'00 rough idle, power loss, no codes

This has been driving me nuts! This has been going on for a while and I can't figure it out, nor can my buddy who is a mechanic.

I asked for some advice here a while ago and because of that determined my fuel pressure regulator was bad (had fuel in the vacuum line). I replaced that thinking that was the problem. Nope. It really didn't change how the truck runs at all. The only thing it DID solve was it doesn't hard start randomly anymore.

Here are some things I know that may help.

1. The way it "misses" is very random. Sometimes it misses a bunch, then it will stop and run fairly smooth, then it may miss here and there, etc.

2. I have watched the tailpipe and every time it stumbles it puffs out a tiny bit of smoke (kinda bluish). Otherwise there is no color.

3. Sometimes when it is really acting up it almost feels like it is vibrating. It's hard to explain, but instead of a random da...da,da.......da....da,da type of miss it's like da,da,da,da,da,da so fast that it feels like a steady vibration. Then it will stop and go back to random as explained above.

4. Runs fine around town but when I get it up to speed there is a definite power loss. It feels like I'm towing something when I go up a long hill by my house. The trans even downshifts into passing gear just to get me up it.

What the heck could this be? Myself and everyone I've talked to is stumped. It throws no codes at all and doesn't have anything stored.

Stats:
2000 chevy silverado 4x4
4.8l V8
80k miles
All scheduled maintenence done by GM on time.

Any thoughts on this would be very helpful. Thanks a bunch.

Chris

the fuel entering the vacuum line caused the engine to run too rich this may have damaged/plugged the cats..check for exhaust restrictions...

the fuel pressures must be checked this must be around 60psi...with engine idling and when shut down hold close to this reading....


the dtc should also be taken to determine its not something else...I would expect the random missfire dtc with your discription...this is common with low fuel pressures...

pull every spark plug out. get a butane torch, or propane, pliers, and heat up plug tips until they glow white. tips and central electrode.
be very particular on plugs. are any of them sooted? gray caked coating?
puffs of bluish smoke might be contributed to plugged converter. but, normally, it is oil getting into combustion chambers. thus, plugs should be the first indicator.
i am leaning towards leaking engine gasket. either oil squirted into the chambers, or air leaked in somewhere, intermittently.
running reach, you should have smelled gas all over you. besides, i have seen nasty stuff going through cats without plugging them. but it's a valid suggestion to check on air flow, it's free at midas.

Thanks for the suggestions guys, I really appreciate it. Couple of things...

1. What is dtc?
2. Isn't bluish smoke also attributed to running rich? As in unburnt fuel?

Like I said everyone is stumped, and I'm certainly no expert, but I keep thinking it has to be something causing it to intermittently dump too much fuel in the mixture. Although gas mileage is great so maybe not...

Thanks again
Chris

Thanks for the suggestions guys, I really appreciate it. Couple of things...

1. What is dtc?
2. Isn't bluish smoke also attributed to running rich? As in unburnt fuel?

Like I said everyone is stumped, and I'm certainly no expert, but I keep thinking it has to be something causing it to intermittently dump too much fuel in the mixture. Although gas mileage is great so maybe not...

Thanks again
Chris

DTC = Diagnostic Trouble Code. You said it didn't have any codes, but I have heard lots of people say that there aren't any codes because the SES light is not on. This is not true, there are dozens of codes that don't turn on the light.
Blue smoke means oil. Black smoke means rich. White smoke means coolant, but sometimes it looks blueish to me looking through a mirror. Check all the fluids to see if you are leaking one into the engine.

Also check the MAF sensor reading, at 1,000 RPM the MAF in g/sec should be close to the displacement of the engine in liters. 4.8L=4.8g/sec 6.0L=6.0g/sec. If not, remove and clean the MAF sensor with intake/throttle body cleaner. Gently blow it dry (hold the blowgun about 4' from it and just let the air flow over it, you don't want to damage the wires in it). After you blow it dry, let it sit for a while to ensure it is 100% dry. Any cleaner remaining on it when you turn the key on can crack the wires and ruin the sensor. If the MAF sensor is reading off, the PCM just assumes it is correct and doesn't set a code unless it is way off.

DTC = Diagnostic Trouble Code. You said it didn't have any codes, but I have heard lots of people say that there aren't any codes because the SES light is not on. This is not true, there are dozens of codes that don't turn on the light.
Blue smoke means oil. Black smoke means rich. White smoke means coolant, but sometimes it looks blueish to me looking through a mirror. Check all the fluids to see if you are leaking one into the engine.

Also check the MAF sensor reading, at 1,000 RPM the MAF in g/sec should be close to the displacement of the engine in liters. 4.8L=4.8g/sec 6.0L=6.0g/sec. If not, remove and clean the MAF sensor with intake/throttle body cleaner. Gently blow it dry (hold the blowgun about 4' from it and just let the air flow over it, you don't want to damage the wires in it). After you blow it dry, let it sit for a while to ensure it is 100% dry. Any cleaner remaining on it when you turn the key on can crack the wires and ruin the sensor. If the MAF sensor is reading off, the PCM just assumes it is correct and doesn't set a code unless it is way off.

I've been dealing with the same type of idle symptoms on my 2000 6.0
When I hook up my AUTO TAP to see what the MAF readings are I'll post the results.

blue smoke:

http://www.2carpros.com/topics/bluesmok.htm

Thanks for the suggestions guys, I really appreciate it. Couple of things...

1. What is dtc?
2. Isn't bluish smoke also attributed to running rich? As in unburnt fuel?

Like I said everyone is stumped, and I'm certainly no expert, but I keep thinking it has to be something causing it to intermittently dump too much fuel in the mixture. Although gas mileage is great so maybe not...

Thanks again
Chris


you must take fuel pressure readings,,,,also a poor idle is usually a vacuum leak do you know what a PCV is and the hoses that go to it///as well as the crankcase vent hose...these componets will give a poor idle if defective worn plugged....

then you can get into intake vacuum leaks and other more expensive complex issues...the one's I have suggested are simple cheap..your fuel regulator failure if very bad can cause expensive damage if it was run a good amount of time like this..

since it appears your knowledge level is limited ,,you are at the mercy of the auto tech's good luck try to find a repair station familiar,and honest that can help you...

I am having similar problem with my '05 5.3 ltr. I went into a puddle (more like a 14" lake) and was stuck at a stoplight in the water. The car started idling rough and my engine light went on. Now it idles rough and blows black smoke when I step on the gas hard. I have taken it to 3 auto parts stores to pull the code and they get a blank screen on their reader (does not register that the code reader is plugged in). I am wondering if I blew a fuse or shorted out a sensor on my cat converter.

I am having similar problem with my '05 5.3 ltr. I went into a puddle (more like a 14" lake) and was stuck at a stoplight in the water. The car started idling rough and my engine light went on. Now it idles rough and blows black smoke when I step on the gas hard. I have taken it to 3 auto parts stores to pull the code and they get a blank screen on their reader (does not register that the code reader is plugged in). I am wondering if I blew a fuse or shorted out a sensor on my cat converter.


If your air filter is wet air will not flow to intake,,,