gravedigger472

just picked up 1993 454 and swapped it im my truck. am having some issues with it, and need to check my fuel pressure.

I know that in 94 the TBI 454's got a higher pressure (30ish?), compared to my old 350 which should be about 9 to 15. but i do not have the donor truck to tell if its a 93 or 94 model year. guy claimed it was 93 but im not sure.

is there a casting number on the throttle body or the regulator that will tell me what year it is? or any other way to visually identify what year the throttle body is, thus determining the pressure requirement?

also if i need higher peressure should i just get a wallbro 190 or 250 LPH pump?
i mean, my 350 pump wont get close to the 30psi demanded, right?

thanks

Ronny

iTrader: (1)

Later trucks(1995-1996) I believe used 45 lbs injectors at the higher(30+) fuel pressure. My TBI unit is 1995-1996 and had the small injectors. Read the #s in the top of injectors to determine which ones you have. My TBI also had the high pressure spring(GM orange I recall). If you search that # you should have your answers. I think the smaller Walbro is preferred. Or use a GM TPI pump.

gravedigger472

i thought the years were 94 to 95 for the higher perssure TBI, as the 96+ is the vortec MPI trucks, with a completely different pump/TB/injectors

thanks for the tip, i will check out the number on the tops of the injectors.

Ronny

iTrader: (1)

You are most likely correct.

gravedigger472

I just ran the number and found that it says
"Late model big block"
GM17084304 RPG 80lb/hr
so im assuming that this 80#/hr rating is at the 12psi and not the 30psi.

or would "late model" denote the higher pressure one

Ronny

iTrader: (1)

deleted post...

RBob

iTrader: (1)

Ronny, you should delete that list from your PC. With the exception of the yel/brn injectors every single one is incorrect. And even at that, there are two different yel/brn flow rate injectors produced.

gravedigger472, odds are that the 17084304 injectors you have are 75#/hr at 13 psi.

RBob.

Ronny

iTrader: (1)

Quote: gravedigger472, odds are that the 17084304 injectors you have are 75#/hr at 13 psi.

Then that means my 80's are in fact 75's? Then, if so, my BPC is incorrect.

I will delete.

RBob

iTrader: (1)

As long as the VE table isn't max'ing out at 100% and the AFR is rich enough, then nothing to worry about.

RBob.

Ronny

iTrader: (1)

Agreed. I prob tuned around that error. I do recall changing the VAFPR/BPC table as I was in fact over 100 in VE around 2400 RPM/50 VAC. I dont think I touched 0 VAC(100 MAP) however.

dctrumpet

iTrader: (10)

The 94-95 7.4L TBI units had a larger base foot print for the IAC Valve passages to each individual bores. Now, there are a number of early 90's 7.4L TBI units that had the larger base footprint as well, but they had 17084304 injectors at ~13psi.

100% of the 94-95 7.4L TBI units that I have seen (about 45-50 of them) had 17104288 injectors which are flowed at 30psi. When those injectors are tested at 13psi (actually 1bar which is 14.7psi) then they are rated at ~45lb/hr). Of course if they are flowed at 30psi then they will be closer to 90lb/hr which makes sense because it needs to support the 7.4L engine! All marine 5.7L TBI's used the EXACT same injector as the 17104288. It's a direct cross reference to a Quicksilver part number. All marine units regardless of V6 or bigger ran at 29-32psi of pressure.

I've literally disassembled 175+ 7.4L TBI units (auto and marine units). So, this is the info that I have found. I've obtained realistic flow ratings for most of the TBI injectors with the help of Gordon at www.WitchHunter.com.

17084304 injectors flow between 820cc/min to 875cc/min at 14.7psi. So, in a nutshell they are a "75lb/hr" injector.

Gordon uses a fluid that has a specific gravity almost identical to gasoline. This is important because when the injectors are flow-tested at his shop and then placed in your vehicle we know with a reasonable degree of certainty what it will flow in your vehicle at a certain psi. Thus, helping a little with setting up the tuning. Yes, there are a ton of other factors as well.

Hope this info helps

dctrumpet

iTrader: (10)

This is what i mean regarding the larger base footprint. Also, every newer style larger foot print 7.4L TBI used the newer style TPS which matched most of the 5.0L and 5.7L factory harnesses. So, it's a good choice to use when swapping out to a 7.4L TBI. It's one less sensor and adapter to buy. The only thing is you will need to buy a base adapter in order to mount it on a stock 5.0L/5.7L TBI intake.

RBob

iTrader: (1)

Interesting changes that GM did for better idle air control. I've seen some minor differences in the IAC passages with other TBI units.

For the '94-'95 BBC 17104288 injectors. At 46#/hr @ 13 psi, they are 70#/hr @ 30 psi.

RBob.

dctrumpet

iTrader: (10)

RBob you're correct. I had to go back and look at my flow sheets for the 17104288 injectors.

At 14.7psi they flow at 543cc/min
At 30psi they flowed at 750cc/min

Of course this is only one pair, lol.

The others ranged from 520cc/min to 555cc/min at 14.7psi and at 30psi they flowed 720cc/min to 785cc/min.

Ronny

iTrader: (1)

Quote: The 94-95 7.4L TBI units had a larger base foot print for the IAC Valve passages to each individual bores.

That makes it critical to obtain correct model year TB base gasket.

dctrumpet

iTrader: (10)

Yes you're correct. There are only two styles of base flange gaskets for 7.4L TBI units. Everything else is the same.