Fuel Milage getting worse on 350 FE rebuild

[nemesis_pyros]

Hi guys i got a question. Just Rebuilt my 88 fuel injected 350 its all stock save for 30 over pistons and a slightly more torquey RV cam. When I first put it in my fuel milage was OK but now its getting bad infact its worse than before the rebuild and just seems to get worse. The truck is a 88 Jimmy with 31's and 3.08's the rebuilt motor has about 2500 miles on it. Other than that the truck is factory.

Thanks in advance
Nemesis


P.S. I also took off that stupid air pump as we don't have emissions regulations in Manitoba.

 

[txfiremank5]

When was the last time you changed the O2 sensors? When my o2 went bad, my gas milaege dropped noticably.

 

[big83chevy4x4]

welcome to CK5

did you get a programbed chip for the computer? im not sure of the exact specs the stock computer can handle but i dont think its not much more than stock. that might be your problem /forums/images/graemlins/dunno.gif

 

[SUBFAN]

How much worse?

Many things can be possible. Is the motor still running strong and sounding good? Are you mashing the gas enjoying the new power? Are the tires aired up? /forums/images/graemlins/dunno.gif /forums/images/graemlins/dunno.gif

A fresh oil change can give you a 1 mpg boost....

 

[nemesis_pyros]

Re: Fuel Milage getting worse on 350 FI rebuild

I'm using the fatory Computer cause nothing in the motor is far from stock. only the .030 over pistons and the "RV like cam". The oil was changed only a few hundred miles ago, the tires have 42 psi in them. I genrally drive like a grandma and 60% highway driving.
Haven't touched the O2 sensor how much do they go for? That might be the place to start is there a way to test them?

Nemesis

 

[big83chevy4x4]

Re: Fuel Milage getting worse on 350 FI rebuild

if you havn't touched the 02 sensor, then thats probably your problem.
they shouldn't be more than $25

edit: not sure if there is a way to test them or not /forums/images/graemlins/thinking.gif

 

[SUBFAN]

Re: Fuel Milage getting worse on 350 FI rebuild

I haven't priced an o2 sensor lately, but some people change them every 60,000 miles or so.

Do a basic going over. No codes in the computer? Is the spray pattern good? All vaccuum lines hooked up? If all the basic stuff looks good, then look into a new o2 sensor or a plugged CAT.

 

[MudFrog]

Re: Fuel Milage getting worse on 350 FI rebuild

Here is the exact O2 sensor you need, it's the same most of us need. O2 Sensor

 

[K5 NUTT]

Just did the same thing except i used 40 over jugs...disconnect the timing wire...give her about 8 degree's andvance...plug it back in then go get all over her and see if she pings...if so repeat the process until you lose the ping...mine seems to rather enjoy 4 degree's.....first trip out was to moab....100 miles...used over a half a tank to do it...recently i did 236 miles on a half tank after the timing adavance...

Do not overlook the importance of the O2 sensor though...

DW

 

[SF87K5]

WOW I only get 268 miles per tank and i am at stock timing. /forums/images/graemlins/thinking.gif I have mine .030 and a mild cam also,(computer freindly) I might have to look into the timing also for mine. I need to fix my exhaust manifold gaskets first. Mine sprung a leak. /forums/images/graemlins/histerical.gif