DIY_EFI Digest Sunday, December 5 1999 Volume 04 : Number 677 In this issue: Re: Ref. Signal off of AMC I6 mem-cal Add-on systems which affect output pulse width? See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- Date: Sun, 05 Dec 1999 09:32:45 -0500 From: Shannen Durphey Subject: Re: Ref. Signal off of AMC I6 > > Date: Sun, 5 Dec 1999 00:56:23 -0500 (EST) > From: Mike Comai > Subject: Ref. Signal off of AMC I6 > > I am currently trying to get my first major retrofit up and running. I > have everything installed and when I try to start it the injector's don't > fire. I was told that I need a filter on the negative side of the coil > and to feed the filtered signal into the Reference line on the ECM (which > I am using a '747). I was given a design for a filter which looks like > this: > 5K 10K > Coil -----/\/\/\/---------/\/\/\/\------------ ECM > | | > ----- ----- > ----- 15uf -----100pf > | | > gnd gnd > >From a mechanic's point of view, (and because there's little other info to work with) why haven't you adapted a GM ignition module to the AMC dizzy? The voltage on the negative side of the coil "bounces" after the plug fires, and your ecm may be getting what it thinks are several reference pulses when it should get one. 'Course this is a rough guess.... you might try to get a scan tool and watch rpm readings during cranking to verify this. Another possibility is that everything is ok but your calibration is wrong, or your injectors are wrong, or the coil isn't firing because the reference line is grounding out the signal from the dizzy. Also, if you're running the reference line from the distributor, do you have the est line connected? Where? One of the great benefits of using an ecm is computer controlled spark. Without it, you're not realizing the full potential of your project. Shannen > When the filter is in place, the injector don't fire. When I remove the > filter and connect the coil directly to the ecm it appears to flood out > the engine :( If someone could explain what voltages levels and shapes are > present on the neg. side of the coil and what it needs to get conditioned > to for the ECM that would be great too. Appreciate any help yall could > give. > > Mike Comai > '79 CJ5 > > ------------------------------ > > End of DIY_EFI Digest V4 #676 > ***************************** > > To subscribe to DIY_EFI-Digest, send the command: > > subscribe diy_efi-digest > > in the body of a message to "Majordomo@xxx. > > A non-digest (direct mail) version of this list is also available; to > subscribe to that instead, replace "diy_efi-digest" in the command > above with "diy_efi". ------------------------------ Date: Sun, 5 Dec 1999 10:33:21 -0700 From: cwagner@xxx.net Subject: mem-cal Does anyone have any sugestions on what memcal I could get for running a 4 cyl engine using a 747 computer? Or could I make one out of some spare resistors. ------------------------------ Date: Sun, 05 Dec 1999 11:43:02 -0800 From: "Andrew Brownsword" Subject: Add-on systems which affect output pulse width? Hello again, After posting my project description yesterday I spent some time surfing the web for add-on computers. All the systems I have seen so far seem to work their magic by modifying the airflow meter's voltage input to the ECU. The ECU is then relied on to "do the right thing". It seems to me that this could be problematic if the ECU was designed to expect a particular voltage range and the stock airflow meter generated that full range ... in other words there is no buffer for going beyond the expected range of values. This seems fairly reasonable for an N/A engine since it is extremely unlikely that the car will have to deal with >1 atmosphere. It seems pretty obvious that most add-on computers are designed to modify input because it is easy. The computer reads one voltage, maps it through a table, and outputs another voltage. The alternative is to modify the ECU's output, which is a time dependant pulse width. It simply isn't possible to have full remapping control over the output because by the time you know what the pulse width is, the time at which you have to send it to the injectors has passed. It occurred to me this morning, however, that an add-on computer could fairly easily extend (not shorten) the pulse width based on input from a pressure sensor. It would read its own MAP sensor to determine the amount of "extra" fuel needed beyond the amount the stock ECU has calculated (being tuned for where the ECU's airflow meter saturates), detect the trailing edge of the ECU's pulse, and keep the pulse going for that extra time. So am I off my rocker here? Is this possible? Has anybody built a product which does this? Is this even an issue, or does a stock ECU program ALWAYS allow enough buffer that input modification is a better approach? I hope I'm not reiterating common questions or wandering too far from the list charter -- I haven't seen a FAQ for this list yet, so please bear with me. And if there is a FAQ, you somebody point me at it? Cheers, Andrew ------------------------------ End of DIY_EFI Digest V4 #677 ***************************** To subscribe to DIY_EFI-Digest, send the command: subscribe diy_efi-digest in the body of a message to "Majordomo@xxx. A non-digest (direct mail) version of this list is also available; to subscribe to that instead, replace "diy_efi-digest" in the command above with "diy_efi".