4MPG on swapped LS3?

[fls350z]

Hey y'all,

So I swapped a BluePrint crate engine into my 2003 350z about a year ago and it's been running rich since I first started it up (which apparently defaulted to an open loop because one of the wires on the MAF plug was swapped, wiring harness problem, not BluePrint's fault, they've been great /unsponsored). So the MAF was never even working in the first place...but I ended up fixing that. The gauge cluster was showing 4mpg (confirmed using old fashioned math) and pretty quick drops at idle, quicker than you'd expect.

So my current hypotheses are that the tune on the ECU (E38 I believe) was suuuper conservative and rich or the computer programmed itself horribly/unfairly given terrible initial conditions (no MAF) or it was a combination of the two.

I'll attach the original tune. The only change I've done was adjusting the PE numbers up a bit because my idle TPS is around 23.5% according to the scanner and the tune PE was starting at like 12% and incremented up to 19. Now, the PE EQ ratio isn't that rich, just 1.170 but I figured it was probably having PE enable at idle thus giving a rich mixture. I also stepped up the PE enable RPM up to 900 from 300. Those are the only changes I've made from the default. If you guys think I should step it back and that it isn't the problem then let me know, I would really appreciate the wisdom. I'm still pretty sure my problem lies within the VVE and MAF Calibration though, just from comparing it to stock tunes on Corvettes around that year.

It is a stage 2 cam afaik, it came with the engine 225/238, .612, .585 and I know that means a bit more thirst at idle...but not enough to bring me down to 4mpg even with very very light driving. I get like 9mpg on the highway, holding around 3k rpm but that probably wont be in the logs. I'll include the Default tune for those who are curious, the v1.2 tune is going to correlate to the 1.2 log, the 1.3 tune is my most recent but I have no log of it because I haven't driven it with it. The only differences between the three is in the PE Hot Throttle table as far as I recall. Again, current tune is 1.3 where I bumped the TPS % down a bit from the 1.2 and set a minimum RPM PE enable.

I'd appreciate any quick glances you guys could provide, I just want to know if I am headed in the right direction. Let me know if I can provide any more info. Many thanks!!

Just to add...I'm just tuning for fuel economy for the moment, gas prices in Florida aren't doing well for my wallet and I'm throwing 93 octane in it which honestly probably isn't worth it at the moment. I know these engines can get AT LEAST 15mpg even with a cam.

[blindsquirrel]

Any idea why you have a P2127: Accelerator Pedal Position (APP) Sensor 2 Circuit Low Voltage?

Thing really just needs to be tuned properly, I think. Trims are all over the place but averaging +20%. Sure you don't have any intake plumbing issues that would allow false/unmetered air to bypass the MAF? No open-element breathers or catch cans? No goofy PCV routing?

If you want to work on the spark timing you'll need to add the channel for cylinder airmass, as that's needed to find a particular spot in the timing table.

[fls350z]

Thanks for the response, the P2127 code is just the gas pedal sometimes not "turning on" or working at startup, just have to cycle the key and it's fine. The position sensor is probably going bad but it isn't a major concern at the moment...I hope.

I'll attach a photo. The line to the intake comes from the crankcase on the passenger side head, that's it. As far as I know everything else is plugged off fine but I'll double check.

[BigTuner]

I took a look and didn't see anything obvious with the tune, you're going to need a wideband though to see what is really going on. Your long term fuel trims show that you are actually very lean on your MAF calibration, but it seems to have been able to bring it back to stoich so I don't know why your fuel consumption is bad, O2 sensors look to be doing their job correctly. You need a wideband to tune your MAF though, I would be worried that you are lean at WOT. For most of your log you were running at stoich so fuel consumption should be normal, only thing I can think of is a large exhaust leak ahead of the O2 sensors, so it thinks you are lean and is adding too much fuel.

[Shnraines]

Is it flex fuel and needs alcohol content meter reset? Will make a stock engine run so rich it fouls plugs and won't cold start.

[fls350z]

I took a look and didn't see anything obvious with the tune, you're going to need a wideband though to see what is really going on. Your long term fuel trims show that you are actually very lean on your MAF calibration, but it seems to have been able to bring it back to stoich so I don't know why your fuel consumption is bad, O2 sensors look to be doing their job correctly. You need a wideband to tune your MAF though, I would be worried that you are lean at WOT. For most of your log you were running at stoich so fuel consumption should be normal, only thing I can think of is a large exhaust leak ahead of the O2 sensors, so it thinks you are lean and is adding too much fuel.

Right now I'm hunting down a leak potentially in the crankcase ventilation hose. I squeeze it off, O2s drop. I release it, O2s spike. I'm going to look really carefully at my cold-air intake setup, lots of rubber that I'm not gonna pour my faith into. Wouldn't be all that surprised if I had an exhaust leak too.

Is it flex fuel and needs alcohol content meter reset? Will make a stock engine run so rich it fouls plugs and won't cold start.

Nah, it's regular 93 octane gasoline. I appreciate the reply and information though.

[Shnraines]

I meant the operating system of your ecm

[blindsquirrel]

Is there a old-style real rattle-valve PCV valve, or the dumb stock LS type fixed orifice valve?

The stock fixed orifice PCV flows too much air, and blocking the fresh air hose simply reduces idle airflow - you can watch the throttle blade (edit) OPEN, and (usually, depends) spark timing rise as you pinch off the hose. Idle speed won't change as the TB/spark compensate to maintain target idle speed.

What you describe is a symptom of the shitty stock PCV system, not an indication of a real leak. Well, it is a leak, but it's air bypassing the throttle from the stupid fixed orifice PCV. As long as the fresh air source is somewhere after the MAF, it's not unmetered air and not screwing up idle/low speed trims.

[fls350z]

I meant the operating system of your ecm

Oh, nah I don't think so but how can I check?

Is there a old-style real rattle-valve PCV valve, or the dumb stock LS type fixed orifice valve?

The stock fixed orifice PCV flows too much air, and blocking the fresh air hose simply reduces idle airflow - you can watch the throttle blade (edit) OPEN, and (usually, depends) spark timing rise as you pinch off the hose. Idle speed won't change as the TB/spark compensate to maintain target idle speed.

What you describe is a symptom of the shitty stock PCV system, not an indication of a real leak. Well, it is a leak, but it's air bypassing the throttle from the stupid fixed orifice PCV. As long as the fresh air source is somewhere after the MAF, it's not unmetered air and not screwing up idle/low speed trims.

Oh. It's fixed orifice, the little L-shaped thing on the passenger side valve cover. Does it pull air or push it from inside the crankcase? I think I get what you're saying, but I'll double check for a leak there and in the cold-air-intake setup anyway. I have the small vacuum line under the throttle body plugged off, I have the rear vacuum on the intake going into my stock 350z brake booster...but that's working fine so I cant imagine that would be leaking unmetered air. Am I missing any other potential vacuum spots on the stock LS3?

[fls350z]

Also, thank you guys for the wisdom, I sincerely do appreciate it. I am looking into a wideband setup because I'm gonna want to pursue tuning this car more seriously. Any recommendations on a sensor and a gauge? I'd like an AFR one on the pillar...cause cool gauge.

[BigTuner]

AEM 30-0334 is easiest to set up on HpTuners

[blindsquirrel]

There are two connections for the PCV - fresh air, which is the hose from r/h valve cover over to the air intake tube in your pic, and dirty air, which is the vacuum hose that connects to either the l/h valve cover or valley plate. The orifice is in the dirty air side, has full manifold vacuum applied at all times. The other side is just to let fresh air in so the crankcase isn't pulled down into vacuum.

[fls350z]

AEM 30-0334 is easiest to set up on HpTuners

Picked one up, should arrive Monday. I'm really curios to see what AFR this thing is running. It smells stupid rich.

There are two connections for the PCV - fresh air, which is the hose from r/h valve cover over to the air intake tube in your pic, and dirty air, which is the vacuum hose that connects to either the l/h valve cover or valley plate. The orifice is in the dirty air side, has full manifold vacuum applied at all times. The other side is just to let fresh air in so the crankcase isn't pulled down into vacuum.

Gotcha. I'm good to leave the l/h side capped off right? Thanks for the insight.

[blindsquirrel]

Well... depends. I can see your fresh air side in the picture. Describe the vacuum side of the PCV - where's the vacuum source? Does it connect to the valley plate? Where is the PCV valve?

[fls350z]

Vacuum is capped off. Valve covers are very similar to this. https://granatellimotorsports.com/images/F198645618.jpg

[blindsquirrel]

So no PCV, then. Your 'fresh air' hose is just a variation on the old road draft tube. Not good for keeping the crankcase and oil clean, it needs the 'positive' part of Positive Crankcase Ventilation, which is a vacuum source keeping a steady flow to draw off blowby and fuel vapors.

[blindsquirrel]

About your original question...

Are you verifying mileage by gallons you actually put in the tank and distance traveled, or only relying on the cluster's calculated numbers?

[fls350z]

So no PCV, then. Your 'fresh air' hose is just a variation on the old road draft tube. Not good for keeping the crankcase and oil clean, it needs the 'positive' part of Positive Crankcase Ventilation, which is a vacuum source keeping a steady flow to draw off blowby and fuel vapors.

I'd like to eventually install PCV system with a catch can.

About your original question...

Are you verifying mileage by gallons you actually put in the tank and distance traveled, or only relying on the cluster's calculated numbers?

Cluster values were confirmed.

[fls350z]

Okay guys so the wideband sensor should get here Monday. I picked up a AEM 30-0334 like BigTuner recommended. Should I pop it in before one of the O2 sensors or in the X chamber (at 9 or 3 o'clock obviously)? And after installation, what's the first thing I should do in order to progress this troubleshooting my 4MPG lol

[ehall8702]

Yep we see that alot on stick engines, for one reason or a other the alcohol content gets too high and it gets real rich. Think accepted content is less than 7* ? Can't remember been a while since I've dealt with this issue tho