16197427 Memcal vs 16196395 Memcal

[corvairnut]

But your also not given us info needed as asked above so we will never be able to figure it out.

Sorry.. I did not see that questions/requests from 1toomany above. BTW the chips that dont work BNBH, BHRD, BNKM (CPI).

The engine readings looked fine in tuner pro.... maybe timing was down about 5 degrees, but would not cause the issues I was having. With a TBI bin on a CPI memcal, Its almost like the engine is loading up at low load/idle area but fine in the upper RPM and higher load. When I run a CPI bin that I changed to my particulars, the engine surges at idle, so I never went any farther From my research on the issue before, the knock board is engine/trans specific and can be transfered to other memcals and did not appear affected by the netres chips. I have read and can document the differences in the chips on my next post.

thanks in advance. Let me know if you need anything else.

Ted

[corvairnut]

Bill Hamilton at binderplanet documented this awhile back. I tried it with another older chip, but failed to work. I want to see it this will work on the blue/white netres as this has to be it. This modification fires the injector every 4th DRP and would explain why im loading up at low load/RPMs with the CPI Memcal. Again, I hate to trash good chips that might can be modified. I will perform the mod Friday night after I get back in town. http://www.binderplanet.com/forums/s...d.php?t=101802

Ted

[1project2many]

Very sorry I didn't reply sooner. I've been stupid busy lately and it's only getting worse with the potential for the hurricane coming in this weekend.

With the problem memcals, the ecm is likely delivering 1/3 the expected fuel most of the time due to the injectors firing on every third reference pulse. The fact that it's better at part throttle was a bit confusing at first but then I realized that the throttle angle probably correlates to PE mode entry where the ecm will switch to asynchronous fuel delivery. In asynchronous mode the ecm fires the injectors based on internally calculated values rather than reference pulses.

Much of the memcal information you can find on the 'net came about due to work over at thirdgen.org and that's a great site to research on. On this forum, Dave W asked about using an underhood ecm such as a 7808 or 7727 with V8 TBI and that in turned into a bit of a project involving memcal differences. Here's some of the info:


http://www.gearhead-efi.com/Fuel-Injection/showthread.php?454-What-If-8D-(1227727-ECM)-for-TBI&p=3374&viewfull=1#post3374

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	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.

The easiest answer for you is probably to use the chart of measured resistances above to modify your CPI / V6 memcal to match the TBI V8. The more difficult aspect is how you're going to do it. The V6 PFI resistances are opposite the values you need. Jumpering to ground does provide the correct voltage for TBI mode. The resistors are built into the netres chip so you can't just disconnect them. If it were me I'd probably try and locate some high quality resistors that are temperature stable. Disconnect pin 56 from the netres and connect the resistors externally to pins 53 and 58 as needed. I've modified the image in the thread you reference to indicate memcal pin numbers.

Now here's another thought for a more professional looking result. The netres is nothing more than a "box" of resistors. GM has a way of reusing technology to save money and past discussions plus experience makes me think the old C3 TBI netres is very similar to what's included in the P4 ecm. If you could get your hands on some old TBI ecm chips to measure resistance chances are good that you'd find they'll work as backup fuel chips. There are TBI V6 and V8 versions so I'd look for a V8 chip to start. This would require more work but you'd have a final product that looked OE.

For curiousity's sake, please let us know how this works out.

[pmkls1]

I don't want to jack this thread, but my question is semi relevant to the topic. I'm still trying to understand the exact functions of the netres chips in GM memcals as I was a little mistaken about them. According to the information you provided above 1project, the netres chips in several memcals appear to function the same even though they are used in applications with a different cylinder count. So, for example, a memcal from a quad 4 in a '749 application could be used in a '427 TBI application with the proper knock board installed ? I have been a little confused as to the function of the netres chips because not all memcals have a knock board. I have a few random memcals and ecm's laying around that I will investigate further now that I know what to look for. If I find any information that I think may be relevant to this discussion I will post it.

[JeepsAndGuns]

If you could get your hands on some old TBI ecm chips to measure resistance chances are good that you'd find they'll work as backup fuel chips. There are TBI V6 and V8 versions so I'd look for a V8 chip to start.

I have a V6 and V8 7747 limp home chips setting here on my computer desk I can measure if you tell me the exact pins to measure and what ohm seting to set my multimeter to.

[corvairnut]

Very sorry I didn't reply sooner. I've been stupid busy lately and it's only getting worse with the potential for the hurricane coming in this weekend.

With the problem memcals, the ecm is likely delivering 1/3 the expected fuel most of the time due to the injectors firing on every third reference pulse. The fact that it's better at part throttle was a bit confusing at first but then I realized that the throttle angle probably correlates to PE mode entry where the ecm will switch to asynchronous fuel delivery. In asynchronous mode the ecm fires the injectors based on internally calculated values rather than reference pulses.

For curiousity's sake, please let us know how this works out.

The Chart and the explaination is exactly what I was looking for. I will get the resistors tomorrow and the 1/8 watt ones will fit very easily under the knock board and from pin 56 to 58.

I will report back soon.

[Six_Shooter]

I still have yet to understand why people think changing from dizzy to DIS makes the LHM mode irrelevant.

In LHM, the ECM has ZERO control of timing, all pf the timing "control" is strictly by the ICM when LHM is active.

If LHM worked with a dizzy, it will also work with DIS, I know this from experience in addition to understanding how LHM works, or more accurately doesn't work (directly) with the ignition system.

[1project2many]

According to the information you provided above 1project, the netres chips in several memcals appear to function the same even though they are used in applications with a different cylinder count.

More specifically the information I provided above shows one function of the netres uses the same value for different engines and nothing more. You might see the same coil on a four and an eight cylinder engine but you should not assume the entire ignition system is interchangeable between the two.

I don't want to jack this thread, but my question is semi relevant to the topic. I'm still trying to understand the exact functions of the netres chips in GM memcals as I was a little mistaken about them.

I've recently discovered some interesting information regarding netres function which appears to be sourced from GM / Delco engineering documentation. It's been around for many years but I don't think too many people have spent time with it. Many of the references are to pages, figures, and diagrams which the author assumes are available to the reader but are not included with my copy so I'm going to try and spend time with it clearing up some of the references if possible.

I have a V6 and V8 7747 limp home chips setting here on my computer desk I can measure if you tell me the exact pins to measure and what ohm seting to set my multimeter to.

Thank you! I'm likely to take you up on that in the future. The LHM programming includes thirty resistors in two networks so there will be a fair amount of work involved.

I still have yet to understand why people think changing from dizzy to DIS makes the LHM mode irrelevant.

IIRC the OP's trigger wheel angle ends up firing significantly ATDC when bypass mode is enabled making engine operation difficult if not impossible in LHM.

[Six_Shooter]

I've recently discovered some interesting information regarding netres function which appears to be sourced from GM / Delco engineering documentation. It's been around for many years but I don't think too many people have spent time with it. Many of the references are to pages, figures, and diagrams which the author assumes are available to the reader but are not included with my copy so I'm going to try and spend time with it clearing up some of the references if possible.

That would be awesome.

IIRC the OP's trigger wheel angle ends up firing significantly ATDC when bypass mode is enabled making engine operation difficult if not impossible in LHM.

Then the ignition system is not set-up correctly and will cause global issues.

[corvairnut]

For curiousity's sake, please let us know how this works out.

Works like a charm. I clipped #56 chip side and installed a 1/8 watt 15k ohm between #53 and #56 pinout side. I then installed a 1/8 watt 7.5k ohm between #56 and #58 and all appears well.

Took her out for a drive today and monitored with Tunerpro. All appears normal except for the IAC counts.... they are high on start and settle down within a couple of minutes, but other than that, exactly the same. This was my original question and I knew there are too many smart people on this forum and my question would be answered.

Thanks again.

Ted

[1project2many]

Excellent!!! Thank you. The only advice I offer is to consider temperature stable resistors. Typical carbon resistors can change resistance considerably if it gets cold out. I tried to replace laser cut resistors in a speedometer once to recalibrate it. Everything was great form temps of about 60 deg and up but at 35-40 deg the speedo read 20mph too fast. I'd hate for someone to start a car in winter just to make sure it's run only to have issues.

I knew there are too many smart people on this forum

That's funny. You, sir, earned quite a bit of respect from me for working out your DIS system by trial and error. Not an easy thing to do. Many people with much education have failed at the task.

[corvairnut]

Now that we know what pins 53, 56 and 58 do and how we can affect them, what does the rest of the netres pins do? Be cool the map them, but I dont even know where to start and what differences they would make if I did. Do anyone have a clue? Be cool if you could move timing and number degrees by inserting a certain ohm resistor (important on DIS). Just thinking out loud.

Ted

[Six_Shooter]

AFAIK, the NETRES has ZERO effect on timing, since it's really only used for LHM, besides the hardware side of the cylinder select.

LHM timing is controlled by the ignition control module alone.