TBI 400SBC questions

[SuperCab]

So, I've been working on the 400 small block for my '87 Suburban, and have a question regarding the TBI system.

The air pump is seized up. I'm thinking I need to replace it because without the air injection in the exhaust, the o2 sensor will read rich, so the ecm will send less fuel, making it run lean. Is this right?


Also, where can I get the underhood wiring diagrams for the tbi?

ALSO, what does the knock sensor hook up to?

Are there any other problems people run into putting tbi on a 400?

thanks

[Layne]

I'd look in the tech pages for the wiring diagram. I wouldn't think you'd run into any probs, just label your wires well

[Jim Rockford]

You are gonna need a new chip anyway, so may as well delete the AIR. some 88-98 1/2 tons never even had it.  www.tbichips.com

[Layne]

I can't find a 400 chip. Does this have to be custom made?

[Blue 82]

You are gonna need more than a chip

Fueling a 400 with TBI is gonna be a challenge
You should look into 9C1 injectors
or perhaps a set of 454 injectors
The stock SBC 1 11/16" throttle body might not flow enough air
so you might also look into a BBC throttle body with 2" butterflies

here's a link that will help get you started
http://www.tbichips.com/winaldl.htm

[VileZambonie]

Don't worry about AIR, it doesn't work the way you are thinking and won't affect your a/f ratio. IF you already have the throttle body just try running it. If you determine it's not enough go with the bbc tbi unit like blue suggested.

[Layne]

So, it's just a pull the 350 and drop the 400 kinda deal? I'd love to do it in my sierra, but all that computer stuff isn't really my thing.  The 454 TB will bolt right up to the intake manifold? But that's only if it runs too lean. Hmmm What about higher flowing injectors? I don't mean to piggyback, but I love my 400 in the c-10 and kinda curious about my sierra, sorry it's not exactly what this forums about

[Jim Rockford]

a set of LO5 injectors from a 9C1 police LO5 are 65LBhr vs 55 for the reg LO5 trucks, and then the 454 lower TB unit will allow more air in .

[Layne]

Isn't the ecm adapative enough to figure out the 400 needs more fuel? I just don't understand the need for the chip. If you put higher flowing injectors on there, and a bigger throttle bore, my thinking is that the O2 sensor will read lean, and then put more fuel in, which the injectors would be capable of supplying a motor with only 50 more cubes. 

[Jim Rockford]

No the prom in the ECM is programmed with a limit of how lean or rich it will correct for, its not a endless table to pick from, you need a new chip, trust me. I had a 350 LO5 in a cop car, just swapping heads I had to get a new prom burned,  its pretty cheap.

[Blue 82]

Isn't the ecm adapative enough to figure out the 400 needs more fuel? I just don't understand the need for the chip. If you put higher flowing injectors on there, and a bigger throttle bore, my thinking is that the O2 sensor will read lean, and then put more fuel in, which the injectors would be capable of supplying a motor with only 50 more cubes. 

That extra 50 cubes will cause you more headaches than you could ever imagine
Please register at www.thirdgen.org and ask for advice
Please contact www.fastchip.com for some pointers BEFORE building your engine
Just the simple act of running a double roller timing chain will cause you problems with your knock sensor (timing retard)
Cam choice is critical-----let me repeat that-----Cam choice is critical

In a perfect world, GM would have designed the TBI with extra fuel capability, and the ability to adapt to increased displacement
In the real world GM designed the TBI for the 350 or the 454
It's one or the other, anything in between is a Tech challenge
Guys that build 383's have headaches getting them fueled
Once they get them to idle, they run lean on the top end (the O2 sensor only works at part throttle)
Once they get the A/F ratio right at the top end, they run pig rich at idle.
It's a balancing act, and you need to see what your engine wants and needs (google winALDL)

If for one reason or another, you think you are gonna build a 400+ hp TBI 400 SBC
and think it's gonna be a plug and play deal,
You are in for quite a surprise

I'm trying to point you to the reality and limitations of GM's TBI
Here's a sample thread on using winALDL to "help" tune a TBI
Read the whole thread, even if you don't understand it, learning the terms will be helpful
http://www.fullsizechevy.com/forums/archive/index.php/t-273752.html

[Layne]

Thanks Blue.  I was just thinking about it. I'm not really a 350 fan, and I absolutley love my 400 that I've got in my 77, but you guys started talking about chips, then reprogramming and all that stuff, and I'm kinda not as interested anymore.  Not that I'm saying it wouldn't be cool or impossible to pull off, but I'd just rather not screw with a tbi if I've gotta tune it to lean out or richen up. I appreciate the help tho guys.

[pwrfool]

here's pin by pin on the harness
http://www.binderplanet.com/forums/showthread.php?t=45293