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Speeometer experts needed

7K views 101 replies 9 participants last post by  zkruly87 
#1 · (Edited)
So I started a thread "Bet u havent seen this b4" where my speed sensor shorted and burned up/melted and the speedometer stopped working, obviously.

http://www.3si.org/forum/f35/bet-u-havent-seen-b4-657722/

Since then, I have received a replacement pigtail connector that I soldered into the engine wire harness hooking the wires up correctly to the existing wire color code. (yellow, black, black w/white) and have now tried two separate used speed senors. However, the speedometer is still not working... no cruise or active aero either. Everything else works, fuse 11 is good.

I have tested for positive and ground at the pigtail connector and are getting both, but not from the wires I was told by escape-performance going by the wiring diagram he was using.

Fact- my positive wire is solid black and ground wire is black w/white stripe, yellow is of course the wire going to the ecu. His diagram said the opposite though- solid black is ground, black w/white is positive... but that's not the case with my 1991.

At any point did Mitsubishi switch/change the engine wire harness section going to the speed sensor so that the sensor's ground wire was solid black and positive was black w/white? I can tell that the pigtail is from a newer year as my "yellow" wire is more of a dingie yellowish clearish looking rubber, but the wire coming out of the pigtail is a nice solid yellow.

Hopefully tonight I will have the time to send 12v to the yellow wire at the pigtail, and using a test light at the ecu connection confirm that the yellow wire is still good all the way to the ecu. If it is still good as I think it will be, then what else could my problem be? The bottom gear section still seems to be fine as the pin won't turn, but I haven't pulled it out to confirm 100%.

Could the ecu have gotten screwed up when the sensor fried? (eveything else works and car still runs great though?!) Or is it just bad luck with the used sensors both being bad? Escape-performance sent me another used replacement already at his expense but it's still a no go as well. I'm positive it's not the gauge cluster because cruise isn't working so it's surely sensor, connection or ecu related.

Any input is greatly appreciated!!
 
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#2 ·
Looking at my hardcopy '91 Stealth manual, which should be the same as your '91 VR4, I see the same thing as escape-performance said. The power should be B/w and ground should be solid black.
I also looked at the '94 manual I downloaded and it agrees.
I don't know how but it looks like your wiring got switched somewhere. Perhaps someone tried to add some kind of aftermarket controller? Either way I suspect that if you can find where they switched you'll find your problem...

Be careful putting 12v to that yellow wire. I'm pretty sure that's a 5v signal going to the ECU (and speedometer). Putting 12v to it will probably blow something up. Like the ECU...
 
#3 ·
First off, thanks for the reply!

What kind of controller are you referring to? The only controller wired into the wires going to the ecu is a SAFCII that I installed and I know it's done correctly.

I plan on pulling the positive cable off the battery, leaving only the ground connected. Then running a separate wire from the positive terminal on the battery to the yellow wire/speed sensors pigtail- then checking the wire port 66 at the ecu's wire harness. The ecu and all other positive power to the car will be disconnected, I will only be running 12v from one end of the harness to the other where a test light will be. I will get the ground source from metal somewhere close by inside the car.

It's odd that the wires are crossed... :confused: Perhaps I switch them around going to the pigtail and the sensor will work?!?? For a fact though 100% I connected black to black, black/white to black/white, and yellow to yellow going to the pigtail.
:wtf:
 
#4 ·
What kind of controller are you referring to?
I have no idea. I'm just taking a guess on how those wires could possibly be switched??

Don't forget that yellow wire also goes to the speedometer. That could also be damaged by 12v. You're probably better off doing a continuity test with an ohm meter. Measure the resistance between the yellow wire and ground at the speed sensor, it should be fairly high. Then put a jumper on the ECU pin to ground and measure the resistance at the sensor again. It should change to near zero ohms. That should be much safer than putting any 12v on that line..

Please don't tell me you don't have a meter.
Please don't tell me you don't have a meter.
Please don't tell me you don't have a meter.
Please don't tell me .......
 
#5 ·
Don't forget that yellow wire also goes to the speedometer. That could also be damaged by 12v.
I am literally talking about testing from one end of the wire to the other and only testing the wire, that shouldn't be a problem right? As in, the speed sensor nor ecu have anything to do with that test as both will be disconnected and I am only testing from one harness to the other. Surely that wire can handle 12v if it's good right? (It's just like all the other wires) That is what I am trying to find out, was that wire damaged beyond just where the melting originally happened. The positive and negative have both tested good, all be it backwards compared to the diagram.
 
#8 ·
Oh man please don't tell me that... lol. I was wondering if that was a possibility.

Nope, no CEL at all. (EDIT- I mean no CEL but I will have to check that it turns on and off at start up like normal...give me a minute. I'm sure it does) Car runs great, totally normal.

Any idea why the wires would be crossed? The speed sensor worked prior to this. I replaced the #11 fuse that blew, added in a new pigtail from the engine harness and replaced the sensor... twice.
 
#9 ·
Wait, I think I see what you are saying... maybe. I assumed the yellow w/white stripe wire at #66 of the ecu connector only went to the ecu and then there was a separate wire output from the ecu that goes to the gauge. Is that not the case?
That is NOT the case and that's EXACTLY what I saying... :)
That yellow wire goes to BOTH the ECU and the speedometer. (And who know what else? The schematics aren't set up to show every point along the way, if you get what I'm saying.. In other words if that wire goes somewhere else that's unrelated to the speedometer circuit the speedometer schematic doesn't show it..)

Tsiturbomightym makes a good point about things may already be fried.
No sense in making that "maybe" a "certainly" though.. ;)
 
#12 ·
Just for fun I flipped through the manual and found two more places that the yellow wire goes to, the cruise control and the ECS. Neither of those is shown on the speedometer page! As a general rule never apply a voltage to a wire that's different than the signal that's supposed to be on it.... For ANY reason!
 
#14 ·
So what are the dangers if I take a leap of faith and re-do the wiring by crisscrossing the black and black/white wires from the engine wire harness going to the pigtail to reflect what the diagram says should be correct? (but in my case is not) Blow fuse? Blow the sensor? It's not blowing the fuse as it is... don't know about the sensors.

It's crazy I have to even ask a question like that! As of now, my positive and negative wires are reversed for whatever reason so I'm totally confussed... hopefully it hasn't fried the sensors that I have already tried. If switching them around would indeed fix the problem, then I'd be REALLY be confused as to why my original sensor was working before under the same setup. (unless the pigtail I was given was for something other than the speed sensor- if there's even one like it that goes to something else, but same 3 color wires?)
 
#13 · (Edited)
Well the ECU *looks* good. There is only one tiny thing that looks rough and that is C3, but it's directly next to where a cap has been replaced when the ECU was rebuilt. The board is slightly damaged right around where the leaky cap used to be which is directly beside C3, so it may just be a cosmetic thing left from the leaky cap.

EDIT- after lightly scraping the top of C3 the char came off and it looks pretty much normal now like all the other "C" parts (diode?) so I think that was indeed just old burned cap residue.
 
#15 ·
At this point I wouldn't hook up anything until you understand what's going on. Too many expensive parts hang in the balance.
A couple questions..
With the sensor disconnected (and the ECU plugged in) do you have 5v on the yellow wire?
How did you test power and ground on the black and black/white wires?
 
#19 · (Edited)
Not sure about 5v from the yellow wire yet. To test for positive and negative for the other two wires, IIRC here is what I did-

I used a cheap boost control gauge that I never ended up using, it has two wires coming out of it to power a 12v light. LOL. Yellow is for positive and black for negative.

To first test for ground in the pigtail, I started out by disconnecting the car's positive battery cable (leaving only ground connected to the car) then connected the test light's positive yellow wire directly to the positive battery terminal. (again, the car's positive cable completely removed)

I then touched the test light's black ground wire to the speed sensors harness/pigtail black/white wire and it lit up. (But only after several confusing hours expecting the ground wire to be the solid black wire from the pigtail) Additional info- At first I was testing for only the black wire to be the ground like it's supposed to be, but got nothing. However, I could indeed touch the test light's ground wire to just about anything else metal connected to the body and it would light up no problem. Running out of ideas, escape-performance suggested trying the other wire and once I tired the same test only touching the test light's black ground wire to the black/white wire in the pigtail... the test light finally lit up.

Only then did I do the reverse of that to test for positive- I left only the car's positive cable connected to the positive battery terminal and connected the test light's black negative wire to the negative terminal on the battery. (or maybe I had to reconnect the car's ground cable so that I could get power to the pigtail in ACC key mode? I don't remember but anyway...) Once I touched the light's positive yellow wire to the solid black wire in the pigtail, the light once again lit up.

Am I missing something here?
 
#20 ·
One would think... but my test results state otherwise. Maybe someone will find a hole in my test somewhere that I'm missing (don't see how though, it's pretty simple) but regardless that the test was done long after replacing the pigtail and sensor and the speedometer still wasn't working, nor cruise or AA.

And I assure everyone, I connected the pigtail correctly to the stock engine wire harness- black to black, yellow to yellow, black/white to black to white. I don't know what to say.... it's VERY odd.
 
#17 ·
The black wire is supposed to be ground, black/white is 12v.

Look at the connector on the speed sensor. There is one gold colored terminal. That is pin #3, the signal wire.(Y/W) The center pin, (#2) is ground. the remaining outside pin that is not gold colored is pin #1, 12V power.

The signal wire splits in several places, and feeds a signal to the speedo, the ECU, and the ECS. There may be more that I don't remember.

According to the diagrams, the ECU provides a 5V reference signal, which the speed sensor pulls to ground to make a signal. Some of what I've read on this forum would seem to contradict that, (people cutting the speedo signal from JDM ECU's and still haveing a speedo) and I've never taken the time to reverse engineer how the system works, so I really can't say for sure one way or another...
 
#18 ·
Look at the connector on the speed sensor. There is one gold colored terminal. That is pin #3, the signal wire.(Y/W) The center pin, (#2) is ground. the remaining outside pin that is not gold colored is pin #1, 12V power.
LOL.. From his other post

I think that melted glob in the middle is supposed to be ground, but I'm not sure which of the other too is gold colored... :) :)
 
#21 ·
Am I missing something here?
Yeah. A METER!!!

At first I was testing for only the black wire to be the ground like it's supposed to be, but got nothing.
Which would mean you're missing ground on that wire...

However, I could indeed touch the test light's ground wire to just about anything else metal connected to the body and it would light up no problem.
Proving the point..

Running out of ideas, escape-performance suggested trying the the other wire and once I tired the same test only touching the test light's black ground wire to the black/white wire in the pigtail... the test light finally lit up.
Which back-fed power to all the other things on that power line. Meaning you powered the ECS and cruise control and every other thing on that side of the ignition switch. All of which was connected to ground. That drew enough current to light the gauge...

Get a meter. Even a $5 one from HF would work (they're crap meters but better than licking wires to see if it tingles... ;) ). Hook the battery back up and test for power at the connector.
I'll bet the power is on the black/white and you're missing ground on the black.
 
#22 ·
I'll bet the power is on the black/white and you're missing ground on the black.
Yes I have a meter, not saying I'm a expert at using it though... just very basic knowledge. However, if I have no ground... why is it I kept blowing #11 fuse until I pulled the wires apart? At least the first part of my test to test for ground was correct, right? Not saying you are wrong, I'm still trying to grasp my head around your last line about back powering. Give me minute to try to understand, I've been drinking my stress away tonight. haha
 
#24 · (Edited)
I finally got back after this problem today because I was waiting to fix a small coolant leak (water neck gasket) in the process. I took the speed gear out and it's in good shape so it's clearly an electrical issue.

I know that the wires and connection are good also so before I shell out a $100 bucks for a new sensor, is there anything else that could be the problem, such as ECU? Does the signal go from the ECU and then to the cruise control/aero? (BTW I opened the ECU and everything looks ok, nothing obviously burned... no smell)

I'm pretty sure it's not the cluster because neither cruise control and active aero work either I've read they indeed still would if it's just the cluster. I guessing that both used sensors I received are bad but is there something else it could be?
 
#27 ·
If I were you I wouldn't spend any more money on sensors until you verify power and ground on the connector. Judging by that picture of your first one something is drastically wrong, and you could be popping sensors as fast as you can plug them in.
At $100 each that's going to be a hard lesson....
 
#28 ·
No matter what method used, right or wrong... the test light lit up on both the positive and negative wire... tell me how that means that they are not making a connection? The wires were melted together and yes it was blowing the #11 fuse but since pulling them apart and replacing the fuse it does not blow and everything works except the odometer and speedometer. I know I have ground, where would the + be coming from... ECU?
 
#29 · (Edited)
My bad, you said sensor and for some reason my brain read fuse... lol. I only paid $25 for both used sensors and a new pigtail/wire. I've already put everything back together so I'm not going to get to it today (my goal was to fix the coolant leak today) but next time I get to it I'll test for positive using a meter and ACC on.

With the meter, do I need to connect the negative pin to ground or can I just pin the positive red wire to the pigtail to test for positive with ACC on?
 
#30 · (Edited)
Ok so I lied.... I was just now able to take the battery out and get the pigtail off, nevermind the scratches on my arm. :D



I hooked the red wire/pin of my meter up to the black/white positive wire in the the pigtail and the meter's black wire/pin up to solid black ground in the pigtail. With ACC on I got a strange reading... -11 volts with acc on. I then hooked up the black to black and red to yellow and got a -1.6

When testing the battery directly, red to + and black to - it read 11.8 like it's supposed to. No - symbol.

I'm confused. All three wires are connecting to somewhere, but other than that it's over my head.
 
#32 · (Edited)
Just sent you a PM, I'll go check what you asked...



Edit- For all other readers this is the relevant info I PM'ed that resulted in Steve's diagram explanation below-

"I'm getting -11.6 with acc on at the positive black/white wire. If I switch the meter's pins and hook the ground pin to the white/black wire and the red pin to the black wire, I get 11.6

Clearly positive and ground coming from the pigtail are backwards compared to how it's supposed to be. How in the world? I have 100% confirmed that the new pigtail is soldered up right- yellow to yellow/ black to black/ white/blk to white/blk. "
 
#34 ·
I think there's more damage to that harness than you've found. You cleared the short where the wires melted together but there's something else going on. I'd guess it's in one of the connectors further back but the tough part is that the power and ground go to different places. I still think you lost ground somewhere, see if you can follow that black wire back some more.
 
#35 ·
I'll try to take a look but I'm not sure what else I'll see without cutting into the engine wire harness. Only the bottom 2 inches of wire were melted together just above the sensor. I cut the factory wire wrap off all the way up until the wires come out of the engine wire harness and all 3 wires appear normal. I'd hate for it to come to me having to tear into my wire harness.
 
#36 ·
I scribbled out a couple diagrams to try to explain what I'm thinking...


This first scribble is a simple circuit, working normal. If you removed a bulb and measured the voltage in the socket you'd get 12v between the two pins, and +12v to ground (with the switches on of course).



In this scribble imagine there was a break in the black wire, between where the two bulbs connect and ground. I've shown the bulb removed to simulate having the sensor unplugged. If you measured from the black wire to ground you would get 12v from the other bulb .
If you look through the diagrams that ground point for the speed sensor goes to a lot of things, including the MFI system... and even though you have the sensor unplugged they are all still connected. That's where you're getting voltage on the black wire from.


One last smear to torture you with...
last, imagine you also have a break in the power wire, between the speed sensor and the rest of whatever is on that fuse. Now you're gonna get 0 volts between the two wires on the socket, 0 volts from the red wire to ground, and 12v from the black wire to ground....


Make any sense??
 

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#37 ·
Yeah, for the most part. (I think... :eek: lol) I don't have a diagram so I don't have a clue where to begin with finding a break in the ground. It sounds like unless I know what starting and ending point to check for continuity in the ground wire then the meter is useless to me.
 
#39 · (Edited)
Yeah but the wire goes into the engine wire harness. Without cutting it up, don't I need to know what all other components it's going to, to check at their (end) connection? I have the 2 volumes of the service manual but couldn't find the wire diagram.

Thanks for being patient with me. :beer:

EDIT, It would seem pretty clear (and probaly what you are saying) that the break would be between a certain component and the speed sensor (and nothing else) because everything else works. The car runs fine and everything else works on that #11 circuit. (and everything else period)
 
#40 ·
That seems reasonable to me. Assuming of course that EVERYTHING else works, including all the weird little things you never look at. It might be worth taking a minute to check all the little things you can, it could help you narrow it down. I doubt it's the vanity mirror but when was the last time you checked the light on that? Evaporator purge solenoid? (When does that even turn on? ;) ) Reverse lights? All the gauges, including boost? AC? The little lights in the footwell? You get the idea. Turn on everything.
 
#41 ·
Yep, everything. Windows, power seat, vanity mirror light, reverse lights, brake and parking lights, turns, all gauges except speedo, AC, lights in footwell... lol... yep everything except speedo/odometer/cruise and aero (active aero works if I toggle the switch manually and the cruise light comes on in the dash if I turn it on) which all need a speed sensor signal. I'm pretty in tune with my car and I've lost a few #11 fuses two or three times over the years between the three 3K's I've owned so I do know what to look for.

(OK, so before I sent the above message figured I'd go and confirm that everything works and the only thing not working is the 12v power socket next to the active aero switch, but I'm pretty sure it's been out for a good while (if not since I got the car) and I never got around to it or cared enough to look into it. I just used the lighter socket when I rarely needed a 12v socket source)
 
#42 · (Edited)
The only fishy thing I can add is that after I repaired the short and looking for those pesky #11 items to be working with a fresh fuse, I noticed that one of my power ways in the drivers seat bottom wasn't working, I think the back bottom section. I forget which section of the power seat is on fuse #11 (seems like I remember it being the bolsters) but I know one of them is. Anyway, I kept toggling the switch while driving and eventually it srtated working again... then briefly stopped but started working again and has been 100% ever since. Probably just sticking or the switch being dirty.... whatever... probably totally unrelated.

Edit- If it's not off the #11 fuse I don't see how it's relevant but I forgot a few things to check and just confirmed them... power mirrors/defrost/dimmer switch, rear wiper, and I already know about the big things that have been working like head lights/popup, fans, radio, electronic boost controller & tune device, factory alarm and all etac items, anything engine related... etc. because I have been driving the car normally using my cell GPS for speed.
 
#43 ·
I'm less concerned about what's on the same fuse as I am about what's on the same ground point (#2). Flipping through the book I came up with this list:
ECU, PTU, O2 and Detonation sensor cable shields (very unlikely), Wiper fluid level switch, Front wiper motor.
Not as many as I thought. I'm sure I missed something but the only thing you haven't checked (I bet.. ;) ) is the wiper fluid switch. And maybe the wipers.
The good news it that wire probably doesn't go too far. The manual shows it as the battery (-) but I'm starting to wonder if it's the ground on the firewall right by the wiper motor?
 
#44 · (Edited)
Front wipers work as well as the single back, and I'm almost 100% sure that the windsheild fluid level sensor works but the sprayer motor, you caught me on that... lol. I'll go check on that as well as the ground connection on the firewall. From memory I haven't exactly noticed that ground connection before but from that pic it can't be hard to spot.


HAHA, I'm the EDIT king tonight-

That firewall ground to battery cable is ok.

But you know what... I did find a possible issue. At first I thought it went off (attention lapse I guess) but my washer fluid light is staying on and I have topped off the front under the hood and now the back in the hatch. The fluid is full and both sprayers work. It's crazy to think that a bad fluid level sensor could wreak such havoc but nothing would surprise me at this point.
 
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