Temperature sending unit.

[jdavidsmi]

One of the things I notice on my truck is it has two temperature sending units. one is located on top of the thermostat housing and the other is on the intake manifold just to the right of the distributor. the one on top of the thermostat is broken off and not connected ,the one on top of the manifold is connected. I have not notice any problems with the gauge.

Which one should be used? or does it matter?

[Gary Lewis]

It would help if you would create a signature that tells us about your truck. That way we wouldn't have to ask each time, and in this case we need to know if your truck originally had a computer. But I'm guessing it did as only the trucks with two sending units had two temp senders/sensor - one for the gauge and one for the computer.

If you go to the navigation menu to the left and go to Electrical/EVTM/1986 EVTM and click on 1986 EVTM you'll get to the top level of that document where you can see an index of everything in it. (I always like to start there.) If you click on 9. Electronic Engine Controls and then scroll down to Page 57 you'll see that at the top center of the page there's an Engine Coolant Temp Sensor (ECT) and that it has two wires to it - a black/white and a light green/yellow. Does one of your two have two wires to it? That's the one that was used by the computer.

Then go back to the top level of the 1986 EVTM and scroll down to 18. Fuel Tank Selector & Gauges. On Page 95 you'll find a red/white wire running to the Coolant Temperature Sender from the gauges. Only one wire as the sender grounds to the engine. And I'll bet that's the one that is being used.

So, let's find out something else about your truck. Do you have an ignition module on the driver's fender? If so, what color is the grommet where the wires come out? Or, do you have a vacuum advance on the distributor? I ask because we need to determine if the computer is still being used. If so, it is going to have its knickers in a twist with that temp sensor disconnected.

[jdavidsmi]

It would help if you would create a signature that tells us about your truck. That way we wouldn't have to ask each time, and in this case we need to know if your truck originally had a computer. But I'm guessing it did as only the trucks with two sending units had two temp senders/sensor - one for the gauge and one for the computer.

If you go to the navigation menu to the left and go to Electrical/EVTM/1986 EVTM and click on 1986 EVTM you'll get to the top level of that document where you can see an index of everything in it. (I always like to start there.) If you click on 9. Electronic Engine Controls and then scroll down to Page 57 you'll see that at the top center of the page there's an Engine Coolant Temp Sensor (ECT) and that it has two wires to it - a black/white and a light green/yellow. Does one of your two have two wires to it? That's the one that was used by the computer.

Then go back to the top level of the 1986 EVTM and scroll down to 18. Fuel Tank Selector & Gauges. On Page 95 you'll find a red/white wire running to the Coolant Temperature Sender from the gauges. Only one wire as the sender grounds to the engine. And I'll bet that's the one that is being used.

So, let's find out something else about your truck. Do you have an ignition module on the driver's fender? If so, what color is the grommet where the wires come out? Or, do you have a vacuum advance on the distributor? I ask because we need to determine if the computer is still being used. If so, it is going to have its knickers in a twist with that temp sensor disconnected.

Thank you for pointing me in the right direction for the information, I'm lucky enough to have the 84 owners manual and it shows that the original owner put a motor in the truck on 1-27-03 the motor had 76000 on it and the truck had 55,500.

The computer attached has a blue grommet

Attached to drivers side fender

grommet has wires that are taped up, almost scared to fix it maybe should just get a different one.

Distributer and the temp sensor just to the right, This one is connected. The wire to the sensor is red with a light color stripe, could be white.

Temp sensor on top of thermostat housing appears to be broken off and is not connected

Yes it does have a vacuum advance, I have replaced the pickup coil inside the distributer. as you can see from the following photo one of the wires was held together with caulking.

 

[Gary Lewis]

Thank you for pointing me in the right direction for the information, I'm lucky enough to have the 84 owners manual and it shows that the original owner put a motor in the truck on 1-27-03 the motor had 76000 on it and the truck had 55,500.

The computer attached has a blue grommet

Attached to drivers side fender

grommet has wires that are taped up, almost scared to fix it maybe should just get a different one.

Distributer and the temp sensor just to the right, This one is connected. The wire to the sensor is red with a light color stripe, could be white.

Temp sensor on top of thermostat housing appears to be broken off and is not connected

Yes it does have a vacuum advance, I have replaced the pickup coil inside the distributer. as you can see from the following photo one of the wires was held together with caulking.

Thanks for the signature info. That helps all of us know something about your truck w/o having to ask.

An '84 w/a 302 would have had a computer, called an EEC for Electronic Engine Control. And the computer would have controlled ignition timing. But it would have been upset because the temp sensor is broken, and who knows what else, so it probably would have locked the ignition timing and your power and MPG would have been poor.

Probably for that reason, someone has done a DS-II conversion, which means they got the wiring harness, ignition module w/a blue grommet, and distributor w/a vacuum advance and installed them. No longer does the computer control the ignition timing. 👍

But you are right, you should replace that ignition module. Those wires are very suspect, an d a failure there will have you stranded on the side of the road.

[Ken Blythen]

I think that 'sensor' is the remains of a ported vacuum switch; these were used to apply vacuum to different items, once the engine reached certain temperatures.......such as the exhaust heat baffles etc.

On the front of your carb, beside the accelerator pump, is a round gadget (which looks disconnected) & originally increased & decreased the accelerator pump volume, according to engine temperature......this was just one thing controlled by a PVS. It was a small fuel saver/emission device that isn't critical.

[Gary Lewis]

I think that 'sensor' is the remains of a ported vacuum switch; these were used to apply vacuum to different items, once the engine reached certain temperatures.......such as the exhaust heat baffles etc.

On the front of your carb, beside the accelerator pump, is a round gadget (which looks disconnected) & originally increased & decreased the accelerator pump volume, according to engine temperature......this was just one thing controlled by a PVS. It was a small fuel saver/emission device that isn't critical.

Good catch, Ken!!

But, an '84 would have had the EEC computer system - right?

[ArdWrknTrk]

Good catch, Ken!!

But, an '84 would have had the EEC computer system - right?

Gary,

Are you sure?

was this an option like efi in '85?

It seems a DSII conversion is easy to make right and wouldn't use any temp sensor.

heck, my '87 has a harness that accepts EEC-IV.

If it is a tcvv it may be for egr, or the distributor.

[Gary Lewis]

Gary,

Are you sure?

was this an option like efi in '85?

It seems a DSII conversion is easy to make right and wouldn't use any temp sensor.

heck, my '87 has a harness that accepts EEC-IV.

If it is a tcvv it may be for egr, or the distributor.

Jim - I'm not sure of much of anything. But my remembrance is that F150's didn't have a heavy enough GVWR to dodge the emissions requirements in '84, so all of the 302's had computers. If that's true, then David's 302 must have been converted to DS-II.

Or did I misunderstand?

[Ken Blythen]

Good catch, Ken!!

But, an '84 would have had the EEC computer system - right?

Yes, AFAIK Gary, & a feedback carb.....unless there was an HO version 302 available in trucks, that had no ECM.

[Gary Lewis]

Yes, AFAIK Gary, & a feedback carb.....unless there was an HO version 302 available in trucks, that had no ECM.

Not sure I understand what you said, Ken. There wasn't a 302HO in any year in the trucks. And this one appears to have had a carb, so it would have been a 2bbl feedback Motorcraft with a computer to drive it. Right?

And with a computer running the carb it would run the ignition timing as well.

Or, am I lost? That would be easy given what is going on right now - more about which later.