Horrible fuel mileage

[ifrythings]

So I finally got my new engine running and in my project truck and the fuel millage makes it undrivable, it's getting around 8 or less mpg and I don't know what's wrong.

Some background info, rebuild 7.3lT with factory turbo with ats hot side housing, 3" dp to 4" back, na pump turned up 2 flats, new standadyne G code injectors, timing is at 8*@2000rpm, electric fuel pump, R&D cam, 460 zf5, 4.10 gears and 33" tires, truck is a 4x4 crewab with a 2.5" leveling kit.

I'm not idling it at all, shifting at or below 2000rpm, not flooring it and not blowing black. I' not sure what to check for besides the obvious leaks or theft of fuel at night. So far I have driven 50km and burnt 1/4 tank

Any help is apprecated. Also I'm comparing this to my old tired 6.9 c6 3.55 regular cab 31" tires 2wd truck that got between 13-16 mpg summer city driving, i understand 4x4 and crewcab should be a bit less but not half the milege!

 

[towcat]

does your exhaust make your eyes water and others complain about your stinky exh?
if so, your pump is about to die. anything less than 10 mpg with your setup is due to a dying pump.

 

[ifrythings]

I know the smell/eye burning your talking about, was about 30 ft away from a powerstroke one time and it was worse than standing if front of a campfire with the smoke going in your eyes.

But no my truck doesn't smell bad or burn your eyes and I haven't been around enough people for them to complain yet, this is the same pump that was on the old 6.9 I'm comparing it too.

Can a worn out pump use a ton of fuel and not produce white or black exhaust? My oil level is not increasing so I know it's not getting fuel into the oil.

Should I turn the pump down and see if it gets better? I don't think it would as everyone says fuel used is by how hard you push down the skinny pedal.

 

[Macrobb]

Does the truck /sound/ advanced or retarded? Mess with the timing. Especially on a worn IP(where the timing curve is all over the map), it'll make a big difference.

 

[sjwelds]

Tank selector switch drawing from the front / returning to the rear / vice versa?

 

[Hydro-idi]

Either way, this sounds like an injection pump problem. Stanadyne injectors are damn good, but pairing an old worn out IP with new sticks will cause problems, including power loss & mpg issues. I would put a new IP on it and play with the timing.
These engines tend to run the best around 7-9 degrees, with 9.5 btdc being my fave. I would go with Russ’s baby moose or one of typ4’s IP’s for your engine.

 

[chris142]

Speedo error? My mpg is lower than others here. But even running 75 mph I got 12.7.

 

[ifrythings]

Does the truck /sound/ advanced or retarded? Mess with the timing. Especially on a worn IP(where the timing curve is all over the map), it'll make a big difference.

I have the timing at 8*btdc @2000, idling has a good clack to it, if I push in the light load advance lever it gets very quiet, as for power it seems to have a ton more then the old 6.9, a test hill I use I can be in 5th at 70km/h and push the throttle down a bit and gain speed, the old 6.9 was down shift and floor it.

Tank selector switch drawing from the front / returning to the rear / vice versa?

The tank selector valve is currently stuck on the rear tank and won't switch over and it's not transferring it to the front tank as that's the first thing I checked for.

Either way, this sounds like an injection pump problem. Stanadyne injectors are damn good, but pairing an old worn out IP with new sticks will cause problems, including power loss & mpg issues. I would put a new IP on it and play with the timing.
These engines tend to run the best around 7-9 degrees, with 9.5 btdc being my fave. I would go with Russ’s baby moose or one of typ4’s IP’s for your engine.

I just find it weird that this ip starts up in one rev hot or cold, seems to have great power to me and doesn't smoke at all besides lugging it which is expected to make black smoke.

I'd just like to completely rule out any other posabilities before spending $1000 bucks on a new ip and having the possibility of horrble milege still.

Speedo error? My mpg is lower than others here. But even running 75 mph I got 12.7.

Speedo is off by about 3-4% which I did composite for (31.7"-32.7" tire difference), I haven' got it up past 90km/h (~50mp/h) as I have a good vibration from either the tires or rear driveshaft that I'm currently diagnosing.

Also the brakes aren't dragging as when I come to a stop in neutral and release the brakes it happily rolls on the smaller incline.

 

[Thewespaul]

Take it for a good drive and get out and immediately feel all the hubs, I’ve had the brakes drag but still roll at a light. Something to consider is a newly rebuilt engine will not make great mileage until it’s done breaking in. @laserjock can attest to this.

Is the clack at idle seem to be a fuel sound or a valvtrain sound?

 

[rhkcommander]

Any fuel leaks will suck that fuel economy down HARD. If you don't see it on the return line kit it could be the tee at the back of the block too.

 

[doofussevilla]

Does the truck /sound/ advanced or retarded? Mess with the timing. Especially on a worn IP(where the timing curve is all over the map), it'll make a big difference.

What's the timing curve suppose to be? I'll time it at all the rpms and map it out and compare to stanadyne's specs. My mileage isn't great, and I do have the eye burning smoke at idle.

 

[ifrythings]

Take it for a good drive and get out and immediately feel all the hubs, I’ve had the brakes drag but still roll at a light. Something to consider is a newly rebuilt engine will not make great mileage until it’s done breaking in. @laserjock can attest to this.

Is the clack at idle seem to be a fuel sound or a valvtrain sound?

Checked the brakes after a good drive and they all feel the same and are fairly cool (I'm running 05+ axles that have huge brakes so they don't warm up very fast)

I was wondering if the break in would be part of this too, I was watching the exhaust this morning after starting it and it's blowing a light haze of blue till it warms up and kicks off high idle and the timing advance, not sure if that's the pump itself or if I have the timing too far advanced even though I set it a 8* when I put the pump on.

I also noticed it does a small puff of black smoke when I shift, maybe I'm shifting at too low of a rpm and lugging it which wouldn't help either.

The clack at idle is fuel as when I push in the light load advance arm on the side of the ip it gets very quiet.

Any fuel leaks will suck that fuel economy down HARD. If you don't see it on the return line kit it could be the tee at the back of the block too.

I had a fuel leak from the fuel filter line that I fixed before putting it on the road and filling up, I don't see any leaks on the ground and nothing on or by any of the injectors, if that line at the back of the engine is leaking bad enough to cause this much fuel loss I should see it on the trans, ground or frame.

 

[ifrythings]

Here's a video of the engine idling, how does it sound to everyone else? I set the timing to 8* when I put the pump on after rebuilding the engine, I haven't checked it since but I can't see it moving at all.

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[frankenwrench]

When I rebuilt my block I got about 9 mpg for the first several tanks. But I'm running the 6.9. Shouldn't be a lot different. Just took a while. Also for first 3 oil changes I'd burn a good bit of oil. Now I loose maybe a quart between changes but that's due to a small leak I overlooked on the pan gasket. Used cork gasket so I goofed there. To me sounds about right till rings wear in with 4.10.