new fun found - manifolds missing bolts?

brewer · 10-06-2008, 12:13 AM

Anyone here ever find that bolts have jumped out of their blocks before?

today I chose to swap out my exhaust manifold gasket because I knew I was missing a bolt. I suspected it broke off when a PO had it, but... when I went to tap the whole - nothing - just dirt inside that hole. So I cleaned it out nice... and double checked all the other holes while I was at it.

I expected I was going to have some snapped bolts while I was working on it, so i bought a bunch of 3/8 - 16 course bolts to match the threads. Good thing too because I found that my manifold had just two bolts - hand tight holding it in place, and just 1 of the 4 intake manifold bolts!! Amazing this thing actually ran as good as it did!! lol!

but alas - now I have a dilema. Now that I have a new gasket in place, and now that it is sealed - I now have an idle cruising upwards of about 2k rpm. this is a jump of about 1k from where it was before I messed with the bolts.

So any ideas what i might have bumped or nudged that ticked off the engine? I suspect the throttle cable but... not certain about that one.

**havasu** · 10-06-2008, 12:24 AM

I'd check the vacuum lines, TPS and throttle cables. And, also check the mounting bolts to your throttle body....them things like to escape just like the manifold bolts!

**vadslram** · 10-06-2008, 06:16 AM

On my 4.2 I have to tighten those bolts about every 4 or 5 months. Even with thread sealer they back out.

Alfons · 10-06-2008, 08:12 AM

I would say that you have in intake manifold leak at the gasket. It may not have been torqued properly or maybe the old gasket wasn't fully removed - the intake and exhaust manifolds & associated gasket are removed and installed as one unit.

You mentioned that you got new bolts to replace some that were missing. New bolts should be grade 8 and the associated hardened, convex washers are very important - they provide an equal pull of the intake and exhaust manifolds to the gasket and block. Weak or improperly formed washers will warp from heat or distort from the torque causing a poor fitment and leaks.

brewer · 10-06-2008, 10:53 AM

suspect vacuum leak - bringing it into the shop at school today to verify where it is coming from. Seal on gasket is tight - WAY tighter than it was before for sure.

As for the bolts - I used ones that came in a kit specifically made by jeep for this application. I didn't buy aftermarket because I didn't want to guess on thread depth or sizing. I believe these ones are marked 9.8 on the head. Oddly enough they didn't come with washers, but I added some nice thick ones cause me no dummy