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Old 10-01-2007, 05:40 PM   #11
MAKG
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An open in the supply wire will give a grounded (too low) signal, not too high.

There is no way to make the signal wire read higher than supply in a resistive circuit, so something is wacky. Given that the signal is almost exactly 5V, I suspect the voltmeter just didn't make good contact when measuring the supply wire (and it's really 5V as well).

But I think the ground side is open. Probably within the TPS itself, or the connector (depending on how the test was done).

A simple ohmmeter will confirm. What's the resistance between the two outer pins, on the TPS with the connector removed? If it's open, you need a TPS. This is not a common wear failure. This is a defect in manufacturing or breakage during shipping or somesuch.
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1991 Exploder, 4.0L, M5OD-R1 manual transmission, electronic BW1354 transfer case, 3.54 gears, 31 inch tires, icky two-tone blue paint with little clear coat, 230K miles.

1972 Chevy C-10, 250 I-6, SM465 (2WD) four-on-the-floor, 3.73 gears in a GM 12-bolt, puke green with a white cab. The "4 wheeled trash can," with x70K miles. x is probably 2.

Last edited by MAKG; 10-01-2007 at 05:42 PM.
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Old 10-01-2007, 05:48 PM   #12
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lol, so your telling me everything i learned in electronic engine managment is wrong? The 5v referince signal is being monitored by the ecm as IT LEAVES the ecm and heads to the tps. IF THAT VOLTAGE does not make it to ground through the tps, it finds its way to ground internaly, through the ecm, which then flags a tps high code. if it it wasnt a missprint in a manual, and it REALY IS higher then suply, then somthing in the ecm is ****ed, and its time for a replacment Fred...... ****in ridiculous electronic device. I duno what some of you do for a living, but i diagnose this stuff at work, and learn about it at school.
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Old 10-01-2007, 06:07 PM   #13
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Not everything, but you're going to have to explain how the computer monitors the 5v reference signal as it leaves the ecm and heads to the tps. There is nothing between there except for the supply wire itself. The computer has no way to know if it "got there" or not. There are precious few redundant systems in an automobile. Running a whole bunch of wires to monitor one might be called for in the Space Shuttle (where that wire failing might kill someone) but it just isn't in a light truck.

If it didn't "make it there," the signal wire is grounded. A resistor with no current is the same as a wire. That's Ohm's Law.

Ungrounded circuits can sometimes behave the way you describe (not one so simple as this one, though). But not unpowered circuits.
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1990 VW Jetta GL, 1.8L 8V gasoline engine, manual transmission, painted in oxidized red paint and ponderosa pine sap, unknown mileage.

1991 Exploder, 4.0L, M5OD-R1 manual transmission, electronic BW1354 transfer case, 3.54 gears, 31 inch tires, icky two-tone blue paint with little clear coat, 230K miles.

1972 Chevy C-10, 250 I-6, SM465 (2WD) four-on-the-floor, 3.73 gears in a GM 12-bolt, puke green with a white cab. The "4 wheeled trash can," with x70K miles. x is probably 2.
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Old 10-01-2007, 06:18 PM   #14
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lol, the signal wire is OPEN if it didnt make it to the tps, its grounded if it contacts a ground wire, or a grounded component of the truck. I can drag this out and explain how the ecm is monitoring the reference voltage and the signal voltage if you like?
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Old 10-01-2007, 06:44 PM   #15
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The reference voltage doesn't change with an open. It would with a short to ground, but then you'll just burn out the VREF circuit and fry the computer.

You're confusing the signal wire with the supply wire. An open signal is floating and will read according to PCM internals. An open supply grounds the signal. It's not floating. Similarly, an open ground sets the signal to reference.

This is a very basic voltage divider circuit, which I'm sure you learned about in school. It's not at all a complex circuit. It's just a potentiometer with a 5V reference.
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1990 VW Jetta GL, 1.8L 8V gasoline engine, manual transmission, painted in oxidized red paint and ponderosa pine sap, unknown mileage.

1991 Exploder, 4.0L, M5OD-R1 manual transmission, electronic BW1354 transfer case, 3.54 gears, 31 inch tires, icky two-tone blue paint with little clear coat, 230K miles.

1972 Chevy C-10, 250 I-6, SM465 (2WD) four-on-the-floor, 3.73 gears in a GM 12-bolt, puke green with a white cab. The "4 wheeled trash can," with x70K miles. x is probably 2.

Last edited by MAKG; 10-02-2007 at 04:07 PM.
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Old 10-01-2007, 07:50 PM   #16
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shit, im an idiot. high tps voltage can mean that the tps ground is damaged. the suply wire needs to be working to get suck a code, correct?
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Old 10-01-2007, 07:51 PM   #17
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makg My mistake man, studying for the exemption test is makin my brain slowly turn to mush haha
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Old 10-01-2007, 07:52 PM   #18
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after a bit more thought, a bad tps wouldnt be the root cause of the problems tho..... a combination if that plus some other problems like fuel delivery could do it tho, no?
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Old 10-02-2007, 09:56 AM   #19
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Quote:
Originally Posted by Ranger5.0 View Post
makg My mistake man, studying for the exemption test is makin my brain slowly turn to mush haha
Oh, BTDT.

At least it's only slowly....

Good luck.
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1990 VW Jetta GL, 1.8L 8V gasoline engine, manual transmission, painted in oxidized red paint and ponderosa pine sap, unknown mileage.

1991 Exploder, 4.0L, M5OD-R1 manual transmission, electronic BW1354 transfer case, 3.54 gears, 31 inch tires, icky two-tone blue paint with little clear coat, 230K miles.

1972 Chevy C-10, 250 I-6, SM465 (2WD) four-on-the-floor, 3.73 gears in a GM 12-bolt, puke green with a white cab. The "4 wheeled trash can," with x70K miles. x is probably 2.
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Old 10-02-2007, 10:00 AM   #20
MAKG
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Quote:
Originally Posted by Ranger5.0 View Post
after a bit more thought, a bad tps wouldnt be the root cause of the problems tho..... a combination if that plus some other problems like fuel delivery could do it tho, no?
Yes, I agree. My original thought was that a broken ground accounted for it all, but the TPS voltage measurement seems to isolate the ground to inside the TPS. I don't see how that could affect the torque converter.

The computer thinks the throttle is wide open, so it's probably very rich. That MAY account for the bad performance.

The right thing to do here is warranty the TPS (it's clearly DOA) and reevaluate. Check spark plugs for fouling and proper gaps.
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1990 VW Jetta GL, 1.8L 8V gasoline engine, manual transmission, painted in oxidized red paint and ponderosa pine sap, unknown mileage.

1991 Exploder, 4.0L, M5OD-R1 manual transmission, electronic BW1354 transfer case, 3.54 gears, 31 inch tires, icky two-tone blue paint with little clear coat, 230K miles.

1972 Chevy C-10, 250 I-6, SM465 (2WD) four-on-the-floor, 3.73 gears in a GM 12-bolt, puke green with a white cab. The "4 wheeled trash can," with x70K miles. x is probably 2.
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