• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Opinions needed - Performed Optical Bump

Hey guys I had something rather interesting happen this afternoon and would like an opinion.

so after redoing all the fuel system new LP, new tank sending unit and pickup tube. I’ve been able to run through a couple of tanks now.
Before I did this I was under the impression that I had a 24 gallon tank and the PO had warned me not to drive over 300 miles without filing up or risk running out of fuel! After fixing the fuel gauge and finding that when I had dropped the tank (truck was at 300 miles). Thinking it was damn near empty I still had 1/4 tank of fuel. Doing the math I figured out it was a 34 gallon tank

since then I’ve been about to go past the 300 miles and still have fuel left. So today I was at 321 miles gauge was showing on the E and during my trip home from work the truck started bucking and running like shit! I was doing good to go 40 mph and I made it home. Grabbed a fuel can, had my daughter follow me to the gas station, made it no problem. Fill The tank with 29 gallons. Did my mileage... 11 mpg! I normally get around 13.

so my question is with a 34 gallon tank and at the time this happened pumping 29 gallons to full considered empty where I almost stranded myself or do I have an issue raring it’s head AGAIN! Lol

I’m just curious when you guys run your tanks down to E and fill. 29 gallons is a norm?
 
I’m probably just over thinking it again. Adding the two electric condenser fans for the AC has been working the crap out of the alternator. Plus I just replaced both batteries (old ones died without warning). Loosing 2mpg’s from an alternator that being pushed to its limits with the added load of the fans is just a side effect. Maybe an alternator upgrade would help. Not sure if the larger ones will produce more with less effort or robing engine power.
 
Will L. said:
What changes were made since the mpg was at 13?
I can’t imagine two electric fans being responsible for 2mpg- no way.
Click to expand...
Honestly nothing. I have done some things like the optical bump and tdc relearn that landed at -.44 I think but my mileage stayed. The only things I’ve done recently where I haven’t monitored my mileage for was after I had discovered the air intrusion that led to the LP not working. Fixed that along with cleaning the tank. New pickup with sender and a inline filter before the LP and did away with the sock in the tank. After that was done I drove one tank through before adding the cooling fan and jacking with the AC plus new batteries.

I have noticed that my voltage gauge gets low now at idle with the fans running. Measured with a meter at the batts and it’s at 12.9 or so until throttling up a bit. Telling me the alternator can’t maintain the load.
 
I will run it the rest of the week and top off the tank and see where it’s at. I’m sure part of the loss is with me idling too. I’ve also got a trip to the junkyard planned this Saturday to go find some things for my daughters Jetta so that trip will tell me more on my mileage
 
Depending on the topography of where you're driving, air can get sucked from the tank when at 1/4 left or less. My driveway is somewhat steep, and there have been a few times where I've started the truck to warm it up and five minutes later it runs out of fuel. With only a few gallons left and the tank tilted back, the pickup tube in the middle of the tank may not reach what's left.

Might be far fetched, but with your air intrusion and a clogged tank sock perhaps you were pulling less fuel overall, more or less "running lean" and possibly affecting your fuel mileage. Now that more fuel is flowing and being burned than before your numbers are different
 
If you are feeling more power- a common problem is the disconnect from the wallet to the foot, interrupted by the hypothalamus (happy juice maker in the brain).

You drive enjoying the better drive and don’t realize the old 0-60 time is 3 seconds less, but the engine correction is only responsible for 1/2 that...

When I added my turbo and turbo injectors, and turned up the fuel screw, my mpg went up 2mpg but I didn’t know it for a couple months because I simply drove faster.
 
When the fuel gauge of My truck gets any where near that redish colored area just above the E mark, I am out of fuel.
Sad part is, seems I have never been able to squeeze in more than about 28 or 29 gallons and, it is the 34 gallon tank.
 
Lol I’d have never thought about driving faster enjoying the feel!

lol. After the oil change this past weekend I did attempt to break rubber going around the corner. I actually heard a light chirp!!
 
Get the bugs worked out, then start going for mikeage.
Mine K3500, CC LB, 4L80E and 4:11 gears gets 18 to the gallon on most days, keeping it about 70-72 MPH.
Run it at 80 and it drops to 16 to 17. I never drive it that fast, the wifey, well, thats another frightening story in itself. 😳😵‍💫😹😹😹
 
Good morning guys, after filling up yesterday is hasn't missed a lick! so Ill pass this one off on being out of fuel lol.

@MrMarty51 I need to get with you to see what all you've done to achieve that kind of mileage! my truck is roughly the same as yours except only two wheel drive!

I'm thinking of looking into an alternator upgrade. last I remember messing around with my amp meter I had tested the batt cable going to the fuse / relay box showing it pulling about 40 amps running. but I can't remember if I had the ac running or not. I know my batteries are slowly getting weaker due to the alternator not bringing them back up to full on short trips with the ac on. this may also be contributing to a few hard starts while it "browns out" the PCM durring cranking. still cranks up strong but Ive noticed all the dome lights are dimming out lately. I may throw the charger on this weekend and give the batteries a good top off, then run some tests with my amp clamp on various places seeing whats pulling and pushing what. that might give me an idea if I need an upgrade.
 
I got almost 18.5 on my only "trip" this summer (still mixed driving). A/C on and therefore cooling fan running. K2500 eclb, 4l80e, 4.10
 
I think you'll find some rigs just get better mileage. My 96 I got about 15-16 on a road trip I got as high as 19. My 99 I get about 13-15 on a road trip I got around 17. Usually the high numbers reported are from a road trip or it's one of those exceptional vehicles.
 
Ok, lets say you are pulling 40 amps. And pushing clear up to 15 volts.
Amps X Volts = Watts. So 600 watts.
746 watts = 1 hp. So basically your added electrical load is 0.80 hp. As in 8/10th of 1hp.

A proper working alternator will top out at 14.44 volts. Say its a 200 amp alternator maxed out.
Thats 2888 watts so 3.87 hp. Still not enough to cause 2mpg loss.
 
Will L. said:
Ok, lets say you are pulling 40 amps. And pushing clear up to 15 volts.
Amps X Volts = Watts. So 600 watts.
746 watts = 1 hp. So basically your added electrical load is 0.80 hp. As in 8/10th of 1hp.

A proper working alternator will top out at 14.44 volts. Say its a 200 amp alternator maxed out.
Thats 2888 watts so 3.87 hp. Still not enough to cause 2mpg loss.
Click to expand...
I think it's a combination of my foot and the added load. with possibly my foot using most of the fuel lol

I measured the load on the fans by them selves. startup draws 27 amps and once fully on they are drawing right at 15 amps. at idle my voltage gauge will drop to where it normally is with just the key on. which is what is bothering me on wondering if I need to upgrade the alternator.
 
I probably measure everything out loaded and unloaded tonight. depending on what I see, Ill start a new thread on gathering opinions. this coming weekend's adventure to the junk yard for VW parts will give me a chance to recheck my mileage while being mindful to lighten my foot on the pedal :)
 
Whenever the battery cables begin to get gummed up on My truck, the volt meter will not go all the way over to the 14 volt mark and slightly above. I also notice that the starter cranks just very slightly slower. I pull the cables off the battery and scrub them to shiny clean along with them side terdamal connectors on the battery. It then goes back to what it should be.
One time when I had the starter off, the starter cable terminal was croded over too, made it shiny and clean and treated it with a very slight coat of bulb corrosion inhibitor and I hope it still is okay.
Also, if You are going to uprate the alternator, check with Quadstar Tuning, I think John has a real nice conversion unit.
 
My 2003 Cummins with a MT got 21 MPG until I turned on the AC and then 16 MPG. Rumor is it can take 25 HP for AC and then spinning the power sucking 10,000+ CFM engine fan. I never got much over 14 MPG with any 6.5TD. Plenty of 7 MPG towing with that asthma attack turbo GM used.

The electric fans at times are a "windmilling" restriction to the engine fan. (and 45MPH+ road speed airflow where fans are not needed for AC.) If the engine cooling fan is running more with the electric fans it's possible they being restrictions is why the MPG dropped. You want to see a fuel gauge move fast: just have a fan clutch lock up from a bad bearing on a long trip.

GM only used one pusher fan. What did you use?
 
You must log in or register to reply here.
Back
Top