Can't find ANY vacuum lines?!

[goborgoh]

I can not for the life of me find one single vacuum line on my 2004 chevy 2500 8.1L, also has no EGR valve. I have an Idle bounce and am trying to figure out what the problem is. Took the fuel pressure at the rail. At KOEO was 55psi, KO pressure holds. At idle it reads able 63psi and will rise some with some throttle. All looks normal to me, anyone think differently?

 

Then took a can of break cleaner to the intake manifold gasket and parts of the TB, nothing. This is why I ask able the vacuum lines, shouldn't there be some or because it uses MAS, MAP, and other sensors to do its calculations it doesn't need vacuum lines?

 

Truck runs fine, no codes, just hate not being able to figure it out!!

 

Regards

 

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[Colossus]

Vacuum line? Didn't they stop using those in the 90s?

[O_J_Simpson]

There are no points or distributor. Is that an issue too?

[muddkatt]

Adjust the idle mixture on the carburetor, then set the timing.

[goborgoh]

Very funny, I get your point. Now that's out of the way, anything helpful to say?

 

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[NSFW]

Plug your (live data) scanner in.. turn the ign on start the truck. Get it up to tempreture. (90deg c, 190F)

You are gonna want to find the fuel trims in the scanners live data section, and the mV o2 sensor data in the scanner.

There will be 4. ST Bank 1, LT Bank 1, ST bank 2, LT bank 2.

Bank one is on the passanger side, and bank two is on the drivers side for reference.

A appropriate ST, LT will tell you 4 things. Manifold is sealed, MAF sensor is working, O2 sensors are functioning, and your injectors are fuctioning within spec.

ST and LT should be close to one another % wize. IF LT is way rich, then somewhere on your intake you have a leak. IF LT is way minus, then it's a MAF gone wonky or an 02 sensor is not reading correctly. Wiggle fuel injectors (all 8 of em have a neroprene ring) Intake gascuts not pulling a seal, or crack in the intake. (YES they crack) you said your EGR is blocked off, so scratch that 0-ring. Check your throttle body gascut, and your EVAP return o-ring.

NEVER change parts untill you KNOW its the part. Check wires, connections, 0-rings, gascuts and PCM wiring, connection.. etc.. 95% of the problems with the sensors are not the sensors but the wiring going to them or the damned gascut-seal on it not doing its job.

Unless its an ABS problem.. in that case the module is a POS.

Hope this helps.

p.s(THIS is an outline, the same way a compass points the way, but doesnt walk in the direction FOR you)

[goborgoh]

Plug your (live data) scanner in.. turn the ign on start the truck. Get it up to tempreture. (90deg c, 190F)

 

You are gonna want to find the fuel trims in the scanners live data section, and the mV o2 sensor data in the scanner.

 

There will be 4. ST Bank 1, LT Bank 1, ST bank 2, LT bank 2.

 

Bank one is on the passanger side, and bank two is on the drivers side for reference.

 

A appropriate ST, LT will tell you 4 things. Manifold is sealed, MAF sensor is working, O2 sensors are functioning, and your injectors are fuctioning within spec.

 

ST and LT should be close to one another % wize. IF LT is way rich, then somewhere on your intake you have a leak. IF LT is way minus, then it's a MAF gone wonky or an 02 sensor is not reading correctly. Wiggle fuel injectors (all 8 of em have a neroprene ring) Intake gascuts not pulling a seal, or crack in the intake. (YES they crack) you said your EGR is blocked off, so scratch that 0-ring. Check your throttle body gascut, and your EVAP return o-ring.

 

NEVER change parts untill you KNOW its the part. Check wires, connections, 0-rings, gascuts and PCM wiring, connection.. etc.. 95% of the problems with the sensors are not the sensors but the wiring going to them or the damned gascut-seal on it not doing its job.

 

Unless its an ABS problem.. in that case the module is a POS.

 

Hope this helps.

 

p.s(THIS is an outline, the same way a compass points the way, but doesnt walk in the direction FOR you)

Thank you for taking the time to give a thoughtful answer.

 

Here's the thing, I've checked all those parameters about a week ago and here is what I found.

 

STFT AND LTFT: +/-5%

O2 sensors: pre cat .02 to .850 transition quickly

Post cat: holds at .650ml

 

The plugs and wires have been replaced, cleaned both TB and MAF and all grounds ohm out.

 

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[NSFW]

I think the throttle body actuator might be gettin on in age.

That's the black thing with the electrical umbilical going to it on the left side of the TB.