I'm chasing down a little problem and need hand. The basics:
Car info: Stock LS6, shorties, Procharger 7 lbs max boost. 60lb inj. BAP, Meth. Configuration hasn't changed in a year +.
Problem: CEL, rich codes, both banks.
My AFR drops into the 11s on deceleration. Nothing happened to "trigger" this event. Just started happening one day. The vacuum is around -9 psi at idle. At -11.5 psi is when it starts going rich (according to the wideband). I'm only pulling -13 to -14 psi on deceleration. Seems low to me, but I don't remember what it was before.

Solutions tried: (one at a time)

1) I've put new vacuum lines on, and added a vacuum manifold on the brake booster line. No change.
2) removed meth from intake and capped off inlet. No change
3) Inspected manifold (off car) and put solvent in it to try and see any cracks. Nothing could be seen, but I don't have anything to check it better.
4) Had the injectors cleaned and flow matched. No change.

So, on to the 'hand' part.. If someone with a digital gauge on a basically stock LS6 (no cam or bolt-ons) could give me a quick report on the typical vacuum at idle, and maybe a reading at XX mph, in XX gear, I can really see that it is in fact, a vacuum problem.

I'm also open to suggestions.

 

Fuel pressure problem, too high? It would explain running rich.

 

For a stock cam, that vacuum is way too low. My setup is similar, and I pull 20-23 inches of Hg. at idle. You say you replaced the vacuum lines? Which ones exactly? What happens when you take a vacuum reading right from the intake (easily done at the reservoir) ?

 

Fuel Pressure at 60 +/- 2. (BAP). It only goes rich on deceleration. Normal driving, it's fine. The more the decel, the more rich. I can actually get it into the high 10s AFR.

I took off all the T connections for the vacuum (problem existed BEFORE I did this) and added the vacuum manifold on the brake line. I have the BAP operated off vacuum as well as the meth inj, the BOV, and the digital gauge. I checked each of the above before putting on the new lines. (injected 30 psi into each line individually and sprayed windex all over the part/junction)

Lucky - I went out tonight and hooked up an analog vacuum gauge at the vacuum manifold (physically next to the brake booster) and I'm getting 20 ish psi. Problem one found.. digital gauge is inaccurate. Still goes way rich under deceleration though.

 

So you have not inspected the vacuum lines under the battery tray, or to the reservoir? When you say deceleration, do you mean coming out of boost, and decelerating?

***edit*** ok , saw your post. Vacuum sounds good now.

 

Just noticed the forced induction part, any chance you blew a vacuum cap off some where. Odd thing is you should be going max lean on deceleration. Has your fuel mileage gone south? When was the AFR gauge installed?

 

I had the intake off the car, inspected the "spigot" in the back of the manifold and the little line that operates the a/c vents. (which all work too). There isn't any vacuum lines under the battery box.

By deceleration, I mean taking my foot off the gas and letting it "engine down".

Fuel mileage.. avg right now.. 29.5 mpg. That's over the last couple hundred miles of city/hwy driving. About normal for me.

It "should" be going max lean, and used to, but it isn't. I even tried disconnecting the MAF and running in SD. Didn't have any effect on the problem. I have had the gauges and blower on/tuned for almost 2 years. About 8k-10k miles. Nothing has changed or been added.

 

Sounds like it's time to take a look at the AFR gauge/sensor......and yes, there are vacuum lines under the battery tray..... .....but it sounds like your vacuum issue is resolved anyways.

 

But if the AFR gauge was in error, it wouldn't explain the CEL which is from the narrow band O2s.. right?

What are the lines under the battery for / to? When I did the vacuum manifold, I didn't plumb anything under there. The only "original" line I left was the a/c vent line on the back of the intake manifold.

 

I expect you're still looking at a missing vacuum cap or broken line. It all points to that. While I'm not terribly intimate with the LS engines I did quite a bit of forced induction on MX-5's and it was quite common to all of a sudden have a problem like you are describing. Usually it was a vacuum port cap that had been blown off due to the boost condition, which is not the OEM design. Most guys would tie wrap or clamp in some fashion the lines or caps to prevent that problem. Normally from the factory this caps or lines only experience vacuum or atmospheric pressure. When you add forced induction they now need to deal with pressure that can blow them off. When you think about the pressure is around what your football, basket ball etc. is at.

 

My bad, I missed this little tidbit. I'll post tonight when I get home the blurb from the OEM service manual on sensors the ECU polls when in deceleration. Could be it's not seeing what it wants from one of those sensors and failing to pull fuel.

 

Thanks. Meanwhile, I'll go find these vacuum lines under the battery Lucky is talking about.

Side note: I'm working with DynoTune on the inaccurate gauge issue.

 

Pulled out the battery and tray.. no vacuum lines in there. I found one hard plastic line that could be a vacuum line however it comes out of a wire loom and goes down and toward the door. No junctions and the like didn't look scuffed/broke/torn. What ever lines were down there must have got taken out when the procharger/BAP was put in.
On the positive side.. I now have a clean battery tray

 

Nope, they are there....and a vacuum reservoir too. No vacuum lines are removed for a SC install. If you are pulling 20 inches of Hg......you're fine.

Good luck with your issue.

 

You were correct.. but dang.. that reservoir is in there deep! Anyway, I inspected the lines and connections and they looked fine. Furthermore, I pulled the hose off the reservoir and heard pssssst. So, once again, you're right. The vacuum is there and holding fine.

I also replaced the MAP sensor (which was a little loose anyway from a broken tab) and replaced the intake manifold gaskets.

The result... CEL

Thanks for all your help Lucky131969 & Peerpsi. I really appreciate it. Keeps the sanity and all.
I'll drag it over to A & A next week and see if Andy can figure it out. errrr.

 

Don't thank me thank Lucky, I'm just the antagonist!

As promised, several days ago, here is the theory of operation for the fuel modes. As you can see from the decel mode there are several sensors polled. I'm wondering if the PCM is not seeing what it needs from one of them and failing to pull fuel.

Fuel Metering Modes of Operation
The PCM monitors voltages from several sensors in order to determine how much fuel to give the engine. The PCM controls the amount of fuel delivered to the engine by changing the fuel injector pulse width. The fuel is delivered under one of several modes.

Starting Mode
When the ignition is first turned ON, the PCM energizes the fuel pump relay for 2 seconds. This allows the fuel pump to build pressure in the fuel system. The PCM calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT), mass air flow (MAF), manifold absolute pressure (MAP), and throttle position (TP) sensors. The system stays in starting mode until the engine speed reaches a predetermined RPM.

Clear Flood Mode
If the engine floods, clear the engine by pressing the accelerator pedal down to the floor and then crank the engine. When the TP sensor is at wide open throttle (WOT), the PCM reduces the fuel injector pulse width in order to increase the air to fuel ratio. The PCM holds this injector rate as long as the throttle stays wide open and the engine speed is below a predetermined RPM. If the throttle is not held wide open, the PCM returns to the starting mode.

Run Mode
The run mode has 2 conditions called Open Loop and Closed Loop. When the engine is first started and the engine speed is above a predetermined RPM, the system begins Open Loop operation. The PCM ignores the signal from the heated oxygen sensors (HO2S). The PCM calculates the air/fuel ratio based on inputs from the ECT, MAF, MAP, and TP sensors. The system stays in Open Loop until meeting the following conditions:

Both front HO2S have varying voltage output, showing that both HO2S are hot enough to operate properly.
The ECT sensor is above a specified temperature.
A specific amount of time has elapsed after starting the engine.
Specific values for the above conditions exist for each different engine, and are stored in the electrically erasable programmable read-only memory (EEPROM). The system begins Closed Loop operation after reaching these values. In Closed Loop, the PCM calculates the air/fuel ratio, injector ON time, based upon the signal from various sensors, but mainly from the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1.

Acceleration Mode
When the driver pushes on the accelerator pedal, air flow into the cylinders increases rapidly. To prevent possible hesitation, the PCM increases the pulse width to the injectors to provide extra fuel during acceleration. This is also known as power enrichment. The PCM determines the amount of fuel required based upon the TP, the ECT, the MAP, the MAF, and the engine speed.

Deceleration Mode
When the driver releases the accelerator pedal, air flow into the engine is reduced. The PCM monitors the corresponding changes in the TP, the MAP, and the MAF. The PCM shuts OFF fuel completely if the deceleration is very rapid, or for long periods, such as long, closed-throttle coast-down. The fuel shuts OFF in order to prevent damage to the catalytic converters.

Battery Voltage Correction Mode
When the battery voltage is low, the PCM compensates for the weak spark delivered by the ignition system in the following ways:

Increasing the amount of fuel delivered
Increasing the idle RPM
Increasing the ignition dwell time
Fuel Cutoff Mode
The PCM cuts OFF fuel from the fuel injectors when the following conditions are met in order to protect the powertrain from damage and improve driveability:

The ignition is OFF. This prevents engine run-on.
The ignition is ON but there is no ignition reference signal. This prevents flooding or backfiring.
The engine speed is too high, above red line.
The vehicle speed is too high, above rated tire speed.
During an extended, high speed, closed throttle coast down--This reduces emissions and increases engine braking.
During extended deceleration, in order to prevent damage to the catalytic converters
Fuel Trim
The PCM controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. The PCM monitors the HO2S signal voltage while in Closed Loop and regulates the fuel delivery by adjusting the pulse width of the injectors based on this signal. The ideal fuel trim values are around 0 percent for both short and long term fuel trim. A positive fuel trim value indicates the PCM is adding fuel in order to compensate for a lean condition by increasing the pulse width. A negative fuel trim value indicates that the PCM is reducing the amount of fuel in order to compensate for a rich condition by decreasing the pulse width. A change made to the fuel delivery changes the long and short term fuel trim values. The short term fuel trim values change rapidly in response to the HO2S signal voltage. These changes fine tune the engine fueling. The long term fuel trim makes coarse adjustments to fueling in order to re-center and restore control to short term fuel trim. A scan tool can be used to monitor the short and long term fuel trim values. The long term fuel trim diagnostic is based on an average of several of the long term speed load learn cells. The PCM selects the cells based on the engine speed and engine load. If the PCM detects an excessively lean or rich condition, the PCM will set a fuel trim diagnostic trouble code (DTC).

 

Well, I thought I'd post my finding for this in case anyone ever uses the "search" buttton

The culprit to the problem... the O-rings on injectors were leaking. Once I R n R'd the injectors, it works fine. A little anticlimactic however if you look at the dates of this thread, and the fact that it started long before this thread.. you'll get the idea of just how much b.s. I had to go through to find the problem.

Now, I've got a bunch of parts to list up for sale.

 

Thanks for reporting update.

 

Great info, I learned alot from reading this thread.

I have a very similar problem, and I am assuming the culprit is the MAP sensor, because mine is also loose due to a broken tab. I am pretty darn sure its not a vacuum leak because currently I have the small hose going to the HVAC system capped off (and zip tied) temporarily while I try to figure out my surging issue. The brake vac hose seems good to go, my brakes work great. I have the hardest time getting a good seal on that 1/8th hose to the dual zone controller and my RPMs were going crazy because of a vac leak everytime I try to connect that line. (I have the surging problem even with this line completely sealed off)

I have a question regarding your old issue... Did you notice any loss of power / difficulty keeping the engine running at low RPM? I have power above 1,700 or so, anything less the engine wants to surge and die.

I am running 42lb bosch greentops and I have no clue what condition they are in. I think I will try the o-ring replacement and cross my fingers

 

No, I didn't have any low rpm issues. Just low boost at upper levels and I was getting the 'rich' codes. As far as the way the car was running.. you'd never know anything was wrong.

As for yours, well, that little hose on the back also goes to a Vacuum reservoir. Since you've capped it off, your vacuum will fluctuate all over the place.