Miata Turbo Forum - Boost cars, acquire cats. - Req

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- - Req_fuel & low z injector help (https://www.miataturbo.net/megasquirt-18/req_fuel-low-z-injector-help-12889/)

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??

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."

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.

You have a 450cc engine in your miata? You need to use 14.7 not 14.0.

450cc per cylinder?? And the manual says to use 14....

does this look right?

Attachment 215805

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.

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.

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.

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

Attachment 215804

Please let me know what you think....I obviously suck at this part....

spark angle 22.4?? rpm 2076??? and it was at about 13:1 a/f....

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)

Tune your fuel so you idle more at more like 13.8. Check your idle speed it could be too high.

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.

Also have you syncronized you timing?

how do you synchronize the timing and what does it do? Also the high idle was a blown vacuum line.

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...

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??

Quote:

Originally Posted by kylelind (Post 156888)

Earths....

Yep-- grounds, but you wouldn't have had the problem without those low-z injectors. They sink ALOT more current to ground due to the low resistance coils, and all of that has to go through the ECU, and on to somewhere. The stock wiring harness just wasn't meant to deal with this-- it was setup to deal with hign-z injectors.

You can add additional grounds to the MSPNP MM9495. There is one that's easy to add on the middle connector. Pin 15. If you still have the problem you'll need to open the box and add more using the top row of extra unused pins on the middle connector. The easy one would be a quick jumper wire over to the ground pad in the breakout area... that would add a second one easily.

It's important that these extra grounds be run back to the same spot on the engine that the factory ECU grounds go to-- on the 94/95 cars this is a bracket just under and to the right of the TB. There's a picture of it in the MSPNP manual.

I suspected this would happen with lo-z injectors on the factory harness... and that's why the manual called for caution using them and recommends Hi-z injectors. It's also why some other PNP EMS's for Miata's aren't PNP really, but right from the start they have you run all new grounds, they know the factory ones are just adequate and become inadequate if you do something like this.

BTW-- good news on the middle connectors, I've got them and we're getting ready to send them out by early next week....

Quote:

Originally Posted by FoundSoul (Post 157045)

BTW-- good news on the middle connectors, I've got them and we're getting ready to send them out by early next week....

Great news. I just wish it had been this week, so I could play with EBC this Saturday while the wife is out of town.

Ben I'll drop by DIY tomorrow and pick up yours. If that's OK with Jerry, that is. Jerry, I know you've got a lot going on, plus you have to play catch up from your vacation.

I did run one ground from one of the center connector pins, bottom row 7 from the left 2 from the right. I ran that to the stock block location by splicing into the wire I ran from the battery to the ecu block ground. So other than that I need to open the MS up and solder more in?? What about just splicing into the ground wire in the stock harness and running that to the battery or block?

Also, should I not be running the car with the bad grounds?

Typically it won't cause any lasting problems, though theoretically it can damage the voltage regulator. I've seen one case (on a full race car, non-MSPNP) where I believe this happened.

The ground I did run is only like 16 guage, is that big enough?

I increased me low rpm low kPa AFRs and now it is not cutting out. I also feel like the ambient temp being colder in morning and night helps?? We will see if it stays away.

So this will not blow up my engine if I am in boost and it cuts out real quick? AKA, should I got to the track if it happens at all??

Quote:

Originally Posted by kylelind (Post 157343)

I increased me low rpm low kPa AFRs and now it is not cutting out.

Decreased fuel helped?

Quote:

Originally Posted by Atlanta93LE (Post 157346)

Decreased fuel helped?

I think he meant richened it up, but year increasing the AFR would be to lean it out.

unless it was that rich it was washing out the spark?

I don't suggest taking your car to the track if it's misfiring. That would be like having sex with a half baked hardon. I don't know exactly what conditions your car goes into when it misfires but it could be bad for the motor if you're hammering on it.

Quote:

Originally Posted by kylelind (Post 157343)

I would sort it out as a top priority-- typically when I've seen this symptom it tends to happen under light cruise most frequently and not so much under heavy load, but if it did occur under heavy load/boost it could have unpredictable results. Extra grounds will be required to sort it out, and as with anything like this, I wouldn't drive the car crazy hard until it's right.

It's not hard to add another ground, quick jumper wire from the GND pad on the breakout area over to one of the pads on the 8-pin header which come out to the middle connector. That would be a good start. You could probably do that without even pulling the PCB out.

FYI-- on the 96/97 cars the factory only provided 3 grounds on the stock harness, instead of the 5 on the 94/95 cars. Weird. We're adding 3 extra grounds on the middle connector by default, and making 3 more very easy to jumper in for a total of 6 extra if needed.

Are there pics or a write-up somewhere of where the GND pad is?? I am not familiar with the board at all. Also what guage and material wire should I run for the grounds?

Ok. I'd make a jumper from these holes with 14-16 gauge wire:

http://www.megasquirtpnp.com/images/.../GNDjumper.jpg

Then run it out this pin, with 12-14 gauge wire:

http://www.megasquirtpnp.com/images/mm9495/conpin.jpg

I think on mine, we took it a step further and in addition to the pictured mod we soldered a wire on a ground pin on the main board to a second header pin on the daughterboard. We then ran 2 additional ground wires from the middle plug to the head. Might even have even been 3. The ground pin on the main board is VERY obvious and labeled, as is the ground pin on the daughterboard.

Jerry said something like, "I don't want to ever hear about ground problems in your car again." :)
And well, I don't think I have ground problems anymore. Friggin car is running GREAT. :D

Thank you very much matt and ben....looks easy!!

So I soldered in the extra ground totaling two extras and was still having VERY RANDOM cutout issues. Some days it is horrible, some none at all. Yesterday at the track it seemed to run best when hot. I could go WOT toward the end of a session with no cutout. Before I got on the track it was running pretty well and it seemed like richening the AFRs helped......dont know what is up. It was fun pulling 10psi on the track though.

Also when driving home for 4.5 hours it was running great and then when I hooked the computer up and changed the fan output settings while my wife drove it started to cutout like crazy......WHAT THE HECK?

It is just so random that I have no idea whether it is the tune or the injectors?

Quote:

Originally Posted by cjernigan (Post 156328)

to defend Kylelind the manaul that came on the CD with the 94/95 MSPNP says "14.0". It made little sense to me so I put 14.7 the following times I set it up(after firmware or injector change)

When you change the injector size, MegaSquirt can handle most of the adjustments with just one variable, REQ_FUEL, which sets the base pulse width. MegaTune can calculate this value automatically if you click the Required Fuel button on the Engine Constants page, where you just need to enter your engine size and injector size, as well as 14.0 for the air/fuel ratio. Using that A/F ratio will reduce the amount of tuning needed when you change injectors significantly as that’s what was used for the req_fuel calculation on the base map with stock injectors.

Quote:

Originally Posted by kylelind (Post 159659)

Anyone have any ideas?? FoundSoul???

It's the injectors. Put your stockers in or put a resistor pack on and see if it goes away.

https://www.miataturbo.net/megasquirt-18/so-close-two-last-problems-my-way-3702/