Vacuum Monster Strikes - long

. TOP POST . Replace your Catalytic Convertor.

Story...

It started right after I went WOT. Transmission would not shift to 3rd. Just got the truck (a month old for me). Changed the modulator. No change.

Put a vac gauge on it. Seems OK. Pull my hair out. Buy 10 feet of vac hose and stick the vac gauge in the cab. Go for a ride. There is no vacuum!

Starting from a stop there is no problem (well a bit) in keeping up with traffic but once she shifts to 2nd. vac drops to 4 or 5 inches and so the modulator won't let her hit 3rd. Take the foot off the gas, vac goes up, trani goes to 3rd. You now just have to look at that gas pedal the wrong way and the vac drops to 4, trani drops to 2nd. You can't even touch it to maintain speed.

Drive around in 2nd. for a day. Now I'm getting a 'code 45' (rich exhaust). Buy an O2 sensor. No change. Drive around in 2nd. some more. Buy a book. Look at the EGR valve. Book says 3 types, - positive or negative backpressure or ECM controlled. I have a solenoid so mine should be ECM controlled.

What the heck I unplug the EGR vac hose at the solenoid. I have vacuum! Truck will now shift and stay in 3rd. at city speeds (hi-way also). But she is a pig! She runs around 9 inches till 3rd. and I still have to help it shift sometimes. Doesn't have a lot of power and does ping (no EGR valve). Computer is mad at me and puts out a 'code 32' (barometric stuff). To be expected I guess.

Pull the EGR valve and it looks OK. It has a 'N' after the number on it meaning it works with Negative backpressure. Well maybe Chevy uses it along with the ECM control. It seems fine, but with it out of the picture I have more vacuum, so I go to the dealership... $135.00. Already hurting from my $40.00 O2 change that didn't help I go to the bone yard. Get one. It works with a little less vacuum (non scientific as I just put a hose on them and see if they work). It also is not black with carbon like mine is. Put it on and I am in worse shape. Truck actually stalls. Seems to work properly. Closed at idle, I then rev the engine slowly, watch the valve open and the engine dies.

So for sure there is a difference between the two valves. Maybe that tells me to buy a new one from the dealership.

Looking for ideas.

It might be the solenoid but still with the valve out of the picture and it not taking any vacuum I'm still having problems.

it won't run with the 'EGR off'.....that makes a huge vac leak, so huge it may not even start

unplug the vac line to the EGR, but leave it in place

That's what she was... a plugged cat. I finally stopped by an old mechanic friends shop. He revved it once, told me a plugged cat and twenty minutes later I was on my way with an additional 100 horse or so.

take off the EGR andO2 sensor, start the engine with your gauge on. If vaccum come up to somewhere near normal then you have a plugged cat