02sierraz71_5.3

iTrader: (2)

I was looking over some logs and noticed my injector pulse width averages 22-24msec between 4500-6300 rpm at 6300 rpm that puts my duty cycle at anywhere from 115 to 125%

I dont have any KR and I dont have a wideband but it does seem to be getting proper fueling, narrowband reads around 930 wot ( I like it a little rich) Does anyone know if there is a way to tune this out to lower the duty cycle? It seems to run fine now, is a larger injector needed?

On long wot runs is where I tend to run into trouble and small amounts of KR can show up, going down the 1/8 it seems fine though

This is on an NA 5.3

horist

if your fuelilng is right, and you're getting that high a duty cycle, probably want to look into getting bigger injectors.

Have you dynoed? any idea what kind of power you're putting down?

Unless you're running really rich though... I'd say prolly time to think about bigger injectors. What size are you running now?

02sierraz71_5.3

iTrader: (2)

Im still running stock injectors, I havent dynoed with the new setup yet. I did run 8.8's in the 1/8 in a 5400 pickup NA so Id say shes making really good power for a 5.3 maybe in the neighborhood of 350 at the wheels. I really need to hook up a wideband, though I wouldnt think my fueling at wot could be that off if with the times Im getting.

Is there anyharm in staying with the injectors even at that duty cycle?

horist

The last line in your sig pretty well sums it up

It's not a good idea to stress the injectors that much for a long period of time... when they're that far over 100% duty cycle greater chance of not being able to provide enough fuel for the amount of air coming in

02sierraz71_5.3

iTrader: (2)

What size would you recommend?
What would I have to do to tune for larger injectors on an NA setup?

I remember hearing something about tricking the injectors into thinking they are larger, is it possible to tune this problem out with the stockers?

RedHardSupra

iTrader: (1)

if you're that far off, you wanna go with svo 42's. cheap, easy to tune, idle perfect, and will give you the 'headroom' you need in this case. well, this is a truck, they take different injectors don't they? hmm..in that case, find some other injectors that fit and flow in the 40+lb/hr range

technical

What about fuel pressure... Does it drop at the higher revs?

02sierraz71_5.3

iTrader: (2)

I havent logged fuel pressure I definately will though, will I need a higher flowing pump

technical

Potentially, if the pump is the weak link you might need a stronger one.
For your HP you shouldn't need much more than 30# injectors.
I don't know what size the trucks(5.3) come with stock....

02sierraz71_5.3

iTrader: (2)

the stock injectors are 24.7, going from a calculator and my 1/8 et., mph and weight of 5400lbs the engine at the flywheel should be around 400. Ive heard of people just swapping over to the 8.1 injectors which I believe are 32 lb/hr.
I would rather have too much than too little in this case. Im going to return my timing to stock tables until I get the swap done and keep it below 3500 rpms.

When I upgrade to larger size like going from 24.7 to 42 will the stock pump be able to supply enough pressure?

What is involved in tuning for larger injectors?

Any other recommendations, thanks for the help

02sierraz71_5.3

iTrader: (2)

so whats involved with tuning for larger injectors
do I need only change the flow rate vs kpa

RedHardSupra

iTrader: (1)

yup, read the stickies in PCM section, it's all there

WS6FirebirdTA00

iTrader: (33)

i would do a pump as well, it will give you that extra little bit and make sure that there is not a large pressure drop in the fuel rail. like redhardsupra said though, go big and u wont have to worry about problems in the future if u get more power. do not go with racetronix though, they WILL NOT run right at lower power levels unless you wanna do it wrong and make the car run rich. i was at the full bolt on level and did everything i could think of and couldnt get it to run at idle unless my fuel trims were about -12 or so. im running about 65% duty cycle on 38# injectors, 43.65 at our pressure, and im expecting to make 430-440 rwhp, just to give you an idea of how mcuh power you could handle

edit: although high z injectors are prob the same, i say this about the ls1 CAR injectors becuase i have no experience with the truck ones, although i assume the same

02sierraz71_5.3

iTrader: (2)

thanks for the input guys,
I got some larger injectors off this board alst night we'll see how it goes.

Racetronix

iTrader: (2)

WS6FirebirdTA00

iTrader: (33)

dude im sick of all your bull **** in these threads, your about the only person that works for a buisness trying to sell LS1 products and is an *** and no help. there is information on your injectors cutting out at about 1.6-1.8 ms, every tuner that i spoke to leaves the car rich so they will run right, to get your product to work on a stock car you HAVE to make it run rich. if you thnk tihs is such BS then back yourself up, you keep talking crap on here but you dont know the first damn thing about tuning so how can you call BS, take a poll of people on here that have these injectors and see what they all have done, on stock motors im sure they didnt do it the right way to make it run right, they make the IFR table too small.

either give us some information or get the hell off our board, im getting sick of your little bitchy comments and no tech help/support.

horist

Do you have any tech info to show him wrong? I haven't used racetronix injectors so don't have any first hand experience with them, but some of his points (specifically about the injectors not responding well when pulse width is too low .. which on a low horsepower car w/big injectors .. .idle pulse width would be really low) are valid...

Rather than posting antagonizing smileys would be helpful to the entire community if you can provide some tech info to dispute his claims?

02sierraz71_5.3

iTrader: (2)

Ok back to some questions,

Is there a way to log fuel pressure with hp tuners, looked for a pid didnt see one

WS6FirebirdTA00

iTrader: (33)

i dont think u can log the pressure but you can get a pressure gauge from auto zone for 35 bucks and check it out that way, you dont have to drive to get a good pressure reading because vacuum is vacuum, the injectors see it all the same moving or sitting still, at least this is how i have seen it

Racetronix

iTrader: (2)

WS6FirebirdTA00 has no experience with the Delphi Multec II SUV/Marine injector.
WS6FirebirdTA00 assumes this injector is the same as the Delphi/Lucas disc injector he uses.

This Delphi Multec II injector (17113739) is the only direct-fit PnP upgrade injector specifically designed to fit the LS1 SUV (or Marine) intake manifold and fuel rails. The 17113739 is a very fast injector (faster than the disc injector) which shares most of the same calibration data with the factory injector apart the increased flow numbers / variables. Only a few minor adjustments are required to the PCM programming and these injectors will fall into place. A search of the truck section on this forum will net good info on this subject.

Here is a short blurb from the GM tech site on the Multec II injector used in the SUVs

The Multec 2 fuel injector assembly is a solenoid device, controlled by the powertrain control module (PCM), that meters pressurized fuel to a single engine cylinder. The PCM energizes the high-impedance (12.0 ohms) injector solenoid (2) to open a normally closed ball valve (3). This allows fuel to flow into the top of the injector, past the ball valve, and through a director plate at the injector outlet. The director plate has 2 machined holes that control the fuel flow, generating a spray of finely atomized fuel at the injector tip. Fuel from the injector tip is directed at the intake valve, causing it to become further atomized and vaporized before entering the combustion chamber. This fine atomization improves fuel economy and emissions.

Perhaps Allen @ Nelson Performance and Geoff @ Thunder Racing will chime in and provide some insight on the use of these injectors as they sell and tune them on a regular basis.


The 2002 Sierra has a rail-mounted regulator return system which is not manifold referenced.
GM calls for (55-62 psi) VIN: (V, T,U)
The PCM does not monitor the fuel pressure only vapor pressure in the fuel tank.