Ever had six sensors go out at once?

DarkShard

Registered User
Okay, here's the story. A few months ago I bought a 90 SC off of e-bay. Paid only $1300 so I thoght I was getting a good deal. A couple months after that, the car totally died, replaced cam sensor, crank sensor and DIS module to get it running again.

Now it's back to the same problems it's had ever since I got it. It runs alright, I guess (I don't know anybody in Austin who has one to compage). The check engine light just will not go off.

I pulled the codes and I get not one, not two, but six different failures all at once. These are the "key on" codes in no particular order (actually, the order I get them in)

51 - Coolant Temperature sensor circuit open
22 - Barometric Pressure Sensor out of range
53 - Throttle Position sensor out of range (high)
54 - Air Charge Temperature sensor circuit open
35 - EGR Valve Pressure Transducer/Position Sensor voltage out of range (high)
67 - Neutral Drive Switch circuit open

Now I know what all of those are except the last one, what is a neutral drive switch? Even without knowing that, I would think that not that many sensors would fail all at once. Other posts say that these computers often just point you in the direction of the failure. Well, the only think that connects that many components that I know of is the ECC itself.

I tried swapping a few sensors from my friend's mustang since the engines were similar, but the same problems were present on my car and no problems showed up on his. Now I only tested the air charge and BAP sensors, but I got the idea that they were working on his.

So....any ideas on what might be causing all these faults? I'm totally confused. :confused:
 
it's the computer!
whenever you get a bunch of different sensor failures, that's when the computer when NUTS!
Hope it helps!
I hope Im right 2!
 
I sure hope not

I've thought it could be the computer, but damn, that's an expensive part to replace if it's not.
 
You should be able to find a used computer. Post on the WTB forum and I bet that you will find one or e-mail one of the many parting out people. I also see them on e-bay quite often.

Bob
 
Does anybody know where I can find which computer codes match up? I know there's a few different model numbers even within the same year.
 
67 can be set by not having the car in park or the switch is bad. It's the one that keeps you from starting in gear or clutch depressed.

Your problem might be wiring related. Like a loose ground, or connector. Check all the grounds between the engine and chassis. bad grounds will give you more problems than a "barrel full of monkey's" as an old shop teacher put it, and that was talking about simple trailer wiring and is more true in anything that carries electrons.

There is a "wiggle test" (test for intermitant connections)that can be preformed when you check codes. I have a scanner (OTC Moniter 2000) that directs you how to do the test so I don't know how to do it without it.

The TPS and temp sensors are easy enough to test with a DMM hopefully you have one. An analog one works well in this application. Set the meter to ohms. Remove the connector and probe the middle pin and one of the other 2 pins. As you open the throttle the resistance value should change slowly and steadly. It is not important which way the value goes because depending on the way you have the leads the value could start high and go low or start low and go high. All you need to see is that the change is steady. This won't test the wiring only the sensor itself. You can test for 5V at the plug by turning the key on and probing the first and last terminals on the connector.

The temp sensors (coolant and air) can be tested in almost the same way except there are only 2 wires on each, and that's where the leads go. Set the meter to ohms. With the car completly cool (hopefully you can start it), measure the resistance and record it. Do the same with the other sensor. Then start the car (or remove the sensors) and heat it up for about ten minutes and then record the readings again. Look in a shop manual for the values they should be. If you can't start the car run hot water over the sensors and record the values hot. Dry the air charge sensor and reinstall.

If you tried to record the values cold and got no reading (nothing changed/infinite ohms/ Open) then the sensor is open, meaning broken.

A value of 0 means that you have select a range too high (like the megaohms scale, in that case reduce the range) or it's shorted,meaning broken.

If all the sensors check out then I would start looking for a bad ground. Remember that you might not be able to return a computer so finding the problem by replacing parts might be expensive quick. Hell it might be a loose connector.

Good luck

Jeff
 
loose wires would be nice

Do you know what the voltage readings on the coolant and air sensors should be when the car is both on and off?

I can start it so I'll try to test those sensors like you said tomorrow. I've been reading so many voltage changes trying to get the blasted cam and crank sensors working, I'm pretty familiar with the procedure now.
 
one more thing

The car is a 5 speed and it won't start unless I press the clutch in. Wouldn't that imply that they saftey switch is working (and shouldn't be throwing code 67)?
 
Ability to Clear codes?

Are you using a Code scanner that will clear codes?

Seems to me that if the computer is "WHACK" if you clear the codes, run it then run codes again you may get a differant result during your test...Also, if you are using a scanner or have access to one try a engine on test, as well as the operation values you can pull while on the fly and see what you are getting...A used computer is pretty easy to come by I think...Sunny is well known in the parts forum, and he knows what will and won't work for you...IMO From what I have read, I would say it is the puter.

Much luck...

BTW, you may try your local checker, shucks, or whatever you got around ya...Some of them will let you use a code scanner for nothing..."In hopes you will buy the sensor in need from them" I am sure...Jus in case you don't have one...

Mine was like 150bux...And has already paid for itself easily and then some...
 
Re: loose wires would be nice

DarkShard said:
Do you know what the voltage readings on the coolant and air sensors should be when the car is both on and off?

I can start it so I'll try to test those sensors like you said tomorrow. I've been reading so many voltage changes trying to get the blasted cam and crank sensors working, I'm pretty familiar with the procedure now.

You aren't going to be measuring voltage in the test I described it's ohms ( the Omega symbol). Basically you are just looking for a change. I THINK they are about 5K cold, but don't quote me on that.

Just make sure you have 5V on the sensor wire when you unplug it and turn the key on if it is lower than 5V then you might have found the problem a resistance in the harness caused by a bad connection.

The clutch pedal thing comes up every time I check the codes and it's not a big deal. there is more than one circuit in that switch one is for the cruise control but I think it's vacuum to kick the cruise off when you push the clutch.

disconnecting the battery clears the codes for the early cars, or you can use a scanner.

Jeff
 
Well, the car is a 90 and I had the battery unplugged for a long time while the DIS was being replaced and it always comes back with the same codes. I wish all I had to do was reset them away.


I understand that testing the sensors requires you to measure ohms. I wanted to measure the voltages on the terminals connecting to the sensors to see if I could possibly find something that's shorted out. When the coolant and air charge sensors were unplugged, I read the voltage from each wire to ground. One side had about 5v the other side was at about 4.5v. Since I've never had the car when the codes weren't present, I don't know what it should be.
In the Ford EVTM, there is a black wire with a white stripe that connects to most of the sensors I have a problem with. This black wire is listed in the manual as "reference voltage." So I would assume that it running at 5 volts would be just fine. It doesn't make sense to me that both the reference voltages and the other connection would both have positive voltages.

One thing I forgot to mention was that I haven't been able to use any code scanner to get the codes from my car. I've tried three different hand held scanners, all of which worked before and after being used on my car. All the scanners do is beep continuously when connected to my car's test connectors. The only way I've been able to check the codes is to connect the STI connector to ground and read the flashes of the check engine light on the dash. Of course, this could be caused by a short or a screwed up computer. If only I could narrow it down to one or the other without going out and buying new hardware I don't need.
 
I had my Computer go out on me last summer and it was a nightmare trying to figure out what the problem was. It would run like a charm when cold but as soon it reached operating temp, CE light would come on and it would run like utter ****. It would throw 27 different codes if I remember correctly. Luckily my mechanic had a SC himself so he just started swapping parts off his onto mine.

The computer isn't that expensive and can be found in any junkyard with a SC in it for they very, very, very rarely crap out. The only way to get the correct # for your computer is to pull it out (located in the passenger side kick panel) I actually put in a different computer than the car originally had, but it has to be of the same transmissin type (ie. 5 speed or auto)

Has the heater core ever blown up?
 
Like I said before, I've only had the car for a while so I don't know if the heater core ever blew up or anything of the sort. The other day I came out there and found some water in my glove box....now that I think about it, the computer is rather close to there. Any ideas how water could've gotten in there?
 
The computer is not tightly sealed at all. I guess its not becuase its not meant to get water in the kick panel.

My computer was fried due to a blown heater core I assume. My mechanic said it looked like heater core had been replaced on it. When opened up the computer, it was all corroded inside it, as if water had goten on the chipboard.

I have no idea how water could have goten in your glove box, but if you have a leak somewhere, water may have found its way into your computer and could be causing a short. Wouldn't hurt to open it up and see. You could probably have access to it within 10 minutes.
 
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sensors seem good

I tested some of the sensors using and ohm meter, and they seemed to test out alright....for example, the resistance on the coolant temperatue sensor went down when the engine warmed up. So I guess the sensors are alright, just a short or the computer now.

Speaking of shorts, a long time ago I read an article on these boards about a thunderbird in the shop that kept blowing DIS modules. It turned out that the crank sensor was putting out too much voltage and causing the DIS to overload. Does anybody have the link to that article anymore.

Also, can anyone tell me what the voltage coming from the crank to the DIS should be (it's the blue wire I believe)?
 
The crank sensor doesn't put out a steady voltage. It is a hall effect sensor which puts out a wave pattern as the metal vanes pass through the pickup. Voltage is supplied to the sensor and the waveform is read by the EEC and DIS. The supplied voltage is a constant 12-14V.
 
If the vane is not passing through the sensor, it puts out 0v. If the vane is through the sensor, it puts out a steady voltage during that pass through period. I just wanted to know what that the output voltage should be through the pass through period so I can make sure my DIS isn't being overloaded.
 
Since there are no step up/down coils in the sensor circuit, then the maximum (peak) voltage you should see is what is put out by the alternator if the car is running and the battery if not. In other words, 12-14V.. Its doubtful that the sensor is overloading the DIS. The DIS is what turn on the crank sensor power and reads the cam sensor output. The EEC does the opposite; turns on the cam sensor power and reads the crank sensor. Neither sensor generates any power.
 
I've been trying to find it, but I swear I saw a web page someone posted that had a Ford tech diagnosing a super coupe.

The car had a bad dis module, it was replaced and then test driven. On the test drive, the car died again. They replaced the computer, started it, drove it, died again. Rather than just replacing more parts, this guy hooked up some metering equiptment to it and noticed that the voltage from the crank sensor was too high which burned out the DIS and eventually the ECC as well.

I think I remember that 10v output was too high (which is what I'm getting) and that it was causing the problem. Since I can't find this article, I was hoping someone could verify what the voltage should be. Since the sensor works by induction, it isn't just a matter of whatever voltage is coming into the sensor from the alternator, although that does play a part in it.
 
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