RonD you had mentioned earlier something about the IMRC being something that occurs at 2000 RPMs and I think that may be causing some of my issues, or rather the delete I did. I had read of people deleting this and not having any issues (on Rangers and other cars too). But I had my scanner recording tonight and under most conditions, the instant that the engine crosses 2000 RPMs (which is where the stuttering suddenly gets better), I see the spark advance go from around 20 to over 40 degrees and the IMRC goes from OFF to ON. I assume going from OFF to ON would open the IMRC flaps (if I had them). A few times I saw the IMRC parameter change to ON at lower RPMs (once 1500 and again 1700 ) but I am not sure why that was the case. Typically it was always 2000 RPMs and it was accompanied by that instant jump in spark advance.

At this point I am considering taking the intake back off and putting the IMRC rod and flaps back on just to see if it makes a difference. Maybe I slightly improved or made no difference with my original poor engine running, but made the problem worse below 2000 RPMs by deleting the IMRC. Like you said, the ECU is expecting the IMRC to be there.

 

Never looked at IMRC so have no info on it, just know its RPM based, and yes the spark advance change would make some sense with IMRC, but could be your computer was the base cause of the issue to begin with

If you read up on symptoms of bad IMRC it might be helpful

 

Yes, at this point I think it is one of two things. Either:

1) I have deleted the IMRC and the computer is adjusting things (like spark advance) as if I have an IMRC, and I don't. So the computer is doing the correct thing, but since I have removed the IMRC, it is causing problems
2) The computer is the source of the problem.

I did find one forum post where a guy had an IMRC stuck open code and had some moderate hesitation/surging down low. He said after he replaced the solenoid the surging (and code) went away. But I have seen many others claim when they had the IMRC stuck open code, they felt no difference in the. But of course it is possible they on theirs it was just the IMRC "monitor" that is on the actuator that was giving a false code and the flaps really weren't stuck open.

 

After all this time with this truck running poorly, I have never had a CEL set. Yesterday it actually ran fairly well, especially above 2000 RPMs. Today I drove it to work and unfortunately didn't have my scanner with me and it was running worse and even above 2000 RPMs I was feeling it cut out. Eventually the CEL came on. When I got home I checked and the code was:

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

The scanner said that possible causes were:
-Spark Timing Retarded Below Spec
-Cylinder Misfiring
-Fuel Pressure Too High
-Damaged HO2S
-Damaged ECT Sensor (I assume it means CHT ?)
-Downstream HO2S Wires Improperly Connected
-Damaged Exhaust pipe/manifold
-Damaged Catalytic Converter

I assuming it was just that the miss was bad enough today that it was affecting the Cat efficiency. Or I guess it could be a bad cat or bad downstream O2S. I took the truck for a drive and looked at the voltage signal from the upstream and downstream O2 sensors. I know the upstream is supposed to be quickly cycling from lean to rich, but once warmed up I am pretty sure the downstream should be more steady. But it almost looked identical to the upstream. The engine had been running for 30 minutes and I was running in 4th gear at a steady 2500-3000 RPMs on relatively flat roads. So I think this is a sign of a bad catalytic converter. I know this means I am putting out more emissions, but would that cause the car to run poorly and get bad fuel mileage? I guess it is possible that it is partially blocked.

 

O2 sensor 1 1(upstream) should show average of about .4v, and move up and down ALOT like both graphs

O2 sensor 1 2(downstream) should be .7-.8volt and a steady line, it will jump up and down now and then, but a straight steady line the rest of the time

O2 sensors only see oxygen
.1volt = High Oxygen
.9volt = Low oxygen
The Cat Converter burns up any oxygen as it burns up emissions, so downstream O2 should show low oxygen level, above .7v

Not a Ford graph but shows what it should look like and should not look like: https://www.troublecodes.net/wp-cont...ensors-Cat.png

So I would say Bad Cat converter, because downstream O2 is jumping around like upstream, so O2 is working, its just that the downstream O2 is seeing the SAME exhaust as the upstream, like there is NO Cat converter in between

 

Thanks! Does "bad" often mean "clogged" as well? If the cat isn't working well, but isn't restricting the flow, I wouldn't think it would be causing the poor performance and bad mileage. But obviously if it was clogged it would.

I was looking through the Ford service manual and for the reference values it says for O2S12: "Downstream O2S will stay close to a constant voltage when the catalyst monitor is off. When the catalyst monitor is on, O2S will switch rich to lean above and below 0.45V DC and never be negative". What is the catalyst monitor? I monitored this downstream sensor for quite a while and it always seemed to swing back and forth just like the upstream. I'm just confused why the PCM isn't seeing this and giving me the P0420 more than just this once.

One other odd thing I have noticed is that under reference values, the manual shows the CHT typical value is 194 degrees. However mine gets up to 260-265 and once warmed up is never below 245. My scanner actually flags the 260 is above "normal", but I am not getting any kind of code because of it. Before I start the car the reading accurately gives the ambient air temperature. I read in another old threat where someone said their CHT was showing 260 and hotter, but their engine didn't appear to be overheating. So am thinking it is normal.

 

Restricted exhaust would show itself, at first, with limited RPM at highway speeds, then get steadily worse over time
Failing Cat would not get as hot as it should, it should be hotter than exhaust pipe in front of it

Catalyst monitor is a test the computer runs now and then to see if Cat is working, computer varies the fuel ratio and monitors upstream and downstream O2 responses

If you Reset computer you will see P1000 code set, this means computer needs to test all the emissions systems again, seen here: Ford Motor Company Driving Cycle

This was added because people were resetting computers to pass smog tests, lol
So P1000 was added and Smog guys won't test vehicle with that code present, usually with ANY code present.

Not sure why CHT is showing that hot temp, and computer is ignoring it?

 

I do seem to have the inability to get to the speed that I once could. On level ground I am not sure I could get much over 80-85. Also the poor mileage would indicate possible restricted exhaust as well. However I read somewhere that you can monitor intake vac to see if the exhaust is plugged: Have the engine at idle and the vac will be around 20 in Hg (10psi) and then open the throttle to maybe 2000 RPM. If the exhaust is not restricted, the vacuum should dip but then fairly quickly come back to near the idle value. But if it is restricted, it will take a while to come back to that idle value or stay low. Using my scanner I saw that mine comes back to the idle value within 1-2 seconds. So that is an indication that it isn't restricted. Also, after a 30 minute drive I measured the temperature before and after the 1st and 2nd cat. The downstream one was about 540 F at the front 640 F at the exit, which I think is an indication that it is working well. The upstream cat is a bit harder to access the inlet side, but it appeared to be about the same temp (540 F) at the inlet and exit. So if I have an issue with the cats, I assume it is with the first one. Because of the downstream O2 sensor, I am convinced that the cat(s) are not working properly, but I am not convinced it is causing my other issues problems because it doesn't appear to be clogged. Maybe the misfires have actually caused the cat problem?

I have noticed that P1000 that showed up after I cleared codes. But the strange thing is that it never goes away. I have driven it three times since I cleared the code and it is still there. Also I looked at the "catalyst monitor test" status and when I first started driving it was "FALSE" but after a while it change to "TRUE", so I assume it was able to run that test. I know there are likely other tests that are required to be completed before the P1000 is cleared, but I am not sure why they won't complete so that this code can be cleared

 

In late 2018 I bought a 2003 Ranger XL 5 speed manual transmission with a 2.3l engine with 110,000 miles unseen in person on Craigslists and un-driven. Owner drove it to my house and I handed $2,500 to him. I wanted a project to keep me busy both body and mind. I didn't know it at the time, but it had been through at least 4 owners before me. It even left Hawaii (where I'm from) to Seatle and back. It ran very poorly and had that same surging between 1500 and 2000 rpm. Not being a mechanic (and not too worried about cost) I through the parts cannon at it and that surge was still there.

It was boiling over when I shut the engine down sending bubbles back to the expansion tank. Ran a block tester test on it and the liquid stayed dark blue. Ran into an article on one of the forums that recommended changing out the electric thermostat to a 2006 model without the heater and installed a resistor in the electric line to make the pcm think the electric thermostat as was stilled installed. Forum said the engine was boiling over after the coolant stopped moving. Truck ran better. No more bubbling in the expansion tank. But that surge was still there.

By chance I found the emissions vent valve separated from the charcoal cannister, I changed it out with an OEM one and the surging inproved to between 1800 and 2000 rpm. Don't know why or how that improved the surging, but, it did.

I changed out the CHT and the surging seemed to improve again. By the seat of the pants test.

By chance again, I found the electrical plug to the Output Speed Sensor (OSS) on the transmission all covered in green corrosion. I cleaned the corrosion off and the surging is just a little noticeable a hair before 2000 rpm. Again, I don't why or how that improved the surging. I'm going to change out the OSS with an OEM sensor to see if that helps. I read somewhere that the OSS does have some input for emission controls. Whether that's true or not I'm not sure.

I too removed those flappers in the intake manifold. When I changed out the valve cover gasket I found the flappers/openings worn, which I think was the reason for the code thrown on my ODB reader. Don't remember the number(s). I did this in the beginning of my parts cannon event. Since the truck was running bad at that time I don't know if removing the flappers hurt or helped the performance.

Oh, by the way when I first stated the parts cannon my gas mileage was around 16 miles per gallon. I don't take the truck very far from home and only travel on backroads. So, I'm lucky if I get beyond 3rd gear. I did take it on the freeway once and got it up to 65 mph without (what seemed) too much effort. After doing the things I've done so far, I'm up to 21 miles per gallon.

Sure like to get rid of that surge or at least know what's causing it.

 

Thanks for the info. What is odd about mine is that it doesn't seem to be running hot (coolant isn't hot and gauge doesn't report hot, and no bubbling), but the CHT is reporting it as hot. I was thinking that maybe the CHT was fine, but the scanner I was using was translating the voltage to temperature incorrectly. But that isn't the case. In the factory manual I see that on the hot end a 2.4V signal from the CHT is indeed over 260 degrees. Then I started thinking maybe it is supposed to run that hot. I know the coolant shouldn't be that hot and I just assumed the cylinder head temp would be similar to the coolant temp. But then I was looking through the manual and it was discussing the catalyst efficiency monitor test conditions. It had several conditions that must be met before the test would be started by the PCM, but one of them was "ECT or CHT is between 170F and 230F". That led me to believe that range was "normal operating conditions". Also in the "reference values" section they list "194F" for the CHT. Mine fairly quickly goes through that range and gets up in the 240-260F range. I have a new Mazda CHT on the way. Most of the time I just grab a Motorcraft part, but oddly enough the aftermarket manufacturers all list different part numbers for the 2003 2.3L Ranger and the 2003 B2300. So just to be no the safe side, I tracked down a Mazda one. I replaced my thermostat a few years back and I went with the expensive electric one instead of using the resistor like you did. It appears to be working, but the scanner I have reports the thermostat heater control (THTRC) to always be 0%. According to the service manual, this electronic thermostat is a just a standard thermostat that is hotter (208F instead of 194F) and then has a resistor element in it that the PCM can add a little heat to under higher loads. This way it runs hotter under light loads and then doesn't get too hot under heavier loads. So if mine is never heating and is always at 0%, that might explain why my CHT is so high?? But I don't understand why the PCM would not be enabling the thermostat heating element with a 260F input from the CHT. Maybe, like RonD suggested earlier, I have an issue with the PCM.

There are two areas that I haven't fully investigated and that is the EVAP and the EGR. I will definitely check out the charcoal canister. Thanks for the suggestion.

My valve cover gasket was leaking everywhere, but it was terrible on the back. It had the entire transmission covered in oil. So the OSS and the connector has been covered with oil for quite a while. I will pull it off and see what it looks like. I haven't paid too much attention to it in the scanner, but the few times I had, it seemed to be working ok.

I am really considering putting the IMRC flaps back in. Not only did the <2000 RPM surging/hesitation get worse after doing that (of course I did replace lots of other parts at the same time), but I read on another forum where a guy had a truck that had a stuck open IMRC code for quite a while and he had surging. When he finally got that repaired, the surging went away. My flaps were in pretty good shape because I had replaced the intake manifold about 8-9 years back (maybe 50k miles ago). If I do put the flaps back on, I will post the results back here.

Not important, but something I noticed yesterday in the service manual. In the workshop manual section, Ford calls this the "IMRC" (Intake Manifold Runner Control), but in the PC/ED section which covers all Ford 2002 vehicles, it describes 3 different types of "flap" systems in the intake. The IMRC is described there as a system that is controlled by a cable or motor, and it provides for 2 air passages to each cylinder. One is always open the other is open and closed with a butterfly plate. The one on our 2.3L engines is referred to as the Intake Manifold Swirl Control (IMSC) Vacuum Actuated System. It is described as a plate that blocks 60% of the opening when actuated, leaving the top of the passage open to generate turbulence. I have always heard both IMRC and IMSC used, but never had read a detailed description of both. BTW, the third one was called the Intake Manifold Tuning Valve (IMTV).

I have a 20-25 min drive to/from work and over half of that is freeway and the rest is a state highway where there is no stopping. So if you are getting 21 mpg, it might be getting close to 25 mpg on my route.

 

As far as the coolant temperature goes, Ford only ran the temperature controlled thermostat for 1 to 3 years. The goal then was to improve gas mileage, but, the high temperature put a strain on other parts of the cooling system - mainly that plastic tee on the return hose. There have many reports of that tee cracking and changing that hose with that tee is a nightmare. Other reports stated that they just replaced that tee with a brass/metal one. Still a nightmare, but not nearly as bad as changing the entire hose.

The report I read replaced the temperature controlled thermostat to a traditional thermostat that opened at 190 degrees instead of the 245+ degrees. My truck seemed to run better (by the pants) and I no longer have that bubbling/boiling over problem.

 

My crank position sensor showed up today and it didn't help either.

But I have been reading a bit more about long term and short term fuel trim. If I understand it correctly, the short term fuel trim should be going up and down which ultimately makes the mixture go back and forth between slightly rich and slightly lean. It does this to help the cat work optimally and this is why the upstream O2 sensor signal switches back and forth between 0.2V (lean) and 0.8V (rich). Then it is the job of the long term fuel trim to try to keep the short term fuel trim near ~0%.

When I was driving today, I noticed that when I was stopped at a red light (idle), the long term fuel trim would be something like -5% and the short term would be near 0%, then if I gave it any gas the longer term would react and quickly move to +10% and pretty much stay there unless I let off of the throttle. When the load would increase (giving it just a little more throttle), the LT would stay at 10%, but the short term would go negative. So with the long term that high, is that an indication that the engine is running a bit lean? Maybe a small vac leak or possible the upstream O2 sensor is off a bit (it is a new Bosch O2 sensor)? I know the O2 sensors often switch back and forth 1-5 times per second, but the old OBD2 interfaces are fairly slow and the PID update rate isn't fast enough to catch all of the switching. But if guessed at the average of the upstream O2 graph, would guess it to be greater than 0.45 (so rich). So if that is the case, why would the long term fuel trim still be at +10%?

 

Yes short term fuel trim is the second by second data of computers injector open time calculation

Long term is a long term average, but its also added to computers base calculation for short term 0

So if long term is -5 and short term is +5 then actual fuel trim is 0

If long term is +10 and short term +10 then its really +20

Long term fuel trim helps the engine and its systems to "age gracefully", and to help engine run better during Cold Start when O2 sensors can not be used

Computer stores long term fuel trims in memory, say its +5
Computer adds that to its calculations on cold start, because it has NO feedback from upstream O2 sensors until they get heated up above 650degF, so 3 to 4minutes
This way computer is pre-compensated for small vacuum leaks, dusty MAF, slightly lower fuel pressure, ect........

Computer knows its running a 2.3l LITER engine, so it knows EXACTLY how much air is coming in at say 1,000rpms, or at 2,500rpms, its just math
It has the MAF and Air temp sensors to tell it the WEIGHT of that air
It "knows" the fuel pressure should be 55psi and injectors are 14pounds/hour, so it "knows" XX grams of fuel will flow out if it opens an injector for 50ms(milliseconds)

And it calculates short term fuel trim(STFT) based on above and then adds Long term and that's STFT 0
If fuel pressure is 45psi or there is a larger vacuum leak then STFT with go up, if it gets to +15% for any length of time then Lean code will be set
But if it stays under 15% then Longer term fuel trims(LTFT) will go up as well and be stored in memory to compensate for next cold start
If LTFT gets above 15% for any length of time then Lean code will also be set

In above example, STFT +10 and LTFT +10 that would not set a lean code at that time, BUT.............LTFT would probably be saved as +15 or +18, which would set a code after next warm up

 

The last several days I have been driving around with my code reader plotting:

1) spark advance
2) IMRC
3) RPM
4) HO2S1
5) HO2S2
6) Short Term Fuel Trim
7) Long Term Fuel Trim
8) Total Misfires

I have noticed a few things (keep in mind the IMRC flaps have been removed):

1) The average value of the upstream HO2S is always around 0.44-0.46. So that makes me think that the computer is doing a good job of keeping the mixture right
2) As stated previously, below 2000 RPMs the spark advance is about 20 degrees and as soon as it goes above 2000 RPMs (or whenever the IMRC would open the flaps...if they were there), the spark advance jumps to about 40.
3) I feel lots of stuttering and hesitation that doesn't register as a misfire, but the hesitation and stuttering is way worse below 2000 RPMs (or whenever the IMRC flaps would have been closed) and this is when most of the PCM registered misfires happen.
4) The few misfires that happen once I am above 2000 RPMs are always accompanied by a large dip in the spark advance from ~40 to ~20 degrees. It is difficult to tell, but it looks like the spark advance dips, then the misfire happens. Maybe the misfire happens and that makes the spark advance drop (just like it drops when you let off of the throttle). Is it possible this dip in spark advance is causing the misfire though? I know I am grasping here, but I really don't have many straws left to grasp. What goes in to determining what the spark advance should be? Knock sensor? Crank and Cam sensors? Intake air temp?

 

Just a refresher for spark advance

Air/ gasoline fuel mix of 14.7/1 burns at a fixed rate, say XXXX milliseconds from spark ignition to FULL explosive power, so its not instant

For maximum power from the full explosion you want it to happen when piston is 8 to 10 degrees AFTER TDC, this is a smaller area between piston and head, and also has good leverage on the crank shaft to push it down to add to its power/spin

So the spark happens BEFORE TDC so we get full explosion After TDC, because of the XXXX delay
At 1,000rpm it takes a specific amount of time for the piston to move from 20deg BTDC to 20deg ATDC, also a known/fixed amount of time, its just math
At 2,000rpm it takes less time to move from 20deg BTDC to 20deg ATDC, same for 3,000rpm, ect
This is called RPM spark advance, very easy to calculate

The "monkey in the wrench" is the fuel mix, when ratio changes from 14.7:1 so does its burn time, a richer mix burns faster.....................
This is called Load spark advance, vacuum advance on older engines

So when accelerating computer richens the mix and RPMs are going up, so RPM advance will go up but Load advance should keep it from going up to fast because of the richer mix then as you hit cruising speed advance will go up a bit more because fuel mix is back to 14.7:1

If spark advance is too much engine will stumbled because spark is happening between 0 to 8deg ATDC so no leverage on the crank and too small of an area for full explosion
If spark is not advanced far enough you lose power when full explosion happens after 10deg ATDC, so too much room for explosion to expand into and less power added to crank
Idle often is like this, full explosion 10-15deg ATDC so engine stays running but doesn't over heat when no extra power is needed

If you remember the old days you would set Base distributor spark timing with Vacuum advance unhooked, say 12deg BTDC
Distributor had springs and weights for RPM advance they remained connected
Then when you put Vacuum hose back on, spark timing would change to 20deg BTDC or so, intake vacuum increased advance
When you accelerate, fuel mix gets rich and vacuum in intake manifold drops which reduces "vacuum advance" but RPM advance increases

Point is your spark timing when accelerating seems to be a bit off

Sorry for the long winded approach but it helps me to remember things, and some of it may even be correct, lol

 

Thanks for the detailed info. i love the "long winded approach", because more often than not, I am learning something new. I knew that spark advance would go up as the RPMs increased, but I didn't know how the mixture would affect it. Driving around watching spark advance I had been confused how the RPMs might stay similar but my advance would drop some when starting to go up a hill (engine load increasing). But now that makes sense.


So I put the IMRC flaps back in (and put in the new Motorcraft cam position sensor while I had the intake off off). This made a big difference in the <2000 RPM range. The bad hesitation that suddenly clears up at 2000 RPM is gone. I had read many reports of people saying IMRC deletes caused no issues, but that was definitely not my experience. However I am still getting registered misfires. On the 25 minute drive to work I had 12 today. This is a little lower though (normally 15-25), but was just one trip. However the bad hesitation below 2000 RPMs was typically not registering as a misfire, bit it was just very annoying. I also still have some hesitation when accelerating under load at >2500 RPMs, but again this doesn't register as a misfire. This and the poor mileage with reduced power are the original issues I have had from before I started all of this work.

The misfires that are registering seem to be mostly happening when I let off the throttle, but a few have been while I am on the throttle.

 

I had mostly given up on ever being able to solve the problem with my truck running poorly (hesitation, low power, poor mileage) but I had one more thing to try that I have been putting off and that was to check to see if the catalytic converter was clogged. I do not get any codes regarding the catalytic converter, but when I look at the waveform of the upstream and downstream O2 sensors, they appear to be nearly identical (switch back and forth at the same rate), and I have read that is an indication that the cat isn't working properly..odd that I do not get a code for that. But when I have taken temperature tests, the rear of the cat does seem to be hotter than the front which indicates it is working. Also I have read that if you hold a constant throttle, if the cat is clogged, the vacuum will slowly drop and I didn't notice that. But I found a like new Lang Tools exhaust back pressure gauge on ebay for about $25 so I purchased it:

https://www.langtools.com/sku-tu-29-...-pressure-kit/

I removed the upstream O2 sensor and attached this gauge and at idle (you read the lower scale) the pressure was right at the edge of the "red" zone but still in the green. Then at 2500 RPMs (you read the upper scale of the gauge) it was well below the red or yellow zone. So this indicated that there wasn't a blockage. I then decided to take the truck for a spin with the O2 out and it ran much better and didn't have the hesitation. I put the O2 sensor back in to plug the hole, but left the O2 sensor unplugged and took it for another drive. I did this because I know that unplugging the O2 made the truck run open loop and it could affect how the engine ran, so I wanted to narrow it down to just changing the back pressure. When I did this the hesitation and low power was back.

I did a few tests like accelerating up a hill and marking where I hit 45mph and also measuring the horsepower with the OBD2 tool I have (OBDLink MX+). I figured it isn't that accurate, but should be repeatable.

With the upstream O2 sensor installed but unplugged:
1. OBDLink MX+ indicated a max of 89hp
2. At max acceleration I would often get pinging and the power would drop significantly
3. I was getting the hesitation that I get
4. I was 150 yards later hitting 45mph climbing the hill

With the upstream O2 sensor removed (and of course still unplugged):
1. OBDLINK MX+ indicated 114hp (25hp more)
2. I never experienced pinging and the drop in power. I was still pulling up to 5k RPM
3. I never experienced the hesitations or misfires
4. I hit 45mph going up the big hill 150 yards sooner and I was accelerating the same and shifting at the same RPM.


Although I am getting mixed messages, am I correct in thinking that I have a back pressure issue even though the gauge seems to indicate that I do not? I guess it is possible that it could be a clogged muffler instead of a clogged cat. I hate to spend the $400 on a new cat without being 100% certain.

 

Yes, you have an exhaust blockage by the test you did

Not sure about that gauge, and for sure not the green/red stuff, lol
You didn't report the PSI readings
1psi at idle is good, 1 1/2 is tolerable
At 2,500rpm 2psi is OK 2.5psi is getting marginal

You have a rear O2 sensor as well, after the Cat converter, take a reading there, that will tell you if its the Cat or Muffler, or leave upstream in and downstream O2 out

 

Thanks for the response.

At idle the gauge says anything above 0.9 is bad and mine was right at 0.9. Then at 2500 it said 2.5 is getting marginal and 3 is bad. I had about 2 or maybe slightly less.

I'm not sure I have much faith in the gauge, so I think I will try to upstream in and downstream out and see how that goes. I figured the downstream would be after the 2nd cat but it seems to be right in the middle of it.

 

I put the upstream O2 sensor back in (red circle), but didn't connect it since I was just wanting to block the hole. I then disconnected and removed the downstream O2 sensor (green circle). I took the truck for a drive and it seemed to run just as well as it did with the upstream out and the downstream in. I would think this would indicate that it is the muffler that has some blockage. However the downstream O2 is in the center of the 2nd cat and not at the end of it, so I thought it was possible the blockage could be after the downstream O2, but before the muffler.

I then reinstalled both O2 sensors, but did not hook up the electrical connectors. I then removed the muffler piper from the end of the catalytic converter mid pipe (purple circle) and pulled the muffler over to the side so mid pipe was completely open. I took it for a drive and it ran terrible again.

So from all of this, I assume it means that the front cat is fine and the blockage as at the end of the 2nd cat.

 

Good testing

I would have to agree with your conclusion
Pull out the green one again, before putting muffler back on just to confirm

 

Good idea! I pulled the green one (down stream) out again and left the muffler detached and took it for a drive and it ran great.

 

After all of the testing I ordered a new catalytic converter and it arrived yesterday. As I took the old one off I looked down into the hole where the downstream O2 sensor is attached and could saw lots of the catalytic converter honeycomb chunks moving around in there. So that made me even more sure that the catalytic converter was my problem. I installed the new one and it ran great. Lots of power, no misfires, and no hesitation. I looked at the O2 sensor data and the upstream looked the same as it always had (switching quickly), but now the downstream was nice and flat at around midscale instead of basically being a duplicate of the upstream like it had been before.

Thanks RonD for so much help!

However two things that I am still wondering about

1. With the downstream O2 sensor being a duplicate of the upstream O2 sensor, why was a code never set? I thought the main purpose of the downstream O2 sensor was to let the computer know that the catalytic converter is working properly, and from its output it was obvious that it wasnt.
2. The honeycomb parts I could see looked nice and clean and not clogged or melted, but of course they where all broken up rattling around. What could have caused that to happen?

 

Yes, a code should have been set if downstream O2 was running under 0.5volt average
Like: P0137 02 Sensor Circuit Low Voltage (Bank I Sensor 2)

Not sure why it didn't do that

Read here on possible causes for early Cat converter failure: https://www.vipermotorsports.com/Abo...erters-to-fail

 

The downstream O2 data looked very similar to the upstream in that it was switching back and forth quickly. So I guess with it doing that, the average was still somewhere in the middle and not below 0.5 volt. Maybe that is why a code wasn't set. When I unplugged the downstream O2 sensor, I did get codes related to the downstream O2.

I once had a somewhat sudden failure of the ignition coil, but I repaired that immediately. I have never had bad plugs or wires in it and I don't think I have any of those other issues either. It uses very little oil and the compression and leak down tests gave good results. I have looked down in the cat from the front with an inspection camera and the honeycomb looks intact and clean (of course all I can see is the front of the front cat) and then when I look in with an inspection camera the rear of the 2nd cat looks perfect too. It appears the front of the 2nd cat is where all of the damage was. So I would think it was some sort of impact but there are no dents. The truck had been wrecked before I purchased it back in 2007 so for all I know this wasn't the original converter.