Now I didn't expect my fuel economy to improve after the turbo, however, I did not expect my cruising fuel economy to get any worse. Before the turbo I would get 19-20mpg on the highway at 65-70mph, now I'm getting 12-13mpg. I can't think of why this is happening.

The narrowband O2's are showing that it's running at stoich because they are switching just fine. The wideband is showing around 14.4 AFR but it could be a bit off. Before the turbo I was averaging about 39 g/s airflow on the highway, now its about 44 g/s. So a little more airflow, but not enough to cause the decrease in fuel economy I'm seeing, IMO.

So if it's not running rich, and the airflow isn't that much higher, then I am stumped as to why the cruise fuel economy took a huge hit. I'm thinking it's probably something in the tune (still working on it with my tuner), but it just doesn't make sense

 

Any exhaust leaks?

 

There are MANY exhaust leaks actually, but they are all after the downpipe. It was hastily clamped together to get it driving, going to weld most of it up soon. It's a Diamond Eye 4" diesel system.

I did not feel any leaks in the hot pipes. Are you thinking an exhaust leak in before the NBO2's would be letting in air causing it to think it's lean?

 

If there is a problem with the nb02s I would guess that the wideband would show it. You could use the wideband/narrow bands to test against each other. Do you have an extremely cold plug or some lazy timing? Is dfco enabled? A few small things could add up also.

 

Plugs are TR6 gapped at 0.028. Cruise timing is in the high 20's. I've increased it up to ~40 in the past and the improvement in fuel economy was virtually none. DFCO is enabled, but it's not active when cruising obviously. The NBO2's are the same ones as before, albeit the bank 2 sensor is now reading a mixture of bank 1 and 2 (this is how KB sets his kits up), and the bank 1 sensor only reads bank 1.

My O2 switch points are 450mV across the board as recommended on the EFILive forum. Does the 450mV come from the fact that it's halfway between 0 and 900mV? My NBO2's rarely get up to 900mV, or even past 800mV for that matter. Perhaps I should lower the switch points. Regardless, the switchpoints are the same as they were before the turbo.

Basically other than the injector data for the larger (83# @4bar) injectors, not much in the tune has changed in the cruise area.

 

You absolutely have me stumped. Going from 39g/s to 44g/s is is only around a 12% change in airflow. To maintain stoich, you shouldn't have lost near that much. If cruise timing has stayed the same then that shouldn't matter much. I have changed o2 switch points before with little difference. Have you checked to see what your power enrichment delays are? Maybe you are tripping into pe while cruising.

 

Have you tried to dial in the VE table in speed density then go back and calibrate the MAF?

 

If I was getting into PE while cruising then my wideband and NBO2's would show rich correct? It's cruising at stoich 100% of the time.

Its not running rich, and airflow only went up a small amount (not sure why), yet fuel economy went WAY down. Makes no sense!

Perhaps the issue is what Atomic might have been alluding to. If there is an exhaust leak that is letting in fresh air before the NBO2's, it would make the NBO2's show lean, so it will add more fuel to try to get back to stoich.

If I calculate my AFR (airflow/fuel flow) it is much lower than stoich, around 10. Before the turbo it was about 13-14.

 

No adjusting of the tune has been done yet, I'm still running on the base tune my tuner sent me. Hopefully he will get back to me with a new tune soon

But even if the VE and/or MAF is out, and it's still running at stoich with a marginal increase in airflow, the MPG should only be marginally less at the same speed, correct?

EDIT: This is a 1 bar MAF tune with a stock OS, so it should still be using the MAF sensor.

 

I'd be curious to see what your issue is.

I just switched to 114 lb/hr injectors and walbro 450 pump and my efi live pid was showing 8 mpg highway, no shitting you. With 44 lb Delphis and stock pump I was getting 12. AFRs are essentially unchanged and I run open loop.