Originally Posted By: Kira
Hello, I looked at your profile to see what vehicle you're talking about and you didn't list it.
Not every vehicle is as well made as others. I had a cat die once. A Walker replacement fixed me up.
If anything is wrong with your cats it should be easily measured with exhaust gas analysis equipment.
I would bet very few (practically none) exhaust shops would have the equipment to test cats.
Provide year, make, model, engine and transmission of this vehicle.
People with similar vehicles are more likely to share their experiences if they know where you're coming from.
Kira
Hi the vehicle in question is a 2002 F150 4.2L V6 with the 4R70W auto trans.
Originally Posted By: 01rangerxl
There are exhaust back pressure testers on the market, but I am not sure how often they get used. A lot of bigger and/or better shops probably do have them. I have never used one, and have never seen one used. Never sold one at work, though we can order them.
I would ask around at exhaust shops and indy shops with a reputation of being good at diagnosis. Chains and stuff will probably just give you a confused look.
I went through this with my truck. Unusually bad gas mileage, down on power, misfire and detonation above 3,000 RPM. The O2 sensors said everything was good. CEL would not set, though it did flash during the misfire events without setting a code. Had an annoying whistle under load too that I couldn't figure out. Fuel filter had already been replaced as PM, and it just didn't seem like fuel...it wasn't cutting out, it was just weak and running bad at high RPM. I cleaned the MAF, replaced plugs, replaced wires, and replaced the cracked ignition coil. That did mitigate the misfire for a little while, but the truck still felt weak. Tried new O2 sensors (Motorcraft), still no go. Even with E85, the truck would detonate! Finally on a highway run, I felt the passenger floorboard and the cats were HOT. Real hot. Got Walker direct fit replacements and all symptoms went away immediately...got the power back, no detonation, no misfiring, and no annoying whistle. Admittedly, I had reached a point of throwing parts at it, but I lucked out when it was in fact the cats. Had my guess there been wrong, I would have been [censored]!
Visually, the old cats did not look that bad, but it was very apparent after replacement that I had finally found the problem. They didn't look like they had actually melted down or anything, the honeycombs were intact, but the engine just couldn't move the exhaust through them efficiently anymore. Not really sure what was up. This went on from about roughly 140K-146K miles...it was not sudden, but rather a gradual increase in symptoms that got to a point where I realized something had to be wrong. The truck had a history of towing before then, and I kind of suspect the heavy loads for a 3.0 (running richer) had a role.
Sounds a LOT like my situation, except I am not noticing misfires on load or excessive floorboard heat (although I had never checked that).
Originally Posted By: Trav
Any CEL or codes? Engine down on power?
Rear O2 readings act as a cat monitor and will tell you (and the ECM) if there is sufficient catalytic action taking place to keep the CEL off.
If the cat is partially plugged the engine will be down on power and possibly misfiring also resulting in a CEL,
A cat that has badly overheated and partially melted will have a damaged wash coat and little or no catalytic action.
Check the fuel trims, this will give you a lot of info.
Using a vacuum gauge is a quick and inexpensive way to check the cat for plugging. This is one of the most important, most overlooked and inexpensive tools in the business.
There are lots of sites that go into interpreting the readings properly.
This info is all generic but relevant to all OBD II systems, basic OBD II codes are generic by design.
No codes being thrown and I have 2 OBD readers. A ScanGauge II and a bluetooth OBD reader that pairs with the Torque application on my Android device. Now that you mention it, I can use vacuum pressure to test because my bluetooth reader can get a pretty good vacuum reading layout.
