Req_fuel & low z injector help - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 09-27-2007, 04:35 PM   #21
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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.
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Old 09-27-2007, 04:36 PM   #22
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BTW-- good news on the middle connectors, I've got them and we're getting ready to send them out by early next week....
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Old 09-27-2007, 04:55 PM   #23
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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.
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Old 09-27-2007, 04:59 PM   #24
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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.
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Old 09-27-2007, 05:28 PM   #25
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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?
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Old 09-27-2007, 06:48 PM   #26
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Also, should I not be running the car with the bad grounds?
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Old 09-27-2007, 11:27 PM   #27
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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.
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Old 09-27-2007, 11:32 PM   #28
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The ground I did run is only like 16 guage, is that big enough?
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Old 09-28-2007, 11:59 AM   #29
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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??
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Old 09-28-2007, 12:17 PM   #30
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I increased me low rpm low kPa AFRs and now it is not cutting out.
Decreased fuel helped?
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Old 09-28-2007, 12:38 PM   #31
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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?
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Old 09-28-2007, 12:42 PM   #32
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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.
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Old 09-28-2007, 12:45 PM   #33
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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??

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.
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Old 09-28-2007, 12:52 PM   #34
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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?
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Old 09-28-2007, 03:06 PM   #35
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Ok. I'd make a jumper from these holes with 14-16 gauge wire:



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

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Old 09-28-2007, 03:13 PM   #36
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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.
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Old 09-28-2007, 07:52 PM   #37
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Thank you very much matt and ben....looks easy!!
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Old 10-04-2007, 11:05 PM   #38
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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?
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Old 10-04-2007, 11:44 PM   #39
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Quote:
Originally Posted by cjernigan View Post
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.
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.
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Old 10-05-2007, 05:13 PM   #40
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Originally Posted by kylelind View Post
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?
Anyone have any ideas?? FoundSoul???
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