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kylecoz88
04-23-2009, 01:19 PM
Hey all, I just picked up my 2nd MN12 SC yesterday after a threey year break(previous car was 1990 XR7 AOD). The "new" one is a 1990 SC with the 5-speed. Couple of things I noticed while driving it home.

1. The speedo is about 6-7 mph fast. Granted, I would rather tell me I was going faster than I actually was, but It is pretty annoying having to subtract 7 mph from what it is telling me.

2. Tach Doesnt work. It just sits at zero. To go along with this it starts "occassionally". As in, it starts every 3rd time or so. From reading on here that sounds lioke a bad cam sensor. Allthough, I have skimmed the recipts that came with the car and they had replace the cam senson, crank sensor, and harmonic balancer 2 years ago. The upshift light does not come on when cranking either.

Could the problem with the tach be in the gauges?

Thanks in advance.

Kyle

S_Mazza
04-23-2009, 01:53 PM
Hello.

The problem with the tach could be the tach itself, but the fact that it only starts every 3rd time makes the cam sensor look pretty suspicious.

As for the speedometer, do you know if the transmission or rear gears were swapped at any point? It sounds like someone either installed the wrong gear for the speed sensor (in the rear of the transmission), or they switched the rear end gears and didn't change to the appropriate speed sensor gear. If you figure out what rear end gears you have and what color the speed sensor gear is, there are charts you can check to see if it's correct.

RedSC93
04-23-2009, 02:17 PM
Sounds like someone before tried to adjust it wrong and it broke the blue gear inside. I just recently bought a 145 mph speed from a guy here at sccoa and the blue gear was missing, like it broke and crumbled to the bottom of the housing. Im sure someone has one laying around for you.

Jerry

kylecoz88
04-23-2009, 02:19 PM
Is there a way to fix a tach if it is the culprit? Are there certian wires I should check to see if it is a loose connection? Or would it be best to get an entirely seperate gauge cluster?

I have no idea if the trans or gears were swaped. I will se if I can get some time to jack the car up and check the rear end gearing.

the-big-e
04-23-2009, 02:32 PM
If the problem is with the tach, it is very easy to replace......

I have a few, if you want to go that route.....

I would also suspect a cam sensor or the DIS module.....

Can you tell what brand the replaced cam sensor is?

S_Mazza
04-24-2009, 09:50 AM
Hey, I forgot to mention in my earlier post that the speedometer itself can be out of adjustment. The needles are precision balanced, and then the motion occurs because a small electric motor works against the tension of a spring. The faster the car goes, the higher the voltage supplied to the motor, and the further the needle moves.

If the rear end gears match the speed sensor gear and the speedometer is still off, then it's probably the speedometer. These can be rebuilt, or you can look for a good used.

kylecoz88
10-14-2009, 04:28 PM
I know I am resurrecting this thread but I have an update. About a month ago out of nowhere my tach worked as normal for a 15 minute drive to work. I shut the car off and out of curiosity I start the car again – Nothing. Tach is back to being dead. I didn’t do a thing to my car to make it start working that day. I was happy that it was working and I now know what you guys mean when you say “our tach tells you where your RPM’s WERE, not where they are.”

I have had a A9U2 code computer in the car since I purchased it. Today I swapped in a LOS code eec and what do ya know, the tach worked on the first start! BUT that was it. I shut it off to try again and it never worked after that.

Where do I go from here? I know the tach itself works. The cam sensor is brand new and must work because I wouldn’t have had a tach signal… Is it somehow computer related? Or could it be a wiring issue.

Side note: I would estimate that 1 out of 5 times I crank the engine the tach needle will bounce a little bit.

Thanks guys!

Kyle

KMT
10-14-2009, 05:36 PM
Does the car have a VMM?

See this thread:
http://www.sccoa.com/forums/showthread.php?t=103268&highlight=vmm

Try to get the VMM to act as a tach -- if it works reliably, the tachometer gauge itself has an issue (do you have a spare cluster, same year?) -- if the VMM can't do the job, the problem isn't in the tach...more likely wiring/grounds and/or intermittent fault with the camshaft sensor. Check connectors and harness there for integrity/cuts/corrosion, etc.

S_Mazza
10-14-2009, 05:37 PM
I think you might have a loose wire. I don't have a diagram in front of me, but I would suggest getting the relevant EVTM (electrical - vacuum troubleshooting manual) and checking continuity.

kylecoz88
10-14-2009, 06:09 PM
Does the car have a VMM?

See this thread:
http://www.sccoa.com/forums/showthre...&highlight=vmm

Try to get the VMM to act as a tach -- if it works reliably, the tachometer gauge itself has an issue (do you have a spare cluster, same year? -- if the VMM can't do the job, the problem isn't in the tach...more likely wiring/grounds and/or intermittent fault with the camshaft sensor. Check connectors and harness there for integrity/cuts/corrosion, etc.

I do have a VMM, but it doesnt get a signial. This is copied from your link: "If only the oil change display flashes in the above sequence, then tach signal to the module is missing, the Self Diagnostics Test canot be entered until the signal is provided." Also, since the VMM isn't getting a signial the oil change side of the VMM will shut off and go blank exactlly 15 min after starting the car.

I have gone over the car before looking for bad wires. I think I need a diagram so I know what exact wires to look at. Anybody have one?

Kyle

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90blkbrd
10-15-2009, 09:30 AM
I have had a A9U2 code computer in the car since I purchased it. Today I swapped in a LOS code eec and what do ya know, the tach worked on the first start! BUT that was it. I shut it off to try again and it never worked after that.

I think you mean COS not LOS.

I'm not an expert here but the A9U2 is a 5-speed computer and COS is a auto computer. So I don't know how that will affect your car or your car with the SCT chip in it.

David Neibert
10-15-2009, 10:05 AM
I know I am resurrecting this thread but I have an update. About a month ago out of nowhere my tach worked as normal for a 15 minute drive to work. I shut the car off and out of curiosity I start the car again – Nothing. Tach is back to being dead. I didn’t do a thing to my car to make it start working that day. I was happy that it was working and I now know what you guys mean when you say “our tach tells you where your RPM’s WERE, not where they are.”

I have had a A9U2 code computer in the car since I purchased it. Today I swapped in a LOS code eec and what do ya know, the tach worked on the first start! BUT that was it. I shut it off to try again and it never worked after that.

Where do I go from here? I know the tach itself works. The cam sensor is brand new and must work because I wouldn’t have had a tach signal… Is it somehow computer related? Or could it be a wiring issue.

Side note: I would estimate that 1 out of 5 times I crank the engine the tach needle will bounce a little bit.

Thanks guys!

Kyle

Kyle,

Even a bad cam sensor can work some of the time. Are you getting a CEL ? New or not, I would replace the cam sensor.

David

toronto_1990sc
10-15-2009, 10:10 AM
very likely cam sensor....i just replaced mine this summer. (90 dollar part at ford...a bit tricky to reach but even a newbie like me did it...have a long magnet in case you drop screws!)

the tach is "driven" by the CS...a dead tach is a good sign it's the cam sensor...also bad starting, stalling etc..

cam sensor.

it's a cheap and easyish fix..start there.

kylecoz88
10-15-2009, 10:26 AM
-No CEL.

-I replaced the cam sensor with a $20 from O'Rileys. I know that they can be bad right out of the box, but it didnt seem to help anything the first time around. Are $90 Ford sensors superior?

-Come to think about it, when I was replacing the cam sensor I recall seeing a wire that might have been frayed, but still connected. I will have to look closer when I go home.

Thanks guys!

COS code not LOS code, funny. My last name is COStigan.

EDIT: the computer I tried was a LOS code. I got it off a guy on here and he assured me that it would work the same as a A9U2. I was skeptical, I mean, the car started up obviously because the tach worked with it. But the high speed fan would come on with the key on accessory and be on high when it ran. Is a LOS code even for our cars?

toronto_1990sc
10-15-2009, 10:58 AM
-No CEL.

-I replaced the cam sensor with a $20 from O'Rileys. I know that they can be bad right out of the box, but it didnt seem to help anything the first time around. Are $90 Ford sensors superior?

-Come to think about it, when I was replacing the cam sensor I recall seeing a wire that might have been frayed, but still connected. I will have to look closer when I go home.

Thanks guys!

COS code not LOS code, funny. My last name is COStigan.

i went with ford part because a dealer here had one in stock. cant say if they are better...but i tend to think OEM parts are the way to go. or maybe it's paying more for no reason..i don't know. but mine worked and fixed all the problems you have. (so far!)

i didnt have a CEL and i did not check for codes.

20 bucks is a good price...but was it new? i wouldn't bother with a used CS.

a bad wire would certainly be a problem. check that.

my 90sc would sometimes lose power at idle, almost stall...occasional hard starting...I had to lurch and shudder and buck a few blocks home...the tach would die then come back sometimes.

the new sensor fixed it all.

are you having any driving problems like that?

kylecoz88
10-15-2009, 12:03 PM
20 bucks is a good price...but was it new? i wouldn't bother with a used CS.
It was new. OK so maybe it was $30, I cant remember.


a bad wire would certainly be a problem. check that.
Checked. The wire that is shotty goes into a little grey connector. It sits directlly above my cam sensor. There are two grey connectors above my cam sensor, it is the smaller one with only one wire going in and out of it.


my 90sc would sometimes lose power at idle, almost stall...occasional hard starting...I had to lurch and shudder and buck a few blocks home...the tach would die then come back sometimes.
The only symptom that I have out of all of those is hard starting. I had posted a while back in a seperate thread that my chip had solved it, but it didn't. I had good luck on a couple of consecutive starting attempts and reported my conclusions too soon. Granted the chip helped, I dont have smoke rolling from my exhaust when I start it anymore (42# injectors).

Anybody know what that grey one wire connection is?

Kyle

KMT
10-15-2009, 01:02 PM
>The wire that is shotty goes into a little grey connector.

That sounds like the ground circuit off the crank sensor, up thr front and back over the middle/top of the engine.

No matter which it is exactly...all wires are important and should be fixed. Just don't get creative. One of those wires has shielding from the factory to prevent EMI from harassing the circuitry. If you can't replicate the original wiring you should start looking for a replacement harness.

kylecoz88
10-15-2009, 01:16 PM
That sounds like the ground circuit off the crank sensor, up thr front and back over the middle/top of the engine.

No matter which it is exactly...all wires are important and should be fixed. Just don't get creative. One of those wires has shielding from the factory to prevent EMI from harassing the circuitry. If you can't replicate the original wiring you should start looking for a replacement harness.

One side of the connection I'm talking about has a covering that almost looks like rope. Obviously very small because it only has one wire inside it.

Do I really need an entire new wiring harness? or a new grey connector?

S_Mazza
10-15-2009, 04:13 PM
Do you have an electrical multimeter? I think you are at the point that you need to put the probe to the wire and find out if the wires are good or not. If the car is running, then it's probably not the crank sensor. It won't run without a crank signal. But cam sensor or DIS wiring, that I could see affecting the tach. Also I wonder if you have been behind the dash at all? Has the tach ever been unplugged from the cluster?

BECERRASC
10-15-2009, 04:25 PM
hey one time in my 92 i had this problem and it was the dis (ignition module) later i a friend had the same problem ... so i though i knew the problem but no i wasn't and find out it was a dis harness a wire cut by the belt! ..;)

kylecoz88
10-15-2009, 04:36 PM
Do you have an electrical multimeter?
I do not.

It won't run without a crank signal. But cam sensor or DIS wiring, that I could see affecting the tach.
The right side connection of the DIS has missing "tabs" that secure it in place. It isn't really loose, but that could be a suspect.

Also I wonder if you have been behind the dash at all? Has the tach ever been unplugged from the cluster?
I personally have never been behind the dash. The farthest into the dash is putting in my radio.

kylecoz88
10-15-2009, 04:45 PM
Would this spliced wire have anything to do with the tach? It is spliced into the wiring and the gray part covering the wire is "floating" over the wire. What I mean by that is the covering is too big for the exposed wire inside. I have no idea what the wire does, so I hjavent touched it.

Kyle

KMT
10-15-2009, 05:11 PM
>The right side connection of the DIS has missing "tabs" that secure it in place. It isn't really loose, but that could be a suspect.

sounds like a real mess, sorry

The right front corner of the DIS is the ground path from inside to the metal base of the DIS, which needs to have good contact with the accessory mount which needs to have good contact with the engine block....which needs to have a good ground path to the negative battery terminal.

After correcting the wiring, replace the DIS and then go from there.

These cars have a heavy reliance on electronics circuitry. Those components rely on correct wiring which includes shielding, specific wire sizes, clean connectors and reliable grounds. DIY methods risk defeating many of the design features so do your best to avoid getting creative when making repairs.

KMT
10-15-2009, 05:14 PM
Would this spliced wire have anything to do with the tach? It is spliced into the wiring and the gray part covering the wire is "floating" over the wire. What I mean by that is the covering is too big for the exposed wire inside. I have no idea what the wire does, so I hjavent touched it.

Kyle

That is the ground wire that originates at the crank sensor.

S_Mazza
10-15-2009, 06:17 PM
Would this spliced wire have anything to do with the tach? It is spliced into the wiring and the gray part covering the wire is "floating" over the wire. What I mean by that is the covering is too big for the exposed wire inside. I have no idea what the wire does, so I hjavent touched it.

Kyle

The stock setup has a spade connector in that spot, but the plastic wears out easily. So some previous owner fixed it with a splice. That's not ideal (because how would you replace the crank sensor without cutting?), but it should be okay, as long as there is continuity.

I don't know if the car would run if that wire was loose.

I will try to find the correct wiring diagram and give you an idea of what wires to check (but you may have to pick up a multimeter to get anywhere with this). Or you can try parts-swapping, but that's not my favorite.

KMT
10-15-2009, 10:12 PM
See if these 1990 examples help...

http://www.sccoa.com/forums/showpost.php?p=760184&postcount=17

S_Mazza
10-16-2009, 10:32 AM
Nice diagrams!

I think wire #4 (from pin 12 of the DIS module) is the one that signals the tach.

I would try to trace that to where it goes ... and if visual inspection doesn't turn up any problems, check it for electrical continuity.

kylecoz88
05-26-2012, 12:06 AM
UPDATE: Thanks to Bryce - 90coug - this issue has been resolved after THREE years. I purchased a used wiring harness for the cam and DIS and it completely resolved my issues. I always suspected that there was a break in the wiring somewhere, but this confirms it. Starts on the first try and my tach now works. I thought I should update this if anyone else is searching for the same problem. :D

Kyle

TbirdSCFan
05-26-2012, 02:42 PM
I thought I should update this if anyone else is searching for the same problem. :D

KyleWe were wondering.. :rolleyes::rolleyes: Now I can sleep after all these years. :D

Actually this is GOOD to know because I have similar problems but not as severe. Often the connector itself is the problem.

SC Freak
05-05-2013, 01:24 PM
I am having very similar problems, so I am glad you posted an update.

My symptoms?

Well.... Car cranks but won't start on a consistent basis, maybe will start 1/5 times the key is turned. Puff of black smoke comes out of the exhaust when it does start and it smells real gassy. The tach doesn't work. It will sometimes come to life intermittently.

I have no idea how to work on the car, but it's nice to get as much information as possible in trying to deal with the problem. This forum has been informative. Thanks guys.

S_Mazza
05-06-2013, 12:00 PM
I am having very similar problems, so I am glad you posted an update.

My symptoms?

Well.... Car cranks but won't start on a consistent basis, maybe will start 1/5 times the key is turned. Puff of black smoke comes out of the exhaust when it does start and it smells real gassy. The tach doesn't work. It will sometimes come to life intermittently.

I have no idea how to work on the car, but it's nice to get as much information as possible in trying to deal with the problem. This forum has been informative. Thanks guys.

Probably a bad cam sensor. Try a search for information on that.

SC Freak
05-06-2013, 07:34 PM
Thanks for the advice Steve.....

I am also looking into a bad crank sensor and any wobbling in the balancer as well..

If I replace the crank sensor, does it make sense to also replace the cam sensor as well?

Or should I only replace what is bad?

Thanks again.

shoalcracker
05-06-2013, 10:20 PM
If you have the availability.

Pull the codes. Key On Engine Off

212-214 Will be Cam Sensor

Paul