What If? $8D (1227727 ECM) for TBI

[dave w]

I'm thinking about trying to use the Under Hood 1227727 ECM for a TBI. I'm thinking of using definition $8D with a resistor network to trick the ECM to thinking the Low Impedance TBI are High Impedance TPI injectors.

I found the information (Formulas) below from a MegaSquirt website.

Injector Resistors
This method has been used by many OEMs as a simple approach to driving low-z injectors. The installer has the option of installing a 5 to 8 ohm resistor (with a 20 to 25 watt rating) in series with each injector (in effect converting them to hi-z.)
1980s Volvos were fitted with a resistor pack that conveniently combines a number of resistors.
To limit the current to under 2 amps, you need:
resistor ohms = (alternator voltage / 2.0 amps) - injector resistance
For example:
resistor ohms = (14.0 volts / 2.0 amps) - 1.2 ohms
=> resistor ohms = 7.0 - 1.2 = 5.8 ohms

The application I am thinking of converting to $8D TBI is a Marine SBC application. Using an under dash ECM is not an OPTION!

Couple things I'm thinking about:
TPI and TBI are different DRP's.
The OEM '7727 TBI definition is not hacked as nicely as the $8D / Super $8D!
Injector flow settings; seems like injector flow of about 15 Lb / Hr would equal one TBI injector of 60 Lb / Hr?

Any thoughts Pro's / Con's are welcome.

dave w

[Six_Shooter]

I believe there was a TBI '7730/'7749/'7727 application. If it was in one of those three ECMs, it can be used ijn the others. I want to say it was a late '80s vehicle, but I don't recall exactly which one.

[EagleMark]

Well since 1227727 is underhood model of 1227730 and 1227730 was already used for TBI, and chips will run the same in both, and we have TBI wiring diagrams for it :
http://www.gearhead-efi.com/Fuel-Inj...CM-information

I think it may be easier than you think? But I am not sure what mask the 7739 TBI uses?

Also a 1227727 system either underdash or underhood would be not only great for marine but also great for Off Roaders who just want TBI!

EDIT: Ha! was posting same time as Six Shooter...

[dave w]

Thanks for the input. I've done some research, and have only been able to find 4 cylinder TBI '7727 / '7730 applications. I think the challenge is getting the '7727 TPI Distributor Reference Pulse (DRP) to work with the TBI DRP's?

From my research, I've seen information saying the TBI DRP is once every spark plug firing.

From my research, I've seen information saying the TPI DRP is once every other spark plug firing.

Any thoughts?

dave w

[Six_Shooter]

Yeah, once you set the "cyl count" to "TBI" (I don't recall the HEX value for that, off hand), the injector firing should take care of itself.

[dave w]

Does anyone have a $89.xdf? I've looked around, but can't seem to find one.

Thanks,
dave w

[EagleMark]

So that's what 1227727 TBI mask is? I went through everything I had and Robert from TP gave me and nothing for that or any bins?

I do have a 7749 2.8 TBI $3F xdf...

Since your probably dealing with a V8? Wouldn't it be better to start with readily available V8 xdf for 1227727? Change to TBI? If the $OD and $OE can do it I'd bet $6D, $8D could but really not sure how... there's also $A1, $88 and I think $55 were V6 PFI with 1227727

[dave w]

Based on the research I've done, $89 was for a 2.5 liter '7727 TBI. TunerCats shows $89 on it's website. I think to best path forward is to leverage the $3F.xdf, based on Six_Shooter's information that 7727 / 7730 / 7749 are interchangeable. I think a bench test is a good place to start. I'll need to do more research on the '7727 TBI pin out.

Howell EFI is advertising a Dual TBI system using the '7730, so I'm thinking a '7727 single TBI pin out is possible.

Any help on a $3F.xdf / $3F.adx is greatly appreciated!

dave w

[EagleMark]

$3F coming right up!

no signs of $3F adx so I will look to see if there is an ads or ALDL/ds for it.

[dave w]

I've done more research on the '7727 Injector Drivers. Here is what I think can be done to get the '7727 to operate TWO peak and hold injectors. The scree shot below is from http://www.exatorq.com/ludis_obd1/quadplugecm.html When D1 and D5 are shorted, D14 will operate a peak and hold injector. When D4 and D8 are shorted, D9 will operate a peak and hold injector. From the schematics I've been able to find; the 1990 ~ 1992 VIN R 2.5 TBI has D4 and D8 shorted, so I'm thinking it would be logical to short D1 and D5 and use D14 for the second peak and hold injector.

dave w

[EagleMark]

Looks like you figured it out...

I did find the ALDL is A97, attached is this in adx format.

[dave w]

Hi Mark,
Thanks for the $3F.adx!

I had noticed the '7730 2.5 Liter TBI Jumper D5 / D7 Injector Driver Low. I was thinking there would be a '7727 configuration that would be set for low Z injectors.

Is there a starter $3F.bin file available?

dave w

[EagleMark]

Have searched all I have collected over the years and the huge files Robert Saar gave me. No signs of any $3F bins? It is not the type of car many would get involved in tuning... 2.5L TBI?

OK I searched CalData and I did find some 2.5L bin numbers for LR8 A96.ads (not A97.ads) which come back as 1227727!
AUAJ, ASLX, AUSS, ASLW, APTW

Did find one, may be more here in bins:
http://gearhead-efi.com/gearhead-efi/

Or at Moates library?

[dave w]

So that's what 1227727 TBI mask is? I went through everything I had and Robert from TP gave me and nothing for that or any bins?

I do have a 7749 2.8 TBI $3F xdf...

Mark,
I'm not sure $3F is a '7749 .xdf? I've bumped into information (maybe conflicting information) that is showing $3F is for the 1227429 / 2.8 Liter TBI using a 2732 chip? I'm thinking a 27C128 or maybe even a 27C256 would be used in the '7727 TBI.


dave w

[EagleMark]

Not sure Dave? I just happened to have what you asked for and I thought it was 7727?... That APTW (above) is listed as 1227727 ECM and A96.ads so if it shows info wrong in $3F then we need to look at hex for proper mask. I really don't know how to do that...

It's a rare oddball 2.5L TBI engine using a MPFI ECM... not much out there on it. But we do have the above bin which is 1227727 and 2.5L TBI!