Hi all..

I am experiencing a really strange issue with my van now. For the last two months, the van when it gets to operating temperature looses some power. It would happen right when, I would suspect, when the system goes into closed loop mode.
I don't know if this has anything to do with the problem I have now, but I thought Id throw it out there.
Now I have an issue where the van wont rev over 3-3500 RPM. It starts fine, and idles good, but when I give it gas, it get to 3k, starts to miss a little, not much, just a little, and a loud, loud groaning comes out of the intake. I also shakes when it does that. I looked down into the intake and it is sparkling clean - no oil, so I think this rules out the belly pan gasket. I am not losing coolant or burning any oil. I also have no codes. I also cant find a vacuum leak. As some of you may know, I went through the whole engine a few months ago. All new heads, gaskets, alternator, plugs wires etc etc etc. I have never seen this problem before. Just to reiterate, the noise is loud, and it comes right out of top of the intake manifold when you have the air cleaner off. To describe the sound, it sounds like a diesel truck down shifting....

Any ideas -- thanks!

 

I had a similar problem on an old Oldmobile Cutlass back in the '70's. As it turned out in that case, the fuel filter inside the tank was clogged up. At high rpms' or under load, the pump couldn't suck enough gasoline through the filter. Don't know about the noise.

 

Mark and pull the distributor. Look at the oil pump driveshaft from above, note the slot and it's orientation. Use a strong magnet to pull out the oil pump driveshaft and see if the gear teeth are all f'd up.

See how the visible camshaft lobes look

 

Cat is clogged up. same thing happened to me last week....no power above 3k rpm and loud intake....I put a pressure test gauge in the o2 sensor hole before the cat and mine was 25 psiwhen it should be 1psi

 

I have a new cat...could I have the wrong one on it? I have gone through two mufflers now since, according to the shop, the exaust gas got so hot it loosened the baffels inside of it..

 

Has the O2 sensors ever been replaced?

 

That's a result of unburnt fuel getting into the exhaust, settling in the CC and burning in it.

 

well, if I have a clogged cat - why I cant figure out why that is happening???

I have gone through this motor almost entirely. It has all new sensors, new heads, new wires, plugs, cap, pick up coil, ignition coil, lifters, rockers, pushrods, rebuilt injectors, new battery, and all the gaskets that go with everything - I can go on and on...even a rebuilt PCM...
The only mod I have done are the HS roller rockers. I dont believe that should really make a difference...
Why then would I get getting unburnt fuel into the cat? Low compression, broken ring, stretched timing chain? I am at a loss here.

The van is a 3.9 with 125k miles - when I did the heads, the water that leaked when I pulled them into the cylinders stayed at the same level for a few days, so most of the cylinders should have good compression, but I dont know I would have to have it checked...

Gee ya know!!!! damn - this really bites.

 

......

 

Just for the record all...

So I ordered an universal cat and went to the muffler shop. My GOD, the cat that was on my van looked like it was full of sand...it had desintigrated that much. No wonder it wouldnt rev over 3k...

So I had a new cat put on and put NTK front and rear o2 sensors in. The van runs strong now. I a still a little surprised an o2 sensor from Bosch could cause that, but maybe that is true.

All I can do is hope it doesnt kill the cat again...

Thanks for the help all -- esp Blackvan -