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What happened to my fuel economy???

R

Rodd

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Antelope, CA
After getting 14-15 mpg's around town after fuel injector swap and new fuel sending unit, I am now down to 9 mpg's. Truck runs fine. The only reason that I know I am down to 9 mpg's is since my fuel guage isn't working right I am calculating how many miles till empty and my wife has run out of fuel 2 times now. The only things that I have done in the past month was add a heath turbo master and I put my air filter box back in and added a new fram filter. The previous filter was a k&N that I was running w/out the air box. I put in the frame because the 3 bolts that were holding the air box on had put 3 holes in the k&N. I think the issue is lack of air. The reason I took the air box off was that I noticed in the middle of summer last year the intake air temp was the same w/ or w/out the box. What do you guy's think?
 
where'd you get the injectors from? age of fuel filter? lift pump running properly? i know my mileage dropped to 13 with new injectors at first. then i remembered i didn't change my fuel filter in a long while. my truck still got 19.5 mpg on the highway crossing CT after the new injectors(still old fuel filter tho). i swapped out the fuel filter(old one was nasty too) and i'm waiting for my next fillup to check my mileage.
 
Did you have the injectors tested before installing them?

What kind of boost pressure are you running?
Higher boost = Lower MPG

Or you could
Fill it - Take the filter off :yikes: - Go like 25 miles and see how much fuel it needs to be full again. That would confirm or shoot down the lack of air theory.

BTW: Personally - I'd run without an air filter only when its raining, when there isn't so much dust in the air. Also, I suggest *like 25 miles* because you shouldn't run it without the air filter for very long at any time, just enough to do the experiment.
At least you'll have an idea if it's the filter that's killing your mileage.
 
iamdave0887 said:
where'd you get the injectors from? age of fuel filter? lift pump running properly? i know my mileage dropped to 13 with new injectors at first. then i remembered i didn't change my fuel filter in a long while. my truck still got 19.5 mpg on the highway crossing CT after the new injectors(still old fuel filter tho). i swapped out the fuel filter(old one was nasty too) and i'm waiting for my next fillup to check my mileage.
Click to expand...

The injectors are rebuilts by Mike, aka diesel pro. No leaks yet. New fuel filter and LP.
 
RadioMan said:
Did you have the injectors tested before installing them?

What kind of boost pressure are you running?
Higher boost = Lower MPG

Or you could
Fill it - Take the filter off :yikes: - Go like 25 miles and see how much fuel it needs to be full again. That would confirm or shoot down the lack of air theory.

BTW: Personally - I'd run without an air filter only when its raining, when there isn't so much dust in the air. Also, I suggest *like 25 miles* because you shouldn't run it without the air filter for very long at any time, just enough to do the experiment.
At least you'll have an idea if it's the filter that's killing your mileage.
Click to expand...

boost = 9 psi wot - it wouldn't matter any way if it were 15 psi since my wife drives like a grandma. She better not be cheating on me at the tracks :D

I still have my old k&n. I should just put it back on and see how she does on a tank.
 
When you do 2 things at once hard to say what the bad actor was/is here you have injectors and the TM, seeing if TM is culprit is easy. I've been to Mike's shop they do good work there so I doubt the injectors are playing up on you, you could call them and see if they have any suggestions, as for air filter just get a OEM paper filter for test, that will flow plenty and you will have protection, underhood temp even with no lid on air box will be okay for a while, minimal mpg loss for elevated underhood temp. Check rubber return jumper lines, those are hard to see leaks that do impact mpg as well.

A TM can cause lowered mpg if run down too far, it holds the wg closed adding back pressure and lowered mpg at higher boost levels, your noticed mpg loss was after the TM install if I'm reading corrrectly, what spring length do you have set for your TM, if more than instructions recommend you will get more boost but less mpg, nature of the beast with the GM-8 turbo, which is why GM has the vac control WG system for better mpg, which sux on power building but improves mpg.

Your trade off for making power is keeping wg closed longer which will impact mpg, how much loss; is right foot and how much wg closure dependent. So try backing off the spring for lower peak boost better mpg,

or you can find a turbo better matched flow but the trade there is reduced spool up performance (A-team or other hi flow turbo) but better mpg/power at working load than GM-8 offers.
 
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Turbine Doc said:
When you do 2 things at once hard to say what the bad actor was/is here you have injectors and the TM, seeing if TM is culprit is easy. I've been to Mike's shop they do good work there so I doubt the injectors are playing up on you, you could call them and see if they have any suggestions, as for air filter just get a OEM paper filter for test, that will flow plenty and you will have protection, underhood temp even with no lid on air box will be okay for a while, minimal mpg loss for elevated underhood temp. Check rubber return jumper lines, those are hard to see leaks that do impact mpg as well.

A TM can cause lowered mpg if run down too far, it holds the wg closed adding back pressure and lowered mpg at higher boost levels, your noticed mpg loss was after the TM install if I'm reading corrrectly, what spring length do you have set for your TM, if more than instructions recommend you will get more boost but less mpg, nature of the beast with the GM-8 turbo, which is why GM has the vac control WG system for better mpg, which sux on power building but improves mpg.

Your trade off for making power is keeping wg closed longer which will impact mpg, how much loss; is right foot and how much wg closure dependent. So try backing off the spring for lower peak boost better mpg,

or you can find a turbo better matched flow but the trade there is reduced spool up performance (A-team or other hi flow turbo) but better mpg/power at working load than GM-8 offers.
Click to expand...


I've got the tm set at 2" per the instructions (possibly 1/16 to 1/8 either way). My wife drives like a grandma and she drives it most so I don't think her driving is doing it but if there is a little extra power maybe she is using it.

So you don't think the k&N would make that big of a diff? Could be the tm causing a 2-3 mpg difference as well as the filter. I will decrease the TM and see what it does then deal w/ the air filter.
 
I ran the K&N on mine when I got the Banks stinger kit I had before going to Heath exh system, switched to Amsoil foam after a study on Page said it was better, being foam it started falling apart with age, I probably could had I been thinking gotten a warranty replacement, ran a OEM filter, now am back with a Amsoil Donelson, mpg I don't think any difference between them. But now I do recall with the K/N if I jumped really hard on the APP I would trip the dirty filter monitor on K&N as turbo spooled up, so possibly there is slight flow restriction with K/N, get a paper filter and see if it changes anything.


Heath folks say TM should not impact mpg, at their setting, so you might want to call them, I do know my mpg is up when going from a TM GM-8 (fully hogged down TM) to A-team turbo with no waste gate, my 2wd Burb with 3:42 is 20+ depending how I drive with a TM at "base setting" I have no gauges on Burb yet so I have no idea on boost/EGT levels.


I emailed Mike to join discussion, he's not at this site yet maybe this will get him to make the trip to this site, maybe one of you guys can PM him at old site and let him know about the discussion we are having.

Any tire change when this happened maybe odometer is off and you are going further than you know
 
No tire change. I ran a month on the new injectors before adding the tm and fram air filter w/ stock air box. Prior it was wastegate solinoid and the k&n w/out the air box. Maybe I ought to put the k&n back on w/ out the air box and see what happens??? If economy increases then I know where the problem is.
 
I think I found my fuel economy problem. Tonight I went to fuel up and I thought I would top it off and the guy behind me noticed fuel leaking all over the place. I took a look under the burb and diesel was coming from the tank area. I am assuming the top of it. I know it put the fsu in right and secured the ring properly over the o ring when I did it in July. This last tank I got 8.7 mpgs. I know this because I ran out of gas again. The prev tank was 10 mpg's so I just used that to calulate my mileage. I was on my way to fuel up when I ran out. I am also thinking that my fsu isn't long enough. When I fueled up today I put in 21 gal and then drove 150 miles. I then went to top it off and it only took 15 gal. My tank is 43 gal and that is only 7 gal in 150 miles. That equates to 21 mpg. Give me your thoughts before I drop the tank this weekend.

Thanks!
 
Seems to me that the next step is to drop the tank and figure out where it's leaking from.

The most likely culprit, if you replaced the FSU, is the rubber gasket that goes between the FSU and the fuel tank. I had a Burb come into my shop back in June, where a guy was up in Idaho and his FSU failed. He took it to another shop up there, they replaced the FSU and said they put a new gasket on it.

He brought it home and noticed it leaking all over the place. Brought it into my shop, I dropped the fuel tank and sure enough, that's where the leak was. I looked at the gasket and it was all chewed up, like it was re-used. Anyways, I put a new gasket on it and it was dry as can be afterwards.
 
jbsaxman said:
Seems to me that the next step is to drop the tank and figure out where it's leaking from.

The most likely culprit, if you replaced the FSU, is the rubber gasket that goes between the FSU and the fuel tank. I had a Burb come into my shop back in June, where a guy was up in Idaho and his FSU failed. He took it to another shop up there, they replaced the FSU and said they put a new gasket on it.

He brought it home and noticed it leaking all over the place. Brought it into my shop, I dropped the fuel tank and sure enough, that's where the leak was. I looked at the gasket and it was all chewed up, like it was re-used. Anyways, I put a new gasket on it and it was dry as can be afterwards.
Click to expand...


What type of gasket is it? All that came w/ the new fsu was an o-ring.
 
I'd suspect the return line fitting, top of tank seal IMO would not leak much as that would be sloshed fuel as opposed to pressurized return fuel, if you will put +12v to your lift pump test/prime lead (red wire black connector hanging out alone in the harness just below the master cyl) lift pump will constant run and pump your fuel out the filter mgr drain if you open it, since lift is only 28gph it will be slow, so siphon or other pump to get out bulk of your fuel then finish pumping dry with the lift
 
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Tim,

What makes you suspect the return line? What do I look for? There was a lot of fuel puddling. When you talk about the filter mgr drain are you talking about t-valve?
 
I think he means the fuel return line "at the fuel tank".......The filter mgr comment was to point out you should "not" drain the tank via the LP......Only use the LP to drain the little thats left after bulk siphoning with another pump.

Hope this helps....and hope I got it right also.
 
You dropped the tank to put in a new sender and mpg went down, when you get a significant change anytime on your truck always look at last maintenance activity, as stated before that big a loos means you have pressurized fuel loss or leak in the tank, you don't have big puddle on gnd so I suspect your leak isn't occuring unless engine/ip is flowing. yes tee valve that is the filter mgr drain
 
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