Runability Issue

[spidersherm]

Hello all! This is my 1st post and is the 1st time I have been this stumped.

I have a 1976 124 that will start and then stall out after 30-35 seconds of running. It will restart each time and the stall out again, I have times this multiple times and it always stalls out after 30-35 seconds. I was on a road trip and as I pulled into my destination it stalled and has not restarted since. Made it from Seattle to Bend, OR no issues. When it is running it sounds normal.

New Ignition components (plugs, wires, cap, rotor, condensers, points, coil) I am not able to check timing as it doesn't stay running for long enough but prior to this it was spot on, dwell @ 55 degrees. New electric fuel pump with filter and I have checked fuel pressure, it is good. New relays were recently installed. Fans operate, it has spark, Carb has been cleaned. I have no Idea where to go from here..... any and all help would be much appreciated!

[18Fiatsandcounting]

A few initial thoughts:

- Your '76 would have had the dual point ignition system, which had one set of points for starting and one for running. It's possible the running points are not set right (or bad, along with the condensor).

- The '76 also had all sorts of emission control devices: smog pump, EGR, etc. Are those all still present and working?

- The other possibility is the idle stop solenoid on the ADFA carb. It should have voltage at all times when the car is on, but if for some reason its +12V supply cuts out, the car will stall if its idling (it won't affect higher speed operation though).

-Bryan

[spidersherm]

Thanks Bryan!
No emissions equipment on it, its all been removed. Ive checked the Aux Points and Running Points, they are both new at .015 gap and were at 55deg of dwell before it had this issue. I had done a major tune before the trip so as to avoid any issues, LOLZ!

It has a 34adf carb on it but I will check that solenoid circuit for voltage drop! Thanks for the lead!

[18Fiatsandcounting]

The stock carb on a '76 spider was a 32ADFA 2/100 (or 5/100 if a California car), so a 34ADF isn't stock. Perfectly fine carb, though.

It could also be a fuel issue. I'm not sure how the float bowl on a 34ADF is vented, but if it's building up a vacuum in the float bowl after a while of running, it would slowly shut off the fuel and it would stall. I imagine that could take 30 seconds or so. Some carbs have a vent for when it's running but not at idle, but again I'm unfamiliar with the 34ADF.

Something else that often happens is building up a vacuum in the tank, but that doesn't sound like the issue because you were able to drive long distances with no issue. One quick check for this is to simply loosen the gas cap a turn or so and see if the problem goes away.

If you can get the problem to repeat, take off the air cleaner cover and peer down the barrels with a flashlight. If you work the throttle by hand, you should see a squirt of fuel coming out of the accelerator pump jet. If no squirt, then your float bowl is empty, and the challenge then is to figure out why.

-Bryan

[spidersherm]

Yes, I changed out the 32 for the 34 a couple of years ago. Fuel pressure is good. I tried the fuel cap test and no change, as far as float vacuum goes I have looked over all of the documentation I have for the 34ADF carb and cannot locate anything on it as far as a vent is concerned. The ICU solenoid is having voltage drop out and is damaged so next step is to replace that and replace the cover gasket (it ripped of course). I am almost 100% certain this is a fueling issue. I guess its time to clean everything out and reassemble and recheck.

[18Fiatsandcounting]

If the idle stop solenoid is damaged, that would be the first place to start. Make sure you get the correct size as there are a couple different versions, and I don't know which one the 34ADF took. The vendors likely know.

There are also some electrical gadgets that supply power to this solenoid, and something could be goofed up along the way. Especially some of the smog control stuff, as some of this also shut off power to the idle solenoid under certain engine conditions.

You can wire the idle solenoid to get power directly whenever the ignition is on, which is what some people do.

-Bryan

[spidersherm]

Update time! So new ICS in, no issues with that after repair.

I have traced the issue to a low oil sender, with KOEO fuel pump operates, relay activates system normal. The second the engine is started the fuel pump turns off and engine will starve until stall. If wire to oil pressure sensor is grounded the pump operates and engine runs until turned off. The sensor was recently replaced in 2023 because of oil leaking from the old one, but I exchanged it anyway with a new unit. Reconnected the stall returned and oil pressure is reading an actual of 43psi. about 10psi or so lower than spec i believe. I am using conventional 20w50 with a zinc additive and have been using this for the last 4 years.

So I guess now I get to find the source of the low pressure......

[18Fiatsandcounting]

Your oil pressure might be fine, and note that the oil pressure sender operates the gauge, but the low oil pressure light is controlled by a separate switch on the oil filter housing, and it grounds the light when oil pressure is low (and opens up when oil pressure is sufficient). That low pressure switch also goes bad over time.

Here's what I jotted down in my notes about how this all works, noting that this is for early spiders and may not be entirely accurate for later spiders:

"For safety purposes, some model years were configured so that the fuel pump would shut off when the low oil pressure sensor on the block was activated, i.e., to shut off fuel flow should the engine stop such as after an accident. However, this would also mean that the fuel pump would not operate when the engine was being started as the oil pressure is too low at that point.

To get around this, a special circuit was added to power the fuel pump by running a green/black wire from Terminal 16 of the ignition switch to the positive side of the fuel pump. Terminal 16 is connected to Terminal 30 (+12V from the starter) inside the ignition switch, but only during START.

Once the oil pressure was sufficient, the low oil pressure light would go out, and the fuel pump would be powered from the fuel pump relay. The fuel pump relay is powered by a pink wire from the input of Fuse 9, through an 8 amp fuse in an inline fuse holder and this powers both the NC input contact to the relay as well as one side of the relay coil. The other side of the coil is connected via a grey/yellow wire to the oil pressure switch on the engine. In this fashion, the relay is activated when the oil pressure is low, breaking the connection from the +12V input of the relay contacts and a connection via a green wire to the fuel pump. However, the fuel pump is still powered as noted in the paragraph above. When the engine starts and the oil pressure is sufficient, the oil pressure switch opens, the relay returns to its NC state, and power is then delivered to the fuel pump via the green wire."

-Bryan

[spidersherm]

Update Time!
OK following your advice I check signal from the ignition switch and low and behold it dropped out once the vehicle was running, replaced the switch and no issues any more! Oil pressure is good after changing the oil.