Hello Folks,

I can not get more than 16MPG, even with lots of highway driving.
65000 miles.
After looking around I think I should get more.

I have done: Spark plugs, o2 sensors before cat, K&N Filter insert, Oil+Filter, Vacuum Lines, spark cables, thermostat. Hub bearings, rear wheel bearings.

No error codes (did read with scanner).
Car seems to be running OK for what it is. It smells like it's running somewhat rich.
Where should I go from here? I have the Jet pro Map programmer. Didn't reprogram anything about timing, fuel etc yet - just transmission shift points (much better driveability by the way).

I know this can have lots of reasons, but I'm kind of stuck. I one thread (https://blazerforum.com/forum/genera...bad-mpg-66569/) somebody was mentioning upgrading the injectors to the "Delphi FJ10565". Are the injectors in this model year bad design? I assume if the injectors would be leaking I should trigger some error codes, because the ECU would try to lean out for proper o2 readings...?

Any input is appreciated.

 

A leaking injector or fuel pressure regulator actually won't throw a code. You need to do a fuel pressure and leakdown test. Hook the gauge up to the schrader valve behind the throttle body. Do the test with the key on and engine off! Your inital number should be between 60 and 65 and not go below 55 for 10 minutes. You can also look down the throttle body with a flashlight. If it looks really clean or shows signs of washing then you either have a leaking fuel pressure regulator or injectors.
The spider the post is reffering to is an updated design. They are better, its an upgrade to the MFI injection system.

 

Thank you for the input.

Did put a fuel pressure gauge on the system. Reads 58-60 initially (new fuel filter), did drop to 46-49 in less than 10 minutes (2 tests total). So it's dropping a bit more than 10 psi in 10 minutes. It's not leaking where I did put the gauge on (did check that).
The ignition was on. Can't see anything washed out in the TB.
With the engine running, pressure drops to about 54.

Is the conclusion that I should get new injectors, especially since it seems to be an updated&improved design anyway. Are there any further information about what the difference in the injectors is and how to change them?

 

Without actually pulling the plenum its hard to say what's leaking.it may just be the fuel pressure reg or it may be an injector. If you are going to have the truck for awhile, I would just do the MFI swap. You may have over oiled the k&n filter. I would take the MAF sensor out and clean it with MAF spray aswell. IIRC, the 2000 had a MAF.

 

I did just order the injectors. Seems to make sense either way! Thank you.

 

That's what I would do as well. If you get the MFI injectors, it will come with a new fuel pressure reg, that's about 50 bucks IIRC.

 

Ok, 16mpg is at the bottom of the average. At least with what i've experianced. Dont just throw money at it if it's running ok. I had a 1996 Jimmy that the highest i ever got was 18 with ALL highway on the way to Florida. 15-16 was average and i'd say i drove 60-75% highway. Higher shift points = more rpm = more gas sucked in. Have a scan tool read out what your fuel trims are doing and what your sensors are reading. Rich? lean? what are o2's doing? Intake air temp? ECT? Did you use ACDelco plugs? The 4.3 is picky about that. No Bosch double platinum 4 tip BS.

 

Didn't put AC delco plugs in. Used Bosch, but not the 4-tip. I have a scan tool, but and see o2 voltages. They go up and down. I don't know if I should see more. The FTRM SFTRM (don't know right now if I spell that right) are always only regulating a very few %. I assume that's OK, isn't it? I did actually set lower shift points, unless it's WOT. I feel that this engine has OK torque and feels not too sparky in higher RMP. So right now I can do 80% throttle and accelerate without getting above 3k rpm. Feels much better and not too weak. Not missing high rpm in daily driving. If I'd pull a trailer, things would for sure be different.

 

Does anybody know a good source for OBD tuning/tinkering.
I have this programmer and all the options are overwhelming. Won't touch engine yet. Just would like to learn something, before I really get to it.
Not only engine, also transmission, TCC, pressure parameters and such things.

 

Well you have proven you have a fuel system leak. It will only get worse, my 99 jimmy I got 19 mpg all highway. I got a blackbear tune and it jumped to almost 22.