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OBD II Data question

My '97 F150, 4.6 V8, is failing to complete the readiness monitor for the CAT. I have an existing Pending Code for P0430, and fully expect the Check Engine light to come on soon with a code, P0420 to accompany the P0430. I have no other codes. (This cycle has repeated itself several times and my Innova scan tool only provides freeze frame data at the moment that the CEL comes on.)

I'm monitoring my condition with the Torque Lite app on my phone and a WiFi scan tool connected to the OBD II Data Port. I have live data available, but I'm too stupid to figure out how to get the logs to email. I'm working getting the logs out, when this happens I'll be happy to share whatever data there is. (The Torque app is new, and I can see more data that helps frame my conditions, so now I am asking what the data means.)

When I look at the pre-CAT sensors, they are active and move within a normal range, both for fuel trim percentage and sensor voltage output. The voltages change within a range of about 0.1 to 0.8, and the fuel trim percentages change with the application of throttle then a return to idle.

The post-CAT sensors read a steady fuel trim of 99.2% and never change, the sensor voltages are active and change within similar parameters as the pre-CAT voltages.

My question is, are my CATs bad or am I facing failed post-CAT sensors?

Is there any other component I should be looking at?

Remember, there are no other codes that are either pending or active.

Reply to
Jeff Strickland
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P0420- Catalyst efficiency

- Three way catalyst converter Bank 1

- Exhaust tube

- Intake air leaks

- Fuel injectors may be faulty

- Fuel injector leaks

- Spark plugs may be faulty

- Improper ignition timing

- Engine Control Module (ECM)

P0430- Catalyst Efficiency

- Three way catalyst converter Bank 2

- Exhaust tube

- Intake air leaks

- Fuel injectors may be faulty

- Fuel injector leaks

- Spark plugs may be faulty

- Improper ignition timing

- Engine Control Module (ECM)

If you are getting both codes it is somewhat unlikely to be either sensor or converters, but it COULD be both converters are bad.

You need to check to be sure you don't have an exhaust leak before throwing money at the cats and sensors. Cracked manifolds are VERY common on that truck and WILL cause the problem..

Reply to
clare

My experience is that one can generally hear an exhaust leak, and I do not hear one. I've done nothing to the truck that involves the exhaust system in any way. It has 158k miles.

My troubles started after changing the plugs. I was getting a misfire on

6 -- that was an actual misfire but I had to wait for the code to be active for my scan tool to show it so that I could know which plug to fix. I got the P0430 after finishing the drive cycles to reset the Readiness Monitors. I swapped the post CAT sensors to see if the problem would go to the other side, it did not. Then I had a leak of the heater core, and the repair effort left a small leak of the heater hose connector(s) that dripped coolant onto the #4 plug well. Another misfire, and then I had the P0420 when the monitors finally reset.

Now, I have no codes except for the P0420 and P0430. I also have a new scan tool that shows pending codes before they go active, my other scan tool does not do this -- I only see pending codes after they set the CEL, which means I only see the pending code after it is active, and by then it is too late.

Will the raw fuel of a misfire for something like 100 miles be enough to kill a CAT? That seems a bit soon to me. I would think that 1000 - 1500 miles would be needed to kill the CAT, but not less than a tank of gas.

Reply to
Jeff Strickland

i assume you did this?

Ford: The catalyst monitor will not run until the HEGO (oxygen sensor) monitor has run and completed successfully with no faults found. The vehicle must then be driven in stop-and-go traffic conditions at five different cruise speeds ranging from 25 to 45 mph over a period of 10 minutes.

If your keeping the truck, i would just change out the O2 sensors and see if it helps. Might even give you better mileage.

I did have O2 issues on one of my tauruses. Turned out a PCM replacement solved the issue.

Curious, what do the short and long term fuel trims look like?

bob

Reply to
bob

Your cats only have 100 miles on them? really? On a 1997?

Cat-efficiency codes typically set when the cat is just plain old and worn out, like those probably are. To check cat efficiency, use the scan tool to graph all four sensors. If the rear sensors are switching just as quickly as the fronts, then the cats are worn out.

GW

Reply to
Geoff Welsh

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