nhromyak

Ok,

Which computer should I be running for my Holley 4 Barrell TBI setup?

I have the '7730 running with $8D now.
What would be easier? (Could I run the $58 code in the 7730 for my TBI?)

I WANT to stay SPEED Density, prefer to use my current chips 27SF512. But if not, then I will order some more.
Should I get the a 7747? Or a 7749? Or something else?

ENGINE
I only have 02, TPS, Temp, Manfiold pressure, IAT, and HEI.
It's currently on a 402 BBC. Holley 4 barrel with an Edelbrock manifold and (probably too large) Doug Thorley Tri-Y headers.
I wired the Knock sensor, and I have a knock sensor for a 350 from a 90 Chevy truck. But I am not sure where to mount it....perhaps on the engine mounts.

Thanks for everyone's help.... :hail:

Grumpy

How is it running?, and why do you want to change?.
Do you have a WB?.

nhromyak

I have been trying to tune this for many months off and on. I just want it done, so I can have good driveability. Of course, now my ALDL cable broke. So no more tuning, until I get a new one (about two more weeks).

I either get hesitation from 1000 - 1800 rpms, OR if I fix that (via AE MAP), I get a horrible rich running in 2500 - 4000 rpms.



I want to change because the knowledgeable ones on this board and the GMECM mailing list, said I should.

I just can't seem to get the code to work right. And I have been told, it is probably because of the Holley injectors, presuming these are NOT P&H injectors.

IIRC - the 7730 uses p&H (high voltage, then a low voltage to keep the injectors open longer as needed) and presumingly my injectors will not do this. Hence, an inconsistent tune.

I do not have a WB.

Grumpy

About 6 years ago, I posted about how firing the TBI injectors in parallel/series would have the injectors, *sound* funny at about 3,000 RPM.

I don't know of an oem ecm that will fire 4 TBI injectors correctly. While the 749 will fire 2 TBI injectors, 4 is out of the question, it will overheat the injector drivers. HOWEVER, there is a posting in the archives here that leads to a URL with a way to rewire the 749 to handle the high current load. It's either that, or using an external injector driver board if you want to get things right.

You might want to double check, but the injectors you're running should be about 1.2 ohms. All the TBI injectors I know of, are low resistance Peak and holds. In the realm of Peak and holds there are low ohm versions, and a higher ohm version, the highs being 2.4 ohms.

nhromyak

I will check the ohms. I know the four are on the two driver circuits on the '7730 in series.

In other words two in series on one driver (1), two in series on another driver (2).

These are placed at a diagonal on my edelbrock dual plane manifold.

On the engine they look like this:

Rear

1 2
2 1

Front


So presuming these are 1.2 ohms each, then they equal 2.4 ohms tot he driver. But more than likely they will not hold after a peak from the '7730 - correct?

Thank you for all of your replies.

funstick

4 injectors in seires at 1.2ohms each eauls 1.2/4= 0.3 ohms. thats like 30 amps of current. if you wired 4 injectors in series you be at 1.2 ohms but the amount of voltage would drop from one injector to the next. now at 1.2ohms the total voltage drop would be something like 4 volts.

the onyl proper way would be to use an external driver board. and the question is where do you get a good reliable p/h injector driver board.

i only know one person

drhoads2@aol.com

RednGold86Z

iTrader: (1)

In series, the Ohms add.

RBob

iTrader: (1)

The '730 ECM only has ONE injector driver. . .

RBob.

Grumpy

Four, 1.2 ohm resistors in series, is 4.8 ohms.
Two 1.2 ohm resistors in series are .6 ohms.


Two 1.2 ohm resistors in series is 2.4.
Having 2 sets of those, in parallel is 1.2 ohms.

BUT, instead of the injectors operating at 14 volts, they're only operating at 7, since they are in series. Injectors are very voltage sensitive. Try using a 12v igntion coil/ballast resistor, on a car with a 6v operating system.


And RBob is correct, there is only one injector driver on the 730s. If in doubt get an ohm meter out, and you'll see 0 ohms resistance. The double wiring is done as redundancy, and to reduce the load on the printed circuit board traces.

funstick

ahh you sure bout that ?

for instance

hot-------1.2 resistor------------1.2resistor------Ground

the

total circut resistance is only 1.2ohms. however you will have reduced voltage as if applied to a 2.4 ohm resistor. the electron pipe is only as big and as small as its narrowest restriction. having 2 resistors in seires does not add resistance in a linear adding fashion. but it will reduce voltage. so in a sense i geuss your right about that. but its not really the reality of the matter. each 1.2 ohm resistor in this case would be lowering voltage thru transmission and energy conversion into heat.

however coils behave differently. id suggest looking into speaker design for more info. 2 4ohm woofers in seire is 4 ohms.if measured with a DVOM however in parrellel they are 2 ohms. coils do not seems to lower voltage as drastically as resistors.

AlexJH

Wrong. The total would be 1.2 + 1.2 = 2.4.

For a detailed explanation (1st year EE):

http://othello.mech.northwestern.edu..._junctions.htm

nhromyak

Oh, interesting. But there are two ouputs. C5 and C6 with C7 as the ground, IIRC.

I didn't mean to start anything, sorry.

Just looking for a good solution.

Thanks!

Should I change the computer or not?

Pick N pull (www.picknpull.com) has a 1/2 off sale this weekend, so I was thinking, if I should, get a 7749 or whatever TBI computer. But if a TBI computer can't handle the 4 injectors, should I try and make my 7730 work?

RBob

iTrader: (1)

Your best bet may be to get a '7747 and modify it for the four injectors. First, why the '730 and $8D code is not the best solution:

The '730 has just the one injector driver. This could be modified to properly handle firing all 4 injectors from the same driver.

More of a problem is the timing of the injector firing. They are either double fired or when the PW gets short, reverts to single firing mode. Double fire is one per revolution (twice or double the intake stroke), while single fire is one every two revolutions (single for each intake stroke).

With a port system, an injector for each cylinder, this works. For a TBI system it does not. Each revolution is going to have 4 cylinders in an intake stroke. Fuel distribution will be poor, probably very poor.

The $8D code being for a port system does not have the proper AE routines for a wet flow manifold. Combine these two issues and one can see why a '730 & $8D code running a TBI system is not going to run well.

A TBI ECM is gong to have the proper injector timing along with better AE routines. The '747 is the old standby while some people are using the newer PCM TBI ECMs (see other thread). These can be run with two injectors in series on each driver, but it isn't the best method.

To have the ECM drive two injectors in parallel on each driver: halve the value of the current sense resistors and put better driver transister/MOSFETs in.

The real choice is whether to go with an older 160 baud ALDL unit such as the '7747, or go with the newer PCM which has the 8192 baud ALDL link.

RBob.

nhromyak

So what is the other computer (PCM) that is TBI with a 8192 baud link?

And, what cars have this computer?

Thanks for all the replies!

nhromyak

Could the 16197427/16156930 95 C/K Truck or Van, 5.7/7.4
computers be TBI? Or are these TPI OBD1 or OBDII?


Ok, I think I am going to crawl in a hole now....

nhromyak

I just found a 7730 computer running a 4 CYL TBI...

What's up with THAT?

Attached is the bin, I have changed the extension to a JPG, as apparently, I can't send up a .bin file. So just change it back.

The problem is it needs a $3E broadcast code.

Anyone know where I can find that?

(but will he get a reply... that is question.)

RBob

iTrader: (1)

Reply. . .

RBob.

nhromyak

LOL

Grumpy

It's a SINGLE injector TBI.
Uno, one...

I'd been to a *few* GM training schools and gone thur the same lession about what the truth was, in reference to the single injector driver issue.....

Grumpy

There are lots of TBI ecms/pcms, but none of the stock ones, will drive 4 TBI injectors. Well, they will for a while, but they will melt the printed circuit board, as well as kill the drivers. If you want to drop by I can show you what happens to them...

There is a link here, how to rewire the 749 to drive much higher injector loads.

nhromyak

I found a website to update the injector drivers of the 7749, but it seems to me, I can simply run with the $3E code on 7730, if I can find it.

nhromyak

What about using the hacks on the 165 ECM for TBI?

Will it work WITHOUT a MAF? I prefer to keep the speed density.

nhromyak

Can I use an 8625 computer?