Running lean

[builds4christ]

Oops, the way I kept imagining it, there was no clean air supply side.

I'm a moron, don't listen to me..

Haha no worries, I almost imploded my engine with vacuum lol!

 

[mikez71]

Ha! Since it didn't oceangate on you... you may have dished pistons now!

 

[dkad260]

What is your vacuum at idle, using a physical gauge, also is the needle steady?

Have you done a leakdown test of the injectors? Verified fuel pressure?

Are the O2 sensors AC Delco or aftermarket?

Miles on plugs, are they AC Delco?

Just a few questions to help try to diagnose.

 

[builds4christ]

What is your vacuum at idle, using a physical gauge, also is the needle steady?

Have you done a leakdown test of the injectors? Verified fuel pressure?

Are the O2 sensors AC Delco or aftermarket?

Miles on plugs, are they AC Delco?

Just a few questions to help try to diagnose.

Hey DK.

I am unsure of the plugs (brand or mileage), but the 02 sensors are Walker. I have verified pressure at the rail to be steady at around 58 psi, if memory serves, but I have to look again. I checked fuel pressure and verified the number, but can't quite remember what the number was lol. There's no misfire history though.

I also have not check vacuum with a physical gage. That's a good idea. What should the vacuum be at idle?

I want to perform a leak down test, but haven't yet. I've never done one tbh.

 

[dkad260]

What should the vacuum be at idle?

I don't know what these are supposed to pull, but I would assume 18-21 inHg.

Can you elaborate more on the history....how long have you owned it, and after you purchased it, what have you done to it and what if any problems were present at time of purchase and did the problems start before or after any service you performed.

Was it acting up when you bought it?

We definitely need to see what the PCM is seeing in regards to alcohol content. Could have alot of E85 in it and maybe it's not a flex vehicle.

 

[dkad260]

Sorry, deleted for wrong thread. My bad.

 

[builds4christ]

Hey guys, back now. Sorry for the long delay, but all this time the truck was getting the PCM tuned.

Well, it ran well for a few days and started acting up again. The o2s are still hanging at high voltage for too long at idle, it's surging slightly, and the LTFT at idle are anywhere between 10% and 14%.

It's got long tubes, but the o2s don't seem like they're TOO much farther down than stock, but I suppose I wouldn't know because I've never seen it with stock exhaust.

ChatGPT was saying maybe they're not getting hot enough at idle.

What do you guys think? This is driving me nuts lol.

 

[West 1]

Are you positive your headers are sealed to the block and exhaust and not drawing air into the system throwing off your sensors? Smoke checking the exhaust can find leaks. Blowing air into the exhaust with a shop vac while searching the pipes and connections with soapy water also works. I fixed a 2010 GMC Acadia using the shop vac trick to find the leak. It does not take much air intake to mess up the readings.

 

[builds4christ]

I don't know what these are supposed to pull, but I would assume 18-21 inHg.

Can you elaborate more on the history....how long have you owned it, and after you purchased it, what have you done to it and what if any problems were present at time of purchase and did the problems start before or after any service you performed.

Was it acting up when you bought it?

We definitely need to see what the PCM is seeing in regards to alcohol content. Could have alot of E85 in it and maybe it's not a flex vehicle.

Hey DK, sorry for the delay. I still have to check vacuum at idle. Been a inundated with other projects and had to put this one down.

I'm going to do a leak down of the injectors tomorrow. I was thinking connect scanner, look at fuel pressure. Turn key to on, and watch what it does after I hear the fuel pump stop priming right? I'll see and get back to you.

So the history, as I know it:

1) It's got a procharger kit making 7-8lbs of boost.
2) 2 bar map.
3) new AC Delco (Denso) 02s.
4) New spark plugs and wires.
5) Long tube headers.
6) Dual catch can setup. Clean side free flowing and ported to intake of procharger, dirty side check valved and ported to top port on intake.
7) purge valve delete (unplugged purge valve and capped intake port, but left everything else running in evap system)

When I started this thread it was running lean and I found a huge vacuum leak at the MAP sensor. LTFTs were in the +15% - +18%s. When I swapped MAP sensors, I did the smoke check and found no leaks.

But after that the LTFTs swung the opposite direction, to -15% - 18%s. Averaging, of course.

During both situations, and this sorta confuses me, the 02s were lazy and hanging in the high end of the voltage too long. So it would swing down to ~200 mV and immediately switch back to ~800 mV and stay there a while, then switch to low and quickly back to high again and stay there a while. So it wasn't switching consistently or quickly.

It's been tuned since then and it's running way better. My tuner says the MAF frequency was way off, that the injectors were tuned incorrectly and a slew of other things. He drove it around a while after his last write and it ran well.

I got it back and it ran well for a couple days until I got the same codes for lazy and insufficient switching of 02s. Checked it again and the 02s were behaving the same way as welhen I gave it to the tuner.

I really kicked myself in the ass that I didn't check the 02s immediately after getting it back from him. I suspect that perhaps he didn't catch it, but he insists that it was fine.

Since then I've been chasing the trims and trying to get the 02s to work properly.

Does anyone have a tune file for this setup that I could look at? Someone out there has to have this procharger kit installed on their 6.2. or maybe not lol.

 

[builds4christ]

Are you positive your headers are sealed to the block and exhaust and not drawing air into the system throwing off your sensors? Smoke checking the exhaust can find leaks. Blowing air into the exhaust with a shop vac while searching the pipes and connections with soapy water also works. I fixed a 2010 GMC Acadia using the shop vac trick to find the leak. It does not take much air intake to mess up the readings.

I inspected the interface to the heads and I didn't find any soot anywhere. I do have a leak at the resonator a little downstream of the upstream sensors.

Maybe I should try the smoke detector on the exhaust and see if I'm missing anything.

 

[mikez71]

Is the O2 behavior only at idle? What are fuel trims now?
Is it running worse after awhile, or just throwing codes?

Might disconnect battery to clear fuel trims, and see if O2's start behaving normally...

 

[West 1]

Since the exhaust system has some drain holes for water drain a smoke test might just llow out those holes. The shop vac blowing into your exhaust puts plenty of flow in there, you can leak test the engine side of the Cats with a soapy water spray. If air is leaking you will see the bubbles form.

Have you spoke to any owners with long tube headers to see how the O2 sensors are working in those cars? There is a reason the manufacturers keep the O2 sensors close to the engine, usually right below the factory header not 3 feet away.

I own a 2008 6.2L and find the power is amazing, that said I rarely use more than 1/3 throttle. It has all the power I need or desire. These things must become an absolute BEAST with a supercharger on them.

Years back I raced an H2 Hummer, I figured we probably had the same engine and I was much lighter in the Yukon Denali, thought I would clean his clock. Through 1st I was a body length ahead. Second gear he was catching up but slowly. 3rd gear he got beside me and my buddy in the passenger seat yells, listen to that. He HAS A BLOWER! (supercharger) Must have outweighed me by 2,000 pounds and by 3rd gear he pulled ahead and was gone. It was silly but roads were wide open that night, no traffic in sight so we played. I lost.

 

[builds4christ]

@mikez71 The 02s seem to be hanging high at all rpms, but less so at higher RPMs. So the delay is more apparent at lower rpms. This is in idle.

At acceleration (load), they seem to act normally, but let off the gas, they get lazy.

It runs well enough for a while iluntil it toasts the 02s. The codes pop and about 24 hours later it really begins running badly. Swap in new 02s, runs well again. Annoying right?

@west that's so cool, yeah man it's fast! I raced a brand new Duramax and it was losing. It took off on me because I didn't know he wanted to race but I caught up quickly because of that AWD!

Yeah man part of me wants to just ditch the kit and go stock to get rid of this problem, but that would likely mean ditching the exhaust as well.

I have to do some digging with the exhaust.

 

[dkad260]

Hey DK, sorry for the delay. I still have to check vacuum at idle. Been a inundated with other projects and had to put this one down.

No worries, I know what you mean.

Have you looked into your tune with regards to the PE (Power Enrichment) table?

Under boost, I believe this is where the tune would be adding fuel. I don't know enough about it to give advice but if you haven't had someone check it out I feel this is what you should verify with someone who is familiar.

 

[mikez71]

It runs well enough for a while iluntil it toasts the 02s. The codes pop and about 24 hours later it really begins running badly. Swap in new 02s, runs well again. Annoying right?

So you're saying the O2's actually foul out? Are the tips blackened?

I hear you need a wideband o2 to really tune your fueling/vve map..

Possible it's too rich when cruising under low boost? idk..