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Catalytic Converter Test

lobo411

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Hello,
96 Explorer XLT w/ 4.0 OHV 160k...For years I had code 0420 intermittently, until I changed the DPFE sensor 3-4 years ago. Then it never came back. However, I nearly failed my last smog check on NOx (iirc fail was 800 ppm and I came in at 798 ppm) and I'm due for a smog check in May. The engine has been running fine since then: no codes, 20 mpg hwy/12-15 city,

I replaced the lower intake manifold, fuel injector, fuel injector manifold, and upper intake manifold gaskets to address a pinging issue and hopefully pass smog. This did improve my overall engine performance. I also bought an infrared thermometer to test the cat. I wonder if someone could check my procedure/results:

All tests done in idle at operating temp
Pre cat temp: Measured where Y-pipe meets the cat flange: 440 deg F
Pre cat temp: Measured Y pipe near driver's side oxygen sensor: 400 deg F

Temp near downstream O2 sensor: 400 deg F
Temp near the thing downstream of the downstream O2 sensor (is this the cat?): 300 deg F (this reading I'm not certain of)

I'm not sure where I was supposed to point the thermometer, to be honest. Thanks!
 
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koda2000

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i believe an exhaust shop can test your catalytic converter for flow. as far as i know that's the only test you can preform and you're basically testing for a meltdown. it's just a ceramic honeycomb coated with precious metals and when it gets hot it does its thing.
 
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SoNic67

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The only way to control the cat efficiency is to compare the O2 sensors readings. The one before cat should switch the voltage often. The sensor after the cat should change voltage less often. This is how PCM monitors the cat efficiency and trows the P0420 code. Sometimes a bad O2 sensor (usually the pre-cat one) will trow that code since the computation cannot be done anymore...
I don't know of a way to 'restore' cat efficiency, I just know that running with rich or lean mixtures will irreversibly damage the cat.
 
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my98nnj

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I think you've done what's needed. Throw a set of plugs, new air filter and an oil change before you rest and you should be OK.
 
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Flash

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Before you go for the smog test take the car for a good highway run to get the cat good and hot so that it works at peak efficiency and maybe burns some crap off it.

I've read on other car forums how using alcohol/gas improves your readings but I haven't done it myself.
 
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lobo411

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Thanks for the feedback all! I've got her pretty well tuned up, so I guess I've done all I should do to get her ready until the "day of" stuff (a good hot run as Flash mentions). I suppose if there's anything wrong with the cat and it fails, I'm in the same boat of having to have a shop do the work anyway since I'm in CA and a private individual can't even buy a cat here legally. I'll update this when I get my smog results in a few months!
 
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rb142

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As mentioned, the only good way to test the cat function is to monitor the fore and aft oxygen sensors (usually on a lab scope) and see whether it is doing what it should. A good shop should be able to do that.

If your issue is too much NOx, you may not be getting enough EGR flow. Check the EGR parts for clogging and proper valve operation.
 
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lobo411

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As mentioned, the only good way to test the cat function is to monitor the fore and aft oxygen sensors (usually on a lab scope) and see whether it is doing what it should. A good shop should be able to do that.

If your issue is too much NOx, you may not be getting enough EGR flow. Check the EGR parts for clogging and proper valve operation.

Ya I was curious about that. I've been lazy about getting a vacuum pump to precisely test the EGR valve, but I did suck on the vacuum port and it seemed to open/shut fine. I did notice light-tan deposits on the internal metal rod (the one you can see when you unbolt the EGR valve from the Upper Intake Manifold) and I thought about cleaning it, but lately half the time when I clean stuff it ends up breaking (the joys of a 16 year old car!). It's not a ton of deposits, but I don't remember seeing them when I first got the car at 110k mi. Think I should clean it up a bit?
 
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rb142

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A little color (deposit) sounds pretty normal. If you can activate the valve (with that vacuum pump you don't have), you should be able to make the engine stumble. But if the DPFE is working, it should already throw a code if there isn't enough flow.
 
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Markaprice73

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lobo411

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1996 Explorer 4.0 OHV w/ 180,000 mi

So it's my smog check year again, and I'm back in this boat. The cat readiness test simply refuses to execute. I've scanned for trouble codes periodically ever since the last time I had it tested (May 2016), and I've never seen the cat readiness test listed as "ready." This is probably 6,000 miles of mixed driving: mostly stop and go city driving with a little bit of short range (10 miles) high speed highway and 30-40 longer range (70-100 mile) high speed highway cruises.

Normally, this would not be a problem. CA used to let you pass with 2 readiness tests "not ready," but in 2015 they changed it to only 1. I can't seem to get the cat or the EVAP tests to run despite extended highway cruises at 55 mph (constant), city driving in the 35-45 range, etc...

I'm going to try replacing the post-cat o2 sensor since it's the oldest one on the car (10 years, 80,000 mi), and it's the one that's easiest to replace. Somewhere I read that a lazy post-cat sensor might prevent the cat readiness test from executing. I really don't want the EVAP test to run because I have a pending p0455 code and I think the EVAP system might have a minor leak. IME, EVAP leaks are un-repairable...you'll never find the leak.

Thoughts appreciated!
 
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96eb96

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1996 Explorer 4.0 OHV w/ 180,000 mi

So it's my smog check year again, and I'm back in this boat. The cat readiness test simply refuses to execute. I've scanned for trouble codes periodically ever since the last time I had it tested (May 2016), and I've never seen the cat readiness test listed as "ready." This is probably 6,000 miles of mixed driving: mostly stop and go city driving with a little bit of short range (10 miles) high speed highway and 30-40 longer range (70-100 mile) high speed highway cruises.

Normally, this would not be a problem. CA used to let you pass with 2 readiness tests "not ready," but in 2015 they changed it to only 1. I can't seem to get the cat or the EVAP tests to run despite extended highway cruises at 55 mph (constant), city driving in the 35-45 range, etc...

I'm going to try replacing the post-cat o2 sensor since it's the oldest one on the car (10 years, 80,000 mi), and it's the one that's easiest to replace. Somewhere I read that a lazy post-cat sensor might prevent the cat readiness test from executing. I really don't want the EVAP test to run because I have a pending p0455 code and I think the EVAP system might have a minor leak. IME, EVAP leaks are un-repairable...you'll never find the leak.

Thoughts appreciated!
1) Our 96s do not throw CELs for anything EVAP related. I was told that by ford. Somehow they got an exemption
2) Before changing anything I would get a scan tool and monitor pre and post cat converters
3) Check for exhaust leaks, I know it is not an issue where you are( think your profile said CA at one time) but the Y pipe can rust away by the heatshield welds.
4) There is (believe it or not) a calibration you can get to fix the cat code issue. They made the monitor very sensitive and the new calibration fixes the issue.

Do you have the offical motorcraft documentation for running the test?
 
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96eb96

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Article No.
00-26-4
  • MALFUNCTION INDICATOR LAMP (MIL) - MIL ILLUMINATED - DIAGNOSTIC TROUBLE CODE (DTC) P0420 STORED IN MEMORY - VEHICLES EQUIPPED WITH 4.0L OHV ENGINE ONLY
  • LAMP - MALFUNCTION INDICATOR LAMP (MIL) ILLUMINATED - DIAGNOSTIC TROUBLE CODE (DTC) P0420 STORED IN MEMORY - VEHICLES EQUIPPED WITH 4.0L OHV ENGINE ONLY
Publication Date: DECEMBER 14, 2000

FORD:
1996 EXPLORER


This article is being republished in its entirety to update the Calibration Information.

ISSUE:
Some vehicles may exhibit a Malfunction Indicator Lamp (MIL) illumination along with a P0420 Diagnostic Trouble Code (DTC) stored in continuous memory with no driveability concerns. This may be caused by the calibration of the Powertrain Control Module (PCM).

ACTION:
If no other failures are observed during normal diagnosis, (physically damaged catalyst, stuck fuel injectors, etc.), reprogram the PCM with the latest level calibration in the application chart. PCM reprogramming should be performed before any emission hardware is replaced. If the vehicle already has the latest calibration, follow normal diagnostic procedures for DTC.
 
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shucker1

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Catalytic Converters actually "burn" while doing their job.

Outlet side of converter should be hotter than inlet side of converter during correct operation.

Of course dependent of the type of converter, 3 way of 2 way.

Most cats these days are 3 way.

From an industrial standpoint a 75-100 Deg rise in temp is optimal.
 
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lobo411

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Thanks for the replies! I finally got the cat to show "ready." Here's what I did today:

7:00 AM: Start. Drove 7 miles at 60 mph, exited the freeway and got back on the other direction, and drove 10 miles at 60 mph. Cat shows not ready. Turn off vehicle.

7:30 AM: Start. Drove 7 miles at 0-45 mph in town, cat shows not ready. Turn off vehicle.

11:30 AM: Start. Drove 12 minutes at 60 mph on the freeway and exited, cat shows not ready (according to the OBDII procedures, this *should* have executed the cat monitor, but it didn't)

11:45 AM: Drove 10 more minutes at 0-50 mph in town, cat shows not ready. Turn off vehicle.

12:05 PM: Start. Drove 3 miles at 0-40 mph in town, cat shows ready.

I don't have to smog until April/May, but I wanted to figure out what the heck I needed to do to get down to only 1 "not ready" (the EVAP still shows not ready).
 
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lobo411

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Well, I passed smog today...somewhat miraculously! I cleared the codes after driving to Wal-Mart, shopped, and then drove across the street (literally) to Costco and rescanned. Somehow, the EVAP monitor showed ready and I was good to go! Crazy...it should NOT have executed...IIRC, it takes a 10 min cruise at 45 mph for the EVAP to execute. But whatever...I'm not arguing!

Anyway, it looks like it's running way cleaner, right? HC emissions dropped by more than half, and CO2 went down a bit too. Maybe it was running rich in 2016? The fuel pump died right after I took my smog test in 2016, so could the new pump have helped cut my HC?

Other measures I took to make sure I passed this time:
1. Techron 2-3 months before the test
2. Oil change a week before the test, using 10w30
3. New PCV grommet
4. Retorqued LIM bolts (they all took a 1/4-1/2 turn to return to spec)

2018 Results:
15 MPH
HC: Max 47, Meas 20
CO%: Max 0.60, Meas 0.12
NO(ppm): Max 494, Meas 209

25 MPH
HC: Max 31, Meas 7
CO%: Max 0.73, Meas 0.12
NO(ppm): Max 747, Meas 226

For comparison, this is my 2016 result:
15 MPH
HC: Max 47, Meas 47
CO%: Max 0.60, Meas 0.11
NO(ppm): Max 494, Meas 300

25 MPH
HC: Max 31, Meas 13
CO%: Max 0.73, Meas 0.22
NO(ppm): Max 747, Meas 136
 
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shucker1

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Cool beans!
 
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