HELP - Engine/intake/sensors problems?

Alright guys so I've been attempting to do my own tune up on my truck (139000 miles).

Truck seemed to be running poorer than I was comfortable with, so I decided it was probably about time to change the O2 and Air/fuel senors (got a scan that said one cat downstream was running at -40 degrees lol). So instead of changing one out, changed them all.

Truck began running even more poorly. Loss of power, delaying response from pedal, rough idle, kinda seeemed to breathe like it was choking. And I know I got all the right parts, triple checked. Took it to autozone for a code (cel was on) - brought up that I needed to buy a new O2 sensor lol. The code also read a bad heater circuit for one of the air/fuel sensors.

Took it to my good friend (ex-auto/mods shop owner). He used his real time scanner. Said the heater circuit shouldn't really effect the way it runs, only warms up the sensor to get an accurate reading while cold. Let him drive the truck around, he noticed the whole second of a delay from flooring it and it generally running poorly. He did a full sweeping check of the vacuum tubes, checked the intake manifold, tested the the cats and the sensors to see if they were running correctly (they were).

He suggested that I get a new MAF, as he personally noticed on toyotas that they can go bad at high milage.

Well, on the way home, I was testing the response of the engine again by giving a good bit of gas...

Engine nearly died. No power on acceleration. Sputtering. Generally really rough. CEL light blinking. Made my heart drop.

Turned it off and back on, rolled home, cel light staying on, no blinking.

Obviously misfired. Took it to autozone on lunch break the next day, came up with a code for multiple misfires. Shit.

Next day, cleaned the throttle body.

Read somewheres online that a bad MAF can cause these symptoms, though what the hell might as well change it out if I'm tuning things up.

Put it in today, idles a lot better, response seems to be a little better. But tested the flooring response and, once again, misfires, engine about to die type of feel.

Buddy thinks it could be some bad coils or plugs, but I've changed the plugs out within the year. Going by his place later today to check out what codes are being thrown.

Just wanted yall's input, thanks

Josh

 

UPDATE:

Just left my buddy's house. Drove around with the real time scanner, results:

MULTIPLE RANDOM MISFIRES 2,4,6

So we swapped the coils to see if it would happen again. It did.

He figured that narrowed it down to either bad cat(s) or fuel injectors, but leaned more towards the cat.

What's throwing us both off is that the trucks engine came to a halt after getting on the freeway and flooring the pedal. Hes more suspicious of the cat over the fuel injector because the problem becomes specific and not consist - throwing out the problem of a bad coil or plug out. The problems only occur under specific loads.

But we're both still unsure. I suspect the cat as well but don't know which one to replace - I don't know which of the 4, but I remember a code about a bank 2 being somewhere in there.

He suggested that I just go straight pipes so I never have the problem ever lol. I'm considering it.

But would really like yalls input, if any.

 

246 are all bank 2, so you tend to look for things that affect one bank. Injectors could be the issue, but it would be very unlikely that they would all fail on one bank.

A plugged cat is hard to diagnose, but easy to confirm. Some people use vacuum gauges, some hook up pressure gauges to the AF sensor. Me? I unbolt the cat and go for a rip!

The cat's bolt to the exhaust manifold with 2 14mm nuts, just unbolt them and see how it goes.

Typically I suspect a plugged cat when I feel super lack of power and a "mooing" engine. I'll sometimes measure temps, but for the most part I like noise.

If it drives fine with the cat disconnected, it's easy to figure out. Beyond that I'd be looking at valve train issues or possible headgasket issues. Both are uncommon with the 4.0 but can happen.

 

There is a very rapid rattle right underneath me. It's coming from the cat, but it could just be a rock stuck inside the shield. When I hit it with my fist, it does make a rattling sound, but it's very light. I need to get around to taking that shield off and seeing for myself.

Any reason you can think of that my truck would run worse AFTER putting in new sensors? My only thought could be that the new sensors are detecting a problem and throwing the system off. When we checked to test the cats, we shot carb into a vacuum tube, read the scanner as it gave numbers. There was one cat that was giving a low number to begin with. That threw him off a little.

Anyway, some more info - the scanner happened to pick up data while my truck decided to almost die out. Everything went haywire on his scanner, misfires all over. Before that, during regular driving, scanner picked up 2 misfiring first on multiple occasions, then 6, then 4 eventually popped up. Same happened after swapping coils.

Buddy thinks the engine is fine, but is really suspecting that a clogged cat is giving the engine too much combustion to the point of misfire.

Any help would be much appreciated, thanks.

I just love my truck too much

 

Also, when the "wanting to die" condition occurs, it doesn't come out of it until I shut of the engine and restart. Once it restarts, just a cel light stays on and it continues running ok.

 

How anyone can even try and work on these vehicles without there own code reader is beyond me.

Then when they do go where ever to get the code read so many seem to forget it is not just the sensor in question but that complete circuit including the ECM

After spending $$$$$ to throw parts it turns out to be a loose connection

 

True, and I get where you're coming from. I had a code read sometime ago, system running too lean code, which led me to eventually getting new sensors. Could've been the cat, fuel injectors, anything along those lines, but wanted to work my way up, fixing one thing at a time. And with one giving off data of one cat at -40 degrees, Needed to be replaced anyway. They came out with a speratic white coating on them.

I should look into relays, if that has anything to do with it. Thanks