DIY_EFI Digest Thursday, September 9 1999 Volume 04 : Number 515 In this issue: RE: O2 Sensor Voltage Modified PCM code to change RAM????? Modified PCM code to change RAM????? Re:Sequential Injection overlap? Re: Sequential Injection injector overlap? See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- Date: Thu, 9 Sep 1999 12:55:51 +0200 From: Putter C Subject: RE: O2 Sensor Voltage Remember that the O2 sensor has no driving capability, so you cannot put an resistive voltage devider on it. (As far as my knowledge reaches) So I suggest an OP-amp with an "Infinite" input impedance (Voltage folower) with the resistive devider after that. Carlo Putter Stellenbosch South Africa Date: Tue, 07 Sep 1999 22:12:46 -0500 From: Tom Sharpe Subject: O2 Sensor Voltage Group, I made a 10 LED O2 display which worked fairly well but was hard to read as I used assorted LEDs, etc. and it flashed a lot. I built another using an LCD display from a cheap meter (0-200 mv), a 9v power supply (7809 chip etc.) and a 1/10 voltage divider (set of 1/4w resistors). It works from a 12V power supply and a 1.5V battery -- reads .1593 volts It has 4 wires - sensor in, sensor ground, +12 and ground. I wired it to my efi harness - replaced the LED display. I used a common ground (same as the LED one). The meter displays 1 indicating the voltage is greater than scale (> 2 volts). My volt meter shows +14v (ok here) and .4-.7 v on the O2 sensor (engine running). What's wrong? I thought O2 sensors read 0-1V. Is the meter too sensitive? Am I getting feedback somewhere? Do I need another ground? HELP!!! TIA. Tom ------------------------------ Date: Thu, 09 Sep 1999 08:47:30 -0400 From: Dave Hempstead Subject: Modified PCM code to change RAM????? Hi, I remember awhile back someone had changed their PCM code, to allow them to modify RAM variables via ALDL. I think they modified the Mode 4 command. If you are still out there, could you send me the mods you made in the code. I remember they were not too complex, and I'd like to do something similar to my 95 LT1 PCM. (I want to continue my reverse engineering of my PCM, and want to be able to modify ram on my bench setup, while running) Thanks, Dave Hempstead dave_hempstead@xxx.com ------------------------------ Date: Thu, 09 Sep 1999 08:47:30 -0400 From: Dave Hempstead Subject: Modified PCM code to change RAM????? Hi, I remember awhile back someone had changed their PCM code, to allow them to modify RAM variables via ALDL. I think they modified the Mode 4 command. If you are still out there, could you send me the mods you made in the code. I remember they were not too complex, and I'd like to do something similar to my 95 LT1 PCM. (I want to continue my reverse engineering of my PCM, and want to be able to modify ram on my bench setup, while running) Thanks, Dave Hempstead dave_hempstead@xxx.com ------------------------------ Date: Thu, 09 Sep 1999 09:29:23 -0400 From: Kihurani Gakuu Subject: Re:Sequential Injection overlap? >Date: Wed, 8 Sep 1999 19:36:34 EDT >From: PHXSYS@xxx.com >Subject: Sequential Injection injector overlap? > >Hi > >I was wondering if anyone knows if the injector pulse widths overlap on >sequential injection. The application is a Chrysler 3.3 v-6, 97 model year, >but I am sure GM is similar. What I mean by overlap is, say injector 1 has >fired, is it possible (or likely) for the next injector to fire while the >previous injector is still on? > >Thanks >Jon I think it is likely. From the standpoint of a 4 cylinder engine, there would be an injection every 180 degrees of crankshaft rotation. At 6000 RPM an injector fires every 5 milliseconds. If the injector pulsewidth is greater than 5 ms, then it's safe to assume that there will be an overlap. I guess what I'm saying is that it depends on the RPM and the injector pulse width. Kih ------------------------------ Date: Thu, 9 Sep 1999 07:29:46 -0700 From: "John Dammeyer" Subject: Re: Sequential Injection injector overlap? >Date: Wed, 8 Sep 1999 19:36:34 EDT >From: PHXSYS@xxx.com >Subject: Sequential Injection injector overlap? > >Hi > >I was wondering if anyone knows if the injector pulse widths overlap on >sequential injection. The application is a Chrysler 3.3 v-6, 97 model year, >but I am sure GM is similar. What I mean by overlap is, say injector 1 has >fired, is it possible (or likely) for the next injector to fire while the >previous injector is still on? > >Thanks > >Jon Yes. ....... OK. I'll elaborate. ;-) Basic rules for injector selection are as small as possible in order to be able to accurately meter out the tiny quantities needed at idle. Otherwise you may find that the injector has been asked to open, then close before the pintle barely even moves off the seat. You can assume that an injector needs at least 1ms as a minimum pulse width. If the injector is too large idle will be rough and erratic. Down side of this is that the injector must then open before the intake valve opens in order to supply enough fuel and at full RPM the injector may be open for 80% of an engine cycle. ie: at 6500RPM (18ms) it could be open for 14ms so it actually turns on during or at the end of the the power stroke of the cylinder. Because each cylinder in a 4 cyl engine has a power stroke the injectors do indeed overlap and you might have 3 of them on at the same time at high revs. There are all sorts of tricks you can use to get around this rough idle. An extra throttle body injector for idle speeds is one. A dual set of injectors, 1 small and the other big much like the two barrel carburetor. Honda, in order to have a smooth idle and raw power at the top end uses a 14lb/hr injector for their 1600cc VTEC engines. They have a smooth idle because the CAM is mild mild mild until 4000RPM at which point the VTEC solenoid is activated and the intake profile goes to HOT HOT HOT. Even so, the 125HP engine can just barely make rated horsepower with 14lb/hr injectors and about an 88% duty cycle. In other words I don't believe the engine in the street configuration is rated for sustained full power at the top RPM without overheating the injectors. But it does run continuously at peak torque RPM of 5200RPM with about 50% injector duty cycle. Regards, John Dammeyer ------------------------------ End of DIY_EFI Digest V4 #515 ***************************** 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".