Chevy 350 TBI ... shitty fuel mileage

Poohbair · Jan 1, 2015

So I bought this 1995 K1500 4x4 w/ a TBI350 / auto

Has really shitty power, and shitty gas mileage. I put on a lot of miles on the freeway w/ the cruise on 75, and I get 12.

Everything I find from people say these should run 15-17mpg regularly. Not me... 12

Temp gauge runs low.. around 180*, and it takes FOREVER to warm up... changed the thermostat, had a 195* in it, put a new 195* in... no change... still takes forever to warm up and the temp gauge runs 180. With my little thermal temp meter right at the thermostat housing it is ~195* when warm, so maybe the temp gauge is just off.

Either way, why does this thing take forever to warm up, and why such shitty mileage? I am wondering if the clutch fan is stuck in the engaged side? Not sure how to check that??

Somebody told me to bump the timing from the stock 0* up to closer to 5-6* advanced?? Anyone done this?

I just know it should get better than 12... my old 91 3/4 ton w/ a TBI 454 and 4spd used to run 13 on a regular basis.. 12 is pathetic.

t1h5ta3 · Jan 1, 2015

grab the fan, see how much resistance there is turning it by hand, will it free spin?
its not to hard to un bolt the fan and run with out it as a test. its cold enough you dont need it...

aside from that, basics, does it run smooth?
tire pressure? a couple psi low is all it takes...
converter locking up? trans shift good?

JOOP · Jan 1, 2015

Do 60mph and see what you get. When I used to commute I did 70mph and got crappy mileage,. dropped down to 64mph and its 5mpg more.

zukkev · Jan 1, 2015

Does the fan sound like an airplane about to take off? If it does, then it's stuck...Also, does the engine stumble just off idle and rpms fluctuate rapidly? If so, then disconnec the vacuum line going to the EGR and drive it again...If the syptom is gone, then replace the EGR valve and control solenoid...I will not go more than about 2 degrees advanced when setting the timing on a TBI.

skinny_pedal · Jan 2, 2015

zukkev said:
Does the fan sound like an airplane about to take off? If it does, then it's stuck...Also, does the engine stumble just off idle and rpms fluctuate rapidly? If so, then disconnec the vacuum line going to the EGR and drive it again...If the syptom is gone, then replace the EGR valve and control solenoid...I will not go more than about 2 degrees advanced when setting the timing on a TBI.

This^. The egr on these rigs can cause some havoc!

leadfoot067 · Jan 2, 2015

check the cap and rotor...they get crappy on these...cat clogged up?

Poohbair · Jan 2, 2015

... I think the cat is going to accidently fall off...

I will check the fan, cap, rotor, plugs, and egr ... thanks for the suggestions!

junkyard jim · Jan 4, 2015

Last, but not least, run some Amsoil PI (performance Improver) through it. When mine gets sluggish that stuff cleans the injectors nicely!

Poohbair · Jan 4, 2015

picked up front brakes and rotors today, **** for an oil change, fuel filter, stuff to clean the aftermarket air filter, and am hoping to have time to get to doing it sometime this week... ****ing swamped at work.. the joys of being self employed.

Clutch fan seems to be OK from what I can tell by how to test it.

Havent had time to mess with EGR or timing yet.

Poohbair · Jan 7, 2015

.. awesome...

tranny ****ed up today.

Was fine last night at 10pm when I parked it, this morning, no OD and no 1st. 2nd and 3rd work fine.

Ran a bottle of valve body cleaner thru it today, and shift solonoids will be here tomorrow.. great, just what I wanted to do tomorrow afternoon in the wet and cold. I need a garage.

TreeClimber · Jan 7, 2015

Poohbair said:
.. awesome...

tranny ****ed up today.

Was fine last night at 10pm when I parked it, this morning, no OD and no 1st. 2nd and 3rd work fine.

Ran a bottle of valve body cleaner thru it today, and shift solonoids will be here tomorrow.. great, just what I wanted to do tomorrow afternoon in the wet and cold. I need a garage.

A bad transmission can cause poor performance issues..... just sayin.