With the mods in my sig, my mpg's have dropped alot. I used to get avg 16-17mpg and 18-20+ on a trip with 30-40hp injectors and everything stock with the laggy h1c. Now with the vgt, 5x12's, fuel pin turned 90*, and smoke screw backed all the way out Im only getting 13-14mpg.

I hear of people with the full power screw turned and all the other good stuff getting decent mileage. Whats the secret?

 

Are you still having fun with your new found power? The way you drive has lot's to do with it. Your afc being set up will have an effect on MPG's also. Who's injectors are they and what's the spray angle and pop pressure?

 

I agree, driving habits make a difference. I tried driving it like it still was all stock and it did'nt help much, even when the afc banjo bolt broke and I plugged the hole in the head it did'nt do real good. All that did was make it run real clean (i liked that part) and took all the extra power away.

What should I try on the afc to help?

The injectors are from SDX, they're supposed to have correct angle and pop pressure but I dont know the specs.

Also, im getting a bit of haze at idle and lower rpm. Under load I get dark gray smoke. Not really any plain black smoke.

 

Grey smoke is a sign that air is getting into the fuel. Tighten the afc, so the fuel comes in once the turbo is lit. I'd call them and make sure they are set right for a Ic ve engine. What kinda lift pump you running?

 

Ok, I actually called SDX yesterday about the idle haze problem. They said to send them down ther and they'll check them out.

Tightening the AFC could help mpg's? I'll give that a try. Its never been adjusted.

The lift pump is s stock diaphram type. The idle pressure is in the acceptable range and I'v never got it to zero under throttle.

Also, the full power screw is at stock or turned 1/8 turn. Wanted to point that out.

Around 20psi boost max. 7-8psi cruising at 65mph.

 

Any chance he's losing timing advance due to fuel starvation? I realize FP doesn't drop to 0, but you still may not be getting enough into it. That'll make it run less efficiently, and thus use more fuel.

 

Try driving a tank worth like "Grandma used to drive" and see it that helps any. I would bet its how you drive it. Oh, and try to keep the boost numbers down, cuz if you have little to no boost, your using less fuel

 

I'll open the turbo up a bit and drive real easy for a tank.

Yesterday the haze got worse and the gray smoke got worse under throttle. Im going to send in the injectors to get checked.

 

For what its worth, the best I get is between 18 and 19 mpg, mixed city hwy (of which 90 % is hwy). That is driving empty, 60mph with 4.10 gears. Not sure what gearing you have? That is with easy going driving. Same truck as yours although mine is a 5 speed. Unless your driving style has changed, I would say there is an issue. However, my bet is that if you drive it like a grandpa you will see your old MPG numbers come back. Nice that they will check out the injectors though.

 

Your fuel mileage shouldn't change with modifications unless your set up to pump huge amounts of fuel into the cylinders. It takes the same amount of fuel to hold a certain RPM regardless of the set up unless that setup is overfueling due to being inefficient at certain RPMs. Fuel pin stuck down or injector problem.

 

Im going to get the injectors tested asap, the haze at warm idle and at lower rpm is surely robbing some fuel. I'll report back with my results.

Post up any more ideas ya'll have.

 

How do we tighten the AFC, and where is the AFC? I looked in the sticky but didn't really see anything

 

Mines 3.54, getrag 5spd. My daily drive to work is about 3miles dirt road(at 20mph), 2.5miles highway (60 mph), and about 1.5miles city(30mph). I used to get 16+ mpg avg with on this daily trip driving fairly easy. I'll try a tank driving real easy before I send the injectors off. Then I'll try it with the stock injectors.
Yea sdx seems to have really good service, they said just send the injectors in and they'll check them out.

 

The AFC is on top of the injection pump, it has the little banjo line that goes from between it and the head and has a torx screw in the center thats usually covered with a cap if it has'nt been messed with. Im prety sure it would be to turn the "starwheel" upwards to tighten it. Look up "star wheel adjustment".

 

Well the AFC being tight will help the fuel at low boost numbers as a result you will see better fuel economy, it won't just give you better fuel mileage but by cause and effect it will help from dumping fuel in to early.

You are saying that a set of 5x12's will not draw the factory lift pump to nothing? There is no way I can see that being correct. Unless you got the most Aad Bss factory lift pump ever produced.

Your have a VGT turbo on your truck...How are you moving the exhaust housing? At what rpm does it light, and while "normal" driving what is the boost it's putting out?