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]

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]

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]

Good catch, Ken!!  

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

[ArdWrknTrk]

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]

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]

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

[Gary Lewis]

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.  

[Ken Blythen]

No, you're not lost at all Gary......sorry, I was replying to your earlier question (post #6).

I would assume originally a feedback carb, & EEC-III or IV.

[Gary Lewis]

Whew!  I thought I'd gone 'round the bend.

Yes, III or IV.

[jdavidsmi]

Been gone over the weekend, thanks for all the information. not sure how much I totally understand, but the gest is don't worry about the second sensor. and with the Duraspark II , I have a fairly reliable system.

Now I just need to find out why my new fuel pump stopped.
 

[Gary Lewis]

Your fuel pump stopped?  Is it mechanical or electric?  I would have thought it would have been mechanical originally.

[jdavidsmi]

Mechanical, Yes it just stopped. about two weeks ago on the way to town it died like I had ran out of gas, gauge showed 3/4 tank, of course it was on a narrow 2 lane with no shoulders. but a friend stopped and gave me a tow to a close parking lot. I have a clear fuel filter and there was no gas in the filter and turning over the motor did not pump any so either fuel gauge wrong or pump stopped. tried to put in 5 gal but it would only take 3 and it was full, so bad pump.  car quest new pump, had truck towed home.
Not knowing condition of tank I pulled it out to clean, pickup tube screen completely gone, ordered new pickup. cleaned inside and outside of tank, new pickup, new fill hose, new rubber fuel line, tested float, and put it back together.

Replace the fuel pump and noticed the oil pressure sensor leaking so I replaced that to. started the truck and everything working as it should.

Went out this morning and no gas to the filter. Gas to the flexible connection at the inlet of the pump nothing on the discharge side. Did I miss some trash in the metal tubing? Anyway I disconnected the fuel ling at the tank and pump and blew out the line again.

Nothing, pump will not pull gas from tank.

Very frustrated closed it up and called it a day. Tomorrow is a new day. Besides its a dark rainy day here in Tennessee, must be time for a nap.

[Gary Lewis]

While it is possible that you got a bad pump, I'm going to bet the problem is with a hose. Did you replace all the hoses?  On a 2-tank setup there will be one from the tank to the steel line, one from the steel line to the valve, one from the valve to the front steel line, and then one from that steel line to the pump. A leak in any one of them can kill the vacuum and prevent pumping gas. And, I've seen original lines leak right through the wall of the hose.

Or, it could be the valve if you have two tanks.

[jdavidsmi]

Gary, I only have the one 16 gal side mounted tank, I think the first thing I'm going to do is disconnect the hoses again and pull a vacuum and see if its holds, I want to believe its a vacuum leak.

[Gary Lewis]

Don't forget to plug the vent.  But, if you pull much of a vacuum you may implode the tank.  Doesn't take much to flatten something that big.

[jdavidsmi]

Wanted to give an update, did a vacuum test on the fuel line from the pump to the tank and found the clamp on the line from the tank to the steel was sucking air, put a better clamp on and solved the vacuum issue.

Thanks for everyone's help. Now on to the next issue trying to determine which model if the 2150 carburetor I have. but that will be a new thread.

David

[Gary Lewis]

Congrats!  One layer of onions peeled. Time for celebration and a small serving of onion rings. And then on to the next layer. 🙈