No spark when hot + weird ignition wiring?

[loglim11]

Hi everyone,

I'm trying to get a 1981 FI going again after sitting for more than a couple years. Apparently it's always had electrical issues, probably why it has sat so long. At this point it will reliably start cold and idle happily. Once hot, if I shut the car off and let it sit for a few minutes it will no longer start. Directly after shutting off it will start again, though.

I've narrowed the problem down to a loss of spark using an inline plug tester. Measuring voltage at the + terminal of the coil, if there is 12V or more then it'll spark and start. When the car won't start, there is only ~11.85V or less, and no spark.

Following the electrical manual, I inspected the wiring and found this, right behind the ignition switch connector:


The blue part has a cover that is pictured open, but closes over the melted looking bit. I don't recognize it, but it doesn't look so good. Does anybody know if it is stock, or even what it's for? Couldn't find many pictures online.

If I read the schematics right, the blue/red and pink wires are connected to fuse A. They also share terminals at the ignition switch with the light switch in the lowest position, and the coil. I mention the light switch because in the lowest position (lights on) the car won't even try to crank, 10V at the coil. If the lights are turned on while the car is running all is well.

Could this blue thing be causing an added impedence in the coil circuit and throwing things off? It does not get hot when running.

Another thing I read about while searching was ignition control modules will sometimes heat soak and fail causing similar symptoms. I may replace that to be safe since they are cheap. What's weird is with the lights in the middle position, I get 11.5V at the coil and it will usually spark when cold. Same issue hot. Because of that I moved on in the manual and tested for spark by holding the high voltage line off the coil close to ground, and there was nothing. This also leads me to believe it's the ICM. Thoughts?

For the full picture, here is the host of other electrical issues to deal with.
- Coolant temperature gauge is dead still no matter what. Fan does kick on though.
- Turn signals are wonky; lights all function but indicators show both blinking on left and both blink only once then nothing on right, but I can see other lights pulsing brightness with the flasher just not the indicators. Hazards work. Probably a turn signal flasher?
- The brake light is always on in the centre dash, even with hand brake down
- The seatbelt light will go off after some time with no seatbelts fastened.
- Maybe not electrical but speedo sits at 10km/hr when stopped. Can't remember if it moves properly when driving.
These are all persistent issues regardless of temperature. All grounding pods have been checked and cleaned. Maybe this is all related through fuse A? I'm unsure since the tach works perfectly.

Apologies for the long post, hopefully this is enough info to get somewhere. Any insight would be greatly appreciated!

[RRoller123]

That blue thing looks like an aftermarket electrical connection device. Usually used to add a wire connection to an existing wire. When the wires are put through the sides of the blue block, the cover is then folded over and set with a pair of pliers, which pushes a sharp connection piece through the wire insulation of both wires and and electrically joins the two wires. They may have done this because they needed power on one of the wires and didn't have it? Who knows, many odd possibilities. It does look at first glance like the connection may have overheated, but it is hard to tell from the picture.

[spider2081]

Looking at the photo:
inside the original Sipea ignition switch there are 3 sets of contacts.
The brown wire powers 2 sets of contact. the blue wire in "start and run" and the red wire in "start"
The black wire powers the 3rd set of contacts the pink wire in "start and run"

Someone must have believed one of the "start and run" set of contacts was unreliable and jumped the switched sides together.

Does the car have its original coil. If not have you measured the resistance of the coil. The ignition control module is designed to work with coils that have a primary resistance of 0.8 ohms. If the wrong coil has been installed that could be an issue.
When the voltage to the coil is low have you checked the voltage at the battery posts?

[SteinOnkel]

Automotive electrical systems are nominal 12V. Meaning they have an operating range around 12.0V, usually 10.5-15.0V.

Your car should have a spark regardless of the 11.85V at the coil. It goes down because as components heat up, their electrical resistance rises. Now, 11.85V* on an ignition coil isn't great - you won't get a very nice spark with that. But it should not prevent the coil from producing a spark at all. If your alternator is properly working and your battery is full, you should see around 13.7V on healthy, positive terminals with the engine running. It goes down the further they are from the electrical source and the poorer the connections.

*However, ignition coils are where it gets complicated. Some older ones run around 9V, so there is a resistor in the positive circuit to take it down to 9. I believe the FI cars do not have this ballast resistor.

I would look elsewhere to find your no spark.

[76was124]

Had the same problem on an '81, for me, the issue was the sensor in the coolant T. Maybe someone else can confirm but I think you can unplug the sensor when the engine is hot and won't start. Then it will start hot. I'll look at the wiring diagram when I get a chance to confirm you unplug it verses jumper it.

[76was124]

Would also be careful messing with the ignition wiring given it starts fine cold and doesn't stop when running hot. Only a hot restart being the problem, not sure ignition wiring is the problem

[18Fiatsandcounting]

Could this blue thing be causing an added impedence in the coil circuit and throwing things off?

Yes, it could. This blue thing is what is known as a T-Tap connector. See: https://www.lowes.com/pd/Utilitech-20-C ... /999956682
What might be happening is that this connection is very flaky with occasional bouts of high impedance. You may be measuring 11.85v on your ignition circuit when no current is being drawn, but if this blue connector is part of the circuit somehow, and it has high impedance (resistance) when current starts to flow, and you get a large voltage drop across this connection, that could be an issue.

So, I would first fix this connector, either by replacing or just temporarily splicing the blue/red and pink wires together. As was pointed out in an earlier post, one of these wires could have lost its connection to 12 volts (or whatever it is supposed to have) and someone just rigged this together to "fix" it.

For the full picture, here is the host of other electrical issues to deal with.
- Coolant temperature gauge is dead still no matter what. Fan does kick on though.
- Turn signals are wonky; lights all function but indicators show both blinking on left and both blink only once then nothing on right, but I can see other lights pulsing brightness with the flasher just not the indicators. Hazards work. Probably a turn signal flasher?
- The brake light is always on in the centre dash, even with hand brake down
- The seatbelt light will go off after some time with no seatbelts fastened.
- Maybe not electrical but speedo sits at 10km/hr when stopped. Can't remember if it moves properly when driving.
These are all persistent issues regardless of temperature. All grounding pods have been checked and cleaned. Maybe this is all related through fuse A? I'm unsure since the tach works perfectly.

Apologies for the long post, hopefully this is enough info to get somewhere. Any insight would be greatly appreciated!

Taking each question in turn:
Dead Temp gauge: Likely either a bad temp sensor, or a disconnected wire. The fan switch is a different sensor.
Turn signals: Usually a bad ground to the light housing, occasionally a bad bulb socket, sometimes a bad turn signal relay.
Brake light: Do you have enough brake fluid? The sensor in the brake fluid reservoir could be bad.
Seatbelt light: I think that is normal. Bugs you for a while to fasten your seatbelts but gives up after a while.
Speedometer: Normal. For some reason the "rest" pin for the speedometer needle on Fiats is not at zero. Look very closely with a strong light and you'll see that rest pin.

-Bryan

[loglim11]

Thanks to everyone clarifying what the blue connector is, that's one mystery solved!

Someone must have believed one of the "start and run" set of contacts was unreliable and jumped the switched sides together.

Does the car have its original coil. If not have you measured the resistance of the coil.

This sounds plausible. The question is why? I'm going to see if I can get some more info on why it was installed in the first place. Worst case I'll re-do the connection, but if possible I'd like to fix it properly.

As far as I know, the car has the original coil but I will confirm the resistance next chance I get. Same with the battery voltage although I don't believe this is the problem since I can reliably replicate the issue regardless of the battery being freshly charged or after days of troubleshooting. Not the best for the battery, I know!

Had the same problem on an '81, for me, the issue was the sensor in the coolant T. Maybe someone else can confirm but I think you can unplug the sensor when the engine is hot and won't start. Then it will start hot.

I did try unplugging the sensor and the first time I did when hot the car would fire but immediately die, unable to get idling. This also only worked once, I haven't been able to replicate it. Measuring the resistance of the sensor at the ECU connector shows to be within spec. I'd be happy to continue exploring this if there's any more suggestions here.

Would also be careful messing with the ignition wiring given it starts fine cold and doesn't stop when running hot. Only a hot restart being the problem, not sure ignition wiring is the problem

Fair. However even if this aftermarket connector is not the ignition problem, I still feel it needs addressing as in my experience melted connectors mean something is not right somewhere in the system.

Taking each question in turn:
Dead Temp gauge: Likely either a bad temp sensor, or a disconnected wire. The fan switch is a different sensor.
Turn signals: Usually a bad ground to the light housing, occasionally a bad bulb socket, sometimes a bad turn signal relay.
Brake light: Do you have enough brake fluid? The sensor in the brake fluid reservoir could be bad.
Seatbelt light: I think that is normal. Bugs you for a while to fasten your seatbelts but gives up after a while.
Speedometer: Normal. For some reason the "rest" pin for the speedometer needle on Fiats is not at zero. Look very closely with a strong light and you'll see that rest pin.
-Bryan

Thanks for your breakdown of these, and the ID on the T-Tap connector too. Doesn't sound like these are all related, then. The seatbelt light is weird because it will stay on with both belts fastened, too.
I didn't even consider brake fluid. That's probably it - the pedal felt like low fluid too but it needs a full brake job so I was going to do it all in one go.