TBI to Port Injection

[Shannen Durphey]

> Date: Tue, 03 Aug 1999 14:12:45 PDT
> From: "David Sagers" <dls2867 at hotmail.com>
> Subject: TBI to Port Injection
> 
> I ran into a brick wall with my DIY EFI project this morning. 
Ouch!  Can you fix it?

 I'm
> converting a '92 Suburban TBI to a '90 TPI MAP system.  I have about all the
> parts including the TPI system, brackets, cables, etc...
> 
> Called this morning to buy the wiring harness and the tech at Painless
> Wiring said that I was headed for a big problem.  
Ohh... LOL
>The speed sensor in the
> Sub runs the speedometer and something to do with the brakes.  
Yes, that something is called ABS, or RWAL (Rear Wheel AntiLock, a
cousin of ABS)

He said the
> problem is that the TPI ECM uses a different speed sensor than the TBI uses.
>   And they are vastly different in the signals they produce, are not
> interchangeable, nor can you run a dual sensor system.
Now the dual sensor comment is untrue.  With a competent machinist and
enough money, anything's possible. ; )
> 
Ok, let's get that pained salesman straightened out.  The
computer is looking for a 2k or 4k pulse per mile speed signal input. 
The VSS in a 90 suburban outputs 40 pulses per driveshaft revolution. 
Now without knowing your tire size, gear ratio, or driving habits I
can definitely say that this is not compatible. However...
Have you seen the term DRAC mentioned on the list?  Maybe in the
archives? (hint, hint)  Well, the DRAC's job is to take that 40
pulse/rev ac signal and turn it into 2k and 4k (and 128k) pulse/mile
square
wave output.  
Are things looking better?

Now you'll need to locate one.  Well, if you remove your
glovebox and reach into the dash toward the driver's side, you should
find a small white box about 3" X 2 1/2" taped or velcroed in.  This
is the beast you need.  
So what to do next?

You'll need some wiring diagrams to connect it to the ecm.  The
schematic for the 747 and the 727 are in "incoming", and there may be
a 730 pinout there also.  Now that I've gotten around to it, you'll
also find a file called dracnfo.zip which has unconfirmed drac
pinouts, some pictures, and some instructions for using the DRAC with
non-original configurations.  For anyone who may have a version of
this that's about 2 Meg, this one's a "lite" version, with some small
corrections in the conversion instructions.


> I remember seeing in a Jegs catalogue that Edelbrock sells a multi-port
> system that uses the the TBI computer but requires Edelbrock's chip to make
> this work.  I called Edelbrock and they do not sell this chip separately,
> only with the full EFI set up.

Edelbrock does very little to their "conversion" chips.  I'm sure a
few other folks can back this up.  

<snip>
> I've already paid for all the TPI stuff and really like the long runners on
> the TPI, not sure I can really afford to shell out another $1000 for
> Edelbrock system.

> 
> Some where in the box with the TPI stuff is a harness adapter that is
> suppose to convert the TBI injector harness to an eight injector harness for
> the TPI.
Really?  I'd like a description of that.
> 
> But the big question.  Does anyone know of a chip maker that makes a chip
> that will allow my TBI computer run a TPI system?

You should stay with your TPI and TPI ECM.
Shannen