Suddenly wont start "checklist"?

[stuartrubin]

Hello FIAT friends,
My '75 124 Spider (with 2.0L engine, 34 ADF carb) had been running fine, but suddenly won't start. The engine turns over with the key, and I can hear the fuel pump running. Beyond that, I cannot say what is or it not working. I am definitely an amateur, so I am going to ask a very basic question.

Is there a "checklist" of things to go through to diagnose the car not starting? In theory, I know we need fuel, air, and spark, but I am hoping for a basic "here's what a mechanic would look at, in order of easiest / most likely culprit" down to the hard stuff.

Thank you very much. All advice is appreciated!

Stuart

[18Fiatsandcounting]

Stuart, I don't have a checklist per se, but here are the two items that I always start with in your situation:

1) Pull off the top of the carburetor air cleaner so you can look down into the carb throats. With the engine off, use a flashlight to look down the two barrels of the carb as you work the throttle by hand. You should see a squirt of fuel from a small jet on the side of one (or possibly both) barrel. A squirt of fuel indicates that you have fuel in the carb.

2) If you have a timing light, put the pickup on the main lead from the coil to the distributor. Crank the engine and verify that the timing light is flashing. This verifies that you're getting a spark. If you don't have a timing light, you can remove the #1 spark plug and (with the plug wire still attached) lay the metal threaded part against the top of the engine. In a relatively dark environment, you should see the spark when you crank the engine. This might require a helper to turn the key while you look for the spark.

Lots of other tests of course, but these are the two that I always start with. In your case, and a very wild guess at this point based on your description, but you could have a plugged fuel filter or a leak in the rubber hose between the gas tank and the fuel pump, so that the pump is pumping air rather than fuel.

-Bryan

[stuartrubin]

Bryan, thanks for the reply. I definitely have the squirts (ha!), at least in the throat which had the choke, which I believe is normal. I ran out of time tonight to pull the plug and see if I can get a spark. Hopefully, I can get to that tomorrow.

I don't have a proper socket for the spark plug, but it looks like a regular one the right size will work. Is that the case? If I need to buy a socket, are the sizes universal, or do I need a particular one?

Thank you!

Stuart

[rridge]

The 124 head takes a common 13/16in spark plug hex. A deep socket 13/16in. or 21mm will work. A dedicated spark plug socket will often come with a foam or magnetic insert which holds the plug in place while you position it. If you still have the factory tool set, you may already have a spark plug socket. A used spark plug is a handy thing to have in the glove compartment.

[18Fiatsandcounting]

I definitely have the squirts (ha!), at least in the throat which had the choke, which I believe is normal.

Yes, that's normal, and so it sounds like the carb has fuel.

rridge already answered your question about spark plug sockets, but to add to that, there are only two common sizes, a larger one and a smaller one. The Fiat spark plugs (Champion RN9Y or the equivalent) use the larger socket. Definitely something you should have in your toolbox.

-Bryan

[stuartrubin]

Ha! I totally forgot to check the toolkit (which I somehow still have). Regardless, I bought a socket and ran the spark test.

No spark.

So, I suppose now I go down the line until I find something that does work. Any tips on diagnosing the distributor? Ignition coil? Relays? Anything else?

Once again, all advice is appreciated!

Stuart

[18Fiatsandcounting]

Do you have the single point distributor or the dual point version? If I recall, model year '75 was the year Fiat switched from the former to the latter, up until 1979 or so.

-Bryan

[stuartrubin]

Bryan, according to the Workshop Manual (pp 55-14):
"IGNITION SYSTEM (to 1978)
DESCRIPTION
The ignition system used up to 1978 is the standard battery ignition type, except that it uses two sets of breaker points."

Is that what you're talking about?

[bobplyler]

2) If you have a timing light, put the pickup on the main lead from the coil to the distributor. Crank the engine and verify that the timing light is flashing. This verifies that you're getting a spark. If you don't have a timing light, you can remove the #1 spark plug and (with the plug wire still attached) lay the metal threaded part against the top of the engine. In a relatively dark environment, you should see the spark when you crank the engine. This might require a helper to turn the key while you look for the spark.

In my (much) younger years, I found you can get a little brother to hold the spark plug wire, and try cranking. If it's getting spark, you can only do this one time.

[SteinOnkel]

Bryan, according to the Workshop Manual (pp 55-14):
"IGNITION SYSTEM (to 1978)
DESCRIPTION
The ignition system used up to 1978 is the standard battery ignition type, except that it uses two sets of breaker points."

Is that what you're talking about?

Bin that immediately and get the 1979 electronic distributor w/ igniter. It's not expensive and a huge upgrade.

I suspect your ignition switch is on its way out, though. Try cranking and wiggling the cables behind it at the same time. You might get a spark.

[18Fiatsandcounting]

Stuart, yes, that was what I was talking about, and SteinOnkel's advice is a good approach. The dual point ignition systems were notoriously tricky to diagnose and get working as they should, and thus caused a lot of problems. Evidently they were put in the cars for emission control reasons, but when fuel injection came out starting in 1979, the dual point systems went away. You can "bypass" the dual point setup and just operate off one set of points, though, should you choose that route.

Bob, I'm glad I wasn't your younger brother! But, as kids, I and my friends used to challenge each other to touch the spark plug wire while another one of us pulled the starter cord on the lawn mower. Crazy stuff, and sometimes I'm amazed that I'm still here...

-Bryan

[stuartrubin]

Bob and Bryan, that's pretty funny! I'm an Electrical Engineer by training, but ironically kind of paranoid about being shocked. I think it's one of those things where the more you know, the more you obsess about what could go wrong... Regardless, I assume that getting shocked by a spark plug (which I think arcs at something like 25KV) would hurt, but not cause any harm. (This fear also gets in the way of my other hobbies from years past - vacuum tube audio, vintage video games, other things with lethal voltages, and maybe some day an electric vehicle conversion. Maybe I should get over this fear!)

I did a little reading and it sounds like the 124 ignition switch is a notorious weak link in the electrical system. l will try to diagnose it.

If there is a problem with distributor, I like the idea of replacing it with an electronic module. I'm guessing that after any incidental parts replacement, might spend just as much as replacing it. I may pop open the distro to inspect that it at least looks reasonable - not filled with oil, spinning, etc.

I don't know if this is a red herring, but I do have another clue. In the last few weeks, when I started the car up, maybe one out of ten times it would not start at first. If I waited and cranked again, it would start This implies some kind of part that might "sometimes" work then then eventually fail - like a part that wears out, or becomes loose, or something like that.

Thanks again.

Stuart

[18Fiatsandcounting]

I don't know if this is a red herring, but I do have another clue. In the last few weeks, when I started the car up, maybe one out of ten times it would not start at first. If I waited and cranked again, it would start This implies some kind of part that might "sometimes" work then then eventually fail - like a part that wears out, or becomes loose, or something like that.

Stuart, that does sound like an ignition switch that's on its way out, as Steiny suggested. Next time this happens, try jiggling the wires that go into the back of the ignition switch as you crank it, and see if that makes any difference. If it does, then it's probably the switch. It could be as simple as one of the push on lug connectors is loose, so you could check that as well.

By the way, my dad was a EE professor, so I picked up a lot of electronics along the way. Including ham radio, back the days of tubes and impedance matching for your antenna and final power RF stage. I got hit a couple times with around 600 volts, but I'm still here. Keep one hand in your pocket when working on circuits, as the saying goes. And stand on a rubber mat.

-Bryan

[SteinOnkel]

Regardless, I assume that getting shocked by a spark plug (which I think arcs at something like 25KV) would hurt, but not cause any harm.

It hurts like a mother, especially because it goes zap zap zap in really quick succession. You determine the voltage by how high the person being shocked gets lifted off the ground. 6" for every 5k volt

Pro Tip: One hand on the spark plug wire, the other in your pocet and NO skin touching the car

[stuartrubin]

try jiggling the wires that go into the back of the ignition switch as you crank it

Holy crap, that worked! Luckily, my car hasn't seen the plastic cover under the dashboard since I've had it, so access to these wires was quite easy. I just put a little pressure on every connector I could see, pulled the rubber boot back from the ignition switch harness and pushed them in a little, too. Next crank, it started up!

So, I guess it's time to replace the ignition switch...

Any last advice before I go parts shopping?

You guys (and every one else who read these) are awesome. Thank you!

Stuart