Hey guys thanks for reading. I have a question, if you all don't mind. Today I started pulling all the stuff on the driver side of the motor so that I can fix (what I believe to be) a cracked exhaust manifold. After I pulled all the important stuff off the intake and took off the air box, I was looking at the exhaust manifold and saw some open port thing sticking out under the intake pointed towards the air box section. It looks like the end of an exhaust pipe just sticking out of the header. So I was wondering if this was a normal thing? And If not, could it be the reason for my awful gas mileage and horrid noise? Thanks guys!

 

What year and which engine do you have there?

 

Oh yeah, forgot about that sorry. It's an 89 with the 4.0. I tried uploading a picture but I'm having a bit of an issue. I'll try again in a little while.

 

That thing you described reminded me of an old Cherokee "Pioneer" that my sister asked me to fix for her many moons ago. There was some kind of a rotted crossover tube that ran from under the manifold near the collector, down and under the engine and up to - I can't remember - on the passenger side. I think it might have been related to the choke. Sorry for the very sketchy/vague memory but, as they say, memory is the second thing that goes as we age - and I already forgot the first!

 

Thanks man I appreciate it, I was kinda hoping I would be able to fix the crack without buying a new manifold. I'm not sure if this is something some sketchy mechanic did as some sort of quick fix, or if it's actually factory. Although, I don't think I've seen anything like this coming off a Cherokee header (not that I'm familiar with Cherokees by any means). But I would assume any open spot on the manifold would throw the compression of for the o2 sensor.

 

Its there because theres suuposed to be a flex pipe thing that goes to the front of the stock renix air box. You will notice theres also a cirlce there, and a valve type thing. It provides hot air and "helps the engine warm up quicker"...
late 80 engineering I know it works but it kills performance!
Every renix era rig is like that!

Heres some more info if you want to know more.
http://www.google.com/imgres?q=jeep+...:429,r:13,s:18

 

Is there a crack or is it just that tube thing? Maybe you can simply crimp/seal it off and you'll at-least make it quieter - no doubt your mileage will also improve...

Take a few extra minutes to look and see if there's a corresponding unterminated fitting elsewhere - like maybe at the base of the carb or the choke housing on the passenger side.

 

That is the "intake preheater," and is there for emissions control (it's a holdover from carburetted engines.)

It is not connected to the exhaust, and won't contribute to a leak. It's simply a sheetmetal duct that allows the engine to draw air ducted over the exhaust primaries, which heats it. The reason to heat intake air on cold starts is to help wit fuel atomisation, which helps with combustion efficiency.

 

Thanks a ton man. You guys never fail to provide good answers. I got to looking at it after reading Kamaran's post and saw what you guys are talking about. I guess I should probably replace that tube that runs off of it. Is there any certain type of material for the flex hose that needs to be used? Is it subjected to high temperatures?

 

Eh, moderately (but more outside than inside, down at the exhaust end.)

You can usually find pre-pack foil hose (I think it's actually heavily aluminised Mylar...) at most parts houses, back by the fuel filters. There are three or four inside diameters available, and the prepacks are about two feet long extended (collapsed, about a third of that. They're on the shelf in the collapsed state - you stretch them out like an accordion.)

As I mentioned, they're a holdover from carburettor days. They're not strictly necessary on fuel-injected vehicles, because the EFI system adapts to intake air temperature, and the fuel is atomised much closer to the cylinder. It's one of the few cases where CA smog has agreed with me - mine's been missing for years, but I never get downchecked on biennial smog tests for it.

Nylon zip-ties won't cut it for securing it at the exhaust end, but will work at the airbox. Secure the exhaust end with a small steel hose clamp instead, or you can use safety wire as a twist-tie. The fit isn't quite snug enough to stay put on its own (the OEM hose comes with a toggle band clamp inbuilt, but I don't know if you can even get the OEM part anymore! I've never looked.

 

Thanks guys. Also, I have another quick question if anyone doesn't mind. I'm trying to remove the intake manifold to get to header. I've removed all the bolts along the top of the manifold but I can't seem to get to any of the ones on the bottom side. They're blocked by the exhaust manifold. Any ideas? Thanks.

 

Sure - go to Sears, get yourself a 9/16" "flex" socket - looks like this: (image didn't parse - http://www.sears.com/shc/s/p_10153_1...3&blockType=G3)

The Craftsman version should cost less than the Allen version, but either will make the job much easier.

While you're there, pick up one in 7/16" or 11m/m to make replacing the CKP easier as well (trust me on this.)