I've been working some bugs out of the fuel economy end on my 1991 Z71.
I've paid very close attention to transmission shifting on reasonable
acceleration up to highway speeds, and it shifts 1-2-3-4 like it should,
when it feels like it should.
I know these units employ a lockup torque convertor. is there a way to know
when the TC locks up? the tc locking up on the highway helps fuel economy,
right? can I "feel" the tc locking? or is there another way to know?
Also, I've heard good things about full synthetic differential fluid, with
many claiming they get a gain in MPG by changing out both diffs. How much
truth to this? I'm looking for every easy MPG I can get!!!
if it has a tach, you should see RPM drop by 2-300 when it locks
when locked, you should be able to 'crowd' the throttle a bit without the
RPM's increasing, while crowding the throttle, tap the brake with your left
foot, the RPM's should immediately jump up 3-400
no tach, but will be installing one to be sure of this. when does convertor
lockup usually happen? particular speed? only highway speeds? cruising at
a specific "load" on the engine?
the truck shifts cleanly in and out of each gear, and I'm sure I "feel" the
convertor unlocking when accelerating from say 90 to 100 km/h on the
once the tach is in, I'll double check as you say to...thanks for the
depends on speed, load and of course throttle opening
on a 91, 4th and lock-up usually happen so close together that you can't
separate the feel
the throttle-crowding / brake test once it's in 4th at about 60 is the best
G already hit the TC question; I'll tackle the synthetic question.
Switching to synthetics in ALL drive units (engine, tranny, TC, front and
rear diffs) will net you a 5-10% increase in fuel ecomomy. I've seen this
in all of my trucks. But you're still calculating your fuel economy
incorrectly so you won't know the difference anyways.
you're killing me man!! I've got it down pat right now (so poop on you :)
Resetting the odometer /right at/ half a tank will yeild around 150 or so KM
on the nose. Same with 3/4 to half. can't tell full to 3/4 or 1/4 to E
cause the gauge is not calibrated, and won't go right to full, and goes well
I would notice a difference now :)
Your wasting your breath. Some people were not meant to calculate MPG
and you have stubmled across one.
Without some sort of static measurement it is impossible to get
relibable/reproducable MPGs. Unless you either fill the tank/refill
the tank and measure how much gas was put back in divided by total
miles driven OR run her completely dry on level ground, refill a
specific amount of fuel and divide the fuel consumed buy the mileage
driven, its' just not going to work. According to Stugat's method, I
am getting 40+ MPGs on my first 1/10 tank. (300 miles to the F mark,
then 100 to E). Oh yeah, "Poop on you" LMFAO.
I used the second (run dry, fill with 5 Litres, run dry) method on both my
My 2L petrol sedan, (now stolen) got 11.5 litres per 100 Km. my 2.8L TD SUV
gets 11.25 litres per 100Km.
the difference seems to be the SUV in top gear can rumble along at 3200 revs
for 100KmH, but the petrol needs 3600 revs, thats 400 revs more for the same
speed, and diesels are more economical anyway.
3200 RPM cruising on a diesel????? you *sure* about that? if your cruise
RPM's are that high for 60 MPH (100kph) you need some seriously higher
gears. my wife's isuzu turns about 2800 RPM doing 75 and it's got 4.30's in
the axles. my pickup with 3.73's turns about 1800 RPM again at 70 MPH
diesel's are more economical because there is simply more BTU's in a gallon
of diesel than gasoline.
I think mines 5. something (5.37?), that'd mean turning the engine 5 times
for every 1 on the wheels, as opposed to 3.7 turns of the engine for every
one of the wheel on your pickup. not sure exactly what mine is anymore have
to go look again at the notes I made. If I can find them, since it's been a
while since i looked everything up and worked out it's perfomance.
5 gear manual '88 Bighorn
I have a 1993 K1500 w/5.7 liter and I can definitely feel the converter
lock. And, after adding that Flowmaster muffler, I can hear the difference.
It seems like it kicks in after I've reached cruising speed, where I'm not
putting a lot of strain on the engine to get up to speed. I noticed, just
recently, that I can feel it kick in even when I'm not in overdrive. It
will go through the first three gears and then I'll feel that kind of smooth
kick, which drops the RPM's. It seems to lock about 2-3 seconds after
reaching a steady cruising speed.
One thing that I've never been able to find out is what the life expectancy
is on the lock. I had one go out in a previous truck and it gave the
computer a brain-hemmorhage. It kept trying to lock and compensate for the
decreased RPM's (which never decreased since the lock was dead) which made
the engine radically fluctuate RPM's as I was driving. It was embarassing!
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.