Exhaust Manifold Crack Symptoms

What are the symptoms? I have a rough idle and appears to me louder and rougher overall compared to my older 1990 22RE that I owned. Is the symptom a 'tick, tick, tick' or can idle and exhaust noise appear too? I have a loud humming noise coming from under the floor when I downshift or let off the gas. I was guessing this was a heat shield for the catalytic converter or muffler but now I am wondering if this all related to the well known cracked exhaust manifold issue?

 

When mine cracked on my old 4runner you could hear air at idle. Kinda a puffing sound from under the hood. Mine was cracked bad though so it would depend on how bad. I think mine did throw off the rpms on idle too.

Tim

 

Thank you. I looked pretty hard with my reading glasses and a flashlight today - no cracks. I will check out the catalytic converter and exhaust pipe areas next for the source of the noises.

 

Exhaust leaks on the 2.7 are quite frequently due to missing donut gaskets between the y-pipe and manifold. They often get sucked into the cat.

 

It's really noticeable from another vehicle while driving or if you drive next to a barrier. I can always here someone else's cracked manifold as they drive by. Like two pieces of metal clapping.

 

I can say it is cracked based solely on the year of your truck.

 

2.7 here. When mine went it was the gasket between the manifold and the first catalytic converter pipe. in the cab it sounded like a butterfly flapping it's wings next to your ear. was noticeably louder when it was cold. but as the truck ran it would quiet down. Also i could not see the leak at all as it was really small. i finally found it when i pulled the entire manifold and pipe out as a whole unit. you could see the black leak out if the gap between the two.

 

I agree! When i relpaced my manifold i noticed the donut gasket was dust! Still had a nice crack though. If no crack then prob a gasket.

Tim

 

Mine ended up being a leak at the catalytic converter. It appeared to be broke due to rust versus a gasket. Although I am not opposed to DIY projects, I wanted mine welded back together. The welder at the shop, cut off the flanges where the gaskets would normally be, and replaced with two short pipes on each side of the catalytic converter. Now I am receiving a check engine light and 'catalyst system' code. I plan to buy a bluetooth OBDII transmitter and software for my Android so I can continue to troubleshoot as I replace parts.

The parts that I have read working are magnaflow aftermarket cat with denso O2's. I am debating whether to try O2's first. Any suggestions on the parts to start out? Do I need the California NOX ratings for everything to clear the CEL? What OBDII adapter works best on the Tacoma? It would be cool to have an RPM and TEMP reading to monitor while I tune my new used Tacoma with only 95K on the odometer.

 

I got my bt obd on ebay for about $5, torque in the play store is free.

I have a failing O2 sensor in my mustang, I get to use torque every other day to kill the check engine light. Some day I'll get off my butt and put a jack under the car. Probably not today though

 

I bought the OBDlink - I am inquiring about O2 sensor output graphs from my scanner in another thread because this one is more about cracked manifolds, which I am watching out for and preparing for on my 2RZ.

 

will a cracked manifold cause burnt exhaust valves? if so, how bad does it need to be cracked to do so, and how long could you drive with the manifold being cracked before it burns the valves?

 

valves burn from not being adjusted properly and the cylinder gases burn the sealing edges.

a cracked exhaust manifold might cause other issues but burned valves is not one of them.

now how in the world can you make a matter of fact statement like that? every truck is different and there is no set expiration date when manifolds are assured to crack. but I do get your point that odds are good something this old "may" stand a good chance of having a cracked manifold.

 

thanks for the info, what other issues could it cause if not taken care of in a timely manner? besides bad gas mileage of course