An ECM Bench My purpose in building this is to be able to verify various addresses in gm ecms. So absolute engine simulation isn’t necessary, but I’ve tried to get resonably close so I don’t have to disable all the malfunction flags. Also, cheap is the big word here. Nothing more then a couple bucks other than the diagnostic stuff. For the first few months, I used a scanner just fine, the Diacom, was completely optional, with everything fixed, and steady, there is no real big gain, other than being able to watch a couple things at once. You’ll also, notice a cheap dwell meter, that was just replaced yesterday with the PC scope. This bench can, be done very cheap. I had a total of $75 in the first draft. That included a OTC 2000 that I got for $20 used from a chev store, and $23 for the dwell meter. The only clever stuff is from the list, I from time to time asked the same question, but from different view points, to get new ideas about how to do something. For loads on the output, the C-3, and P-4s don’t seem too do any current monitoring, so for injectors, radiator fan relay, EGR, Charcoal canister, TCC, IAC, I just use a 1K resistor, and a LED. On some later ecms using a 100 ohm resistor should work. While the IAC LED might seem like a waste of time, it is interesting to watch. Watching it park after engine off, just fasinates me. The ecm wants to see, three “pulse” type inputs. Ignition VSS Vehicle speed sensor. O2 (it’s, analog, kinda sine, in the real world, but the ecm doesn’t care, so long as has the right signature) And in some cases a MAF signal that is also pulse, but may be voltage. I have yet to do any actual MAF calibration experiments, but can offer this. On the 86-87 buick GN turbo engines the MAF is 50% duty cycle, 5v (30-130 Hz). Then there are some resistor type loads. They would be the, CTS, and, IAT. Then there are several voltage, the TPS, and MAP (where used). The hardest thing to do, is the feedback O2. I don’t have a final solution for that, but by using the ignition coil signal as a trigger for a 555 (adjustable for “on” time), you can generate enough feeback to keep a cross count running, and not have the ecm get to dumb, or set any codes. To get a .9v regulated signal I ran the 555 output to a 1K resistor, then a LED, a LED has about a 1.8v drop across it. So two 10K resistors across that give you a voltage divider of 2, and an output of .9v.. Now, there are several things you can do to make life easier on yourself. ie avoiding trouble code. Have a master power on for all the 12v stuff, so if smoke starts you can kill the bench. For me it’s using a alligator clip for the battery connection. Then each ecm’s power switch is fused. There is an ignition on power switch, so I can turn off the ecm, and keep any stored codes. Then for an ignition run, and MAF run I used a double pole double Throw switch, some ecms look at the MAP between power on and Crank so you need to run a voltage divider pair of resistors, for the MAP in the ignition off, posistion. Then when on the ignition pulses go to the Module, and voltage switches to a pot for varing the MAF signal in the Run posistion. Next switch is also a DPDT, and that is for the neutral safety, and VSS Inputs. Now, rather than look for specific pulses widths and make things to darn Complicated I just run the ignition pulse generator threw a flip flop to Give everything a 50% duty cycle. So far that has worked out OK for Both the optical and meagnetic VSS. If your using Diacom, might as well just wire up two ALDLs, and a Second ecm harness, that way doing the 160 baud stuff ain’t too hateful. If you have any idea of never doing other than one ecm, might as well Forget that. Once, ya play with one you’ll want to do more. While mine looks like a confused birds’ nest, it’s been threw 4 serious revisions. Now, I have the injectors, permentaly wired into place, and tie wrapped too the board. You might have noticed there are 16 injectors, two groups of 8, so that I can load the ecms any way I want or run two atta time. That tier (2nd level) is for the chargers for the laptops, and their batteries. The battery is down low, and the is also a “Power Strip” for the chargers. The jury is still out on a 3rd laptop, I might try one for the emulator, or just share it with the PC Scope. If you look close you’ll see how I’ve got the ZIFs on a memcal. Two Styles of memcal, one with 4th chip, and one for just the 3 chips. If your speedo is of the magnetic type then you need to put a .01 mfd Cap in series with the + side of the VSS. If optical then the 50% works fine. Now in diferent ecms they use different pull up/pull down resistors, For the resistive loads. So for that reason I ran tandem pots for the TPS IAT, CTS, MAP. Then I incorporated a “normal” max value and min., Value. So like the TPS, min is .55, and max 4.85v and so far I have yet to set a code. To better explain this: The pot has three terminals. The two ends of the resistor, and the slider, on both ends of the resistor, I placed another resistor so that at 100% TPS was 4.6v, and 0% was .55v. Same thing with the MAP. Since the internal pull ups/downs vary I didn’t record any specfic values. On the MAP I set the resistances so that max MAP was 99%, and min Is like 15 K/Pa. On some calibrations, when the ecm applies the EGR, the ecm expects to see a MAP change, or richness, so just wire in a 4066 with a comparator on the MAF line to increase the MAF signal slightly. Stated another way. When a voltage appears for the EGR, it’s used to trigger a 4066, and that in turn, applies a new voltage divider to raise the MAP voltage. List of materials: Garden Tractor Battery Trickle charger 6’ of lamp cord two ATC fuse holders 4- 10K Pots 2- pots for VSS + RPM controls 2- 555s, +misc resistors/caps 4-On/Off switches 4-DPDT switches 16 misc saturated injectors couple dozen LEDs + 1K resistors misc 1-4.7-10-22-100K+-1M resistors ZIFs+Memcals as needed Have John Flagg GMP Parts Co phone number handy (916) 685-1055 (he has ecm weatherpack stuff, at reasonable prices) Heatshrink tubing. Mug holder hooks for using rubber bands to hold things in place and remove easily 1x2’ sheet of veneer/plywood 2x3’ “ “ 4-L Brackets Misc wood screws You can get by with a DVM, and Dwell meter for intial testing. But, a scanner is very worth while. Diacom best. Using a dwell meter in conjunction with the scanner gets you two items to read for some things. Cheers Bruce