Fuel Injector swap go bigger or smaller??

[nfsroadsta2786]

I have a stock 2003 Trailblazer LS 4.2L i6

i want to know what the stock fuel injectors run at like the cc or the fuel flow
whatever its calculated at

what i want to do is increase the mpg a bit

also should i go with slightly bigger fuel injectors or smaller??

 

[limequat]

I have a stock 2003 Trailblazer LS 4.2L i6

i want to know what the stock fuel injectors run at like the cc or the fuel flow
whatever its calculated at

what i want to do is increase the mpg a bit

also should i go with slightly bigger fuel injectors or smaller??

Your best bet is to back slowly away from the truck and put the wrenches down.

 

[jimmyjam]

Best mileage mod is put a 4" piece of 2x4 under your gas pedal

Fwiw the stock injectors are around 29#. I think you are very confused as to how efi fuel delivery works

 

[ScarabEpic22]

Best mileage mod is put a 4" piece of 2x4 under your gas pedal

Fwiw the stock injectors are around 29#. I think you are very confused as to how efi fuel delivery works

The only reason to adjust the fuel injector size is if you are making (significantly) more power than the engine does in stock form. I've never seen a reason to go with a smaller injector.

Plus, if you start doing this, you cant simply swap a different size injector in and expect everything to work. Smaller means you'll run lean, bigger means rich. Neither are good for power, longetivity, or MPG. If you want to get technical, you need to retune the PCM for the injectors (which brings in the small pw, offsets, etc. The P10 PCM doesnt handle adjustments to these things very well either...).


If you want better mileage, simply get a PCM tune. Best bet, hands down.

 

[nfsroadsta2786]

Your best bet is to back slowly away from the truck and put the wrenches down.

i am ase certified lol
im just looking for input an what i should do

Best mileage mod is put a 4" piece of 2x4 under your gas pedal

Fwiw the stock injectors are around 29#. I think you are very confused as to how efi fuel delivery works

lol only problem with that is i need to be able to drive

The only reason to adjust the fuel injector size is if you are making (significantly) more power than the engine does in stock form. I've never seen a reason to go with a smaller injector.

Plus, if you start doing this, you cant simply swap a different size injector in and expect everything to work. Smaller means you'll run lean, bigger means rich. Neither are good for power, longetivity, or MPG. If you want to get technical, you need to retune the PCM for the injectors (which brings in the small pw, offsets, etc. The P10 PCM doesnt handle adjustments to these things very well either...).


If you want better mileage, simply get a PCM tune. Best bet, hands down.

i have been thinking about the going with a tune but the down time is whats stopping me
im talking abt getting a pcm tuned from PCM of NC
and as far as swapping the injectors out and getting a tune i know that much same goes with any intake mod or exhaust mod or anything that has to do with the engine for that matter

 

[kawaholic]

As far as tuning goes, pcm of nc has a few different options available which will leave you with no down time. You could go with the "core program" or the "loaner program".

Available Tuning Programs

Core Program

In the core program, we send you a tuned core PCM (and TCM if applicable). We start by using GM software to program your vehicle's VIN & calibration, and then tune that file. Once you receive the core, you may send yours in back for the core refund, or retain both modules. If you choose to send in your stock PCM/TCM for the core refund, it must be postmarked with seven days of receiving the tuned PCM. The core program requires a CASE relearn and security relearn also.

Loaner Program

The loaner program sends you a stock PCM/TCM to borrow so that you can send in yours for programming. When we receive your PCM, we tune it and return it to you, and then you send in the loaner for the core refund. The loaner PCM will need a security relearn, but there are no CASE relearns required. NOTE: Expedited shipping on loaner programs only covers one shipment. To upgrade both shipments to express, please contact us!

HTH, Tom

 

[ScarabEpic22]

i am ase certified lol
im just looking for input an what i should do

i have been thinking about the going with a tune but the down time is whats stopping me
im talking abt getting a pcm tuned from PCM of NC
and as far as swapping the injectors out and getting a tune i know that much same goes with any intake mod or exhaust mod or anything that has to do with the engine for that matter

No...you dont need to swap injectors with just a tune. Ive tuned a bunch of I6s, and if you dont believe me ask PCMofNC because they've tuned hundreds of I6s. NONE need an injector swap until you do more than an intake/exhaust (which if you have an I6 means you're in a select few people).

Do PCMofNC's core program and buy an extra PCM, or do their loaner so you dont have to do the CASE relearn.

 

[jimmyjam]

it sounds like you are talking about injectors like they are carb jets...

 

[chief0299]

i am ase certified lol
im just looking for input an what i should do

What are they teaching at schools now days? It's surprising that someone with an ASE cert doesn't understand that the PCM controls the metering of the fuel. Yes, changing the injectors will result in a richer or leaner condition, but the O2 sensor will see it and the PCM will make adjustments as necessary to maintain the pre-programmed A/F ratio or voltage readings from the O2 sensors.

I'm not personally trying to dig on you, but this is pretty simple stuff that is normally taught early on. Granted, I got my cert in 1998, but it was taught then about how electronic fuel injection systems worked.

 

[limequat]

What are they teaching at schools now days? It's surprising that someone with an ASE cert doesn't understand that the PCM controls the metering of the fuel. Yes, changing the injectors will result in a richer or leaner condition, but the O2 sensor will see it and the PCM will make adjustments as necessary to maintain the pre-programmed A/F ratio or voltage readings from the O2 sensors.

I'm not personally trying to dig on you, but this is pretty simple stuff that is normally taught early on. Granted, I got my cert in 1998, but it was taught then about how electronic fuel injection systems worked.

Yeah, well maybe he's talking about his Trailblazer furnace. Did you ever think about that Mr. Smartypants?

 

[chief0299]

Yeah, well maybe he's talking about his Trailblazer furnace. Did you ever think about that Mr. Smartypants?

lol, I did not.

OP, I apologize if I came across as a jerk.

 

[gmcman]

Only real benefit I can think of is if you are able to find an injector that can spray a finer mist. The injectors are angled and set so they can mist behind the intake valve and not produce droplets along the intake runner. I think the best you can get is have the injectors professionally cleaned and have a flow test where they get all the injectors flowing the same amount.

 

[HARDTRAILZ]

Way to rain on his parade....

 

[strat81]

what i want to do is increase the mpg a bit

Drive slower
Run ~35 psi in your tires if they are rated for such
Remove excess weight (junk in the cargo area, cross bars off the roof rack)
Avoid ethanol blended fuel
Run fresh synthetic fluids in your crankcase, transfer case, differentials, and transmission
Maintain your vehicle
Install 3.42 gears

Don't putz around with larger/smaller injectors as they will have little to no effect on fuel economy in this application.

 

[nfsroadsta2786]

Drive slower
Run ~35 psi in your tires if they are rated for such
Remove excess weight (junk in the cargo area, cross bars off the roof rack)
Avoid ethanol blended fuel
Run fresh synthetic fluids in your crankcase, transfer case, differentials, and transmission
Maintain your vehicle
Install 3.42 gears

Don't putz around with larger/smaller injectors as they will have little to no effect on fuel economy in this application.

i drive slow i don't floor it and i ease into the gas
the only thing thats in my truck is the spare tire as the mount underneath the truck is broken as far as cross bars i took it off a while back i didnt like the way it looked
im already running full synthetic everywhere
i just got a code for the coolant temp
and ima look into the 3.42 gears

 

[strat81]

What are your goals/expectations with regard to fuel economy?

 

[Playsinsnow]

i drive slow i don't floor it and i ease into the gas
the only thing thats in my truck is the spare tire as the mount underneath the truck is broken as far as cross bars i took it off a while back i didnt like the way it looked
im already running full synthetic everywhere
i just got a code for the coolant temp
and ima look into the 3.42 gears

3.42 gears will definitely help. How high do you want your mpgs? What are they at now? K&N or Green filter will help as well. Run a few bottles of techron through the gas too. Not sure how high you think you can go and the cost effectiveness of any mods. Possibly a tune.


Gut the hell out of that thing. That will definitely boost your mpg and you will make $$ selling the parts?

 

[gmcman]

i just got a code for the coolant temp

That will hurt your MPG's for sure. Replace the stat and the coolant temp sensor at the same time if either is your root cause for the code. If you have changed your plugs recently or have not changed your upstream O2 sensor I would do that also. You can verify it's laziness by a scan tool and ensure it's changing it's value at least 1HZ or greater. If it's changing quickly or faster than 1HZ then maybe leave it alone. But generally after about 80K miles they start getting lazy.

 

[HARDTRAILZ]

Don't torture your motor with a K/N....get something that actually filters the air.

 

[nfsroadsta2786]

Don't torture your motor with a K/N....get something that actually filters the air.

hows volant cai sound??

idk what i can gut out lol
the only thing that comes to my mind is the big @$$ muffler

and i seafoamed it by splitting it into two part half in the gas and the other half in the vacuum line for the brake booster

as far as getting out of it i do want to get the SS lol once that happens mpg can go out the window, cuz its gonna get dropped/stanced, cammed, boosted, tinted and shaved
ill pick up some other high mpg car for a daily

 

[HARDTRAILZ]

hows volant cai sound??

idk what i can gut out lol
the only thing that comes to my mind is the big @$$ muffler

and i seafoamed it by splitting it into two part half in the gas and the other half in the vacuum line for the brake booster

as far as getting out of it i do want to get the SS lol once that happens mpg can go out the window, cuz its gonna get dropped/stanced, cammed, boosted, tinted and shaved
ill pick up some other high mpg car for a daily

Best CAI for these, but just gut the stock setup and save your money.

Muffler and tune helped my MPG out. Tune more, but the muffler seemed to help on the butt dyno.

However...he meant gut the interior....fender liners...seats...anything that is not needed to drive it. The weight loss will help w MPG.

 

[Shdwdrgn]

...ima look into the 3.42 gears

Boy can I hook you up!
What gears do you have now?

 

[nfsroadsta2786]

Boy can I hook you up!
What gears do you have now?

what ever the stock ratio is i never looked into it lol

 

[nfsroadsta2786]

Best CAI for these, but just gut the stock setup and save your money.

Muffler and tune helped my MPG out. Tune more, but the muffler seemed to help on the butt dyno.

However...he meant gut the interior....fender liners...seats...anything that is not needed to drive it. The weight loss will help w MPG.

do u know where i can get the smooth pipe from (connect the air box to the throttle body) and i dont want metal ones
and which filter should i go with i was thinking abt spectre or air raid, since k/n is crap, ill see if i can get my hands on a volant blue filter

hows a flowmaster series 40

 

[gmcman]

Keep in mind there will be a significant increase in noise from deleting the intake resonator, not at a steady cruise so much but under load.

 

[nfsroadsta2786]

Keep in mind there will be a significant increase in noise from deleting the intake resonator, not at a steady cruise so much but under load.

i love that sound lol

 

[Blckshdw]

do u know where i can get the smooth pipe from (connect the air box to the throttle body) and i dont want metal ones

Some people use PVC piping from your local hardware store. I opted to go with silicone tubing, little more pricey, but still much cheaper than those manufactured intakes.

http://gmtnation.com/f25/diy-air-intake-intake-air-temp-sensor-582/

 

[CaptainXL]

A towing guide I read said that going from 3.75 to 3.42 gears is only about .75 mpg. 1 mpg if coming from 4.1 gears. But of course this is with the 5.3. Could be more like 2 mpg with the 4.2l. Do any towing? If so I would stay with the higher ratio

 

[Shdwdrgn]

what ever the stock ratio is i never looked into it lol

There were three different gears available. If there were a single 'stock' ratio, why would I bother asking?

PVC works good for the intake, just don't use the grey electrical pipe for your curves... they are formed under heat, and tend to straighten themselves out again from the heat of the engine.

Keep in mind there will be a significant increase in noise from deleting the intake resonator, not at a steady cruise so much but under load.

There is? Funny, I never noticed. Certainly a slight increase in noise, but nothing that sends me off screaming "Oh yeah, feel that power!"