TPS voltage?

Hello, what voltage reading are you getting up to the OL reading? The TPS should have a 5volt reference wire, ground and signal. So, when opening the throttle plate the voltage reading should be either roughly around 0-5volts or the opposite, 5-0volts. I would check that there is a full 5volts on one of the wires with the key On. It is possible another sensor that uses the same 5volt reference is partially shorted to ground, causing this issue.

With the key on the voltage is .8 and as I engage the throttle it goes up to 1.9 then reads ol. That's at approximately half throttle. While driving, with my foot on the accelerator there's a loss of power then it stalls and won't start again.

Here is the wiring diagram for the engine wiring harness and the TPS min and max voltage readings. If you are reading almost 5 volts at half throttle it's possible one of the wires is shorted to a 12volt power supply causing a high voltage reading. Where are you getting the new sensors from?

Thanks for the diagram. The first sensor was on the truck when I bought it and the second came from rock auto.

Thats a very strange issue, with the sensor disconnected and key on do you read 5 volts okay on your meter on one of the wires?

You are sure your meter is set on at least a 20-volt scale? It's very odd for it to read Out of Limits.

You may want to check the MAP sensor's reference voltage too, just to compare.

I'd be very interested in hearing what the issue is on this case, the only time I have seen a meter read OL for voltage is when its set to a lower scale.

Okay. so, I'm dumb. It was at 2 not 20. My issue must be something else. I have sudden loss of power and the truck stalls and won't restart. I had vacuum leaks, but they were fixed. It was running rich and getting bad mpg now it won't stay running. This morning it was warming up and once it was warm it stalled. I was able to get it started then it immediately lost power and stalled. It idles high and then the RPMs drop, and it stalls.

This only happens when it gets hot? And does it restart right away, or do you have to wait for it to cool down?

It's seems to run okay until it warms up, but I can't say for sure. It's been super cold, and I've been warming it up before I drive it. I've tried cranking it, but it won't get high enough idle to stay running. Then it'll start and idle momentarily. Then it wants to shut off again. It has all new injectors, some sensors, new battery, timing is 10 etc. Seems to run rich but since yesterday it's really struggling.

Rich running as smoke out the tail pipe?
So, you can't keep your foot on the pedal to keep it running, it still stalls out?

I can feather it and keep it running momentarily. If I push the clutch and take the load off it shuts off. It's that eye watering exhaust smoke. Not burning oil or anything.

So you may have injectors leaking, or possibly a sensor not reading correctly and the PCM is over fueling. I would see what the front Oxygen sensor voltage is reading, with a multimeter you will only get the fastest average voltage the meter can read, but if you see the voltage stuck low (the front 02 should read a fluctuating 0.2-0.8volts), if its stuck below 0.4v the PCM will enrich the mixture constantly due to a false 02 reading, basically the PCM will think the mixture is lean and keep adding fuel to compensate for that issue. A bad coolant temperature sensor can do the same thing, if it's reading a cold engine constantly the PCM will keep the mixture rich, but I assume you are seeing a normal temperature reading on the cluster since you see it reach operating temperature.

This would be something to observe on the live engine data of a scan tool, also check the fuel pressure regulator, there's a vacuum hose that goes to it from the intake manifold, check that no fuel comes out with the vacuum hose disconnected, if the regulator is bad it will pull fuel into the intake manifold through the regulator and the mixture will be extremely rich.

This is what you would see a normal oxygen sensor doing if you could observe the voltage fluctuation in real time. The first half is normal, and the second half is a slow responding sensor. But with a meter the signal is too fast so it will read the average as best it can. Here's a couple guides as well that may help. If the oxygen sensor were stuck at a low voltage due to the heater element inside the sensor not working or the sensor is just bad, the PCM would react by enriching the mixture.
But weak spark, low compression, or excessive fuel getting into the intake by some other means will cause fouled spark plugs with a lot of soot on them showing as a rich mixture as well.

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

https://www.2carpros.com/articles/why-an-automotive-engine-will-run-rich

When I got the truck, the timing was set at TDC, and it had clogged injectors from a rusty gas tank. Before replacing the injectors, I changed the plugs wires, o2 sensor and distributor cap. I just finished chasing down vacuum and exhaust leaks. I drove about 2 days with it before my current issue.

Where did the injectors come from?

They were installed by the shop doing my inspection. I'm not sure.

Are the spark plugs soaked in gas? And if the gas tank wasn't changed, I would be worried about possible rust making its way to the fuel injectors, after checking the condition of the plugs, you may want to get a fuel pressure gauge on the fuel rail or line going to it and see if fuel pressure is leaking down when the key is turned off, if the shop just rushed through the job and replaced the pump without really inspecting what else may have been in the tank. I can see debris migrating from the tank to the fuel rail over a 2-day period. If you're getting exhaust that is really that bad. Technically speaking, after all those repairs you should have good spark, good fuel control, and not the rich exhaust you're experiencing. I would bring it back to them, because really it's a come back for them.

Okay, I will get ahold of them. Thanks. The tank was replaced before the injectors. I appreciate all your help.

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.

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.

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.

Both grounds were reading 4.68.

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?

I measured from the ground wire of each sensor to the negative battery terminal. I get 5.05v from the MAP sensor.

I am also getting OL when testing from one pole to the other on the unplugged sensors.

well that doesn't sound good, what voltage range are you set on when checking across the 2 sensor wires? 20volt scale I assume?

Yes 20 volt.

That's from one terminal to the other on the sensor itself not the harness plug wires, correct?

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.

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.

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.

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.

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.

Codes 21 and 24 are gone but I still have 12, 13, 30, 23, and 41.

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.

Sorry 33 not 23.

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.