Newb question of the day.

[mentordrift]

Okay, so here is the premise.I have a S1 RB25DET into an 1995 240sx, auto-> manual swap. Everything is good, besides a little bit of engine knock at WOT that will be addressed with a bigger fuel pump and new FPR.

My problem is the speedometer. My tachometer works fine, though it is definetly not reading correctly - but I understand that there is a resistor fix that I can do to make it read right.The speedo, however, does not read at all, period end of story. Nor do the odometer or trip.The company that I sent my wiring harness to sent me the following email after asking them about the remaining two plugs on my RB25 bellhousing, one being for the reverse lights:"The sensors are only for speed limiting features of the ecu. They are not used for any other reason other than fuel cut at 120mph"I am about to buy an Apex'i rev/speed meter and just be done with this, but I would really like to have a working speedometer.

The plugs in question, I have to assume are the vehicle speed sensor and neutral position switch, but I feel that I am wrong, because the electrical nature of the RB25 speed sensor, and the mechanical nature of the KA24 speed sensor.

A little bit of guidance in this would be greatly appreciated, or a fix woudl be grand and I will honest to god send the solver (when my problem is fixed) a crisp $10 bill for 6-pack.

[gawdzilla]

what the wiring ppl told you is wrong... the speed sensor in the trans is responsible for the speed cut and the speedometer reading. the s14 KA is an electronic based speedo, and so is the r33/34 rb25 trans. they are directly compatible

the speedo sensor is the frontmost sensor on the trans. those 2 wires need to run to a large plug underneath the fuse box on the s14. if you look at the FSM, it is plug E201, pins 3 and 7
Modified by gawdzilla at 9:07 PM 3/11/2008

[Carl H]

I absoloutely love how wiring 'specialists' claim the speed wire isnt needed, well the truth is that it does much more than activate speed cut.Its there to idle the car up on decel to keep the car from stalling on hard decel, there to mantain a proper idle, there for ac controls and other system subprocesses.Sure it kills the speed cut but it also drops drivability.

[l0nestar]

...I will honest to god send the solver (when my problem is fixed) a crisp $10 bill for 6-pack.

I don't have anything to add about the wiring explicitly, but I really like the 'incentive' you propose.

[Shocker]

I never had my speedo hooked up, she drove just like a regular car.

[Darius]

Carl - How does it go about keeping the car idling upon hard deceleration? Does it lean/enrich the fueling or factor into the load cell calc somehow??

[Joe]

what the wiring ppl told you is wrong... the speed sensor in the trans is responsible for the speed cut and the speedometer reading. the s14 KA is an electronic based speedo, and so is the r33/34 rb25 trans. they are directly compatible

the speedo sensor is the frontmost sensor on the trans. those 2 wires need to run to a large plug underneath the fuse box on the s14. if you look at the FSM, it is plug E201, pins 3 and 7

Modified by gawdzilla at 9:07 PM 3/11/2008

the speed sensor is the REARmost sensor on the trans. its right next to where the driveshaft comes out

[gawdzilla]

the speed sensor is the REARmost sensor on the trans. its right next to where the driveshaft comes out

sure about that?

short of going under the car, pretty sure the order from front to back is speed, reverse, neutral

[Joe]

oh holy **** its in a totally different place on the 25 trans. i had no idea. i thought it was rearword like on the ka/sr/20 trans hahaha

my baaad.

[neonbomb]

Mentordrift, if you dont mind me asking, who did you have do your wiring? Im almost positive i was told the same thing, to which i knew right away was wrong. Thank goodness Carl knows what hes talking about. Us college kids r so smahrt!

[Carl H]

ecu just changes the duty cycle of the iac when decel...nothing terribly fancy.

[mentordrift]

*edit*

Okay, phew, wow. I am amazed at all the responses, where to begin...

If the speed sensor is indeed what I am lacking in having a working speedometer, I am also missing the wire from the lower ka24 harness now. Unless there is a way to just splice into the speed sensor and just run wires to the plug in the engine bay, assuming that 3 is signal and 7 is ground (or something like that).

I can have the car up on a lift in a few hours if that's what is needed, even though I will have to lower the transmission a bit (d'oh..)

I sent my wiring out to Import Intelligence in PA, they did a really good job with the wiring...although lack of the speed sensor is kinda tossing me for a bit.

I am also assuming that the Apexi Rev/speed meter will not read my engine speed as there is nothing there to read as it is...
Modified by mentordrift at 5:34 PM 3/12/2008

[mentordrift]

okay, I have been doing some reading on the factory service manual, and I need to get some feed back about my new ideas brewing in my head.If I am looking at this picture correctly, it looks like Plug e201 plugs into e17. Which from what I would assume would plug into e216 that is the speed sensor. Theorhetically, I could run wires from e216 to e17/e201, and then the speedometer would work, because the ECU would then be getting a signal from the speed sensor?I went outside and checked all of my wires that are currently there, and I have wires to the 4 plugs , but only one of them (the reverse lights) has anything running to the transmission.

[Carl H]

ecu will only get signal if it was wired in thru the f3 plug on the efi harness...your speedo should function if you connect the speed sensor to that plug...iirc the speed sensor wires are both red with diffrent colour tracers; its been awhile since ive done a lower harness.did they not wire in the neutral position switch either?tisk tisk...leaving things out.

[gawdzilla]

okay, I have been doing some reading on the factory service manual, and I need to get some feed back about my new ideas brewing in my head.If I am looking at this picture correctly, it looks like Plug e201 plugs into e17. Which from what I would assume would plug into e216 that is the speed sensor. Theorhetically, I could run wires from e216 to e17/e201, and then the speedometer would work, because the ECU would then be getting a signal from the speed sensor?I went outside and checked all of my wires that are currently there, and I have wires to the 4 plugs , but only one of them (the reverse lights) has anything running to the transmission.

you're on the right track. i THINK the reverse lights and the speed sensor share the e201 plug under the fuse box (verify in the FSM. that is the best approach). I know the e201 plug has 8 pins, and pins 3 and 7 are the speedo.

in order for the ECU to get the speed sensor reading (assuming you haven't touched the body harness) on the s14 chassis, it goes through the speedometer first. once it hits the speedometer, it splits off and goes to the F3 plug, which you then need to wire from the F3 to your ECU.

first, i'd get the speedometer working, then worry about the ECU. so run the two wires from the speed sensor to that e201 plug. if you do that correctly, that is the only thing keeping your speedometer from working. after you get that working, check your F3 plug and see if you have a wire going from there to the speed pin on the ECU.

also... its probably not possible that your speed sensor isn't there. if it's missing there will be a hole in the trans that leaks fluid. i'm 99% sure its just not plugged in.

[mentordrift]

Okay, I think that this might be my project for the next day or so...e201 has 8 pins coming out of it, but the fsm puts it in a different position than I have it, and makes it seems like it only has 3 pins, but I am going to try both when I get under there just to be 100%

yeah, I have a speed sensor down there, i tucked all its wiring and wrapped it in electrical tape so it wouldn't get damaged from water...no hole though lol.

Okay, so I looked up which pin is the VSS pin on the ECU, and I am going to double check that to make sure the car acutally has that pin wired in. Just to make sure I am following you correctly, I want to:Wire from the Speed sensor to e201 pins 3 and 7, and then from there, trace that wire(s) to the ECU to the pinout?Or should I just start with the e201 pin and work from there.

[Carl H]

the s14 fsm is useless, pins are in the wrong spots and colour codes are wrong...i'll check later and see if i can find my speed sensor notes.

[craz4240]

My speed sensor is hooked up to my e201 plug properly however my VSS wire isn't hooked to my ecu as well....once the snow lets up here in canada eh I gues Carl it would be good for me to wire the VSS wire in...I have the proper diagram.

[mentordrift]

Good news is I have the wire on the ECU plug (F3?) that runs to the speed sensor.That gives me some moderate hopes that this might work after all.The bad news is on the way to Border's to return a book my girl bought me, my passenger rear brake caliper blew out. Yeah.

I have a few days I guess while that gets replaced to study up on the wiring schematics.