I just wanted to let the group know that I have now finished my second intake manifold gasket and intake pan gasket change. This time, it was on my dad's '99 van with 3.9L..
Indications of the problem:
- Starting the engine, it would make a clackety-clack valve noise, audible through the doghouse at idle.
- Had to replace the IAC (gummed up) and TPS.
- Cat and O2 sensors were replaced at unknown time.
- Van was using a quart of oil in 750 miles of driving, and check engine light (P0420) would come on when exiting the highway after a long stretch of open throttle.
- Drove it for a long long time (about 30k), until I started the thread about another dodge I was working on. Steve W. told me about the TSB for the intake pan.
- Power was definitely down, transmission seemed to be letting the engine rev higher than it should to shift, and shifts felt mushy.
- Rode with rear doors slightly open, due to long load in the van. Every time we slowed down from highway speed, a huge smell of partially burnt oil would rush in through the rear.
So, I already had the gasket set and decided now was the time. Immediately obvious upon removing the intake manifold was the fact that both intake gaskets were leaking. There was a trail of sand/ dirt/dust down between the ports on each side of the engine. I suspect the engine was taking in a good portion of air through there. Removal of the intake pan revealed that it, too, was leaking.
Immediately upon cranking when re-assembled, the engine did not do the initial hunt upward then back down to idle. Still heard valve noise, but not nearly as loud. No hiss from IAC. Transmission shifts firmly now. I can maintain ~65mph with about 1/8 throttle or less (guessing).
I still smell a bit of oil, but it seems to be lessening. Now, I can smell fuel because the previous owner broke a bit of the filler nozzle such that it doesn't seal any more. Vapors are blowing out past the gas cap. Reckon I'll have to go to the wrecking yard to get one.
Obviously a very common problem with these engines. Relatively easy to fix, also. Just time consuming. Actually, I liked doing it in the van much better than in the pickup truck.