1979 Ford Thunderbird suddenly not starting

ford
thunderbird

#1

Hi! I have a 1979 Ford Thunderbird with a V8 5.0 liter engine. Here’s the mysterious problem… the engine turns over when I turn the key but stalls when the key is released. Thinking that the alternator died, I replaced it with a new re-manufactured unit and the car’s symptoms stayed the same. Also checked the fuses and the fuel filter and found that plenty of fuel is getting to the carburetor. This issue with the car not starting appeared literally overnight after I attempted to install a new radio. Prior to this the car ran reasonably well – always started easily and ran without a problem. Wondering if there is a possibility that I fried some part of the electrical system when I fussed around with all the wiring under the dash. Someone else had attempted the radio installation previously so the wiring there was already a mess of cuts and re-connections and was hard to sort out. Any advice or assistance would be greatly appreciated. Thank you! -Joe


#2

Are you saying It acts like it’s starting ok, then stalls when you release the key? Sounds like it could be a bad ignition switch. But if this problem occurred right after the radio installation, you probably messed up the wiring. No way to tell how from here.


#3

If you mean the engine starts when cranking it over, but stalls as soon as the ignition switch moves to the run position might point to a defective ignition module.

Ignition modules function in two modes. These are the start and the run modes. When starting the engine the module goes into the start mode which allows full battery voltage to the secondary ignition system. This ensures the spark is strong enough to start the engine when it’s cold and the fuel mixture is rich. Once the engine starts and the ignition switch moves to the run position, the ignition module switches over to the run mode. The module then steps the voltage down to the secondary ignition system so the voltage being supplied to the battery from the charging system doesn’t cause the voltage to be too high where it fries the secondary ignition components.

So the problem might be that the start mode of the module is functioning, but the run mode of the module is failing.

Tester


#4

Yes, it acts like it is starting ok, but then stalls when the key is released from the crank position. Is there a way to test the ignition module? Is there anyway that I could have fried it by short-circuiting something with the radio or other electrical issue under the dash? Thanks for your help!


#5

There is an inline resistor wire for “run”…you can replace it with a chrysler balast resistor as the resistance is built into the main harness and you don’t want to do that, I’m sure…common problem, easily fixed…just Key-ON 12V into the resistor and out to the coil +. The ignition module has nothing to do with it. and DTW, the Chrysler module will also work just as well as the DuraSpark if you translate the wiring correctly.


#6

Auto parts stores use to have the capability of testing OBDI ignition modules. Call around to local auto parts stores and ask if they have the capabilty of testing the Ford EEC-IV ignition module.

These ignition modules were prone to this type of starting problem. When I had my 78 Ford LTD, I had two modules mounted on the fender well. So when one failed, all I had to do was open the hood and plug in the second ignition module and I’d be on my way.

So the connection between the new radio and the no start condition could be a red herring.

Tester


#7

A '79? \Iif that’s true, the EEC-IV engineers were still in high school…EEC2…blech and EEC3 survived a couple of years but, was pretty bad and I doubt you could get parts for it. However, Duraspark which is what this T-Bird (79) ought to have, is available almost wnywhere. However, be warned that you may and probably do have an open resistance wire (~8 Ohm) in the main harness. Don’t replace it, just bypass it and use a Chysler balast resistor for repair simplicity.


#8

With the key in the run position check for voltage at the coil + terminal. 8+ volts should be indicated there.