MrWillys

When using a V6 memcal and cutting the 15k resistor the circuit then becomes V8 and Limp Home Mode works as any V8. I cut the pin and removed the 28 pin chip and it ran in mine with the SES light on as it should.


Hopefully this will put an end to misinformation being given here on this Forum.

Tuned Performance

iTrader: (92)

Do you ground to correct for firing rate ?

MrWillys

This post lead me to a test. The memcal shown on the right where the pin to the 15k resistor is cut runs in Limp Home Mode. The memcal on the left where the 15k resistor is grounded does not run in Limp Home Mode. Therefore, cutting the 15k resistor pin is the superior method if you still want to have Limp Home Mode.

Tuned Performance

iTrader: (92)

So no cyl select cal 56 ?
Or is it you can have correct cyl select or lhm but not both ?

MrWillys

You can have both. Look at this picture.

RBob

iTrader: (1)

It appears that you grounded the wrong pin... Yes, no?

RBob.

MrWillys

I grounded the 15k pin? Always worked except LHM.

RBob

iTrader: (1)

Wrong pin. Need to ground the one that corresponds to pin 56 of the MEMCAL (next one over). Basically you shorted a +5 volt feed to the MEMCAL to ground. Which is likely why LHM doesn't work.

RBob.

MrWillys

I ground pin 56 and it ran in LHM with an SES light so I soldered in a chip and burned it and it ran without any codes. So either cutting pin 58 or grounding 56 will work.

RBob

iTrader: (1)

Not really, cutting pin 58 also denies +5 volts to the CAL 60 resistor. So whatever that resistor controls in the RFD no longer does correctly.

So we are back to what we the forum have been saying all along. To use a 6-cylinder MEMCAL for an 8-cylinder engine, ground pin 56.

RBob.

Tuned Performance

iTrader: (92)

Additional information regarding knock sensor disabling.
https://www.thirdgen.org/forums/diy-...d-density.html

MrWillys

I will just have to disagree with your assesment because grounding can leave a cold solder joint so cutting 58 is more reliable.


https://pcmhacking.net/forums/viewto...t=214&start=20

Tuned Performance

iTrader: (92)

Not grounding 56 causes running issues. I have fixed a few of some other programmers memcal lately. One is from jims performance the other unknown.

MrWillys

Disagree and have tuned more than 1000 vehicles in 15 years. What detriment do you speak of? Are all the guys down under wrong too?

RBob

iTrader: (1)

They are also wrong. Note that they are ID'ing knock filters by the build code, also not correct. Losing the CAL 60 resistor is the result of cutting the pin. That can't be good. On top of that it isn't easy getting under the knock filter to even cut the pin. Let alone not putting pressure on the knock filter board and cracking it.

And from your first post:

> Hopefully this will put an end to misinformation being given here on this Forum.

Apparently you are the one spreading misinformation. We the forum have been correct all along with grounding pin 56...

RBob.

MrWillys

My point was to simply point out that LHM mode does function in V6 memcal conversions and will now stay true to my word to keep my post count low on this my way or the highway forum. this thread has made my point quite clear and the responses speak quite clearly. Have a good day!

Six_Shooter

iTrader: (2)

It may work, but it won't be the same as using a true V8 RFD chip.

I could claim all sorts of LHM inaccuracies, because I've used turbo V6 MEMCALs with the "wrong MAP sensor" (2 BAR vs 3 BAR), it would allow the engine to start and run, but in no way would I claim that it is correct, or just as good as using the proper matching components.

I've used 4 cyl MEMCALs with V6s, and the engine would run, again, in no way would I say that this is a correct application of parts, simply because the engine started because it's not.

Even a broken clock is correct twice a day...

jwscab

I haven't replied on the boards in YEARs, but what is said above is correct. the memcal for 730 ecms contains three parts. prom, knock board, and resnet. each has their specific purposes. each memcal is unique and can be verified by measuring pin 48 of the memcal. the knock value and resnets are configured to match the engine it's designed to run with, including limp home values and knock frequencies. each one has a unique resistor value.

here is a snippet from one of the boards of long ago, maybe diy-efi.org or gm-ecm. can't remember. bottom line is grounding to set the pin to zero volts should set the memcal to believe it's 8 cylinder port injection.

I've just discovered how to select the number of cylinders in the P4 ECM
> hardware. The number of cylinders is selected by the voltage on pin 11
> on the 34984 (aka 79435) chip. This is U13 in a '727, '730, and '749.
> The pin 11 voltage comes from pin 56 of the MEMCAL. This in turn
> connects to pin 13 of the 16 pin resistor network in the MEMCAL.
>
> Here's how the voltages are interpreted:
> 0 to 1 volt : 8 cylinder port injection
> 1 to 2.5 volts : 6 cylinder port injection
> 2.5 to 4 volts : 4 cylinder port injection
> 4 to 5 volts : throttle body injection (any cylinder count)
>
> The '727 I tested this on defaulted to "4 cylinder port" when pin 11 was
> not driven (no MEMCAL).
>
> The CPU can read out the pin 11 mode selection. Code 41 will be flagged
> if it doesn't match the cylinder selection stored separately in the
> MEMCAL's EPROM.