Req_fuel & low z injector help - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


MEGAsquirt A place to collectively sort out this megasquirt gizmo

Reply
 
 
 
LinkBack Thread Tools
Old 09-26-2007, 12:31 AM   #1
Junior Member
Thread Starter
 
Join Date: May 2007
Location: Mountain View, CA
Posts: 220
Total Cats: 0
Default Req_fuel & low z injector help

I am trying to do the req_fuel calc right now and am inputting 450cc displacement, 440cc/min injector, and 14.0 afr. Is this correct?? It gives me 7.1 as my req_fuel but then a bunch of errors for the ms, ms/v, ......should I just enter in manually what it says to put if you are not an expert?

Also how do I set it for low z injectors??
kylelind is offline   Reply With Quote
Old 09-26-2007, 12:37 AM   #2
Junior Member
 
Join Date: Nov 2005
Location: Down Under
Posts: 252
Total Cats: 0
Default

Have you read the MS-Extra Manual???

The answers to most of your questions are in there.

Quote:
Setting the PWM Criteria

To tune the PWM [pulse width modulation] values for your engine, you need to know what kind of injectors you have: low impedance or high impedance.

* If you are running high-impedance injectors (greater than 10 Ohms), then set the:
o PWM Time Threshold to 25.4 msec, and the
o PWM Current Limit (%) to 100%.

In essence you are disabling the PWM mode. This allows full voltage to the injectors throughout the pulse widths.

* For low-impedance injectors (less than 3 Ohms), you need to limit the current to avoid over heating the injectors. To do this, there is a period of time that you apply full battery voltage [peak] current, then switch over to a lower current-averaged [hold] current, i.e. peak and hold. Alternatively, you can add resistors in series with the injectors. See the Injectors and Fuel Supply section of this manual for more details.

To run low-impedance injectors with the PWM current limit mode, you need to set two parameters - the "PWM Current Limit (%)" and the "PWM Time Threshold (ms)" - both are on the “Constants” page. The current limit % is the percent duty cycle when the current limit is invoked. The time threshold is the amount of time from when the injector is first opened until the current limit is activated.
Quote:
On the Settings/Constants page:

If you are running high-impedance injectors (greater than 10 Ohms), then set the:

* PWM Time Threshold to 25.5 msec, and the
* PWM Current Limit (%) to 100%.

If you have low impedance injectors (less than 4 Ohms), set the:

* PWM Time Threshold is the time required to open the injector, this is when full power is used to open the injector. Start at 1.0 msec, and
* PWM Current Limit is the Pulse Width thats used after the Time Threshold, this actually pulses the injectors on and off, keeping the injector from over heating at high duty cycles. Try starting at around 75% (30% if you have installed the 'Flyback Board' daughter card or if using a V3.0 pcb with the Flyback components installed).

You will tune these after getting the engine running. See “Setting the PWM Criteria” in this section. Failure to perform these steps can result in damage to your injectors. If you have high-impedance injectors, set these values to 25.5 ms and 100%, and you do not need to tune them further.
Quote:
Required Fuel – (Req_Fuel) this is top field of the Constants window. It has a calculation dialog to help you find an appropriate value. It should contain the injector pulse width, in milliseconds, required to supply the fuel for a single injection event at stoichiometric combustion and 100% volumetric efficiency.
Ensure that the NUMBER of CYLINDERS has been set before using the wizard!

In order to come up with this value, MegaTune provides a calculator that will suffice for 99% of applications (those for which it will not work generally require changes to the MegaSquirt controller code itself, and that is beyond the scope of this manual). To use the wizard, click on the Required Fuel button, and fill in the fields (Engine Displacement, Number of cylinders, Injector flow, and Air:Fuel ratio(14.7), then click 'Okay').

For a 4-stroke, a complete stroke cycle is 720 degrees of crankshaft rotation (i.e. two revolutions); for a 2-stroke, it is 360 degrees (this is also factored in the REQ_FUEL value down loaded to MegaSquirt).

In the tuning software, the upper REQ_FUEL box is the amount per cylinder, as noted above. The lower REQ_FUEL box is the value down loaded to MegaSquirt. It is the REQ_FUEL number on top, but scaled by your selected injection mode (number of squirts and alternate/simultaneous), this can be ignored as it is the upper number thats the important value.

For example, if you inject simultaneous and one injection, and have the same number of injectors as cylinders [i.e. port injection], then REQ_FUEL on the bottom is the same as REQ_FUEL on top. Same with alternate and two squirts. If you put in simultaneous and two squirts, then REQ_FUEL is divided in half - because you squirt twice, you need to inject 1/2 the fuel on each shot.

Note: if you choose alternating for port injection, make sure your number of squirts is an even number (2,4,...) and evenly divisible into the number of cylinders. For example, with an eight cylinder engine, you could use alternating and 2, 4, or 8 squirts/cycle. With a six cylinder, if you choose alternating, you MUST use 2 or 6 squirts/cycle. Also, the only possible combinations for an odd-cylinder count engine are either 1 squirt/simultaneous or N squirt/simultaneous combination, where N is the number of cylinders."
Aussie Driver is offline   Reply With Quote
Old 09-26-2007, 12:44 AM   #3
Junior Member
Thread Starter
 
Join Date: May 2007
Location: Mountain View, CA
Posts: 220
Total Cats: 0
Default

I will look there for pwm but what should me req_fuel and such be?? It does not seem right that I get all of those errors.
kylelind is offline   Reply With Quote
Old 09-26-2007, 12:53 AM   #4
Elite Member
iTrader: (13)
 
cjernigan's Avatar
 
Join Date: Oct 2006
Location: Atlanta, GA
Posts: 8,147
Total Cats: 6
Default

You have a 450cc engine in your miata? You need to use 14.7 not 14.0.
cjernigan is offline   Reply With Quote
Old 09-26-2007, 12:55 AM   #5
Junior Member
Thread Starter
 
Join Date: May 2007
Location: Mountain View, CA
Posts: 220
Total Cats: 0
Default

450cc per cylinder?? And the manual says to use 14....
kylelind is offline   Reply With Quote
Old 09-26-2007, 12:59 AM   #6
Junior Member
Thread Starter
 
Join Date: May 2007
Location: Mountain View, CA
Posts: 220
Total Cats: 0
Default

does this look right?

Name:  engineconstants.jpg
Views: 4
Size:  47.1 KB
kylelind is offline   Reply With Quote
Old 09-26-2007, 01:09 AM   #7
Elite Member
iTrader: (13)
 
cjernigan's Avatar
 
Join Date: Oct 2006
Location: Atlanta, GA
Posts: 8,147
Total Cats: 6
Default

The manual says 14.7 for gasoline, he even posted the quoted manual for you.
"To use the wizard, click on the Required Fuel button, and fill in the fields (Engine Displacement, Number of cylinders, Injector flow, and Air:Fuel ratio(14.7), then click 'Okay')."

You need to ender your full engine displacement which is liek 1850cc not the per cylinder displacement.
cjernigan is offline   Reply With Quote
Old 09-26-2007, 01:12 AM   #8
Junior Member
Thread Starter
 
Join Date: May 2007
Location: Mountain View, CA
Posts: 220
Total Cats: 0
Default

Ok I did that with 1835cc, saw that somewhere, and get 7.0 for req_fuel. Is all that other stuff good? I dot want to blow my engine.
kylelind is offline   Reply With Quote
Old 09-26-2007, 01:15 AM   #9
Elite Member
iTrader: (13)
 
cjernigan's Avatar
 
Join Date: Oct 2006
Location: Atlanta, GA
Posts: 8,147
Total Cats: 6
Default

I just calculated it and got 6.9, 7.0 should be fine. Different engine cc values will make it vary that much I suppose.
If you have a wideband, you have no excuse if you blow your own motor. Long as you use the timing tables DIY provided and tune fuel from rich to lean you should be golden though.

Last edited by cjernigan; 09-26-2007 at 01:40 AM.
cjernigan is offline   Reply With Quote
Old 09-26-2007, 02:05 AM   #10
Junior Member
Thread Starter
 
Join Date: May 2007
Location: Mountain View, CA
Posts: 220
Total Cats: 0
Default

I just got it running but it is idling very high and does not go down when warmed up?? here is a log:

Name:  idlenewinjectorswarm.jpg
Views: 4
Size:  53.5 KB

Please let me know what you think....I obviously suck at this part....
kylelind is offline   Reply With Quote
Old 09-26-2007, 02:06 AM   #11
Junior Member
Thread Starter
 
Join Date: May 2007
Location: Mountain View, CA
Posts: 220
Total Cats: 0
Default

spark angle 22.4?? rpm 2076??? and it was at about 13:1 a/f....
kylelind is offline   Reply With Quote
Old 09-26-2007, 02:46 AM   #12
Junior Member
Thread Starter
 
Join Date: May 2007
Location: Mountain View, CA
Posts: 220
Total Cats: 0
Default

And bye the way, that constants page is incorrect. I had not opened a .msg file so the fields were not automatically filler in.

How do I get the idle to come down? And where should the spark angle and a/f ratio be (14.7 I think)
kylelind is offline   Reply With Quote
Old 09-26-2007, 02:57 AM   #13
Elite Member
iTrader: (13)
 
cjernigan's Avatar
 
Join Date: Oct 2006
Location: Atlanta, GA
Posts: 8,147
Total Cats: 6
Default

Tune your fuel so you idle more at more like 13.8. Check your idle speed it could be too high.
cjernigan is offline   Reply With Quote
Old 09-26-2007, 09:26 AM   #14
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,809
Total Cats: 1,780
Default

give it a little more fuel and then physically turn down you idle on the TB.

make sure the thing is fully warmed, ie +160° coolant.
Braineack is offline   Reply With Quote
Old 09-26-2007, 12:16 PM   #15
Elite Member
iTrader: (5)
 
akaryrye's Avatar
 
Join Date: Jul 2006
Location: Central California
Posts: 2,526
Total Cats: 0
Default

Also have you syncronized you timing?
akaryrye is offline   Reply With Quote
Old 09-26-2007, 08:33 PM   #16
Junior Member
Thread Starter
 
Join Date: May 2007
Location: Mountain View, CA
Posts: 220
Total Cats: 0
Default

how do you synchronize the timing and what does it do? Also the high idle was a blown vacuum line.
kylelind is offline   Reply With Quote
Old 09-26-2007, 09:51 PM   #17
Junior Member
 
Join Date: Nov 2005
Location: Down Under
Posts: 252
Total Cats: 0
Default

Aussie Driver is offline   Reply With Quote
Old 09-26-2007, 10:53 PM   #18
Supporting Vendor
iTrader: (5)
 
Join Date: Jun 2006
Location: Duluth, GA 30097
Posts: 798
Total Cats: 0
Default

Kyle's been in touch with us-- anytime you've made changes to your engine, particularly injectors, and then you start idling this high, first thing you want to check is for a vacuum leak. I checked his datalog and the idle valve is doing everything it can to bring the idle down, it's at the minimum 9dc, but it's still idling around 2000rpm even when fully warmed up. Air is getting in somewhere else. He's noted that there's at least one small leak, I've seen a couple cases though where the injector seals themselves are leaking and that's a common culprit after changing injectors.

Do the injectors all rotate freely or are any of them bound up? They should all rotate fairly easily after the rail is bolted down.


I wouldn't recommend adjusting the idle screw since in his case it was fine before, and should be fine still-- changing it will just be one more variable to get right later, and it's right now-- he's got a massive vacuum leak somewhere...
FoundSoul is offline   Reply With Quote
Old 09-27-2007, 11:44 AM   #19
Junior Member
Thread Starter
 
Join Date: May 2007
Location: Mountain View, CA
Posts: 220
Total Cats: 0
Default

Yeah, when I went to start the car for the first time I primed the pump 3 times because I could hear air bleeding off. The problem was that on the 3rd prime I heard a big bang and a clunk. I had blown a cap off of the #4 intake runner nipple. It was causing my high idle. Plugged it back up and now it is fine. The injectors do rotate freely as well.

My problem now is that I am getting a stumble or very fast cut-out while cruising, where the car jerks and the tach drops. After that it is fine. I have not had time to dig into the cause yet but does anyone have ideas of common causes??
kylelind is offline   Reply With Quote
Old 09-27-2007, 11:58 AM   #20
Elite Member
iTrader: (1)
 
Join Date: Jun 2006
Location: Warrington/Birmingham
Posts: 2,658
Total Cats: 39
Default

Quote:
Originally Posted by kylelind View Post
Yeah, when I went to start the car for the first time I primed the pump 3 times because I could hear air bleeding off. The problem was that on the 3rd prime I heard a big bang and a clunk. I had blown a cap off of the #4 intake runner nipple. It was causing my high idle. Plugged it back up and now it is fine. The injectors do rotate freely as well.

My problem now is that I am getting a stumble or very fast cut-out while cruising, where the car jerks and the tach drops. After that it is fine. I have not had time to dig into the cause yet but does anyone have ideas of common causes??
Earths....
richyvrlimited is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 57 07-19-2017 05:11 PM
Changing from 460cc to flow force 610cc in diypnp 90 Turbo MEGAsquirt 19 10-19-2015 04:23 PM
Going back to stock. Need some 1.6 parts. Trent WTB 2 10-01-2015 01:15 PM
Time to start learning and play with tuning The Gleas MEGAsquirt 3 10-01-2015 10:30 AM
Low oil pressure after 1.8 swap and new turbo setup JesseTheNoob DIY Turbo Discussion 15 09-30-2015 03:44 PM


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 08:27 PM.