TPS Sensor Wire Cut

Macros

SCCoA Member
Here's an interesting one...

I picked up a 1995 SC with a broken Harmonic Balancer (the fun kind where the nose is still wrapped around the crank and the bolt is lodged inside). After reading the forums here, and some coaching from Dave D. (Thanks Dave!), I was able to remove the broken piece and install a new BHJ Balancer and March Pulleys.

After putting the car back together last night, it cranks over but will not fire. I am getting fuel pressure and the plugs are clean. I also pulled codes on the Key On Test, but everything passes, so I have some more investigation to do.

In looking over things a bit closer and checking for any leaks, I noticed that the TPS sensor wasn't plugged in. In fact, it looks like the previous owner actually CUT THE SENSOR OFF!!! The cut wires were tucked under the throttle body. (see photo).

MY question is this: Why would someone cut this out? I would think the car needs the TPS connected to continue to run properly.
 

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yea, that is weird. hopefully when you get that plunged back in the motor don't knock bad, or the trans. their has to be a reason why .
 
Sounds like someone gathered up a bunch of parts and put it back together without worrying if it was able to run.

They found a throttle body w/TPS at a wrecking yard, and when they pulled it there they cut the harness to save time (?)...when it went onto the car you have now, they simply bolted it on and tucked the harness down (to save time?) to make it look like the job was done.

Needless to say, no telling what else you'll find like this on the car over time, sorry. I'd be checking every fluid, every fastener, every mount, every wiring connection, lugnut, tensioner, belt, hose, filter, latch and adjustment I could think of. I'd say that it looks like someone really slapped that thing back together, but that might be too kind.

I see mis-routed lines and missing clamps and brackets in that photo alone...be sure to check for oil in the supercharger before you run it - if it gets that far.
 
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Actually, the car is extremely clean, and nothing else is missing. The car was a single owner for 14 years (CarFax Verified). It was only sold because he thought the crank was shot when he saw part of the balancer was still embedded in the front of the crank. He had changed the wires and routed them underneath the supercharger for looks. I hadn't rerouted them as I have new wires coming with the aluminum wire looms.

As I had just put the new balancer, pulleys, and belts on, I still have more work to do. I had heard that the car can run with the TPS unplugged, and thought that somewhere along the way a shop may have cut it for some reason.
 
I think it might idle as fare as that, but driving it while it's unplugged i don't think you could. maybe not though lol.
 
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If the tps is cut it won't start as the eec will see 5v, which to the computer looks like a clear flood condition and it stops injecting fuel.
 
If the tps is cut it won't start as the eec will see 5v, which to the computer looks like a clear flood condition and it stops injecting fuel.

That's not correct. If the wires are cut, the computer will see 0 volts. The TPS completes the circuit for the signal return, and with it disconnected there is infinite resistance across the circuit, so nothing is seen by the computer.
 
Beg to disagree but 5v is an open which is what the eec sees when disconnected.
0v is a short to ground.
You might want to rethink your electrical theory there,disconnect yours and check across the two wires(can't remember colors right now)you will see 5v.
Take it from a mechanic 5v open,0v shorted.
 
Well then I'll explain to help you out here. There are three wires, a reference 5V, a signal return, and ground. The TPS is a potentiometer. The reference voltage goes into the sensor and is fed through the resistive element, where it exits on the signal return wire. This is what the computer sees as voltage from the TPS. At closed throttle, resistance is at its maximum, generally outputting less than 1V. At open throttle, resistance is at its minimum, generally outputting around 4.5V. Now, if the sensor is disconnected, as is the case here when the wires are cut, there is no path from the 5V reference to the signal return. Therefore the computer sees nothing. Since you are a mechanic, I suggest you go back to school on electrical. The only thing you were correct about is that if I measure voltage across the 5V reference (Brown/White Stripe) and ground (Gray/Red Stripe), I'll see 5V. But, as you now know, that's not what the computer sees for the TPS signal.

Also, I'll add a bit about shorted and open circuits on the TPS to help you out some more.
5V reference open = 0V seen at computer
5V reference short to ground = Blown PCM fuse or other effects
5V reference short to signal return = 5V seen at computer
Signal return open = 0V seen at computer
Signal return short to ground = 0V seen at computer
Signal return short to reference = 5V seen at computer
 
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Eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeen!!!!!!!!!! WRONG.
Open is refrence 5v,always has been and always will be,shorted or grounded is alway 0v always has been and always will be.
But hey have it your way,who you gonna believe a tech or a guy who thinks he know,hmmmm,case closed.
 
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