Running lean

I've been resetting the LTFT's with my scanner before every test drive.

If the MAF was over-reporting, would the LTFT's show rich? What're the LTFt based off of? What's do you guys think about the BOV going bad?

The oil being saturated never occurred to me. How would that work? Through the PCV system?

I drove it around for a good bit, at least 10 minutes. If you guys think it will help, I can take it for a longer drive to see.

builds4christ said:

I've been resetting the LTFT's with my scanner before every test drive.

If the MAF was over-reporting, would the LTFT's show rich? What're the LTFt based off of? What's do you guys think about the BOV going bad?

The oil being saturated never occurred to me. How would that work? Through the PCV system?

I drove it around for a good bit, at least 10 minutes. If you guys think it will help, I can take it for a longer drive to see.

Click to expand...

LTFTs are based on the history of the STFTs at certain loads. So if you're resetting the LTFTs then they should be affected only by the current STFTs.

Yes, the fuel vapors are in the PCV system and take time to burn out. That's the purpose of a Positive (closed) Crankcase Ventilation system. In the olden days (LOL) the crankcase was ventilated into the atmosphere through a filter on the rocker arm cover, and the vapors weren't re-burned.

EDIT: calculating the correct actual fuel trim is done by adding the STFT and LTFT for each bank. The sum of those two numbers (per bank) is the complete fuel trim value.

Fless said:

LTFTs are based on the history of the STFTs at certain loads. So if you're resetting the LTFTs then they should be affected only by the current STFTs.

Yes, the fuel vapors are in the PCV system and take time to burn out. That's the purpose of a Positive (closed) Crankcase Ventilation system. In the olden days (LOL) the crankcase was ventilated into the atmosphere through a filter on the rocker arm cover, and the vapors weren't re-burned.

EDIT: calculating the correct actual fuel trim is done by adding the STFT and LTFT for each bank. The sum of those two numbers (per bank) is the complete fuel trim value.

Click to expand...

Thanks for the explanation.

Strangely the stft don't look too off. I've seems them go +/- 10% but then settle around 0.

Idk. I guess I can just drive it around tomorrow for a while and see.

I was "talking" with chat about this and it came up with the idea that maybe they tuned the truck with the map seal leak. Not sure about that, but I wonder.

If the short term FT is staying close to zero you are running perfectly. The front or close to engine O2 sensor gives your computer the information to tune with. The after cat O2 sensors only tell the engine if the cat is working proper or not, they do not help with the tune at the rear position.

Fless said:

One thing I notice is that the MAF appears to be way over-reporting.

Click to expand...

Partly maybe because he's supercharged.
He's idling around 50kPa, when usually it's around 40kPa (7psi vs 6psi)
Also his RPMS are 700 vs 525 stock.

If everything checks out, MAF? (might have to swap with someone to know forsure, but new is a pretty good bet)
...vacuum leaks, exhaust leaks, boost leaks, quality injectors, etc...
I suspect the tune is just NOT SUPER dialed in, as kit manufacturer's probably spend just enough time to get it running OK.
(So I've HEARD) Besides, many buyers will have various other mods that could use tuning.. That's the nature of custom builds..

mikez71 said:

Partly maybe because he's supercharged.
He's idling around 50kPa, when usually it's around 40kPa (7psi vs 6psi)
Also his RPMS are 700 vs 525 stock.

Click to expand...

Yeah, I wasn't taking into account the supercharger.

Question guys. Any chance where I run the catch can return can affect it? So I have both PCV runs meeting at a tee, then going to the catch can. Then it returns to the front of the super charger, that is before the charger intake near the air filter. It doesn't seem like a good seal there either.

I plugged off the top PCV port on the intake. I was thinking of switching the return to that port instead as it's a better seal. On the other hand, why would crankcase pressure variances cause this?

I know I'm hunting, but at this point I'm looking for any and all options.

You guys have given me lots of potential things to look at. I'm really hoping it's not tune related because that's costly. The other thing is, it was not doing that until recently. The only thing that changed is that map sensor seal.

Also, I agree that if the STFT good, the LTFt should be as well, but that doesn't seem to be happening.

I drove it a good amount today and the codes popped again. I'll drive it around again tomorrow and see.

Boosted setups have to vent, so what you're doing sounds right. So long as it's not leaking after the MAF, you should be fine. (Your MAF is after the blower I'm assuming)

If you routed one PCV line to the intake, you would need a check valve so you're not blowing metered air into your crankcase. And you would need to vent the other cover, so you would also be drawing in unmetered air through the vent when not boosting..

How was the PCV routed before? Perhaps if it was tuned with a different setup? idk

mikez71 said:

Boosted setups have to vent, so what you're doing sounds right. So long as it's not leaking after the MAF, you should be fine. (Your MAF is after the blower I'm assuming)

If you routed one PCV line to the intake, you would need a check valve so you're not blowing metered air into your crankcase. And you would need to vent the other cover, so you would also be drawing in unmetered air through the vent when not boosting..

How was the PCV routed before? Perhaps if it was tuned with a different setup? idk

Click to expand...

I think we're on to something.

So during the time it was initially screwing up the LTFT, both were PCV's going into the inlet of the charger.

Right now it's setup so that both PCV ports are going to the intake port. No check valve. Just a tee and a catch can. Haven't run it like this yet, but I just did the mod and read your comment right after.

Ok, I'm thinking I routed these incorrectly.

I believe the stock port on top of the intake is check valved... Am I wrong? Probably wrong lol.

Even so. If there both tee'd together, at boost the Case won't venting and it should be.

So, I have a couple evil energy check valves on the way and another catch can. Just going to double the cans, check valve the hoses, and return them back to their OEM configurations.

Damn, hope this works.

Right, I think you should install a check valve if plumbing PCV into the intake manifold, so boost pressure won't fill the crankcase. If it was tuned like that, possible you will still get codes with a check valve installed? Maybe won't set a code, if it only checks during idle/vacuum periods.

But your tune might be off when boosting, if it was allowed to leak pressurized metered air into the crankcase before, and now you're stopping the leak with the check valve.

Hmmmm. Dang it.

Well, let's see. The stuff should be coming tomorrow morning. I'll report back.

And I'm not saying it won't run well.

Should run the same under boost as when you re-routed the PCV to blower inlet..
(blowby might pressurize somewhat without a vent, but less than it was before with intake manifold unchecked into your PCV!)

And at idle, run like it was originally setup/tuned. Hopefully enough to stop the codes!

mikez71 said:

And I'm not saying it won't run well.

Should run the same under boost as when you re-routed the PCV to blower inlet..
(blowby might pressurize somewhat without a vent, but less than it was before with intake manifold unchecked into your PCV!)

And at idle, run like it was originally setup/tuned. Hopefully enough to stop the codes!

Click to expand...

Alright, got some stuff to report.

Drove it today and it ran badly. A couple things to note. There was surging for one and LTFT were still showing the ECM pulling fuel.

Not much has changed.

Got some questions though. I was idling and decided to check the purge solenoid position. It was commanded @ roughly 35% at idle and 100% while cruising down the highway at 1500 rpms.

Is that right? What does yours do? I parked it and removed the purge from the system. I plugged the intake port and the trims did improve slightly, but it still didn't seem to be happy.

The other thing is PCV. While idling, I removed the oil cap and there was noticable suction and a whoosh. When I hold the cap close to the neck with a gap of about 1/8" from sealing, it noticably sucks it down. Is that normal?

That is odd that it's running so differently from when you got it?
I suspect the vacuum is normal, but maybe because you're sucking on two PCV vents when it's usually just vacuum on one?..idk

Might try just venting them and seal off the intake..

Or suction on one, vent the other. Check valves on both so you never draw through the vent, and never boost to the crankcase? idk

Your purge valve operation seems normal, but that's another thing I hadn't considered regarding boost.... Disconnecting seems like a good (temporary?) solution.. another spot metered air could leak out under boost or pressurize the fuel tank (maybe not enough to matter?..idk)

If all else fails, return everything how it was. How is your PCV venting currently? And are you surging at idle or under boost?

If you want to see my GMT800 purge operation, I have some logs pictured here... and on the second page

Thread 'Fuel tank pressure vs. evap purge'
https://www.tahoeyukonforum.com/threads/fuel-tank-pressure-vs-evap-purge.158425/

Yeah I agree.

I think maybe the pcv system is screwed up man.

When it was setup stock, the port on top of the intake was attached to the rear PCV without a check valve. Not surprisingly, the reason main is leaking haha.

I wonder what the best approach for this is. I could return things to stock and keep the boosted side check valved, but is pulling vacuum from only on side enough to relieve crank case pressure under load?

When I get up into boost, only one side will be venting.Thabks for giving me that link! I'll take a look.

Stock only pulls from one side, and you need to vent from somewhere..

My thoughts regarding two check valves.. what you're considering above I believe..
When under vacuum, PCV will suck and vent will be closed.
When boosting, vent will vent, and PCV will be closed.

Whether one PCV vent is enough to relieve crankcase pressure under boost?
If not I would just vent both.. Like you had it before going to the intake of blower..

I wonder if the new MAF is upsetting your tune.. Might throw the old one on if no solution..
If the old one works better, but throws a MAF code.. it might be time for a tune..

I watched this video for the explanation of a 2 can 2 check valve system. I am not boosted but installed the full system anyway. 2 catch can 2 check valve system

builds4christ said:

Yeah I agree.

I think maybe the pcv system is screwed up man.

When it was setup stock, the port on top of the intake was attached to the rear PCV without a check valve. Not surprisingly, the reason main is leaking haha.

I wonder what the best approach for this is. I could return things to stock and keep the boosted side check valved, but is pulling vacuum from only on side enough to relieve crank case pressure under load?

When I get up into boost, only one side will be venting.Thabks for giving me that link! I'll take a look.

Click to expand...

https://motionraceworks.com/collections/catch-can-pcv makes catch cans for boosted applications.

Thanks all. I'll check out all your stuff.

I removed the check valve from the breather (clean) side. Definitely ran better and stopped bogging. Vacuum died down a bit in the crankcase as well. It makes sense. If the dirty side is going to be alternating from suction to static (because of the check valve) then the other side should be able to vent in both directions. When idling the suction from the dirty side was way stronger than the clean side and so it needed that air to be able to change direction.

@mikez71 I tried running both old and new MAF with similar results.

Another thing that my buddy mentioned that didn't occur to me was the evap purge solenoid. When it's open, and it is always commanded open by the ECU for some reason, and I'm under boost, I'm pressurizing the fuel tank.

So I'm going to delete it, but I'm no expert on how to do that. I can easily enough stop the ECU from reporting on it, but not sure about the physical aspect.

The other thing is, I ran and logged yesterday with and without the evap connected. Fuel trims were marginally better without, almost 4% in the mid rpm range.

Ok last but not least, I'm going to do a injector leak down test today.

I have to try and find what values I should be seeing. Do you guys know how much leakage is acceptable over X time?

Thank you all for your input!

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

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