Topic: Gas gauge finally fixed

[Mattb]

I wouldn’t be surprised if back in the day there was a test machine for them. However since in my experience they tend to fail intermittently just changing it is probably more cost efficient. Labor to change it should be minimal. A couple of screws hold it to the fender and there are two wire harness connectors. You can always order the module through the net but most likely you can source one locally. Looks like Rock Auto has Motorcraft unit available but Ive had luck with NAPA. One thing you might have to watch out for is if your car came with factory “ altitude compensation “. In that case the module would have 3 wire harness connectors and you might have to do a little more searching to find one.

[caravan3921]

Update on car stalling: another mechanic looked at it today and assessed it on a full gas tank, when it runs beautifully. He suggested that the sending unit that was 'fixed' back in December actually needs to be completely replaced. He is suggesting that when the gas tank is half or less, that's when we experience all the hesitation/stalling issues. We are going to test his idea, let the tank get to lower, and observe if it then starts to act up. If his theory holds true, then the sending unit was the issue all along.

[caravan3921]

Confused as to which sending unit to get, and where...
Any way to make this easy?

[Mattb]

My 77 sedan uses a Spectra FG 179B. ( I believe 77 and  78 were the same). Same sending unit used in 4 cylinder Mustang II of that year. I got mine from Rock Auto a few years ago but they seem to be difficult to find now. There does appear to be one on Amazon right now. There is also a 178B which I believe is correct for the 74-76 cars and a 178 and 9 A which do not have the second pipe for the return line from the fuel pump. The single pipe units were used on the V8 Mustang  IIs.( at least my that’s  what my 78 V8 Mustang II uses).
   The 178 series units look dimensionally similar to the 179 series units but have a slightly different ohm rating which presumably would have some effect on gauge accuracy. Naturally the 178B appears to be much more plentiful and cheaper.
  Hope is helps.

[Mattb]

Just another thought. Earlier in the thread you mentioned the fuel tank was repaired. Since the tank will need to come out to replace the sending unit now is the time to consider should a new tank be installed. A lot depends on how damaged the tank was, how it was repaired and how much rust inside. Same tank as the Mustang II. Spectra F81A I believe.  They seem in limited supply and who knows in the future.

[nnn0wqk]

Read most of the post and I am not getting a clear idea of when it acts up for you. Hot only, cold only, hot and cold, or just when ever it feels like it. Reason I ask is it is not that hard to duplicate hot or cold issues with the ignition module. Heat gun will warm it up and a trip to the freezer will cool them down. And not that hard to connect back into the system to see the results if it has been in the freezer. The one item that has not been mentioned in the ignition system is the pickup unit inside the distributor. The leads flex all the time as the vacuum advance does it thing. Add heat and forty years of time to the wires and if that has never been replaced it is very possible the wires are starting to break inside the insulation. That pickup causes all sorts of interesting issues as it fails. Back firing, no start to name a few. A way to test is put a vacuum pump on the vacuum advance unit and pump it up and down a few times with engine running and see if you can duplicate your issues. You can heat up the coil while running with the heat gun to see if you can duplicate the issue.

These are just some easy ways to test this stuff, does not always show a problem but if heat related about 95 percent of the time you can find the issue this way. My experience over the years has been usually/not always the module will just die. The pickup coil on the other hand will cause you to go bald if you do not think to check it.

I would really have my doubts that a vacuum delay would be causing you any issues. When you think about it all they do is DELAY they do not stop the vacuum.

Another item on the engine that can cause issues but usually more at idle than else where is if the EGR valve is not sealing well. Hard to adjust idle mixture if the EGR is leaking.

What engine and transmission? I do not believe I saw that information. There are other things I can suggest for you to check but I need a clearer idea what the symptoms are.

I am ASE Master Auto Tech, ASE Master HD Truck tech and own a 74 with 230k and at one time worked in an Auto repair shop the specialized in drivability issues. A Pinto really is not that hard to make run right IMHO. Sounds like the shop you have been trusting your Pinto to really does not have good grasp of what is going on.


One last question; when did this problem show up? After the sender was replaced or before. And was any other work done to the car at the time the sender was replaced?

[caravan3921]

Just an fyi that no progress on the hesitation issue. It seems to still slightly jerk when driving it. It's very random. Life events have gotten in the way of solving the problem once and for all. Will revisit this fall after triple digit temperatures have passed!