engine from cold but I think that's because the crack opens as the exhaust warms up.

 

[vegas]

Well, suspecting an exhaust leak I removed the heat shields from the exhaust manifold to take a closer look. While removing the back heat shield I discovered a lot of soot on something that shouldn't be covered in soot. So I grabbed a bottle of soapy water and sprayed everything down and started the engine. Here is the exhaust leak. Fixing this should fix the noise.