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Old 01-25-2008, 09:52 PM   #1
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Default low z injectors not working with mspnp?

the problem:
only injectors 2 and 4 are working and 1 and 3 are dead(no fuel)

the setup: currently running low z 450cc dsm injectors with a honda resistor box and megasquirt pnp 94-95 ecu...
--harness modifacation: the main pos+ injector wire that leads to the ecu(white with red stripe) connects to 4 individual white/red wires connecting to the injectors...however each injector also has its own color coded wire that goes to the ecu(injector controller)...i cut the 4 white/red and wired it into the resistor box and then wired the main white/red wire from the ecu to the resistor box(resistor box has 1 yellow wire and 4 red, thus ecu main pos+ connected to yellow and resistor box red wires to injectors)...clips were also changed with dsm clips...

the situation: I had low z 550cc injectors(rx-7) installed and had the car running for a couple of days and somehow after installing the lc1 wideband(running the ground wire under the injector harness to connect to megasquirts suggested ground) the car started missing...(unplugged stock o2 like megasquirt recommends while connecting the wideband to mspnp)

Diagnose: I checked for spark in all cylinders...results came out postive(spark jumped when grounding)...bogging on cylinders 2 and 4(normal) but not on 1 and 3. I even unplugged each injector and bogging only happens on 2 and 4. I rechecked wire harness and there arent any loose wires. I installed a fresh set of spark plugs and only #2 and #4 had carbon deposits. I also checked volts on each clip with the engine off but ignition on and got 12 volts on both sides of the clip(not normal and should have a volts consisting of 12 and 0)...i unplugged the mspnp and plugged in the stock ecu and got the 12v and 0 on each injector clip...i turned the car on and still the same missing 1 and 3 cylinders...

Questions: Is the mspnp bad?...Is there something im missing to check?...is the harness connection incorrect?
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Old 01-25-2008, 09:58 PM   #2
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Did you set up the injector settings for low-z injectors correctly?
http://www.msextra.com/manuals/MS_Ex...Manual.htm#pwm
Read here about how to setup your low-z injectors settings. Not doing this can cause damage to the injectors.
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Old 01-25-2008, 10:13 PM   #3
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im using a resistor box and no settings need to be changed since voltage will get regulated thru the box...diyautotune also recommended using the resistor box/resistors if going the low z injector route...less hassle with the grounds and the change of settings.
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Old 01-25-2008, 10:26 PM   #4
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I don't know enough about the california cars and the MSPNP to help with how it's wired. Sorry I missed the part about the resistor box. If it changes from 12v on both pins with the MSPNP to 12v and gnd with the stock ECU then I would assume something is a little backwards on the MSNPNP. Unless you've made some irregular modification to the injector harness for the resistor boxes.
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Old 01-26-2008, 11:04 AM   #5
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Quote:
Originally Posted by o.e.boost View Post
the problem:
only injectors 2 and 4 are working and 1 and 3 are dead(no fuel)

the setup: currently running low z 450cc dsm injectors with a honda resistor box and megasquirt pnp 94-95 ecu...
--harness modifacation: the main pos+ injector wire that leads to the ecu(white with red stripe) connects to 4 individual white/red wires connecting to the injectors...however each injector also has its own color coded wire that goes to the ecu(injector controller)...i cut the 4 white/red and wired it into the resistor box and then wired the main white/red wire from the ecu to the resistor box(resistor box has 1 yellow wire and 4 red, thus ecu main pos+ connected to yellow and resistor box red wires to injectors)...clips were also changed with dsm clips...

the situation: I had low z 550cc injectors(rx-7) installed and had the car running for a couple of days and somehow after installing the lc1 wideband(running the ground wire under the injector harness to connect to megasquirts suggested ground) the car started missing...(unplugged stock o2 like megasquirt recommends while connecting the wideband to mspnp)

Diagnose: I checked for spark in all cylinders...results came out postive(spark jumped when grounding)...bogging on cylinders 2 and 4(normal) but not on 1 and 3. I even unplugged each injector and bogging only happens on 2 and 4. I rechecked wire harness and there arent any loose wires. I installed a fresh set of spark plugs and only #2 and #4 had carbon deposits. I also checked volts on each clip with the engine off but ignition on and got 12 volts on both sides of the clip(not normal and should have a volts consisting of 12 and 0)...i unplugged the mspnp and plugged in the stock ecu and got the 12v and 0 on each injector clip...i turned the car on and still the same missing 1 and 3 cylinders...

Questions: Is the mspnp bad?...Is there something im missing to check?...is the harness connection incorrect?

At first glance I'd thin it could be something in the wiring, or possibly a problem with the MSPNP which we'll be glad to take a look at, and even throw it back on our test car for another round of testing...

But did I read that last sentence right that you're having the same symptom even on the stock ECU? If so that would seem to me to indicate a wiring issue or problem with the resistor pack probably... If not, like I mentioned we'll be glad to check out your MSPNP and rule that in/out for you real quick..
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Old 01-28-2008, 03:30 AM   #6
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that sounds like a good idea where do i ship the mspnp to?...and i really cant pin point the problem...im sure compression has nothing to do with the issue since cyl 1 & 3's spark plugs still look new...I also took out one plug at a time and left the spark plug wire in and cranked the car to see if there was some sort of compression and the test came out positve...can some chime in with the wire diagram on a 94 miata maybe?...

--also i've driven the car with mspnp and the stock injectors...then installed my low z setup, rx7 550 and rescaled for the 550 via megasquirts instructions...the car ran fine...then installed lc1 wideband and used the stock miata ecu ground on the manifold...then started the car and missing cyl...? so the only thing i could think of is a loose wire but all clips have voltage... and i just swapped injectors 2 and 4 with 1 and 3?...i think im just going to buy a new stock harness and try that out!!!
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Old 01-28-2008, 09:19 AM   #7
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Our address is:

DIYAutoTune.com
3690D Burnette Park Drive
Suwanee, GA 30024

You'd want to include a note referencing this thread and/or giving details on what you need tested...


BUT, before you ship it out, you did say it's doing the same thing on the stock ECU now right? And that your MSPNP worked fine before the Low-z injector install... soooo.... I'm really thinking it's not the MSPNP and is the wiring. have you checked your wiring for continuity between the ECU connector and the injectors to make sure they are all in the loop?

Google 'Miata Wiring Diagrams' and you'll find the Madracki site with all the diagrams, those are pretty good and in some cases as or more helpful than AllData.
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Old 01-28-2008, 11:12 AM   #8
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Old 01-28-2008, 11:13 AM   #9
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Old 01-28-2008, 05:29 PM   #10
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let me give that a try!!!...thanks for the links
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Old 03-06-2008, 01:16 AM   #11
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i finally got the car running...the culprit happened to be some corrosion on the coil pack connectors...i cleaned that out and everything works...stock ecu and mspnp...thanks guys...
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Old 03-06-2008, 10:28 AM   #12
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Excellent-- glad to hear you got it sorted out man!
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