TPS voltage?

Tiny
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Okay, I will get ahold of them. Thanks. The tank was replaced before the injectors. I appreciate all your help.
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Tuesday, January 28th, 2025 AT 1:54 PM
Tiny
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That's what I would do, since they know what sections of the engine have been worked on and what to check first. Let us know the outcome.
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Thursday, January 30th, 2025 AT 4:29 PM
Tiny
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I got an obd1 scanner and I'm getting 2 codes. Cooling temp sensor and intake air charge temperature sensor out of range. So, I'm guessing the 38-year-old wiring harness may be to blame since the sensors look pretty new.
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Thursday, January 30th, 2025 AT 5:44 PM
Tiny
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Okay, both of those sensors use a 5v reference and also share a Ground. So start with unplugging either sensor and with the key On, check one of the 2 wires for 5volts, the other wire should be a sensor return (ground), when checking the 5volts you can use battery negative for the multimeter ground first to make sure the full 5volts is there, then use the other wire to verify ground. The meter should still read 5volts. Both of those sensors will affect the air/fuel ratio, especially the ECT.
If you can read live engine data, and either sensor is an open circuit, it should read -40 degrees on live scan tool data. If that's the case, the ECM could be flooding out the cylinders, due to misreading the temperature. It might be a bad ground on both sensors since they are shared.
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Thursday, January 30th, 2025 AT 6:23 PM
Tiny
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Both grounds were reading 4.68.
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Saturday, February 1st, 2025 AT 6:23 AM
Tiny
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So with the intake air charge temp sensor to begin with, when you have the sensor unplugged and the key On, are you measuring voltage across the two wires of the sensor, or are you measuring them one at a time using battery negative as your ground?

***It's really important to know how you are testing**, if you are reading 4.68volts from the SIG RTN wire (Ground) which is both sensor's Grounds and the other meter lead on battery negative, then you are reading voltage drop on the ground side of the circuit, threw the ECM to the battery Negative. I did my best to explain a thermistor's operation in the diagram below. It can be confusing at times but shows why knowing which wires were tested from is so important.

If you are measuring across the two wires of each sensor and getting 4.68volts, that might be within spec for a 5volt reference, it's a little low. But on older vehicles it was not as precise as on modern vehicles. So, if this is the case and you are reading almost 5volts across the two wires of each sensor, Check the MAP sensors 5volt ref too. Just to be sure the reference voltage is the same at the MAP location.
Next you can check to see if the ECT and ACT sensors are open circuit inside by measuring their resistance while unplugged. I know they look new, but you need to know why these codes are setting,

Because again, on an older computer like this there is only 1 voltage regulator for the reference voltage. A regulator that takes the 12v down to 5v for sensor use. But that reference voltage is extremely important to the ECM to function correctly. It might be that the 4.68v (if that's the reference you're reading) might be too low for those sensors. It's tricky with temperature sensors because they cannot directly share the 5v Ref with other sensors. Since their signal is determined by how much the sensor's resistance changes the 5volts.
Also do you notice the temperature gauge on the Cluster working?
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Saturday, February 1st, 2025 AT 8:09 AM
Tiny
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I measured from the ground wire of each sensor to the negative battery terminal. I get 5.05v from the MAP sensor.
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Saturday, February 1st, 2025 AT 8:31 AM
Tiny
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I am also getting OL when testing from one pole to the other on the unplugged sensors.
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Saturday, February 1st, 2025 AT 8:34 AM
Tiny
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Well that doesn't sound good, what voltage range are you set on when checking across the 2 sensor wires? 20volt scale I assume?
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Saturday, February 1st, 2025 AT 8:38 AM
Tiny
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Yes 20 volt.
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Saturday, February 1st, 2025 AT 8:39 AM
Tiny
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That's from one terminal to the other on the sensor itself not the harness plug wires, correct?
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Saturday, February 1st, 2025 AT 8:42 AM
Tiny
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No when checking the sensors themselves, set the meter to resistance setting, sorry for not being clear on that. You want to see if they have any resistance internally, they can be up to 5k-10k Ohms or more (10,000 Ohms) for temperature sensors.
When checking the resistance of the wires going back to the ECM, a rule of thumb is 5ohms on wires. From the sensor to the ECM. And technically you should have a reading from the ECT to the ACT on one wire of each as well since they share a ground.
Below is for checking from the ECM connector to each sensor. See what you get with resistance testing to see if any wires are open circuit. I will get back with you shortly.
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Saturday, February 1st, 2025 AT 9:09 AM
Tiny
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On pin 7 with the negative battery cable off and the multimeter set at 20k ohms. I'm getting. 85 on the hot side and ol on the ground side. That is true for both sensors. Both on pin 7.
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Saturday, February 1st, 2025 AT 10:21 AM
Tiny
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Okay, sorry for the delay, so much going on lately,
So, for simplicity and clarity, the ECT signal wire from the sensor's two wire connector goes to ECM pin 7, the other wire goes to ECM pin 46 (SIG RTN- Gnd).
The Air Charge Temp Sensor's signal wire goes to ECM pin 25, and its other wire also goes to ECM pin 46 (SIG RTN-shared Gnd).
The purpose of disconnecting the ECM connector and each sensor's connectors is to isolate each wire, so you measured from the ECT signal wire to ECM pin 7 with the sensor disconnected and the ECM disconnected and got 85 ohms, if that's the case then there is high resistance on the ECT signal wire going to ECM pin 7,
But these wiring diagrams don't show any possible connectors in between the sensors and ECM, so you will have to note the wire color and try to follow it as best as possible. My diagram below also shows how to check each wire for a short to ground, but also not knowing the wiring harness's routing, makes it a bit more difficult. Most of the time a sensor Ground like this will be a direct wire to the ECM, so not grounding to the engine block first like many other grounds are done. This is to preserve the sensors signal quality. The high resistance can be and is most likely corrosion somewhere in the circuit. Ie inside a connector or even a pin hole in a wire can cause it to corrode inside and it just grows right inside the wire insulation. This usually causes the insulation to discolor in places but can be difficult to spot.
You'll have to excuse my artwork below, but this should help simplify testing. Let me know what else you find, I apologize if you need to retest, it's not always easy to explain circuit testing. The method I would use is even more difficult with load testing a wire, but stick to resistance testing for now, since it sounds like you're onto a wiring issue here.
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Sunday, February 2nd, 2025 AT 10:38 AM
Tiny
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So, I changed out the plugs, going to the sensors and the codes disappeared. I'm still having issues, but it seems to be the wiring harness connectors. I ordered a new o e for the o2 sensor, as that is one of the other codes. When it arrives, I'll give an update.
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Sunday, February 2nd, 2025 AT 11:03 AM
Tiny
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What are all the codes you're getting? You may be dealing with pin tension inside the connectors, tightening up the female pins can help. We use pin terminal sets to check the tension of female pins by using a pin a little bit smaller than the one in the sensor.
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Sunday, February 2nd, 2025 AT 11:09 AM
Tiny
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Codes 21 and 24 are gone but I still have 12, 13, 30, 23, and 41.
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Sunday, February 2nd, 2025 AT 3:07 PM
Tiny
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So still a TPS code and a lean code, lean can still be a vacuum leak or an oxygen sensor thats stuck lean. Its tough not knowing what the oxygen sensor voltages are. The code 41 System always lean, sounds like the ECM is still seeing a lean condition regardless of enriching the mixture. A bad intake manifold gasket can cause something like this but so can a bad sensor or wiring.
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Sunday, February 2nd, 2025 AT 3:31 PM
Tiny
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Sorry 33 not 23.
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Sunday, February 2nd, 2025 AT 3:40 PM
Tiny
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33 is EVP not closing properly, EGR valve not closing, that will definitely cause issues at idle. The EGR valve is used under heavy throttle loads to allow a small amount of exhaust gas back into the intake manifold to lower in-cylinder temperatures to help prevent NOX emissions gases. But it should not be open at idle, obviously exhaust gases being introduced into the intake at idle will cause running issues. Heres the pinpoint testing for the EGR related codes.
The old school ford EGR valve will have a solenoid that controls manifold vacuum to the valve to open it when needed. It will have a tube running down to either the exhaust manifold or pipe. You can google 1987 ford EGR valve to get a better idea if youre not sure what they look like, but they can leak in a number of ways, the valve can get stuck open due to carbon build up, allowing exhaust gas in all the time, the diaphragm inside that applies the vacuum to pull the valve open can rip and become a vacuum leak allowing unmetered air into the engine (lean condition). You can unbolt it and see if its stuck open, or whats even easier is to just put a piece of sheet metal over the hole for the valve, basically deleting it from the engine for testing purposes. If the idle issue improves, youve found one of the more major issues. Thats what I would do, the truck is so old it probably doesnt even fall under the emissions standards anyway,
But take a picture of your engine so I can see what the setup looks like.
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Sunday, February 2nd, 2025 AT 4:07 PM

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