STRONG Exhaust smell

[Gorilla]

Hey guys, I picked up a 03 RCSB Silverado a while ago. It was originally a v6 truck but the person I bought it from did a 5.3 gen 4 swap along with a 4L8e swap. He replaced the heads to 706 heads that are lightly ported. He did a Btr stage3 cam kit, DOD delete & used 6.0 truck intake and injectors. He put a new magna flow muffler on it as well.

So far I have replaced the mass air flow sensor on it with a new OEM one. I put a new 02 sensor on it as well. There were codes being thrown for these replaced parts.

 

But ever since I bought the truck it has a strong odor of exhaust. There are no leaks in the exhaust. It sounds really good with the magna flow muffler but the exhaust smell is enough to knock you out when standing by the tail pipe.  It smells at idle and will fill up the garage instantly. Outside you dont smell it in the cab with the windows closed but you will smell it at idle with the windows down if the wind blows your way.

 

I do have a EVAP large leak that is intermittent and kicking the CEL at times. Im currently trying to find that leak. 

 

Can anyone share some advice on what I can check to cure the strong smell? Is it possible it's the magna flow muffler itself?

[richard wysong]

Are the cats functional? with so many mods it must have some form of a tune on it that may need to be tweaked. Is it just at idle or all the time?

[Gorilla]

So far i believe the cats are working correctly. No other codes other than the EVAP large leak.  When the o2 sensor went, it thru a code instantly. It was the one on the driver side before the cat that needed replacing.

It is all the time that you smell it.

I believe the cats are original as welll. Could they be carboned up and not blocked? Can they be cleaned out?

 

Is there any way I can find out if there is a tune on it?

 

If it helps any I had a 95 2 door tahoe with the stock 5.7 350 engine and stock trans and it had a flowmaster muffler on it and it smelled the same way. Strong fumes at idle.  No ecu codes on that truck either. Original cats too. Never figured that one out.

 

 

 

Edited January 18, 2023 by Gorilla

[richard wysong]

What are you using for fuel?

[newdude]

Sounds like it smells like there is no cats or high flow cats on it?  High flows or no cats will produce that old school 1960s/1970s smell.  

[CamGTP]

Probably has gutted cats or no cats at all.

[dna9656]

Can you run a 5.3 on a V6 computer PROM? How's the mileage? With bigger(presumably) injectors and intake maybe the PROM is keeping the injectors open trying to fill the intake, could the vacuum signal being received by the PROM upset things?

[CamGTP]

It won't run right if it had the V6 calibration file on it but you can write a V8 calibration into the V6 computer because both vehicles use the same controller.

[Gorilla]

On 1/18/2023 at 3:19 AM, richard wysong said:

What are you using for fuel?

It doesnt seem too bad on fuel consumption. If I go 17 miles one way the needle barely moves. I havent done the exact mileage count as I only stick around $15 to $25 in it. Never enough to fill the tank yet due to this inflation nonsense. I have gotten a full tank a few times since I bought it but again I dont think its using a whole noticeable amount. I could be wrong though.

 

On 1/18/2023 at 10:07 AM, newdude said:

Sounds like it smells like there is no cats or high flow cats on it?  High flows or no cats will produce that old school 1960s/1970s smell.  

 

 

On 1/18/2023 at 8:59 PM, CamGTP said:

Probably has gutted cats or no cats at all.

You guys brought up a good point that I havent thought about. I know they dont looking like high flow cats at least not to my limit knowledge anyway. When I was last under there it looked like the original cats are on it but Im wondering if anyone knocked out the inside of them?

Is there any way I can tell if the cats are working correctly or still there? I have a zurich z13s code reader but thats about it.

You're correct it really does remind me of the old 60-70s or even the square body 350 exhuast smell. It does smell like raw fuel it just smell like strong fumes.

 

On 1/18/2023 at 11:03 PM, dana9656 said:

Can you run a 5.3 on a V6 computer PROM? How's the mileage? With bigger(presumably) injectors and intake maybe the PROM is keeping the injectors open trying to fill the intake, could the vacuum signal being received by the PROM upset things?

Sorry I dont have anything but a zurich z13s and limit knowledge about all this. Ive been reading and doing some research and asking questions to anyone and everyone since I cant find a shop that tunes in my area. Its a rural area and not many of the garages are into this around here. At least i havent found a shop yet anyway. I was thinking about taking it to the dealer and seeing what they say but I dont want someone that doesnt know what theyre doing poking around on it just incase it is set up decently.

 

Im gonna get some video of it idling soon and post it up. If anyone would take a quick listen of it when I post it, that would greatly be appreciative. Again i think its running fine as it sounds like its purring. The idle is set at 1100 rpm for idle which I thought was a little on the high side but after viewing a video on BTR's website I hear different set ups on each truck featured in the video. Im thinking a higher idle will offer a smoother idle with this cam.

 

 

I'm thinking I have this cam. I cant be certain as I wasnt there when the seller put it in the engine.

 

 

 

 

[dna9656]

Strong exhaust is usually attrib to an over rich (more than 14.7 to one/ Stoichiometric0 fuel to air mix. This is what the O2 sensor is all about. It measures O2 level in the exhaust and sends a signal to the computer and it adjusts the rate the injectors operate (opene and close) measured in Hz or hertz (cycles per second) along with what the mass air flow sensor tells the computer. The computer controls it all. If you have no operational cats shouldn't the computer be telling the the injectors to stay open; I mean the signal being sent is not what would be sent if they were operational you should have a check engine light (CEL) so the amount of gas not enough to get the correct signal to the computer so it opens the injectors longer, it never sees the right signal so you run (prolly) in closed loop/limp home mode. I'm guessing here from memory but I think that's what's happening. I wonder if the PO took the bulb out of the CEL socket. The CEL comes on for other GOOD reasons, it's not just a bother it could be when we still had throttle body injection. You need a functioning CEL. Get the "Torque" app for your phone and a Blue Tooth OBD2 connector that's compatible with the App.

[richard wysong]

It would be running in open loop if it doesn't see the parameters needed to switch to closed loop. An infrared thermometer can tell you if the cats are working, they should be hotter at the outlet than the inlet if they are working

[newdude]

7 hours ago, Gorilla said:

You guys brought up a good point that I havent thought about. I know they dont looking like high flow cats at least not to my limit knowledge anyway. When I was last under there it looked like the original cats are on it but Im wondering if anyone knocked out the inside of them?

Is there any way I can tell if the cats are working correctly or still there? I have a zurich z13s code reader but thats about it.

You're correct it really does remind me of the old 60-70s or even the square body 350 exhuast smell. It does smell like raw fuel it just smell like strong fumes.

 

 

Im gonna get some video of it idling soon and post it up. If anyone would take a quick listen of it when I post it, that would greatly be appreciative. Again i think its running fine as it sounds like its purring. The idle is set at 1100 rpm for idle which I thought was a little on the high side but after viewing a video on BTR's website I hear different set ups on each truck featured in the video. Im thinking a higher idle will offer a smoother idle with this cam.

 

 

 

Any chance you could grab a picture of the exhaust at the engine?  So a picture of the pipes coming off the manifolds/headers and the y pipe (if there is one).  Curious to visibly see what's there.  

 

 

7 hours ago, dana9656 said:

Strong exhaust is usually attrib to an over rich (more than 14.7 to one/ Stoichiometric0 fuel to air mix. This is what the O2 sensor is all about. It measures O2 level in the exhaust and sends a signal to the computer and it adjusts the rate the injectors operate (opene and close) measured in Hz or hertz (cycles per second) along with what the mass air flow sensor tells the computer. The computer controls it all. If you have no operational cats shouldn't the computer be telling the the injectors to stay open; I mean the signal being sent is not what would be sent if they were operational you should have a check engine light (CEL) so the amount of gas not enough to get the correct signal to the computer so it opens the injectors longer, it never sees the right signal so you run (prolly) in closed loop/limp home mode. I'm guessing here from memory but I think that's what's happening. I wonder if the PO took the bulb out of the CEL socket. The CEL comes on for other GOOD reasons, it's not just a bother it could be when we still had throttle body injection. You need a functioning CEL. Get the "Torque" app for your phone and a Blue Tooth OBD2 connector that's compatible with the App.

 

 

Another thought on this, instead of pulling the bulb, the tuner could have used HP Tuners (or equivalent software) and straight up turned off certain DTCs from activating at all, which is entirely doable in HP Tuners.