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

[dave w]

EDIT: Found some...

Awesome!

I'll do some homework and get back to you in a day or so. I need a break from this research.

dave w

[1project2many]

Back home now.

I didn't think of it earlier today but the best way to get TBI and weather tight P4 together is probably $58. It will support TBI mode and a gent from the UK named Robin Handley has done a bunch of work setting it up to run 1 BAR NA with 4 cyl race cars. Combine this with the Bill Shaw injector driver change and you've got 2 TBI injectors running on a V8. Plus it's upgradeable to PFI, or to pressurized tbi if desired.

Dual ecm cals are $6B mask. Cals include ARHM6030, ARPZ6720, and ANZF9577. Some quad 4 wiring had dual crank signals sent to the ecm from the ignition module, while others did not. The 8707 / 08 may have hardware designed to work with the additional signal. The code may check for the presence of this hardware then set a mode flag if found.

The 4 cyl TBI 7727 cal I have is FML7554. It is $3E mask. I just looked and knumcyl (number of cylinders) is selectable in this cal, unlike many of the 4 cylinder calibrations. So in theory it could be adapted to an 8 cylinder engine.

Why are you looking to get a quad 4 memcal? It's very inappropriate for an 8 cyl. If it's for testing / measuring, I have several here in various state of disassembly. I'm willing to check / measure these memcals. As far as running q4 code, it will run just fine in other 4 cyl memcals and IIRC it ran on a 7730 V6 memcal with no complaints.

The problem I'm facing with making TP defs is the time involved. I'd be happy to contribute $6B, $3E, and $89 defs if I didn't have to sit here and pull all the values from one software and manually enter them in another. It looks like that's the only option at this point. Anyone have any suggestions?

[dave w]

Back home now.

I didn't think of it earlier today but the best way to get TBI and weather tight P4 together is probably $58. It will support TBI mode and a gent from the UK named Robin Handley has done a bunch of work setting it up to run 1 BAR NA with 4 cyl race cars. Combine this with the Bill Shaw injector driver change and you've got 2 TBI injectors running on a V8. Plus it's upgradeable to PFI, or to pressurized tbi if desired.

Dual ecm cals are $6B mask. Cals include ARHM6030, ARPZ6720, and ANZF9577. Some quad 4 wiring had dual crank signals sent to the ecm from the ignition module, while others did not. The 8707 / 08 may have hardware designed to work with the additional signal. The code may check for the presence of this hardware then set a mode flag if found.

The 4 cyl TBI 7727 cal I have is FML7554. It is $3E mask. I just looked and knumcyl (number of cylinders) is selectable in this cal, unlike many of the 4 cylinder calibrations. So in theory it could be adapted to an 8 cylinder engine.

Why are you looking to get a quad 4 memcal? It's very inappropriate for an 8 cyl. If it's for testing / measuring, I have several here in various state of disassembly. I'm willing to check / measure these memcals. As far as running q4 code, it will run just fine in other 4 cyl memcals and IIRC it ran on a 7730 V6 memcal with no complaints.

The problem I'm facing with making TP defs is the time involved. I'd be happy to contribute $6B, $3E, and $89 defs if I didn't have to sit here and pull all the values from one software and manually enter them in another. It looks like that's the only option at this point. Anyone have any suggestions?

I've spent many hours of research, trying to figure out if there is a practical under hood ECM for TBI service. With any venture from a stock OEM computer set up, there are trade offs. Some of the trade offs include cost ~ availability ~ time. At the moment, the 1228708 seems to be a practical option for an under hood TBI ECM. Having the $A8 / $8B .xdf ~ .ads ~ .adx ~ .bin / files for the Quad 4 available is a huge time saver!

Going forward with a 1228708 TBI project would not require any more time or information than you have already invested in this tread. Going forward with a 1228708 TBI project, for me, requires getting some parts together and scheduling time to get things assembled.

I think we are good for now.

dave w

[1project2many]

Going forward with a 1228708 TBI project would not require any more time or information than you have already invested in this tread.

I think we are good for now.

This thread seemed to have a lot of energy but some of the ground it was covering looked familiar to me. The 8707 / 8708 have been called out as possible replacements for the 7749 and 7730 several times throughout the years but I am not aware of anyone successfully using code written for a different ecm in these boxes. I have more than a passing interest in solving this riddle.

If you are choosing to use TBI over PFI you are choosing a fuel system with more required compromise. From my perspective, with years of working on stock and modified vehicles, it doesn't seem like a huge challenge to find an ecm or code that will get the job done. The only requirements I've seen stated here are minimal: The ecm needs to be weatherproof. If you have others which are not stated then I may unknowingly suggest solutions which are not appropriate. As a practical suggestion, the 7727 is more common that the 7808. The 7727 was installed in W body cars with 60 deg V6 from 88 to 93. The 7808 was installed in W bodys with 2.3 in 90 and 91. The V6 sales far outnumbered the Q4 sales.

I have not complained about the time I've invested here nor am I complaining about the lack of time for the projects I'd like to do. I am simply stating facts. Since forums don't convey context clues well, and since I don't know you well enough to interpret your post accurately, I will ask up front if this is an invitation to become uninvolved in this project. No harm no foul either way.

[EagleMark]

I know Dave and when he asks? Your input is welcome!

The reason of TBI over MPFI is a simple EFI conversion to a boat or off roader with a readily available weatherproof ECM. I think that is the bottom line?There's no question MPFI would be better. But complicates matters and raises cost beyond what most people would consider.

Because of the pure numbers or 1227727 ECMs out there, and the work done on them far out numbers anything done with Quad 4 ECM I would have to agree it would be a better starting point.

I am interested in learning to write XDFs so if files are available with information to write information on a new xdf from I may take that on when a decision is made to which ECM and mask. It may make my next learning challenge of understanding hex easier as well. It was a lot of hours to learn adx but I seemed to succeed there with working files that no one else ever accomplished!

[dave w]

I have not complained about the time I've invested here nor am I complaining about the lack of time for the projects I'd like to do. I am simply stating facts. Since forums don't convey context clues well, and since I don't know you well enough to interpret your post accurately, I will ask up front if this is an invitation to become uninvolved in this project. No harm no foul either way.

I invite your input! I feel collecting information and sharing information is a benefit to all.

Let me try to do a chronological order of my research in an attempt to think thru the options of building an underhood TBI ECM EFI System.
1. Use $8D with resistors in series for PnH injectors. My research revealed the DRP's are not the same TBI / MPFI.
2. $89 seems like a good path forward. The research revealed the '7727 has only one injector driver for PnH? $89 would require development of both a .xdf & .adx.
2a. I have not researched $3E.
3. $A8 & $8B seems like a good path forward, both .xdf & .adx are developed. The 1228708 ECM has two PnH injector drivers.

Based on my research, the Memcal cylinder select voltage will configure the DRP rate of injector fire. The Quad 4 will fire the injectors once every DRP, which is the same DRP rate as a TBI EFI System.

Maybe the 4 cylinder Memcals for both 1227727 and 1228708 have the same Memcal cylinder select voltage?

Some design considerations I think are important to me in an EFI system. Very low cost is highly desirable! The service parts (sensors, ignition system, and computer) installed in an EFI system should be OEM and unmodified. I think from my EFI design considerations, saying the underhood TBI system is really just a Quad 4 EFI system, with a custom programmed PROM Chip appeals to me. Being able to set up a scan tool, like an AutoXray or something similar, for a Quad 4 EFI vehicle application also appeals to me.

From what I've looked at $A8 & 8B have very nice Timing and VE Tables compared to the $42 TBI Timing and VE Tables.

I hope this lets everyone know where I'm coming from.

dave w

[EagleMark]

I hope this lets everyone know where I'm coming from.

dave w

Yes! We are still in development!

I think the XDF and ADX can be done, so that is not an issue. Will the end result be something a scantool can be used for? Not if we develope the XDF and ADX exclusivly for the project! So my question is, does the 1227727 have capibility of running TBI with 2 injectors? Which mask?

[1project2many]

Thanks for the reply. Glad I'm not stepping on toes.

I worked for many years with unmodified or easily duplicated modifications as a basis for many projects. These days it's becoming harder to find stock replacement parts for older vehicles. For example, many ecm's are no longer available from the aftermarket or from the dealer. So at this point I guess I feel the old arguments for stock sensors and control parts are less valid. Regardless, I'll work within these confines as it always makes the excercise more challenging.

The Quad4 calibrations I've looked at are not reconfigurable for a different number of cylinders. They are designed specifically for the Q4. Quad 4 code displays many small differences over other P4 code such as the use of 6811 opcodes vs 6809 instructions and a lack of configurable options found in many GM calibrations. Lotus manufacturing was involved in the development of the engine and may have been heavily involved in the code / calibration as well. Lotus uses the 7807 / 7808 in their cars and there are a couple of neat versions of Lotus turbo code floating around.

If the Q4 code cannot be made useful for other engines, and if other versions of P4 code cannot be made to run in the 7808, then the 7727 will be the next logical choice. I realized today the 7727 and 7730 have an additional quad driver over the 7749. I don't remember the details but I'm thinking there was a link between the second injector driver and the additional quad driver. I'll have to dig that info out later.

Regarding injector firing and DRP's... I think your research may not have revealed all the information and in fact the only ones who have it may be GM. The relationship between DRP's and injector firing for pfi is referenced in GM service literature as "synchronous batch fire" and "quasi-synchronous batch fire" modes. Thes modes may be affected by memcal resistance, but I will say for certain that stock pfi engines with stock size injectors will use synchronous batch fire mode almost all times and will fire the injectors with every DRP. In a few cases where I've worked on engines with very large injectors, including the 2.2 engine in the Cavalier, I've had to modify calibration data to enable "quasi-synchronous batch fire" at idle and low rpm. The primary reason for this mode is to prevent the minimum injector pulse width from becoming smaller than the injector allows. If you double the calculated pulse width and open the injector 1/2 as many times you still deliver correct fuel without the injector dripping, dribbling, or completely failing to open. Some of the syty guys switched their chips to this mode years ago and ran them there all the time just to avoid the work of making the transitions between modes smooth. Maybe this trick migrated to other groups as well.

I have never delved fully into the relationships between memcal, software, pfi, and tbi modes but I probably should. I have a memcal from a 4 cyl 7727 tbi here for comparisons and a pile of good reading material. Maybe I can ring in the new year by revisiting some old GM books.

Another thought I had while organizing the barn today is that the best ecm for the job might actually be the OBDII "black box" ecm used in a gazillion S10's and 1/2 ton pickups. I realize it's a complete different direction for you guys but it's available cheap and there's supporting software available. There's a partial disassembly available at thirdgen as well. Now I know for a fact that this pcm uses a 4X crank signal which could be reproduced inside the distributor, and the software changes from sequential mode to batch fire mode when the cam signal isn't present so it can fire all injectors on every crank / DRP. There are a host of other desirable options ( E trans control, one bit open loop selectable, high octane spark tables, economy / power mode switch present, etc) so if things don't seem to be working out for the OBDI box this might be worth considering.

[JeepsAndGuns]

Ok, mabey I am just stupid like this, but if this is simply going into a boat, and waterproof is your main goal, and unless its a show quality boat, would it not be much easyer to put the ecm in a waterproof box?
Simply run down to the local surplus store and pick up a dirt cheap ammo can. They are waterproof, sturdy, easy to open, and easy to mod. Simply cut a hole for the wires, then seal them up good with some sealant. Instant cheap waterproof box for whatever ecm you want. They come in many diffrent sizes.

[EagleMark]

Ok, mabey I am just stupid like this, but if this is simply going into a boat, and waterproof is your main goal, and unless its a show quality boat, would it not be much easyer to put the ecm in a waterproof box?
Simply run down to the local surplus store and pick up a dirt cheap ammo can. They are waterproof, sturdy, easy to open, and easy to mod. Simply cut a hole for the wires, then seal them up good with some sealant. Instant cheap waterproof box for whatever ecm you want. They come in many diffrent sizes.

Thats what AFI used to do...

[1project2many]

I've done a bunch of reading and some testing. From the hardware perspective, here's the cyl select data. Bear with me if it seems repetitive. I'm trying to get this all together in one place.

Pin 56 of the memcal is the cylinder select pin. On some web pages it's referred to as cal56, on others it's VRFD, and in another it's called "pin 11" because it's connected to pin 11 of another chip. The voltage on this pin determines the fuel mode selected. Voltage is controlled by resistors connected between pins 56 and 58 and between pins 56 and 53 of the memcal. 58 is +5V and 53 is gnd. There are 5 modes available:

	MEM/CAL Mode Selection
Application Mode	Input Voltage (R29/R30 ratio)	Frequency Of Injection
1. Alternating TBI	2/3 VRFD + 10%	ALT. Every REF pulse
2. Single Injector TBI	VRFD + 0% - 10%	Every REF pulse
3. 4 Cyl. PFI	2/3 VRFD +/- 10%	Every 2nd REF pulse
4. 6 Cyl. PFI	1/3 VRFD + 10%	Every 3rd REF pulse
5. 8 Cyl. PFI	GND -0% + 10%	Every 4th REF pulse

Using this information and the schematic referenced earlier in the thread I went ahead and measured some memcals I have here.

ECM	CAL	APPLICATION	RFD CHIP NO	RESISTANCE TO GND (PIN 53)	RESISTANCE TO VCC (PIN 58)	CALCULATED CYL SELECT VOLTAGE
1227165		89 VETTE TPI	16133420	7.5K	INFINITE	0
1227165		1987 VETTE TPI	16055376	7.5K	INFINITE	0
1227727		3.1 PFI ENGINE		7.5K	15K	1.7
1228706	AYZD	1992 3.3 V6		7.5K	15K	1.7
16197427		1994 4.3 CPI		7.5K	15K	1.7
1227730	ADPS	2.8 V6		7.5K	15K	1.7
1228253	AJRZ	3.8 SFI		7.5K	15K	1.7
16196396		94-95 TBI TRUCK MANUAL TRANS		15K	7.5K	3.3
1227749	AMDD	1988 QUAD 4		15K	7.5K	3.3
16197427	BJYA	1995 TBI TRUCK AUTO TRANS		15K	7.5K	3.3
1227128	ARZW	W BODY 3.1		15K	7.5K	3.3
1227730	BABM	92 BERETTA 3.1		15K	7.5K	3.3
1227749	AMDD(2)	1988 QUAD 4		15K	7.5K	3.3
16197427	BPKW	4.3 VIN W		15K	7.5K	3.3
1227165	ACKD	4 CYL TRUCK TBI		INFINITE	7.5K	5
1227807	ASDD	W BODY QUAD4		INFINITE	7.5K	5
1227165	ACWS	2.5 TBI		INFINITE	7.5K	5

According to the info in the first table, 5V is single injector TBI, 3.3V enables 4 cyl PFI or alternating TBI, 1.7V sets 6 cyl PFI, and 0V is 8 cylinder PFI mode. Almost all the measurements make sense except the Q4 memcal set for "single point TBI" and the cpi equipped 4.3 engines set for "alternating bank TBI or 4 cylinder PFI." I still need to understand the relationship between software controlled firing and the cyl select pins. I realized last night I don't even remember my logic gate diagrams anymore.

[dave w]

I've done a bunch of reading and some testing. From the hardware perspective, here's the cyl select data. Bear with me if it seems repetitive. I'm trying to get this all together in one place.

Pin 56 of the memcal is the cylinder select pin. On some web pages it's referred to as cal56, on others it's VRFD, and in another it's called "pin 11" because it's connected to pin 11 of another chip. The voltage on this pin determines the fuel mode selected. Voltage is controlled by resistors connected between pins 56 and 58 and between pins 56 and 53 of the memcal. 58 is +5V and 53 is gnd. There are 5 modes available:

	MEM/CAL Mode Selection
Application Mode	Input Voltage (R29/R30 ratio)	Frequency Of Injection
1. Alternating TBI	2/3 VRFD + 10%	ALT. Every REF pulse
2. Single Injector TBI	VRFD + 0% - 10%	Every REF pulse
3. 4 Cyl. PFI	2/3 VRFD +/- 10%	Every 4th REF pulse
4. 6 Cyl. PFI	1/3 VRFD + 10%	Every 3rd REF pulse
5. 8 Cyl. PFI	GND -0% + 10%	Every 4th rd REF pulse

Using this information and the schematic referenced earlier in the thread I went ahead and measured some memcals I have here.

ECM	CAL	APPLICATION	RFD CHIP NO	RESISTANCE TO GND (PIN 53)	RESISTANCE TO VCC (PIN 58)	CALCULATED CYL SELECT VOLTAGE
1227165		89 VETTE TPI	16133420	7.5K	INFINITE
1227165		1987 VETTE TPI	16055376	7.5K	INFINITE
1227727		3.1 PFI ENGINE		7.5K	15K	1.7
1228706	AYZD	1992 3.3 V6		7.5K	15K	1.7
16197427		1994 4.3 CPI		7.5K	15K	1.7
1227730	ADPS	2.8 V6		7.5K	15K	1.7
1228253	AJRZ	3.8 SFI		7.5K	15K	1.7
16196396		94-95 TBI TRUCK MANUAL TRANS		15K	7.5K	3.3
1227749	AMDD	1988 QUAD 4		15K	7.5K	3.3
16197427	BJYA	1995 TBI TRUCK AUTO TRANS		15K	7.5K	3.3
1227128	ARZW	W BODY 3.1		15K	7.5K	3.3
1227730	BABM	92 BERETTA 3.1		15K	7.5K	3.3
1227749	AMDD(2)	1988 QUAD 4		15K	7.5K	3.3
16197427	BPKW	4.3 VIN W		15K	7.5K	3.3
1227165	ACKD	4 CYL TRUCK TBI		INFINITE	7.5K	5
1227807	ASDD	W BODY QUAD4		INFINITE	7.5K	5
1227165	ACWS	2.5 TBI		INFINITE	7.5K	5

According to the info in the first table, 5V is single injector TBI, 3.3V enables 4 cyl PFI or alternating TBI, 1.7V sets 6 cyl PFI, and 0V is 8 cylinder PFI mode. Almost all the measurements make sense except the Q4 memcal set for "single point TBI" and the cpi equipped 4.3 engines set for "alternating bank TBI or 4 cylinder PFI." I still need to understand the relationship between software controlled firing and the cyl select pins. I realized last night I don't even remember my logic gate diagrams anymore.

Thank you very much for the tables and information!

I seem to have found some good information with my research, but nothing near as complete or as comprehensive as the post above!

Here is what I'm thinking.
I'm thinking maybe I could use an ohm meter on the '7727 injector driver pins and see if the '7727 has two PnH drivers? Maybe I need to short the PnH pins also to establish if the '7727 has two PnH drivers.

I'm thinking maybe I could use a '427 PCM TBI Memcal installed in a '7727 ECM and read voltages for the cylinder select pin? I'm thinking maybe the '427 PCM Memcal and '7727 Memcal share the same Limp Home and Knock Sensor circuitry?

The pic below is circuit board I purchased from a TGO member (who is not currently active) for a '7730 454 MPFI project I did a few years ago. I have the skill set to make a circuit board like the one pictured, but I would need a schematic. I use PCB design software at work! The circuit board pictured does not have the knock sensor circuit, but has the limp home mode. I think it it would be cool board to make, provided the cylinder select voltages could be adjusted to provide the 5 modes listed above.

dave w

[1project2many]

I found pictures of that memcal board assy on thirdgen. I've read so many threads I'm not sure who designed it... jwscab? ryan hampl? Anyway, there are a few schematics on thirdgen as well as one archived from "iroczone.com". I also know someone who has offered to reverse engineer some V8 resistor networks and reproduce them for sale. He already produces custom resistor networks designed to work with a specific 4 cylinder engine he sells. I think a jumper based configuration would work great for cyl select. The last hurdle, the old problem of unobtanium knock filter circuiry, has been worked around with options to use the old style external knock filter or the later plug in knock filter from an OBDII pcm. But the real cool trick would be getting the document that describes the entire resistor network so you could offer memcals with the correct backup fuel for a specific configuration.

By all means try the TBI 7427 memcal in the 7727. The RFD (backup fuel chips) and the knock filter are likely to work. In the P4, one injector driver will work in either saturated or peak and hold mode. The 7727 and the 7730 do not have a second injector driver but there's no reason why "4 cylinder TBI mode" can't be used with two injectors. If you do this, use the resistor trick to limit current and do not connect the "injector jumper" that loops injector current to the sense resistor.

I'm still working on the software side of the issue and how it all plays together. It really puts a crimp in things not having the diy / gmecm archives available. I *know* there are some posts that are relavant but they just don't show up in any searches.

[Six_Shooter]

I have two of those same MEMCAL boards pictured above. IIRC it was jwscab that I bought them from.

[EagleMark]

Back home now.

I didn't think of it earlier today but the best way to get TBI and weather tight P4 together is probably $58. It will support TBI mode and a gent from the UK named Robin Handley has done a bunch of work setting it up to run 1 BAR NA with 4 cyl race cars. Combine this with the Bill Shaw injector driver change and you've got 2 TBI injectors running on a V8. Plus it's upgradeable to PFI, or to pressurized tbi if desired.

Dual ecm cals are $6B mask. Cals include ARHM6030, ARPZ6720, and ANZF9577. Some quad 4 wiring had dual crank signals sent to the ecm from the ignition module, while others did not. The 8707 / 08 may have hardware designed to work with the additional signal. The code may check for the presence of this hardware then set a mode flag if found.

The 4 cyl TBI 7727 cal I have is FML7554. It is $3E mask. I just looked and knumcyl (number of cylinders) is selectable in this cal, unlike many of the 4 cylinder calibrations. So in theory it could be adapted to an 8 cylinder engine.

Why are you looking to get a quad 4 memcal? It's very inappropriate for an 8 cyl. If it's for testing / measuring, I have several here in various state of disassembly. I'm willing to check / measure these memcals. As far as running q4 code, it will run just fine in other 4 cyl memcals and IIRC it ran on a 7730 V6 memcal with no complaints.

The problem I'm facing with making TP defs is the time involved. I'd be happy to contribute $6B, $3E, and $89 defs if I didn't have to sit here and pull all the values from one software and manually enter them in another. It looks like that's the only option at this point. Anyone have any suggestions?

Well if this goes back to $3E I have a disassembled bin...