7-9 MPG? (Dash display.) Really?

I remember, 11 used to seem bad. So what has changed? Or is it just me.

2008 4.6
TVS 1900 12-13 psi
Colder plugs
https://www.levittownfordparts.com/sku/m-12405-3v12mm.html
127300 cams
LT headers
Off road H


I'm going to post some logs to this thread, I would like to ask Lito about it as he's a pretty good trouble shooter, but not for free, so I'll do that in a minute.

Did an IR reading on all of the header tubes, really tough with the LT's but they are all in the 500+F range which means there's fire in all 8. I'm going to replace the plugs - so when the new ones get here I can take a look at the old ones. They're many years, but not too many miles, old.

Also going to grab a smoke machine in the near future to look for vacuum leaks. Car sure doesn't run like it has a leak, but the STFT's are often -10% or more, or usually in the negative. Vacuum is say... -15 in hg at idle. I always remember it being more than that. **The purpose of this thread is for someone with cams to chime in and say, "yes, that's out of whack, or no that's in line with what I see."

Also going to think of replacing the O2 sensors. I have one brand new NTK 22060 (Lito recommended,) so just need another. If anyone has good/bad luck with NTK's let me know, AFAIK the car is on the original 91k mile Ford units right now.

The car has a 405 pump (walbro, stock hat,) and a voltage booster. I wonder if that is confusing the computer readout as it pumps more fuel rev - but you'd think that would make it display _better_ mileage.

Last thing, will pull the H off and seal as it's a slip fit to the headers - if air is getting in here and blowing back up to the O2's the computer will be adding a lot of fuel to compensate.

Forget the dash display. I use the aeroforce gauge plugged into the OBD port. It takes a snapshot every 100 msecs...and gives u mileage in real time. The dash display is a rolling long term average. IE: Mileage on the hwy on a long trip is good. Get back into town (with a stop sign / red light every 1-2 blocks) and mileage stays good for the next 3 days...which of course is bs....then goes back to crap on day 4+5..and stays crappy.

I get maybe 12 mpg around town (imperial gallon, not US gallons), and 20-24 mpg on the hwy at 50 mph, in OD, at 1500 rpm.

Plan B.... keep hitting the re-set button often, esp when coasting down hills...and you will be happy.

Plan C..... don't check mileage when stuck at the tail end of the local Tim H drive through. By the time I get to the till, my mileage is like 5 mpg. I'm the poster boy for shit gas mileage here in town..... and you don't wanna know how much Chevron 94 cost per litre these days.

Mash the blower on at full boost, in 2nd gear....and cringe when I look at the real time milage on the OBD....like 2-3 mpg...and FPDC at 80%.

The fuel level sending unit on the Walbro pumps are not always accurate in the S197s.
Note the white arm on the float lever.
Compare that to the black arm on the Motorcraft unit.

I chased an inaccurate fuel gauge for over a year until JeremyH informed me of the difference. I modified my Walbro pump with the Motorcraft unit and it solved my problems.

My mileage is about 11-12 mpg and I run a similar setup. Whipple with 12 psi but a much milder cam. I notice that my commute is a few more miles on the freeway and it does creep up past 13 every once in a while. I reset mine about every 3-4 tanks.

Bought a nice used 14" thinkpad to log after futzing around with my huge heavy alienware for an hour (USB doesn't work right..) did some logging and all actually looks great. I think this car just gets _abysmal_ mileage at idle, so when I'm out actually driving and not in heavy stop and go, I am seeing my usual 11.1 mpg with plenty of WOT blasts. I got up to 19-20 on the freeway for a while. Good enough. I'll still order some plugs but I think the O2's are good based on watching the log, and I'm still going to seal up the H with cement for now. Next year.. rebuilding the whole exhaust with v bands which will probably leak even worse

Changing settings on dash mounted ultra gauge away from STFT's - can't watch them anyway and it just makes me paranoid - I did not infer the same thing from the ultra guage vs these logs.

Re: pump/gauge: I have the 405 in the stock hat w/stock fuel gauge that I modified. It's worked awesome since day 1 - except when I had a stock retaining screw that went through the bottom of the hat turned in juuuuust far enough and it grounded the pump body. Key on = pump on max.

https://drive.google.com/file/d/17LO689mqaziUIkic2mjBC4LJdUTJAgPr/view?usp=sharing

link to the log above if anyone cares to look at it...

You have to reset the mpg function but you also have to let it stabilize. Don't reset it going down hill. It will tell you you're getting 100mpg. I reset mine weekly at least.

BottleRocket said:

You have to reset the mpg function but you also have to let it stabilize. Don't reset it going down hill. It will tell you you're getting 100mpg. I reset mine weekly at least.

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I like resetting it...while going downhill. It's the only way I can get...'good gas mileage'.
I sure as hell don't get 27.4 mpg (US gallon) at 80 mph either.

I felt a dead miss at idle headed out at lunch, nothing says "change your plugs" like that. Revving/running the car hard cleared it. I had the same experience before I tore the engine down last time finding terribly pitted exh. valves. That was after like 80k miles though. Only 15k or so on this valve job.