New member here and this van is giving me a big headache!
Anyways I bought this van with some problems which most are resolved, but I have a issue with the van not wanting to get above 4000 RPM's even in neutral also the vents want to go to the defroster under moderate acceleration / load.
Things that I have checked
Fuel pressure is within spec as well as regulator
EGR operation (replaced the EGR solenoid today because the diaphragm that is under the solenoid was deteriorated and leaking vacuum.)
Watched MAP, O2, TPS, IAC with snapon scanner (didn't have much time with it) but they looked good and switched properly (except the ST stayed at 0 and did not change and the PID labeled Baro stayed at 97 but other PIDs that show MAP data switched and also using my meter I checked referance voltage and also output voltage on the MAP sensor and all seemed well)
And tested the EGR solenoid with the scanner and the van had no change in RPM when I activated it so I suspected either the EGR or solenoid troubles, and I returned the scanner cause I though I found the issues but that's not it....
Coil pack resistance within spec.....

I have replaced the plugs and wires with high quality replacements
PCV valve and elbow

I purchased a vacuum pump today and at idle it pulls 20 hg steady and when I burp the throttle it drops to 0 quickly then recovers and stays steady, and when I increase the RPMS it will drop a little then recover. I didn't have enough time today to take it out on the road and watch the vacuum while under load.... But I'm confused with this beast and now my head is pounding........ lol anyways hopefully you guys will have some other things that I can check. Also there are no fault codes stored either.

 

How about replacing the Catalytic conveter? Maybe you have a cracked flex plate which would retard timing and kill power.

 

a decent muffler shop can drill a small hole and put a pressure gauge in your exhaust pipe to measure backpressure. if cat is bad pressure will be a high. All cracked flex plates I have heard are noisy.

 

I have a cracked flex plate that didn't make a peep. I check exhaust BP with removing the O2 sensor and installing my gauge.

 

I'm going to pull the O2 sensor tomorrow to see what that does, and I do have a pressure gauge just need to see if I can find an adapter that will fit the O2 bung. I'm hoping it's the cat and not the flex plate; The van does not make any weird noises like what I've heard from a broken flex plate in the past... well more testing tomorrow...

 

Today I checked my back pressure and that came out perfect, and while I was under there I put a new fuel filter on and I did the standard blow test through the old filter and it was not clogged... I hooked my vacuum gauge up and shot come video of the symptoms that I am experiencing. I hope they will help point me in a direction. Thank you everyone for your help so far on this thing. here are links to the videos I made on youtube.

http://www.youtube.com/watch?v=mYvbRaebET8

http://www.youtube.com/watch?v=NmuENoHzfv0

http://www.youtube.com/watch?v=_0yXiGHFOuM

http://www.youtube.com/watch?v=X9b6mdkUbCQ

 

It seems to get stuck around 4k RPMs and your guage is bouncing around. My first instinct would say a vacuum failure somewhere causing the engine to sputter, causing your defroster to malfunction.

 

A top end rev limit won't be a vacuum issue. A timing issue sure would cause this. Does check the exhaust after running a while, see if it's getting cherry red. Or maybe some broken valve springs. At low rpm no problem at high rpm valve float and no power rough running, fluctuation of vacuum? Maybe worn out cam? Low rpm opens valve enought to run but under load or high rpm, not enough lift/duration for power?

 

What is the resistance specs for the cam and crank sensors? I unplugged the crank sensor and the van would not even start (should it? other vehicles I have worked on would run without the cam sensor hooked up and just set a DTC) This van has all the power in the world until it hits that wall, it doesn't miss a beat... I guess I need to get an oscilloscope to watch the cam and crank sensors...

 

Of course it won't run w/o crank sensor. That's the trigger for spark. I don't recall you changing PCM's maybe you got a rev limiter issue in the programming?

Has someone else worked on this before? did this problem happen all of a sudden?