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Post by bunbun / Hank on Feb 25, 2006 5:02:42 GMT -5
Good lord Trevor, I thought I was the ONLY one who got these weird "Twilight Zone" problems that defies all logical explanation. Ya got me a bit stumped also. But! lets see what we can come up with that might help.
First thing I would do is disconnect the harness at the TPS and the ECM. Make up a jumper wire if you need to and hook one end of the jumper to the POS. on the battery. Hook the other end to each wire in turn at the TPS end of the harness. Now, take your volt meter and measure voltage at the ECM end of those wires. If you have battery voltage going in, you should have battery voltage coming out. I know you did a continuity check with an ohm meter. BUT! you could have only ONE little bitty strand of copper wire connecting both ends and it would show a complete circuit.Lets see how it stands up to 12 volts, will it carry that load. A bad wire could account for the .122 volts that you are getting at the TPS end. Thats a lot of resistance.
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Post by bunbun / Hank on Feb 25, 2006 5:18:12 GMT -5
Now, as to why you have 12 volts output at the ECM end of the wire when you should have only .5 volts is an even more interesting question. Are you SURE you probed the correct wire? If the answer is YES, my first thought would be the ECM is bad. BUT!! You may also have a short in the harness and 12 volts is feeding over into the TPS wire from another circuit. Let me post this so I don't loss it, and I'll take a look at the wiring diagram and see what I come up with. HANK.
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Post by bunbun / Hank on Feb 25, 2006 5:52:20 GMT -5
I'll toss this out for what its worth. It might not mean a darn thing, BUT.... In looking over the wiring diagram I noticed a TAN wire that goes to the Air Intake temp sensor. And a YELLOW wire that goes to the Engine Coolant temp sensor. NOW! both of these sensors have a BLACK ground wire that merges with the ground wire from the TPS. So there is a tie in there. So, just for the hell of it try probing those circuits for any voltage anomalies. The RED wire at the ECM is Battery voltage coming IN, just in case you did not know that. Thats about all I can think of to tell you at this time. I will see what else I can come up with and check in with you later. HANK.
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Post by Sir Trevor on Feb 25, 2006 11:27:12 GMT -5
Thanks. I'm going to get back out there and do some more probing.
I'm wondering if the harness runs through a voltage regulator somewhere to drop that 12 volts down to .5
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Post by bunbun / Hank on Feb 25, 2006 12:24:42 GMT -5
The wiring diagram shows NO voltage regulator other then the one in the alternator that regulates current to the battery. So I believe you have 12 volts GOING INTO the ECM and that the computer itself is regulating, or stepping down the voltage via resistors and things like that. Much the same as a portable radio the works off 110 voltage or C or D cell battery voltage. Little magic pixies living inside do their thing. Talk on ya later. HANK.
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Post by Sir Trevor on Feb 25, 2006 15:01:36 GMT -5
Ok, figured out I had the wrong wire (Even though a continuity test showed I had the right one) Anyway, too low a voltage coming out of the computer I was thinking, for a temporary fix. Any idea if any other circuits run off the same amount of consistent voltage? If I understand things correctly, this is just constant juice that is put into the sensors. How much comes through the sensor tells the computer what is going on. If I can supply another power source, it should work.
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Post by bunbun / Hank on Feb 25, 2006 16:36:25 GMT -5
OK Trevor... The manual shows a SECOND gray wire listed as a 5 volt ref. (they might mean 0.5 volt, but the printing is so damn small I cannot make out any .
Now this one runs to the Manifold Absolute Pressure Sensor.( MAP, for short) The book shows this as being located on the pass. side firewall, near the alternator. It should have a vacuum hose connecting it to the intake manifold.
I would test that for proper voltage, and if it seems to be correct maybe you can splice into that and run a wire over to the TPS. If you are not getting proper voltage OUT of the computer it sounds like that took a crap on ya. HANK.
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Post by Sir Trevor on Feb 25, 2006 16:43:35 GMT -5
Is that the only other one? Because the MAP and the TPS splice together in the wire harness, then go back to the ECM.
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Post by bunbun / Hank on Feb 25, 2006 17:04:04 GMT -5
In my manual it DOES NOT show them as being spliced together. I show three wires coming off the MAP sensor. A PURPLE, which is the ground. and a LIGHT GREEN and a GRAY which run back to the ECM. Now, it shows a splice in the GRAY that then goes to the A/C Comp. Pres sensor. But I am showing two completely separate GRAY wires. # 7 ( their reference num.) which goes to the TPS. and # 12 which runs to the MAP. Those are the only two labeled as 5 volts ref. ( there might be others putting out 5 (or.5) volts but those are the only two designated as such.)
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Post by Sir Trevor on Feb 25, 2006 17:35:27 GMT -5
Ok, I'm going to have to do some more digging in the wire harness then.
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Post by Sir Trevor on Feb 25, 2006 18:10:51 GMT -5
Looks like I am working with the MAP Wire come from the MAP and goes to the harness, where it, and another grey splice to a larger grey and go to the computer. What I would like to know, is why the hell do the wires have to go all over the place? Look at that picture. You can see the TPS and the wire harness behind it. Does it go right over there? NO! It has to go down behind the motor. Then come up, then run down to the fan. Then over by the battery, then back to the firewall. Then all the way across the engine compartment over to the other side. Why!
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Post by bunbun / Hank on Feb 25, 2006 19:07:41 GMT -5
As to WHY. Mostly I think it is just to PI** you off. I have wired cars from scratch(hot rods and such) and it is NOT as complicated as they make it. I know what you are saying, this crap just drives you crazy. Nice photos, by the way.
Now, the manual I am using covers from 1982 thru 1994. And they only show the one wiring diagram for the 3.1 V-6 engine. (they show others for the 4 cyl. but the one I am using is as close as I can come to what you have) Now in that 12 year period they could have made some changes that I am not showing. You would have to get a manual specifically to your make,year, and model. I think the first picture of the MAP shows what is probably the gray wire from the MAP and the gray wire from the A/C comp pres sensor spliced together and running back to the ECM.
The TPS GRAY wire should be totally separate from those two.
The biggest problem with factory wiring jobs is they have every connector for every accessory you can get on the car, even if you DON'T have that accessory. That way they only need to make one harness and lets say you and I order identical 2006 Whizzbangs and you want A/C and I don't, but I want power seats they just plug into the correct connector as they are ALL there.
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Post by bunbun / Hank on Feb 25, 2006 19:18:32 GMT -5
I got a bad feeling tomorrow is going to be a lot of fun for the both of us. The weather is getting a lot colder, BRRRR! and my buddy called and wants me to come over tomorrow and see if we can get this 1987 GMC he picked up running. I think he is going to scrap it out but if the motor runs he wants to keep that (probably a 350 Chevy engine. I think he wants it for his Studebaker hot rod he is building) Since I have a 1986 GMC I might be able to scrounge some parts off it I can use if he does scrap it out. But it will mean working outside. AH, just like the "good ole days" ya, right! After 3 years in a heated garage I'm getting spoiled! HANK.
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Post by Sir Trevor on Feb 25, 2006 19:59:48 GMT -5
Hey hank, I might have mispoke before. It is a 4 cylinder, not a 6
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Post by bunbun / Hank on Feb 25, 2006 20:59:17 GMT -5
OOOPS! Ya, back in "How much Snow" page 12, reply 176. you stated the car was an 89 Skyhaw (I assume you meant Skyhawk) 6 cyl. So that is what I have been working off of. NOW!! Which 4 cylinder are we dealing with? The 1.8-2.0-2.2 liter Over head valve.**** or the 1.8-2.0 liter Over head cam 4 cylinder From what I can see of your valve covers in the photos I would guess Over head valve. So at this point, let me go back to the manual and see what I can find on the four cyl. Let me know A.S.A.P. just what engine we are dealing with in case there are any important differences. I'll post as soon as I find anything significant. HANK.
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