If the Catalytic Converters go bad, will there always be codes thrown.....?? Brief history, just did the Phasers, chains, etc.....starts and runs great. Until you put it in gear. Engine still runs fine, but absolutely no power.......??? undriveable.....Vehicle 2006 F150 Lariat, automatic, RWD.......175K

 

Bad Cats will ALWAYS "-EVENTUALLY-" throw a code. (Sounds like a politician, I know). But there are more than one way CATS can be 'Bad'. 1). Melted into a glob inside, 2). Crumbled up in a pile of rocks inside, 3). the honeycomb coated with contaminates and ineffective, or 4). plugged up partially or completely. The fourth type CAT failure can result in your described sluggishness symptom. But it is one of the more difficult ones to diagnose.

With any of the CAT failures the 'Catalyst Monitor' test ran by the ECU during each drive cycle will -eventually- fail on the required two successive drive cycles and produce a P0420 and/or P0430 DTC. Perhaps not as quick as you would expect. That's because the monitor consists of two tests. 1). measured time it takes for an Over Rich, AND Over Lean condition, intentionally created by the ECU, to effect the catalyst and show up in the post-cat O2 sensor reading, and 2). calculating the 'switch ratio' between the downstream O2 sensor and upstream O2 sensor (nominally > 0.50 and < 0.75 index/ratio) during some different driving conditions (including normal cruising 25-30 mph). There are several sensors that have to pass _THEIR_ diagnostic test first, and numerous other conditions that must be satisfied before the cat monitor test will even start, and a host of driving events and other engine failure conditions that can 'cancel' a given cat monitor test.


The 'complex' (and interesting) little rascal is covered in detail in the Motorcraft OBDII Theory of Operation Manual at pages 4 of 98 through 6 of 98.


There is an OBDII switch or flag available ("CATSTAT") that is set 'true' when the monitor completes successfully during a current drive cycle. Not a DTC, just a readiness 'flag'. If it EVER gets set - NO Catalyst DTC is forthcoming. In that circumstance, I would think that most of the catalyst problems are probably eliminated except possibly the worst case of number 4. That condition gets hard to diagnose. See this thread for ideas on THAT condition: https://www.ford-trucks.com/forums/1...e-no-code.html

 

Listen to the exhaust - a clogged system can make a hiss instead of the usual sound. Look at it on a cold morning to see if the velocity/amount of vapor appears normal. Feel the exhaust to see it feels like it should. Do you smell a 'rotten egg' odor in the exhaust? Look for damaged exhaust pipes. If it is not driven every day you might have rodents storing winter food in your muffler.
Check the engine air intake tract starting with the air filter and box as well as the whole cold air pick-up apparatus. Rodents love to get into a filter box and fill it up with a nest and winter food.

 

Just a quick update.....Replaced both Cats.....no change in performance, or lack of it. Next step is new plugs and cops....!!

 

Ever get a P0420 or P0430? If so, has it come back? Any other codes? If not, do you have 'live data' scanner? New Cats are kindof' an expensive parts throwing exercise. Plugs - boots - springs are not going to hurt, (even wallet so bad) but it would be nice to see if something else is going on.

 

Is 2006 when they dropped the EGR valve and controlled EGR via VVT?

Can you verify that the cams are now in time? Like can you o-scope the cam and crank sensors to verify offset even though VVT is in play? IDK.

 

Not sure what a VVT is......did you mean VCT..?? I don't have access to an oscope, not would I know how to use one.....!!

 

@pdqford, my 2004 5.4l uses 'V'ariable 'V'alve 'T'iming to accomplish EGR. Each driving cycle, the PCM runs a diagnostic monitor routine for "I/M Readiness" (define as Inferred Mass Air Flow), or in other words if it is doing adequate Exhaust Gas Recirculation to satisfy emission standards.
Generally, (if we don't have a scope) the complex PCM software has to be trusted to tell us if something is amiss through DTCs or live data monitoring if there are no DTCs. If the OP has, or has acess to, Torque Pro, I have put together a Dashboard to monitor the VVT system and all parameters involved there. Details and a downloadable file is posted here: https://www.f150forum.com/f4/final-r...4/#post5133357