Crack in Intake Manifold on 2F

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

cruxarche

cruxarche

SILVER Star
10 Year
Joined
Mar 30, 2012
Threads
55
Messages
309
Location
Davis, CA
I have a crack in my intake manifold. My mechanic thinks this could be adding to my many smog problems, but is not sure. Is this a common problem? I just pulled another intake off a spare 2f and it appears to have a TINY crack in the same place. It almost looks like it is just a mark form casting.

Is there any "test" to see if the crack is actually leaking air, or sucking air from the exhaust side? Just trying to figure out whether it is worth swapping out...

Thanks.
intake.webp
 
You have a faulty heat riser flap. It redirects exhaust air across the bottom of the intake until it warms up. The flap then moves and the exhaust is routed further away from the intake. Excess heat from the stuck open flap is what caused the crack. Common problem.

Either repair your intake or source a good one. And possibly delete the flap to prevent further issues.

If you use a different intake be sure to get the exhaust/ intake assembly flat to get a good seal on the head.

I'm not sure how one would test to see if it is leaking, but if it was leaking the truck wouldn't run very well.

Hope that helps :)
 
Intake test, spray carb cleaner around the suspect area.

I'd recommend fixing the heat riser if you live in a cold area, the 2F runs like crap without it when the temps get near or below freezing.
 
carb cleaner works if you can access the crack. This crack is between the intake and exhaust manifold.

Honestly, remove the intake from the exhaust manifold and see if the crack goes all the way through.

If it does, repair the crack and fix the exhaust flapper (technical term).

Or get a header and run coolant to the underside of the stock intake.
 
you can also attach a gauge to the manifold to see if you're getting the right kind of pressure
 
yes, a vac gage on the intake manifold will give an indication of a vac leak..
 
In any case, you need to get the crack fixed, as stated. Yes, it can effect emissions as well as performance... The replacement manifold with the hairline crack is a big crack in the making. Have it welded. If you can run headers, go that route (don't run cheap headers). If you can't run headers, you'll have to have the int/exh combo resurfaced after reassembly and before reinstalling it. There are a couple of threads on this, and may be in the FAQ.
 
Any test on this baby better be done while hot.

If running cold, you would probably notice running fine for the first 30 or so seconds, then starts bucking going thru the rpm shift bands. That, i believe, indicates the crack opening up and disturbing mixture on the intake side. Ask me how I know....
 
thanks for all the replies. Not sure exactly of next steps. I have got to the carb straightened out, then the smog system. Then, I will focus on this i guess. Any idea how much it will cost to get that thing welded and resurfaced?
 
I had one welded up for $75. It's not a big deal.

You can get a solid plate to install below it and prevent this from happening in the future.
 
I had the exact same crack on my FJ40. Took it in and had it welded up. That was 15 years ago.
 
Is the solid plate an aftermarket part or just something you fabricated?
Thanks.
 
They only work if you have a header.
 
Re Welding: take note of separating the intake/exhaust.

When reassembled, the plane of the intake/head and exhaust/head interfaces have to be pretty exact.

Because one set is a swivel operation, they have to be fixed (tack weld) before machining the head mating surfaces. You might get away w/o close plane line-up by keeping the intake/exhaust interface bolts loose, mount to head with correct torque, then tighten up the interface bolts.

On second thought, probably want to do a combination of manifold to head and intake to exhaust tightening so stresses are kept to a minimum and low change of cracking bolt holes.

All that being said, I've never done it, but have bought a few OEM manifold assemblies to avoid those risks.
 
If it is cracked, it is going to have pretty major vacuum leaks.

Mine was having severe loss of power and running really rough once the engine warmed up. Especially when running in fourth gear at highway speeds. It would barely run unless under load. It would also idle really rough. I pulled off the carb, and sure enough there was a crack.

I had a tig welder fix mine. He welded in a plate to cover the fins. This has worked fantastic!

PXL_20260317_030134612.webp


IMG-20260328-WA0018.webp
 
You must log in or register to reply here.

Share this page

Back
Top Bottom