1999 2.7 L misfiring and rattling catalytic converter following head job

[pendragon]

1999 4runner, 2.7 L, 2WD, 232k miles, auto here.

I just had a head replaced and as I was paying, the shop owner commented that the cat. converter was rattling. The rattling got worse over a few days, and I started getting some occasional misfires out of #2, I believe. Engine performance dropped and the CEL flashed on my way out of the driveway this am, so I parked it. The misfires are accompanied by a puff of air out the exhaust. No smell to the exhaust. The front O2 sensor is bouncing steadily around about 0.5 V, but the rear sensor is popping rapidly from close to 0 up to like 0.8 or so, according to torque. My noncontact thermometer says the CC inlet is about 750 F and the back of the CC is about 550 F.

My OBD reader had pending codes for:
P0402 Powertrain - EGR flow excessive detected (PENDING)
P0420 Powertrain - Catalyst System Efficiency below threshold (bank 1) (PENDING)
P0302 Powertrain - Cylinder 2 Misfire Detected (PENDING)

It got new Denso plugs, properly gapped 8 months ago and the number 2 was very tight to remove and had a worn ground electrode. The plug wires are from 5.5 years ago, NGK, and look fine.

So anyway, I am concluding that the blown head gasket and cracked head wrecked the catalytic converter and I should replace the CC. Could I please get some feedback on my diagnosis?

Assuming I need to replace the CC, I was thinking of going with EASTERN CATALYTIC 40685
More Information for EASTERN CATALYTIC 40685

It comes with gaskets, and I assume it just bolts on. I guess I need new hardware, but do y9u usually have to remove anything else that will need to be replaced? Should I also do the O2 sensors?

I just dropped $2300 on the head job, timing chain kit, and injector seals, so I am bummed to be immediately shelling out again.

 

[tcwfalcon]

Interesting. I would be surprised if the skipping and the cat were related, unless the o2 readings are seriously throwing the fuel ratio. I would expect the noise and the CEL, but not the skip. My best guess is that you have two separate issues. If the cat has to be replaced either way, I would start there.


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[gamefreakgc]

The shop should warranty their work, find out how long that is. When you say "just done", as in a week ago? A few months ago? I would start there. Poor engine performance could be a direct result of the head job if the did not do it right.

Also, the cat will rattle if the exhaust has too much vibration from a mis-firing engine. If the exhaust is not vibrating, then it's the contents of the cat that are loose and have failed and would need to be replaced. Seeing you are in MS and I don't think they have strict smog laws, almost any replacement cat will do.

Fix the misfire first, then deal with the cat if still needed.

 

[pendragon]

The shop should warranty their work, find out how long that is. When you say "just done", as in a week ago? A few months ago? I would start there. Poor engine performance could be a direct result of the head job if the did not do it right.

Also, the cat will rattle if the exhaust has too much vibration from a mis-firing engine. If the exhaust is not vibrating, then it's the contents of the cat that are loose and have failed and would need to be replaced. Seeing you are in MS and I don't think they have strict smog laws, almost any replacement cat will do.

Fix the misfire first, then deal with the cat if still needed.

I picked up the truck from the shop last Friday. They took over a month to get it back to me! First, they took a week to get the head to the machine shop, then the shop took a week and a half to x-ray the head and tell them it was cracked, then they took a week to order a new head and wanted me to pay $1000 up front to cover the parts, then they wanted to do the timing chain, then it was almost a week before they got everything installed, and finally an extra two days for new injector seals. It just felt like I was being taken for a ride, but I stayed polite and patient since they had my car in pieces. I'm not keen on going back to them, but they have a 90 day warranty, so I guess that's my next stop.

I don't think the rattle and the misfiring are completely connected (but I could be wrong). It seems like the misfiring is sporatic, especially if the RPM drops to arund 750, but the rattle goes on even when I don't think it's misfiring. I get a strong vibration at idle (has been going on for 6 years or so and nothing I've done has diagnosed it) which is when I notice the rattle. The rattle was present before the head job, but it wasn't as bad. I can reproduce the rattle by banging on the CC with my fist when the car is cool.


Below is a 10 second readout of the O2 sensors from Torque, by the way. The 4runner was at operating temp and RPMs were held at 2,500.

 

[gamefreakgc]

I picked up the truck from the shop last Friday. They took over a month to get it back to me! First, they took a week to get the head to the machine shop, then the shop took a week and a half to x-ray the head and tell them it was cracked, then they took a week to order a new head and wanted me to pay $1000 up front to cover the parts, then they wanted to do the timing chain, then it was almost a week before they got everything installed, and finally an extra two days for new injector seals. It just felt like I was being taken for a ride, but I stayed polite and patient since they had my car in pieces. I'm not keen on going back to them, but they have a 90 day warranty, so I guess that's my next stop.

I don't think the rattle and the misfiring are completely connected (but I could be wrong). It seems like the misfiring is sporatic, especially if the RPM drops to arund 750, but the rattle goes on even when I don't think it's misfiring. I get a strong vibration at idle (has been going on for 6 years or so and nothing I've done has diagnosed it) which is when I notice the rattle. The rattle was present before the head job, but it wasn't as bad. I can reproduce the rattle by banging on the CC with my fist when the car is cool.


Below is a 10 second readout of the O2 sensors from Torque, by the way. The 4runner was at operating temp and RPMs were held at 2,500.

Torque readings and O2 sensor readings are hard to decifer. the FSM doesn't state specific voltages for checks, rather how many rises in a 10 second period and Torque doesn't read them well enough. If you cat is indeed broken, the only things that will clue you in is a P0420 code or a failed emissions test (which I don't think your state has). You could try and see if it's just the heat shield that is loose, perhaps that's all it is.

You'll notice a misfire most at idle, so that's not surprising. My guess is that the shop some how messed up the valves so it's losing compression. I know the shop kind of messed you up time wise but if they didn't do it right and damaged the engine, they need to fix it. An engine swap by a shop is $2500+