This is a ranch truck I drive around our place. I had to gut out the catalyst converters on it because I was worried about catching a hay field on fire. They get to hot. I ran a code tester on it and it came back lean on bank 2. During this time my brake booster went out. I kept hearing about a loosing vacuum could cause it to run lean. I have check all the other vacuum lines by spraying carburetor cleaner on them a long with the plastic intake and the engine never changed it's sound. It only make the popping sound when I am driving it. The engine idles fine when it's sitting. I have also replaced the upstream 02 sensors and put spark plug non foulers on them and replaced the EGR valve. The craziest thing is all this start when I placed the thermostat housing. I also replaced the sensors on the housing twice. This is on a 2006 ranger with a 4.0 4X4. It's been a pretty good truck until all this started.

 

With no Cat converter you should have other codes beside Lean
What are they?

The popping is caused by unburned fuel being ignited by hot exhaust , a "back fire"
So you should feel/have a misfire occurring

The thermostat wouldn't cause any popping issues, that I can think of
But the gutting of the Cat could

All engine computers add extra fuel to keep Cat converters hot so they can clean the exhaust gases, because Cat is not working the rear(downstream) O2 sensor will be showing high oxygen levels, to the computer that means a COLD Cat converter, so ADD MORE FUEL, to get it hotter, so that could be causing the "pop"

When Cats are working they burn up emissions and burn up most of the oxygen in the exhaust doing that, so rear O2 shows a steady 0.7-0.8 volts as a result
Yours would be lower volts which should set a code, which is why I asked
If this is the case Google how to eliminate downstream O2s, there are some "fixes" to simulate downstream O2 feedback to computer, not legal in any state so I won't recommend any here, lol

 

This truck never sees the black top and hasn't had inspection since we got it. I had a good friend that had f150 to work around his place. He was driving it across his hay field to get to his tractor and set his field on fire from the catalyst converters. He pretty much lost his hay crop and one tractor that they couldn't get out in time. Wish they would insulate those converters so these things want happen. This ranger had three on it , two small ones and one big one where the pipes come together. I guess I will have to talk to my mechanic and see if he has some kind of trick to fool the dam computer. I was told the spark plug non foulers would work but they haven't.

​​​That's the only code I have on the code reader I have. A good friend of mine calls it the popping yellow ranger like the popping John Deere tractors when he hears me coming.

 

Odd posting recall, this is a test post

 

I posted a reply to your post earlier but it didn't show up. I may have been in a bad cellphone area. I will run another code test tomorrow and post what I get bad.

 

Sorry about not getting back sooner but had some issue with some cattle. I got a friend's tuner to check what codes I am getting and his pulled some different codes than my. Here is what I am getting.

PO174 System to lean bank 2.
P0141 Heater circuit bank 1 sensor 2.
Then we did a koeo test and got these.
P0054 H02S Heater Resistance bank 1 sensor 2.
Then with the truck running on koeo test.
P1116 engine coolant out of self test range.
P0161 02 Heater circuit bank 2 sensor 2.
I have replaced the coolant temperature sensor twice and still get this code. It's never ran hot or anywhere close to hot. I have also replaced the upstream sensors on both side and have spark plugs non foulers on them. I have also check the coil on it and all 6 ports makes a good blue spark. I just hope I can get it going without having to put catalyst converters back on it. Out here in the rural area they don't check emission. All they really check is lights, blinkers, horn, and the license plate light. The funny thing is just about everyone has the license plate light busted out from hooking up bumper pull trailers. Do you the those MIL eliminators with fix this problem?

 

On the 2006 4.0l there should just be the one ECT sensor on the top of T-stat housing, and if you have replaced it then one of the wires is bad
And you kind of need that as it sets CHOKE mode
Should be a grey/red stripe wire and if you look at the throttle sensor you should see same grey/red wire, same wire runs to most sensors, its 5volts from computer
You can use an OHM meter, key off between these 2 grey/red wires and should see 0 ohms, a direct connection
In 2006 this might be a Green/white wire on both

The other wire on the ECT sensor runs back to the computer, pin38
If hooked up key on that wire should show 3-4volts on cold engine, under 1 volt after full warm up

O2 sensors have 2 parts inside
The sensor and the heater, thats why there is 4 wires, 2 for sensor 2 for heater
O2 sensor needs to be above 650degF to work, so there is a heater inside to warm it up as fast as possible so computer can use it

With key on the heater fuse powers on and sends 12v to each O2 heater, the heaters are GROUNDED in the computer, so with key on the computer expects to see 12v on each heaters ground wire
If one is not showing 12v then it sets that O2s "heater malfunction" code, so its not am "O2 sensor" code its the heater part code

O2 "sensor 1's" are upstream sensors, closest to engine
"Sensor 2's" are downstream, after Cats
Bank 1 is passenger side
Bank 2 is drivers side

So P0141 Heater circuit bank 1 sensor 2.is passenger side rear O2 location
In this location the problem is usually a melted wire because it was touching exhaust, have a look
P0054 H02S Heater Resistance bank 1 sensor 2,.can mean 1 of the heater wires is not broken all the way but almost

Unless you have Factory DUAL exhaust there is no Bank 2 sensor 2
Fuse 41 in engine bay powers the O2 heaters but without upstream heater codes as well it won't be a fuse issue

PO174 System to lean bank 2
If only 1 bank on a V6 engine has Lean code then its usually a vacuum leak on that banks lower intake or an exhaust manifold leak on that side, it sucks in air
Could be the upstream O2 sensor on that bank as well

"Lean" code means computers calculated open time for the injectors on that bank had to be increased by more than 15% to get upstream O2 sensor to read correct Oxygen level in exhaust
It does NOT mean engine is or was ever running Lean, not what those codes mean at all

 

I pulled both downstream sensors off and did see a white wire right at the sensor showing wires. I put some liquid tape on it, not really sure how that stuff will work on it. The other side sensor looked ok on the wires. I will check the that sensor on the intake wires. I will have to get me a vacuum gauge to check it. A buddy of my told me to spray carburator cleaner over the intake housing and vacuum lines and see if the motor sound changes. I did that yesterday and it never changed a sound. So it has to be either a exhaust leak at the manifold or the flange with the tail pipe bolts to it. I used to love working on old cars and trucks as a kid. But while all this computerized vehicles it's not fun anymore. Miss the old 302, 305, 350, 351, 454, and 460 with Harley 4 barrel carburetors. Those was the days.

 

I may have found a spot where it was getting some air that not meter. I had a young man put the thermostat housing on it and he took off the front part of the intake. Well when he put it back on he used some silicone along with the gasket. Well the bottom part of it housing didn't have any silicone on it. When I spray some more carburator cleaner around that intake the motor changed it's tone some. I scraped the silicone off and just used the gasket and it ran a little better with not as much popping sound. I will check those wires tomorrow, my 9v battery for my voltage meter died.

 

Did you ever get that issue fixed? Im having the same problem with a backfire only while I drive.

 

A back fire is different from the popping noise of Cat converter metal expanding too much

A back fire means a cylinder has misfired and its unburned fuel is pushed out into the exhaust manifold where it is ignited by the next firing cylinder's HOT exhaust coming into the exhaust manifold
You should start your own thread and list other symptoms, you should feel the misfire and possibly get a flashing CEL(check engine light) or CEL comes on steady while driving

 

Thank you for replying, I thought it was a backfire but it sounds very familiar to what your truck was doing its just a popping noise down the exhaust near the catalytic converter.