Here's the deal. I need to find out how to change the pulse width of the injectors, i.e. add more fuel. GM issued a TSB for my car to replace the injectors with ones that "flow richer at a low pulse width".. and they cost $700. I am looking to just up the fuel flow at "low pulse widths"... I realize I could perhaps change the VE table at low rpm/low map, but wouldnt the computer over time realize that, and change it back to a 14.6 A/F ratio? How can I do it without the computer compensating?
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11:45 AM
PFF
System Bot
Maetrix66 Member
Posts: 621 From: Hartland, ME, USA Registered: Nov 2002
I haven't gotten my AutoProm yet, so I haven't had a chance to play with this. I do know where you can find the answer. Go to www.60degreev6.com, and post in the computer tuning section, put the name "Mechanic" in the subject so he sees it. He may be in here, since he has a tuboed 3100 in his 88 fiero, but I don't know his handle here. He wrote (or co-wrote) GMPCM, so I am sure he could answer your question.
why do have to do this in the ECM? most people get more fuel by either raising the fuel pressure, or using higher flow injectors. both of which are much cheaper than $700. Is this a Fiero or some other car?
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04:57 PM
ryan.hess Member
Posts: 20784 From: Orlando, FL Registered: Dec 2002
why do have to do this in the ECM? most people get more fuel by either raising the fuel pressure, or using higher flow injectors. both of which are much cheaper than $700. Is this a Fiero or some other car?
As far as I know, doing either of these will work until the ECM "relearns" the engine... Also, raising the FP and/or using high flow injectors makes it rich across the whole board. I was looking for specifically raising 500rpm - 1500rpm *only*. Edit: 3.4 DOHC engine... also, I may have found the problem. Fixing the symptoms would have helped, but fixing the root of it all is better long term. Keep you posted.
[This message has been edited by ryan.hess (edited 02-24-2004).]
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05:58 PM
Raydar Member
Posts: 40686 From: Carrollton GA. Out in the... country. Registered: Oct 1999
Here's the deal. I need to find out how to change the pulse width of the injectors, i.e. add more fuel. GM issued a TSB for my car to replace the injectors with ones that "flow richer at a low pulse width".. and they cost $700. I am looking to just up the fuel flow at "low pulse widths"...
Not sure if this will be useful or not... I have heard that, in Fieros, disc type injectors, even with the same lb/hr rating, will tend to flow more than pintle type injectors at low pulse widths; i.e., at idle. This was because the disc type injectors respond much more quickly to the pulse than the pintle type, resulting in a longer effective "on" time. This was actually given as a drawback to using disc type injectors in Fieros. Was supposed to cause a hunting idle because of the increased flow.
------------------ Raydar 88 3.4 coupe.
Coming soon... 88 Formula, presently under the knife.
[This message has been edited by Raydar (edited 02-24-2004).]
Get an SAFC and you can tune many rpms not just low ones. It will work on your car. ebay price aruond $200 for them and have many different parameters to adjust to change injector pulsewidth
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newbie extreme
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10:43 PM
Feb 25th, 2004
Pyrthian Member
Posts: 29569 From: Detroit, MI Registered: Jul 2002
the "pulse width" is not a set number that applies to all RPM's. the ECM learns the fuel requirements for different RPM's, I think at 200 rpm steps, and constantly adjusts by O2 readings. Are you saying you want the motor running rich at idle? Is this to keep a turbo spooled up more?
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08:47 AM
ryan.hess Member
Posts: 20784 From: Orlando, FL Registered: Dec 2002
the "pulse width" is not a set number that applies to all RPM's. the ECM learns the fuel requirements for different RPM's, I think at 200 rpm steps, and constantly adjusts by O2 readings. Are you saying you want the motor running rich at idle? Is this to keep a turbo spooled up more?
No, it's to prevent it from stalling. GM determined that under low RPM/ high load conditions, that the 3.4 DOHC needs more fuel to keep from stalling. Hence, they put out some $120 injectors (x6) in a service bulletin. I'm trying to figure out how I can bypass that expense... Tuning the ECM seemed the logical choice, but I'm open to other options, including keeping it in open loop if necessary (it never stalls in OL)....