This is my first post here at Third Gen. I'm hoping to find a schematic of the Limp Home part of a Memcal. I'll be quick to the point...I would like to reverse engineer my own Memcal printed circuit board (PCB).

I can't understand why the price of Memcals are so expensive lately. I've designed circuit boards for my current and previous employers. I could design the DIY Memcal to plug in like the original Memcal, allowing for PROMs to removed and replaced very easily, and still fit under the ECM removable cover. I've done some small 4 layer PCB's that cost only $45 each, (when ordering 50 PCB's) that had just over 100 components on the board. I guess when Memcals were $50, not much interest in a DIY memcal...but at $200 (or even more $$) a Memcal...I'm motivated to try and make a DIY Memcal.

dave w

 

I found this web site...which helps. http://www.iroczone.com/resnet165.htm

 

There was a guy on the GN board long ago who actually worked developing the ESC circuit portion (knock sensor signal conditioning etc) of the cal-pak.. from what he said there was millions of dollars and some alien technology that went into creating it. I imagine there are some components specially made for GM by contracted manufacturers that you couldn't duplicate without some serious hardware and skills.. and even then, your package size would be 6x theirs using available parts.

Perhaps start out duplicating everything except the ESC circuit.. then decide if you (or others) really need that (My knock control stuff is almost ignored ;P )

I don't want to be a negative-nilly.. but usually a post like mine bring the real experts out who like to show someone else is totally wrong .. and unless they capture my quote.. I can always edit it out and continue pozing ;P

 

92Z-666 thanks for the response. I work with (to some anyway) the alien PCB technology. Surface Mount Technology (SMT) has drastically changed PCB's. SMT resistors are very small, the 603 SMT resistor is only 0.060" x 0.030". Getting a production run of a few dozen boards is the miminum order. It's very common to get SMT components placed on both top and bottom of a PCB. I've hand solder some real fine pitch IC's (about 100 leads on a 1" x 1" square) using a low power 10x microscope so I can see each individual pin.

Once I get the schematic into the PCB CAD software, the auto-routing will do the board traces (up to a 7 layer PCB). There are several freeware PCB CAD Software Programs, like http://www.pcb123.com

I am more than willing to provide the freeware PCB files if I'm ever able to get the resistor pack schematic. I'm very lucky to live close to an area with several semiconductor type companies...so getting a PCB produced and assembled is a fairly straight forward task in my corner of AMERICA.

 

look for memcal threads under my username, there is alot of info, regarding the resnet chips and the knock circuitry.

for the knock detection circuitry, if you are handy with digital programming microcontrollers, you could use an intersil part that is most likely what is used in current pcm's. I can't recall the part number, but I have posted it.

the most valuable thread is quite recent, within a few months, title included 730 749 and memcal, but I don't recall the exact thread.

I've built memcal boards using discrete resistors and sockets, with no knock circuitry. I still have some left.

the reason they are so expensive is that they have been discontinued for quite some time now, it's a matter of supply and demand. I haven't had the time to design anything that used the knock circuit, plus it seems that the demand for new memcals and older stuff has quite died down lately. some are already built/content and don't need anything, others have moved on to the newer pcm's and don't need a memcal any longer

 

Dave W, Is it the '165 ECM you're needing to deal with? It looks like that link you have will get you there as long as your measured values MATCH that chart. The 7730 ECM calpak has the scarey ESC circuit riding over the net-res chips. I think that the tools needed to reverse engineer that sucker would cost half as much as the lawyers you'd need for defending yourself for accomplishing it! I think there are about 30-40 little packages on the top side. If some of the chips are the custom, multi-pin, un-numbered type.. I think it would be hard to reverse and in fact if you DID accomplish it, you wouldn't have far to go to create an inexpensive standalone ESC system with knock protection! something hot-rodders would go GAGA over I bet.

For the '165, you'll still have to find some boneyard V6 donors for the plastic parts unless you want to use the ol ribbon-cable method.

Geeze.. one of those links leads to a place I wrote a geeky article in '97 and it's still there. I haven't read it since 2000.. still interesting stuff today... too bad some of the things we're into just has the wrong effect on da chicks ha ha

JWSCAB, How do I get one of your pieces? sounds cool! Are yours for '730 and are there different options for the different resnet types?

PS - Here is the thread I beleive JWSCAB is talking about:

techboard/diy-prom/447242-730-727-749-memcal.html

 

Thanks jwscab and 92Z-666,
I'm looking for 730 information, and the information posted is very useful. I'm new to 165 /730 TPI's, but have moderate experience with 7747 TBI's. I think for now...I'll go a with a used Memcal a Moates.net adapter board, and program my own prom. Seems I might have over-estimated the interest in a DIY Memcal board.

 

eh, I don't really know if you've overestimated the demand, maybe if you had something affordable people would buy it. I just don't know. I never finished it becuase I didn't have extra cash to burn through buidling multiple units that might just sit around and never get sold....

92z-666, shoot me a PM, I'll give ya the details. the memcals I built I already assembled with V8 resistor values, becuase I figured those would be in highest demand. I'm not asking alot for them, basically recoup the money spent to build them, plus a few bucks for the effort.

it should be easy enough to build your own knock circuit with the intersil part, not necessarily inside the memcal, per se, you could build a little black box. would be a nice neat project, and since the part is fully programmable, it could work for just about anything.

 

This was the thread with some good info,
https://www.thirdgen.org/forums/diy-...49-memcal.html

I'm still interested in finding what resistors to change to eliminate excess fuel on Limp mode. With bigger injectors and high fuel pressure it fouls plugs pretty quick when there is a problem.
like everything else... No time to play with it much.

 

For now, I'm mostly interested in learning how to program a prom for a '730. I'm mostly been involved with 4x4 engines / TBI tuning...that why I have moderate '7747 experience. Currently I'm focused on retro fitting a late model MPFI 454 (1999) system to '730. I've been considering a ‘730 using a PROMinator, but with '730 V8 memcal prices being so expensive a Dyamic EFI ECM is looking cost competitive to the ‘730 option.

Maybe the PROMinator will evolve into a 'plug - n - play' single board that will incorporate the resistor pack? What I'd really like to have is an underhood '727 that I can tune like a PROMinator or Dyamic EFI, and still be weather resistant. We all know the deal...if you can't purchase what you want...DIY.

 

at one point, I remember a post from Grumpy that talked about changing the resistor values, now, I think it was on diy.efi.org, on one of the old posting in the archives, and probably for a GN or '747 ecm. I wish I remember when it was. There might be some info on here too, but again, like ya said, if there was more time......

when i first played with the board, I tried to see if there were any RC oscillator circuits made of the resistors, since if it was a true analog circuit, those would be parts of op amps and comparators, etc, I would expect to see voltages or triangle waves or something. All i really saw were static voltages, so I didn't get a chance to dig any deeper.