5.3 initial startup running extremely rich

I'm attempting to help a friend of mine get his new 5.3 build running but we are chasing our tails trying to figure out why it's so rich. It's just the engine sitting on a 68 Camaro subframe. We have already tried all of the basic troubleshooting, and initial tune setup steps for a larger cam, and while some of this helped, this thing is still pouring way too much fuel.

It is a 2000 5.3 out of a tahoe, changed to DBC from DBW that it was in the tahoe. The heads are ported stockers, the intake is an open plenum aluminum(not sure of the brand) with a 102mm throttle body(probably too large?). The cam is a Howards 226in 234ex .525 lift with a 109 LSA. Stock injectors.

I have bumped up the idle RPM/airflow settings. I have advanced the timing down low. Also, I've subtracted nearly 30% off of the VE table in the idle/low RPM areas, which seems like too much to me, but it still isn't making enough of a difference.

Compression reading around 180psi all cylinders. We have smoked the intake looking for leaks(none found). Fuel pressure reading steady 60psi. We pulled the intake with injectors, cranked the engine and looked for any leaking injector(none found). Checked grounds to PCM and all sensors, all seemed to be good. And a lot of other checks I'm sure I'm forgetting.

It does run, and has a rough idle. After running a while, it will foul the plugs and when you shut it off there will be fuel puddling in the intake ports. Weirdly it also will have oil in the intake, but the only place this could come from is the rings getting washed out from all the fuel(PCV is NOT connected)? Or bad valve seals, but all that is brand new.

Anyways, I'm getting stumped, maybe there is something in the tune I'm not catching(new to tuning). Hopefully some of you might have some ideas? Any and all help is appreciated.

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Originally Posted by RedLT4

It's just the engine sitting on a 68 Camaro subframe.

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Open exhaust I bet. You cant do that with O2 sensor feedback. If you must run it that way unplug the O2s and run it in open loop untul you have full exhaust hooked up.

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Originally Posted by 2xLS1

Open exhaust I bet. You cant do that with O2 sensor feedback. If you must run it that way unplug the O2s and run it in open loop untul you have full exhaust hooked up.

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We thought about that as well and have 2ft pipe extensions off of the 3inch header collectors. The readings could still be off due to the O2 placement on long tube headers, but wouldn't it read lean if outside air was getting to the sensor and not rich?

We also tried running it without O2s, but didn't seem to make any difference. I hooked them back up so I could at least see if the O2s agreed about how rich it seemed to be running and they certainly do.

O2s near open exhaust see free oxygen outside of the exhaust and through fuel trims add unnecessary fuel causing a rich condition.

Just curious, how much fuel pressure are you running??

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Originally Posted by 5FDP

Just curious, how much fuel pressure are you running??

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60psi on the gauge while idling.

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Originally Posted by 2xLS1

O2s near open exhaust see free oxygen outside of the exhaust and through fuel trims add unnecessary fuel causing a rich condition.

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Makes sense, but during open loop it does the same, and with the O2s unplugged, same, very rich.

Curious - did you ever get this resolved? exact same issue I do have exhaust on mine - 5.3 with comp cam, ls1 intake Start up tune runs super rich.

Unfortunately no, hoping to work on it some tomorrow.

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Originally Posted by RedLT4

Unfortunately no, hoping to work on it some tomorrow.

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Here ya go. Give this a try. This will let you get the VE table dialed in without the MAF influencing the fuel.
I assume you have stock 24.8 lb Tahoe injectors?

Attachment 98777

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Originally Posted by kevin87turbot

Here ya go. Give this a try. This will let you get the VE table dialed in without the MAF influencing the fuel.
I assume you have stock 24.8 lb Tahoe injectors?

Attachment 98777

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Yes stock injectors. I could not open the file for some reason, "unsupported or newer version detected", but I have the latest software revision?

DId you just set the MAF fail frequency to 0?

Here ya go. Let's try this again. I have version 4.6.3.

Attachment 98784

I did set the Freq fail to 0 Hz. I also removed a little more fuel from the VE table and made a few other small changes.

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Originally Posted by kevin87turbot

Here ya go. Let's try this again. I have version 4.6.3.

Attachment 98784

I did set the Freq fail to 0 Hz. I also removed a little more fuel from the VE table and made a few other small changes.

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Huh, I have 4.4.2, which says it's the latest, are you using a beta test version?

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Originally Posted by RedLT4

Huh, I have 4.4.2, which says it's the latest, are you using a beta test version?

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I'm not. Yours just needs to be updated to the latest version (even though it says otherwise.)

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Originally Posted by kevin87turbot

I'm not. Yours just needs to be updated to the latest version (even though it says otherwise.)

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Thank you Kevin, got it updated, did a run with your changes and definitely an improvement. Log attached. It is still pretty rich however.

Do you think I should pull even more from the VE table in the idle area?

The O2 sensor bungs on these headers seem to shroud the sensors. This does not seem right and now I'm thinking the O2 readings have been way off from the start.

Can anyone confirm if this looks wrong:

Attachment 99034

More recent log file attached. It seems to run OK until closed loop, then it says it's reducing fueling, but something is going haywire according to the smoke that starts coming out of the exhaust.Attachment 99081

Did you reset LTFT @ 5:20 timeline? Are both O2 sensors that close to the merger as it looks in picture? I thought it's to be at least 6 inches from collector output or can pick up individual cylinder, not the bank and overlap /reversion will play havock. Your CL is kicking your butt. As you increase RPM things kinda normalized in latest scanner. The flow is more constant and the difference of metered air vs actual diminishes. Hard to explain why no change in TPS or any other scanned PID and yet 1 bank has way different STFT. It seems like an external influence. The o2 volts are showing lean on B1 yet STFT B1 do not change at 3:50-53?

I would try tuning the MAF instead of the VE here... Or fail the MAF, tune VE, then tune MAF (with ALL fuel adders removed)... Which is the typical order for full calibration. You're running closed loop, so MAF is making a lot of these airflow calcs.. Though its biased towards VE at lower RPM, it's still a blended model. Adjusting only VE is only going to correct part of the problem. That's why most tune the VE first with the MAF failed and all adders turned off... Including trims.

In your case, just to get it idling, trims can be used as corrections, but later, a wideband will be needed.

Also, the open pipes are not helping you. I have cutouts, and my wideband is about 2 feet in front of the driver side... and it zeroes out (goes past high lean on the gauge) with the cutouts open at idle. On that gauge it's like 30 to 1 max ratio, so that gives you an idea on how much air is making it's way back up the pipe.

The sensors detect the "difference" in oxygen level between the inside of the pipe and the outside. They do not detect fuel. Probably why they are called what they are called lol. But yeah, any additional oxygen in the pipe can throw them off. It's already been stated above, but I doubt 2 feet is enough pipe, especially with reversion and pulse going on. You also have to make sure they are sealed real good too. I use band/strap clamps with some tinfoil as a "gasket". Works fantastic.

Hopefully that helps.