Sulfur smell

Tiny
JUSTINBLANTON
  • MEMBER
  • 2015 GMC SIERRA
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 80,000 MILES
For about two months I have had a pretty strong sulfur/rotten egg smell in my truck. The smell comes and goes but seems to get stronger when driving slow or in reverse. I believe it’s getting sucked in through the air conditioner. I’ve taken it to two mechanics who have looked over the exhaust system and haven’t found any cracks. We have replaced the catalytic converter and battery. It has been to the dealership almost ten times and they cannot figure it out. The dealership has run tests to make sure its not running rich. They have also test the charging system for the battery.

This smell started happening two months ago after towing roughly 5,000 pounds for one to two hours in snowy conditions.
Any ideas?
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Friday, March 22nd, 2019 AT 12:19 PM

13 Replies

Tiny
ASEMASTER6371
  • EXPERT
Good morning,

Were there any codes that were set during this issue?

What is the charging system voltage with the engine running?

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Do you have a scan tool that can read trim readings while under a load?

Roy

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Saturday, March 23rd, 2019 AT 5:16 AM
Tiny
JUSTINBLANTON
  • MEMBER
The dealership said they ran intensive tests on the charging system.
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Saturday, March 23rd, 2019 AT 5:20 AM
Tiny
ASEMASTER6371
  • EXPERT
There are no intensive tests on the charging system. It is simple testing.

Do you have a voltmeter to give me voltage readings?

Again, do you have a scan tool to read live data?

Roy
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Saturday, March 23rd, 2019 AT 5:23 AM
Tiny
JUSTINBLANTON
  • MEMBER
I have monitored the voltage readings pretty heavily with a volt meter, thinking that the battery was getting overcharged and creating the smell. It s nothing out of the norm.
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Saturday, March 23rd, 2019 AT 6:47 AM
Tiny
ASEMASTER6371
  • EXPERT
Again, What is he voltage?

Roy
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Saturday, March 23rd, 2019 AT 6:50 AM
Tiny
JUSTINBLANTON
  • MEMBER
Anywhere between 14.2 and 15.3. The vehicle can create the smell within three minutes of being started though.
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Saturday, March 23rd, 2019 AT 6:52 AM
Tiny
ASEMASTER6371
  • EXPERT
There is your issue.14 to 14.5 is the target. Anything above 14.6 volts and you are cooking the battery.

15.3 is no good and is causing battery damage.

Roy
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Saturday, March 23rd, 2019 AT 9:55 AM
Tiny
JUSTINBLANTON
  • MEMBER
This is strait from GM as far as how the charging system works in their vehicles. (See below) There is no way I m cooking the battery enough in three minutes for it to start making the smell. Plus when smelling under the hood, the smell is much stronger on the driver side. The battery is on passenger side.

The estimated battery temperature is less than 0 C (32 F).
Battery State of Charge is less than 80 percent.
Vehicle speed is greater than 145 km/h (90 mph)
Current sensor fault exists.
System voltage was determined to be below 12.56 V
When any one of these conditions is met, the system will set targeted generator output voltage to
a charging voltage between 13.9 15.5 V, depending on the battery state of charge and estimated
battery temperature.
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Saturday, March 23rd, 2019 AT 9:59 AM
Tiny
ASEMASTER6371
  • EXPERT
Got that.

I still think that is too much voltage for the system.

I read the article but do not agree with it at all.

I will defer to my associates to see if any of them have any better idea for you.

Roy
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Saturday, March 23rd, 2019 AT 12:08 PM
Tiny
JUSTINBLANTON
  • MEMBER
I would appreciate that.
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Saturday, March 23rd, 2019 AT 12:29 PM
Tiny
PATENTED_REPAIR_PRO
  • EXPERT
If this battery has cell caps, remove them and watch to see if the water/acid boils and also if the smell is stronger with the caps off. Also if the strong sulfur smell is there when just removing the caps even without the engine running.
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Saturday, March 23rd, 2019 AT 12:41 PM
Tiny
HMAC300
  • EXPERT
Sooner or later he will have a sulfated battery and wonder why.
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Saturday, March 23rd, 2019 AT 2:37 PM
Tiny
CARADIODOC
  • EXPERT
Hi guys. Allow me to add a few tidbits of great value. 15.5 volts is definitely too high. The reason GM gets away with that is the original battery has calcium in the grids of the plates. That reduces the effects of over-charging. They started using that in their "Freedom" batteries in the late '70s, and those were the first ones to have sealed caps. Their thinking was with less tendency to heat the acid, the water would never boil out or need to be checked or filled. They would still fail in other ways with the lead flaking off the plates, as happens in all batteries. Of course they wanted you to buy all your replacement batteries from the dealer, with the same characteristics. Standard aftermarket batteries at that time were not able to withstand that higher charging voltage. Funny thing is when I was the battery room attendant at a Sears Auto Center, you could see through the white cases on those traded-in GM batteries, and almost all of them were low on acid. Once part of the plates becomes dry, it never comes back after the cell is filled, so that part is useless. Who knows how much more life could have been gotten out of those batteries if they could have been filled.

The other reason for the sealed caps is one of the standard tests was to use a hydrometer to check state-of-charge. The acid formulation in the Freedom battery was different than that used on all other batteries. They didn't want you taking a hydrometer that had some residual standard acid in it, and using that on a Freedom battery because of acid contamination.

Another misconception had to do with their use of a built-in hydrometer, that little green eye. We were told if it was green, the battery was fully-charged and any electrical problem had to be caused by something else. In fact, that was misleading and incorrect. That built-in hydrometer only tested that one cell, not the other five. The real purpose of that eye was if it was green, the battery was charged enough to allow it to be tested, that's all.

Today the latest thing is "absorbed glass mat" batteries. I don't have any training on those except for what I learned from an employee of the battery store I visit quite often. I apparently have one of those in my 2014 Ram truck. I let it sit all winter and allowed the battery to discharge. When it wouldn't take a charge in the spring, I bought a "reconditioned" replacement, a lot smaller than the original, but the salesman refused to take the old one in for the core charge until I charged it further to prove it was really bad. We used to tell people to charge a dead battery at a slow rate for an hour or two. With this AGM battery, he told me they would not test it until it had been slow-charged for three days. Sure enough, it came back and still works fine. There's more to the story I don't know yet, but in the truck, charging voltage sits right at 14.6 volts in warm weather.

Charging and discharging a battery is a chemical reaction, and those always go faster with higher temperatures. That's why with the voltage regulator inside Chrysler's Engine Computers, and now with the addition of external monitoring in most other brands of charging systems, the target charging voltage is stepped up a little in cold weather. That's why the battery temperature sensor or the intake air temperature sensor is an input now to the charging system. That temperature compensation was even built in to Chrysler's first electronic voltage regulator in 1970.

There's one more reason GM lists acceptable charging voltage so high. Any time a vehicle comes in for a warranty repair, the manufacturer always has a real long list of what must be found or performed before they will pay for the service. Batteries, brake pads, wiper blades, clutch discs, and tires are never covered under the warranty because those are considered "consumables", and as such they are expected to need periodic replacement, and the manufacturer has no control over how well or how little the owner takes care of those things. The only time they will pay to replace a battery is when it failed due to something else that is covered under warranty. In this case it would be the voltage regulator that's built into the generator. If charging system voltage goes too high, it will damage the battery, and in very rare extreme cases, it can take out multiple computers. Another real common problem that only applies to GM vehicles, is since the engineers redesigned their generators for the '87 model year, they develop huge voltage spikes that can damage the internal diodes or voltage regulator, and they can interfere with computer sensor signals. The battery is the key component in damping and absorbing those harmful spikes, but as they age and the lead flakes off the plates, they lose their ability to do that. An old battery, even though it still cranks the engine just fine, is the biggest cause of generator failures on GM vehicles, and failure to replace the battery at the same time, unless it is less than about two years old, is the reason owners often go through four to six replacement generators in the life of the vehicle. The battery must be replaced at the same time to reduce the number of repeat generator failures.

Those voltage spikes cause current spikes, and current through a wire sets up a magnetic field around it. That is what "induces" a voltage into adjacent wires and wreaks havoc on sensor circuits. You'll never see a light bulb flicker by changing the voltage 0.2 volts, but as little as a few hundredths of a volt means a real lot to an Engine Computer's sensor circuits. Tired, old batteries, and a failed diode in the generator are two common causes of elusive engine performance problems that defy diagnosis on GM vehicles.

This is one of the "customer-unfriendly" business practices GM is famous for, but a few other manufacturers pull the same tricks. The acceptable range of charging voltage varies, depending on which text book you read, but will never exceed 13.50 to 14.75 volts. The trick GM pulled is by listing the maximum at 15.5 volts, when they demand the charging system be tested as part of any warranty diagnosis, if charging voltage is between 14.75 and 15.5 volts, they won't pay for any repairs related to that high voltage. You could equate that to your insurance company saying they won't cover your kidney stone because you listed your level of pain at "7" on a scale of "1" to "10". They only cover ailments with a pain rating of "8" or higher. It's a trick to shift the burden of paying for the repair from them onto the customer. When you confront a GM trainer on this issue, their response is, "there are times when charging voltage can be expected to reach 15.5 volts". The rest of the story is that only occurs at minus 40 degrees.

The solution, when dealing with your pain, is to lie, and write down "9", then it will be covered. The solution at the dealership is to lie, and write down "15.6" for charging voltage. "There, now GM will pay for the repairs". That is from a friend who used to be a service writer at the local Chevy dealership. Another friend was the suspension and alignment specialist at the local Ford dealership. Ford has all kinds of trouble with steering and suspension parts since the late '70s, but for warranty purposes, some play is allowed in their ball joints. That same play is not acceptable when the car is out-of-warranty and the customer has to pay the bill. When the customer has to pay the bill is when he ends up with a safer car because those worn parts got replaced. It was real common to see an '80s Escort come in on a tow truck with a separated outer tie rod end at 15,000 miles. At 14,000 miles, there might be only slight play in that part, but by Ford's standards, it was still within allowable limits, so it did not warrant replacement. Try explaining to your customer that part is going to send them into the ditch or into oncoming traffic in 1,000 miles, but it's not bad enough to replaced under warranty. This is why we called them, "killer cars". What we consider unsafe, or unacceptable, is quite different from what the manufacturer says is okay when they would be on the hook paying for it.

For the smell, this should be easy to locate by sniffing at the tail pipe and at the battery. The battery is not going to over-charge right away. That could take from 15 minutes to more than an hour before the smell shows up. Keep in mind too that catalytic converters cause the smell after being overheated from burning too much raw gas inside them. Much of what could cause too much unburned gas in the exhaust system is monitored, will set a diagnostic fault code, and turn on the Check Engine light. When too much unburned gas is calculated to be going into the exhaust, the Check Engine light will flash on and off. If there are no related fault codes, and the flashing Check Engine light has not been observed, chances are that is not where the problem lies. Also understand that unburned gas in the exhaust system can not be detected. Oxygen sensors only detect unburned oxygen. If you have a spark-related single-cylinder misfire, unburned oxygen and gas go into the catalytic converter where they burn, causing the overheating. Only the oxygen is detected as an excessively-lean exhaust mixture, but at the tail pipe, you'd smell the unburned gas as a rich condition. Since 1996, all models can detect a single-cylinder misfire, and the number of the fault code indicates which cylinder is responsible. By 2015, the ability of the Engine Computer to do that is pretty sophisticated, so if there has been no Check Engine light, and no related fault codes, the smell coming from the tail pipe is not a good suspect.

I should mention too that your Engine Computer can detect well over 2,000 defects and set fault codes specific to each of those. There can be over a dozen fault codes related to one sensor circuit, but they mean very different things. About half of the time, when a sensor or other part is referenced in a fault code, it is not actually the cause of that code. That's why so many people replace a part two or three times without solving the problem. Of those 2,000 fault codes, only about half of them refer to things that could adversely affect emissions. Those are the only fault codes that turn on the Check Engine light. Just because the light isn't on doesn't mean there are no fault code in memory.

There's two other things I can think of, but these would be real uncommon. One is if driving in heavy stop-and-go traffic, fumes from one or two cars in front can get sucked into your fresh air vent. The other one is a few years ago, Honda had numerous complaints of off-gasing from interior trim panels. The complaints always involved headaches and dizziness, not smells, but you might consider a plastic container that is sitting on the floor where the rear heater blows hot air onto it, and things like that. Gasoline exhaust smells a lot different than it did 30 years ago. You might pay attention to where you bought gas last when you smell this again. Perhaps one brand has some additive that no other company uses. If exhaust fumes really are getting inside the passenger compartment, the issue isn't a leak in the exhaust system; it's a leak in the body. There's holes in the floor that have round or oval plastic plugs. Some people remove those or cut holes in them to run wires. Also check the condition of the rubber seal that runs along the rear edge of the hood.
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Saturday, March 23rd, 2019 AT 8:03 PM

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