Fixed Issues... Worse Mpg?

[sen2two]

I had crappie old plugs. Leaks from the head gasket on up. Stock heads and everything else really. Ran OK at best and would stall if I braked to hard. I would always have to tap the throttle after start up or it would stall.

I put a set of fresh gt40p heads with all the goodies, arp studs, all new gaskets, plugs, and a Systemax 2 with Holley 75mm TB. I cleaned an INSANE amount of carbon off the pistons. I mean, over an 1/8 inch thick covering the entire piston in 3 of the 8. The rest weren't this is bad, but were still bad.

I went from 21 down to 17 mpg. WTF...!?

The car now idles better, no stalling issues, and even the engine temp is steady instead of fluctuating like it use to. All in all, it's vastly improved after the work was done. But why would I lose 4mpg? I would think it would have gotten better.

Any ideas?

 

[A5literMan]

Any codes? Any other symptoms? Have you kept your foot out of it? Did you change timing or fuel pressure settings? How about maf or injecters-still the same? Any more idle time than before i.e. Warming car up before leaving etc? Did you unplug the battery for a ecu reset?

 

[sen2two]

Driving the exact same route/time, and I drive very consistent. Timing is still the same and fuel pressure is still at the stock setting. Stock injectors and MAF still as well. No codes or other new problems. I have not disconnected the battery since the work was complete. But it was disconnected the entire time I did the work for 2 days.

 

[General karthief]

I'd be happy with 17 mpg, I tried a couple things including lighter shoes even no shoes, also can't keep tires on the rear. What gives?
Sorry could't resist, I'm just a boob.
BTW is that city driving or highway?
Bout how many miles one way trip?

 

[sen2two]

About 70% highway. Work ride is 17.5 miles each way which is the majority of the miles.

The number isn't the issue. The issue is that losing 4 mpg would normally mean a problem. Especially when things have been fixed. I track my milage constantly because it's an early indicator of an issue.

 

[Mustang5L5]

Are you just enjoying driving it more?

 

[General karthief]

Plenty of time on that run for warm up, I would think even at 65 or 70 mph it would get that 19 figure, or even 20.
Stick or auto? Stock rear gear?
Regardless, somethings changed
Recheck timing, run codes again.
Oh, check to see if you got a prius stuck under it somewhere
Maybe jimmy hoffa hiding in the trunk, he's a pretty hefty guy, well maybe not by now.

 

[Noobz347]

I put a set of fresh gt40p heads with all the goodies, arp studs, all new gaskets, plugs, and a Systemax 2 with Holley 75mm TB. I cleaned an INSANE amount of carbon off the pistons. I mean, over an 1/8 inch thick covering the entire piston in 3 of the 8. The rest weren't this is bad, but were still bad.

I went from 21 down to 17 mpg. WTF...!?

You're flowing more air, making more power, and likely leaning on the fuel peddle a bit more re-convincing yourself that it's in fact, pulling harder than it used to.

Welcome to the sickness my friend. You'll be spending money soon that will bring that number closer to 10 in the city.

 

[sen2two]

Well... it would make sense that I would be pushing it more. But I know for a fact I have not.

I have put 4 tanks of gas through it since I did the head swap. I made sure to drive it exactly as I always did. Same exact route, MPH at cruise, and take off from red lights as usual. I knew the 1st tank would be lower as the ECU was rest with the battery being disconnected for 2 days. But I got 17 mpg for all 4 tanks. And a consistent 21-21.5 mpg for a year strait. I drive very consistent.

I'll pull the plugs this weekend and see if they tell me a story. I also have a dual innovate wideband ready to go in. This could also help as I'm sure my old 02 sensors could use to be replaced.

 

[Noobz347]

I also have a dual innovate wideband ready to go in.

This will tell you everything you need to know.

 

[General karthief]

Its the winter blend gas
It's a conspiracy

 

[Noobz347]

Was a leak-down test ever performed on the bottom end since the removal of of the Exxon ring-seal?

 

[TOOLOW91]

I have to say it should be getting more. My car with the blower avg almost 18mpg back and fourth to Nicks which is 80 mi each way. And that was with some nasty pulls from 45-120 a few times. My cam is almost 250 deg of duration on the exh side and .600 lift so it isnt the most friendly thing economy wise...

 

[Mustang5L5]

I've never done a MPG calculation with my car. All I know is, I drove it ~35 miles this summer, and that used up 1/2 tank of gas

 

[90sickfox]

If your o2 sensors are old they could be reading a false lean condition..... causing the car to dump more fuel. With explorer heads I would think the mileage would go up. Those heads are more efficient than the e7 heads. You've got to figure that you're moving more air with TB, intake, and heads. More air = more fuel.

 

[Adieu]

I'm just a boob.

@Noobz347 CT?

 

[General karthief]

@Noobz347 CT?

Maybe I should have said I'm like an old boob, I just hang around be'n totally useless

 

[Mstng93SSP]

No boobs are useless.........

 

[General karthief]

No boobs are useless.........

Is that no, boobs are useless or that every boob has a use, wait, maybe I'm a useless boob, or I don't have any there for I'm useless.
Doesn't matter cause I'm confused, boobs or not.

 

[General karthief]

All this poor guy wants is better gas mileage and I derail it.
I would be glad with 17 mpg, maybe the car was running lean before the tuneup and now it's back in sync.