Aftermarket Intake trouble shooting MPG

Matthew Jeschke said:

Ah super cool! I am so annoyed that they come up with all these technological gadgets to boost MPG. When we had it several decades ago with small commuter cars. Additionally, Germans are AWESOME at MPG (they also over engineer other things to insane levels but another topic).

I was FACINATED by the YouTube video "40MPG V8! Lawn Mower Carb..."

I theorize he got more efficiency by shifting peak vacuum to lower RPM than from the carb alone. He made the intake REALLY small. I'd thing that'd dramatically increase piston scavenging and improve fill at lower RPM. He probably completely cut his top end off... but who cares. Lamborghini used to make a variable geometry intake manifold so they could maximize Torque curve. I don't know why manufacturers chose a completely different route over the years. Surprised Koenigsegg hasn't tried something like that yet... I'd thought you could take a cross section of a root style compressor and adjustable geometry by degreeing the compressor one way or the other so you could maximize cylinder scavenging on intake stroke. But maybe I'm just crazy.

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Mid 80's Air management was at best a hotwire sensor for flow. I think the MAP Sensors/computers could not think fast enough or were just bad programming. I really liked the Mitsubishi System used thru 96 or so.
Just for kicks, look up Paul Pantone or GEET.

@exp500 wow that's facinating https://paulpantone.com/

@SnowDrifter I think I found the underlying issue. Still testing to confirm. But times to gas station for filling up and I got 15MPG.

Last weekend I took time to key my written fuel log into the computer. I compared it's dates with my tuning log. Seems I didn't roll back tune versions far enough. I needed to roll back one additional version. That version had turned of LTFT and installed HP Tuners RTOS, speed density only.

I suspect HP Tuners RTOS probably doesn't meter fuel quiet as well as factory. It's a hunch I have as the dumb PCM randomly gets stuck below 14.0:1 AFR. It only comes around if I plug the tuning cable in which is really odd. I asked on their forum but honestly, nobody has a clue there. I've also checked wiring which seems fine. I suspect it's an oddity with their RTOS but need to confirm.

It's looking more and more like turning off LTFT caused my fuel mileage to take a nosedive. I had one rouge tank at 21+mpg in there where I drove something like 100 miles before turning off engine and immedately filling up. I think that mileage was possible because I didn't turn the truck off (and STFT had adjusted correctly). Otherwise, I'm driving 20 or 30 miles typically then turn off and back on again.

Still surprised LTFT could have that large of an impact. Makes me second guess if my VE table is that well tuned but it's pretty darn close, well w/in 5% on open loop, and within 1% to 2% max in closed loop.

Do you work at nasa by chance!?

Eldiablo said:

Do you work at nasa by chance!?

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its a huge compliment sir.

Eldiablo said:

Do you work at nasa by chance!?

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Thanks! I am truly flattered. I just haven't had time to check the posts for a few days. My life is an absolute disaster as of late. I used to work as an engineer. Switched to sales. I use my truck to get my engineering fix lol

Gal darn, my fuel mileage took a dump again. I plugged in my scanner though and realized fuel trims are at 20+%!!!!

I had tuned to well within +/- 5% on open loop. Closed loop got me down to within a percent. Long story short, I think I possibly uncovered a mechanical gremlin.

First I verified IAT is reading correctly.
I swapped back in the aftermarket intake I tuned with no difference.
Tried adjusting VE table (in tune) both up and down. No change.
Forced Evap Purge closed, no change.

It's on start-up, after closed loop engages the trims tighten up. However, it runs like crap until then, is over 18:1 AFR until closed loop turns on.

I suspect fuel pressure and need to go get a pressure gauge (issue could be either fuel filter or pressure regulator ~ replacing either way)
I also need to test for a vacuum leak in the intake system
If no luck, I plan to force over to MAF only and see if maybe it's a bad MAP sensor... currently I'm running MAP only in speed density mode.

Matthew Jeschke said:

Gal darn, my fuel mileage took a dump again. I plugged in my scanner though and realized fuel trims are at 20+%!!!!

I had tuned to well within +/- 5% on open loop. Closed loop got me down to within a percent. Long story short, I think I possibly uncovered a mechanical gremlin.

First I verified IAT is reading correctly.
I swapped back in the aftermarket intake I tuned with no difference.
Tried adjusting VE table (in tune) both up and down. No change.
Forced Evap Purge closed, no change.

It's on start-up, after closed loop engages the trims tighten up. However, it runs like crap until then, is over 18:1 AFR until closed loop turns on.

I suspect fuel pressure and need to go get a pressure gauge (issue could be either fuel filter or pressure regulator ~ replacing either way)
I also need to test for a vacuum leak in the intake system
If no luck, I plan to force over to MAF only and see if maybe it's a bad MAP sensor... currently I'm running MAP only in speed density mode.

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Try revving the engine while monitoring the fuel trims. Try 2k, 3k, and 4k rpm. If they improve with increased RPM, chase vacuum.

If no improvement or even get worse, suspect fuel delivery issues, especially if both banks are identical.

DANG thanks @strutaeng

I'm in process of ordering new parts... Pressure regulator has 270k on it, fuel filter probably around 50k so need replaced regardless but I'm trying to find ways to narrow down my troubleshooting. That's super helpful!

I'm also going to give truck and adult dose of injector cleaner just cause why not.

UPDATE NOTES: LTFT don't taper down as RPM increases... They remain the same around 20% lean. Need to see if banks are identical. Forgot to look at that.

I made note of MAP sensor reading, it's 13.1PSI with ignition off.... However, when I calculate pressure for my altitude I get 10.62 PSI... and weather station reports 14.51 PSI. so the 13.1 PSI is probably close.

This is a fuel problem. Rented a fuel pressure gauge.

Rail pressure is 50 PSI running. Should be 55 to 62 PSI.

Rail doesn't hold pressure. After turning engine off see an immediate ~2 PSI drop and over course of a few minutes it continues to slowly fall.

Fuel pump is new. I don't see gas leaking anywhere. Injectors are used from a L59 / flex fuel... my previous injectors leaked and created really hard starting condition. I don't have the hard start this time so hopefully isn't injectors again.

Can the return off the fuel pressure regulator create a leak back condition? I don't know how that check ball works on the pump.

NOTE: I got a P0300 random misfire code, no surprise it's running WAY lean on start up.

STOCK fuel pressure for a non-Flex pump is 55-62 psi at the rail, Key On, Engine Off (KOEO). It should go down some when the engine is started and the regulator works. Typically running pressure is 45-ish psi. But ultimately dependent on your mods, YMMV.