manifold leak

Hey all, I just replaced my cracked exhaust manifold with an apn header and now im having an issue with a manifold leak. I though maybey the gasket was the issue so I went and bought another new gasket, took it apart, and replaced it for the second time today. The leak is right underneath the first upper bolt in the front of the vehicle. Ive tightened, and retightened, and then again but the lowest I can get it to idle is about 1k. It idled perfectly before I swapped in the new header, but the ports were pretty gunked up so im wondering if all the goo I cleaned off was actually sealing it up. Anyone had this issue and if so what did it take to fix it? Its on a 97 4.0 5spd in case your wondering....thanks.

did you try resetting the ECM afterwards? Disconnect the battery overnight.

did you check all the vacuum lines for leaks? did you hook them all back up?

might sound silly but it happens, last time I did major work I couldn't get the engine to start afterwards ... in a panic I started going over everything again ... I had forgotten to reconnect the oil pressure sender.

you may get a leak if the flange thicknesses differ too much and normal washers or flanged fasteners are used ... the use of domed exhaust washers helps solve the problem. I haven't seen them much lately, but the older 80's motors they were standard ... I got mine off my old ford 300cid inline 6 truck engine, but they should be available new.

I dont think its an ECM issue. Ive sprayed carb cleaner all around the manifold and when it gets to that spot the rpms drop. Thinkin I might just take it apart tomorrow and stick a little of that copper rtv stuff on it, see if that helps at all.

could also try doubling up on the gaskets ... but I've never had luck with that .. others have reportted it working well.

Did you have any clearance issues with the new manifold? On my 97 4.0 the APN manifold was making contact with the intake manifold and had to be massaged a little to clear and not make contact. Could be the 2 are hitting each other and you are not getting good contact to create a seal.

iwannadie said:

Did you have any clearance issues with the new manifold? On my 97 4.0 the APN manifold was making contact with the intake manifold and had to be massaged a little to clear and not make contact. Could be the 2 are hitting each other and you are not getting good contact to create a seal.

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This. Usually it's a problem on the 99's due to the larger intake. But, I could see it happening on others as well.

Also, the manifold may not have been manufactured properly. I ran two APN's on my 99. First one got taken out by my broken motor mount, and the second one was not manufactured properly, but I didn't realize it until I installed it and had a bigger leak than before. If you paid attention, you'll see how runners 1-3 are welded to one flange, and 4-6 on another flange. On mine, those two flanges were not level when the manifold was made, so it didn't seal properly against the head. Hopefully this isn't the same issue you have.

One other thing to double check, make sure both the exhaust and intake manifolds are properly seated on the alignment dowels that are on the block. It's real easy to not get either manifold seated properly on one of the dowels when putting it back together.

I agree with what UNC_99XJ says. It's easy to overlook something like a slight defect in the manifold when you're getting it installed. I would take it back apart and look really closely to make sure it's seated all the way down on the head, and that your intake manifold isn't touching somewhere on the exhaust manifold causing it not to seat. Check the flange surface on the new manifold with a straight edge in multiple places and make sure it's flat all the way across and doesn't have any burs that would cause it not to seat all the way. Check the surface on your intake manifold, make sure it's nice and clean (I use a small air powered abrasive wheel to get ALL the old gasket gunk off both the head and the manifold). Make sure the studs are fully seated in the head so that when you torque down the nuts on the three that use studs, they are fully tight.

IMO, don't use two gaskets or try to smear some extra copper goop stuff on there. That's not the correct way to do it, and would just be a band-aid fix that you'll probably end up having problems with later. You've got a defect in the manifold, or something is not perfectly flat or has residue or a bur on it, and you need to address the real problem not band-aid it.