 Stock 914 Fuel Injection Pulse Widths |
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| JeffBowlsby |
 Jun 22 2005, 10:02 PM
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#1
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914 Wiring Harnesses  Group: Members Posts: 8,485 Joined: 7-January 03 From: San Ramon CA Member No.: 104 Region Association: None 
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I stumbled on this chart of pulse widths courtesy of Brad Anders...Hopefully it is a starting point for anyone tuning an aftermarket FI ECU who also use stock injectors and fuel pressure.
0.1ms resolution is necessary. The charts give data for PW based on manifold vacuum and RPM. Stock 914 FI pulse widths |
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| McMark |
Jun 22 2005, 11:39 PM
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#2
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914 Freak! Group: Retired Admin Posts: 20,179 Joined: 13-March 03 From: Grand Rapids, MI Member No.: 419 Region Association: None |
Thanks, Jeff. I'll compare it next time I'm tuning. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)
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| SLKWrx |
Jun 23 2005, 06:59 AM
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#3
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Member Group: Members Posts: 317 Joined: 28-September 04 From: Woolwich, NJ Member No.: 2,845 Region Association: North East States
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I really wish I understood this stuff. Anyone have a page that helps explain how all this works?
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| lapuwali |
Jun 23 2005, 08:54 AM
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#4
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Not another one! Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743  |
A web page, no, but an excellent introduction to how ALL electronic fuel injection systems work is Bosch Fuel Injection and Engine Management, Charles O. Probst, Bentley Publishers. He covers all of the major flavors of Bosch fuel injection, including those used on the 914 (D-Jet for most, L-Jet for the US 1.8). Highly recommended. Very briefly, the pulsewidths are the length of time the injectors are held open. The injectors are simply valves, the injection is done by holding the fuel pressure on one side of the injector fairly high (usually about 2-3 Bar, or 30-45psi), and simply opening the valve into the intake manifold, where the pressure is relatively low (0.3-0.9 Bar). Holding the injectors open longer sprays in more fuel, thus enrichening the mixture. So, you can control mixture across a wide range by just changing the pulsewidth from short (lean) to long (rich). |
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| Mueller |
Jun 23 2005, 09:02 AM
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#5
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914 Freak! Group: Members Posts: 17,146 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None
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this page explains it somewhat...you can ignore most of the math.....there is a little program on the page that allows you to plug in different variables and you can see the changes with different numbers...that might help
how Megasquirt works (basic EFI) |
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| TravisNeff |
Jun 23 2005, 10:17 AM
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#6
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914 Guru Group: Members Posts: 5,082 Joined: 20-March 03 From: Mesa, AZ Member No.: 447 Region Association: Southwest Region
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Hey that'd be one of my MPS in the chart, forgot about that. Brad is a good guy, he came over with his testers n' stuff and fixed a couple things on my 2.0 car. that saved me a ton of time and in the end probably a ton of money.
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| lapuwali |
Jun 23 2005, 11:51 AM
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#7
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Not another one! Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743 |
Interesting bits of trivia here: the shortest pulsewidth is 2.3ms, which is longer than I've seen some settings shown here, even for smaller injectors. The longest duty cycle is 73%, which is well under the usual 80% ceiling noted for most injectors.
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