Bad gas mileage

[Orangeaid]

Got about 164k on the engine just replaced injectors, high pressure lines and add a FASS lift pump. Truck seems to have more power based on seat of the pants testing. Mileage before was about 9 around town, it now dropped even more to about 8. The truck does have a 12' service body on it and weighs in at around 10,000lbs verified by the scale.

Fuel filter is new
Oil and filter is new
Predator 40hp tune only
No black smoke under heavy foot
Not using coolant or have stiff upper rad hose
No fuel in the oil

Could the FPR be causing this, if so then how come no black smoke?

 

[zakkb787]

What year truck? Who’s injectors? Why did you replace them? If you’re talking about a Diablosport Predator tune, I’m sure that’s not helping.

 

[2004LB7]

What year truck? Federal or cali?

Please fill out your signature with vehicle details in question

 

[Orangeaid]

2003 lb7 with cali emissions

S&S SAC00 injectors

Replaced because balance rates were +-4 on 3 of them plus was smelling diesel in the exhaust and white smoke out of tailpipe after idling for 3-5 mins

I understand the tune isn't helping mileage but mileage was just as bad before the tune

 

[zakkb787]

You would do much better getting a tune for those injectors from a reputable EFILive tuner. SAC injectors are much different than standard VCO injectors, and while a factory style tune will work, there is much more to be desired. Also, making sure your intake and y bridge are clean from the EGR on the truck could do some good as well.

 

[Orangeaid]

You would do much better getting a tune for those injectors from a reputable EFILive tuner. SAC injectors are much different than standard VCO injectors, and while a factory style tune will work, there is much more to be desired. Also, making sure your intake and y bridge are clean from the EGR on the truck could do some good as well.

It's a work truck and was just looking for a little bit better tuning than the factory restricted shit, kinda wanted to avoid the $700 for the EFI live. I know it's as good as people say but I'm not drag racing this tank, if it will increase my mpg and help pay for itself, that's what I thought the predator would do, I'll get onboard. Who do u recommend for tuning?

I understand the SAC style injectors are different then the VCO, but I figured 00 SAC injectors have the same flow rate, just different nozzles then the VCO, can you elaborate on the differences so I can be better informed.

I'll do some research on cleaning the EGR and check that next.

Thanks for the help Zak

 

[zakkb787]

There’s a thread on here about SAC injectors that’s a good read. It can give way more info than I ever could

Any of the tuning vendors here can take care of you for EFILive. Single tunes can be had for a LOT less than $700. There’s no substitute for a custom tune tailored to your specific truck and needs. Ever. No question.

If you don’t live in Cali, get rid of the emissions crap. You wouldn’t believe the choking it does to an engine. Sure you may pay a bit for a y bridge kit and up pipe, but lb7s get the best mpg of any of these truck. Even at your weight, I’d imagine it should be a lot better than you’re getting.

 

[TheBac]

Just take the predator off. Its not helping.

You cannot expect a truck that weighs 10K+ to get "good" mileage like a comparable pickup might. You may have another issue going on thats contributing to the problem though.

Have you put a scanner on the truck and read actual/desired fuel pressure to rule out the regulator yet? Usually they start to lope the engine at idle when they are going bad.

 

[zakkb787]

Just take the predator off. Its not helping.

You cannot expect a truck that weighs 10K+ to get "good" mileage like a comparable pickup might. You may have another issue going on thats contributing to the problem though.

Have you put a scanner on the truck and read actual/desired fuel pressure to rule out the regulator yet? Usually they start to lope the engine at idle when they are going bad.

Tom, just to make sure I didn’t spread false info, the truck should still be getting better than. Shouldn’t it?

 

[2004LB7]

Does your truck have a cat installed?

 

[snowman22]

Time to boost leak test the truck and make sure it doesn't have any leaks in the intake. It could be a hole from the power steering line on the hot charge pipe or an EGR not fully seating.

Either way a tune for the SAC injectors is probably best, but stock is better than the predator.

 

[Bdsankey]

You would do much better getting a tune for those injectors from a reputable EFILive tuner. SAC injectors are much different than standard VCO injectors, and while a factory style tune will work, there is much more to be desired. Also, making sure your intake and y bridge are clean from the EGR on the truck could do some good as well.

Time to boost leak test the truck and make sure it doesn't have any leaks in the intake. It could be a hole from the power steering line on the hot charge pipe or an EGR not fully seating.

Either way a tune for the SAC injectors is probably best, but stock is better than the predator.

Do we know if SAC00 actually need a tune tho? I know S&S worked with Bosch and got them CARB certified and claims no tune adjustments are needed to make them run properly. That said, I fully advocate for removing that garbage predator and replacing it with a good efilive tune. I know when my LB7 grosses ~24k I average 10-12mpg pretty consistently with my gooseneck.

 

[Orangeaid]

So predator tune will be removed tomorrow and to answer your questions

Zak- I live in Cali, so emissions crap stays on

TheBac- I understand mileage won't be comparable to a regular pickup, but 8 mpg... if that's the case I'll rip out the duramax and throw in a built 8.1 and save a shit ton on the rebuild and parts in 10 years.Don't have a scanner that will read FPR info, guess that's my next purchase, but no lope at idle, smooth as a silk

2004LB7- yes I have a cat installed

Snowman- I did inspect the hot pipe for holes a couple weeks ago when I did the injectors, will pressure test in the next week when I have time.

Bdsankey- I think you're correct in saying the SAC nozzle doesnt matter when it come to a tune. I spoke with Kennedy diesel today and when I mentioned that to him he straight up said "that doesn't matter"

Thanks again for the help

 

[Orangeaid]

On a side note, is the single efi live tune for $700 Kennedy diesel is asking for worth it or should I be looking somewhere else?

 

[gmac32]

Make sure your maf sensor is reading correctly. It can effect fuel mileage

 

[Bdsankey]

On a side note, is the single efi live tune for $700 Kennedy diesel is asking for worth it or should I be looking somewhere else?

$700 for a single tune is high IMO. Most shops are less than that for a DSP5. The hard part is you’re in Cali and some tuners don’t ship there. Do you have any friends with an autocal or V2 where you could buy a vin license and get tuners from who ever their autocal is linked to?

 

[TheBac]

My apologies, I didnt mean to come off like I did....


You really need to get the truck checked out with a scan tool to make sure all the sensors, like the MAF, MAP and ECT (coolant) are reading correctly. You need to start ruling things out in order to narrow it down.

 

[2004LB7]

So predator tune will be removed tomorrow and to answer your questions

2004LB7- yes I have a cat installed

Reason why I ask is when I had an LB7 my first tune was a diablo predator and my cat got clogged up. The milage dropped big time until I took it off and cleaned it out. I was only getting something like 15 on the highway unloaded and worse in town. Cleaned out all the soot and it went to 16 mpg in town and 20 to 22 on the highway

I then got me a V1 and started my own tuning shortly after

 

[Orangeaid]

Gmac- I cleaned the MAF last week, but fuel gauge is still dropping quick

BDSankey- don't like a lotta people, so no to the friends with Autocal or V2

TheBac- no worries, nothing to apologize for. I understand that I drive a pig of a truck but when guys are towing 12000+ and getting 10 mpg I figured I could get atleast that, esp after dropping 3G on new injectors and installing them correctly. I had to use a 20" pipe wrench with the injector in a vice in order to separate the cup from the injectors, that's how bad the copper washers didn't seal.

On that note, what scan tool do u recommend?

 

[Orangeaid]

Reason why I ask is when I had an LB7 my first tune was a diablo predator and my cat got clogged up. The milage dropped big time until I took it off and cleaned it out. I was only getting something like 15 on the highway unloaded and worse in town. Cleaned out all the soot and it went to 16 mpg in town and 20 to 22 on the highway

I then got me a V1 and started my own tuning shortly after

Mileage has been in the 9's since I bought the truck, it was used by a paving co. before I picked it up, so couldn't get any history on it.

How did you go about cleaning the cat, drench in brake clean?