79 spider stalls on electrical load

[ari]

Only happens when car reaches operating temperature. Initially it will stall when cooling fan kicks in. Disconnected wire leads to fan. Eventually applying brake pedal in conjunction with flashers recreates problem. Turning on the radio, wipers, heater fan or headlights does not recreate the problem. When the stall occurs, any lights, (dash or headlights) do not short out or dim considerably as you'd expect, but the stall definately is electrical in nature, power to the coil is interupted. It's the same type of stall as happens during an alternator test (when you disconnect battery terminal while power loading a defective charging system) except battery and alternator operate normally. Car starts right up again. No symptoms as car is warming up. Disconnected fuses one at a time, cannot eliminate trouble. I'm at my wits' end Please help.

[So Cal Mark]

get a voltmeter and start checking for a voltage drop

[ari]

Thanks for the tip Marc. There is a voltage drop showing when i hook the fan manually. I disconnected the positive wire to the coil and made a direct battery connection. No voltage drop, No stall. Then i gave it the brown wire surgery (12 gauge wire) using the extra 30 terminal on the ignition switch since i cannot keep continuous current to the coil. I'm still getting the voltage drop. It seems like it drops to 11.5 volts as it stalls, less likely scenario at higher idle, but still possible for the stall. So now, where should i look next? Bad ignition switch? A new coil might be more likely to withstand power surges? Alternator not charging sufficiently (however battery connection should compensate)? Fan motor robbing too much power? No considerable voltage drop showing with headlights etc. (but everything on at the same time creates stall). For the record, this problem appeared after a 5 month winter storage of the vehicle, it was never an issue before.

[jlferris]

I recently had a similar problem turned out to be voltage regulator

[ari]

To date i have changed the distributor cap, pick up coil and module. The alternator and voltage regulator has been rebuilt as well (still get the voltage drop). I tried a coil from a mid 70s GM vehicle but that coil will not allow me to idle under 2000 rpms so i re-installed the old Marelli coil. A Bosch coil is not readily available unless i order it from IAP. Can i assume that i have a tired coil that cannot withstand power surges? It's a $200.00 gamble at this point, i don't mind spending it but i want to make sure i cure the problem. Any suggestions anyone?

[majicwrench]

Coil is not likely your problem. LIke was said, you need to test voltage. Does battery have 12v?? Is 12v getting to ignition switch?? Just keep following the wiring, somewhere tween the battery and the coil, voltage will drop, and that is your problem.
To help create a load, get an old headlight and wire it into the postive side of coil. I'll bet it just barely glows. Find the voltage drop.
Keith

[Zippy]

I have read all the posts and looked at the wiring diagrams and I think the common point is the fuse block. See if you can find corrosion or signs of overheating around fuses 9 and 10. If these loads are pulling excess current due to faulty connections it might cause the voltage drop at the other end of the fuse block.

[ari]

Ok so here's the scoop. My tests came down to the nitty-gritty. Wiring. Crap. I even came to the point to replacing the pink wire, (ignition switch to ignition coil). I routed a new Brown wire (BW surgery) straight from the battery to the ignition switch (an extra terminal on the ignition switch allowed me to hook it in addition to the existing brown wire). Here's the results to certain tests:
New brown wire jumped to new pink wire (bypassing ignition switch) : No stall
Old brown wire jumped to new pink wire (bypassing ignition switch) : Stall
Old brown wire, new brown wire and new pink wire through ignition switch : Stall
New brown wire and new pink wire through ignition switch : Stall
My observations:
Ignition switch is creating the trouble. Darn, three ignition switches in 3 years and every one fails differently. (Fiat switches or aftermarket ones, they're hopeless).
My solution:
Installation of a 50 amp toggle switch (new brown wire and new pink wire).
Old brown wire still powers the ignition switch.
New pink wire piggy-backs onto the circuit with the fuel and temp gage as well as warning lights ( just as the old pink wire did from factory).
Another observation: Voltmeter reads 13 volts at idle, drops to 12 volts with all accessories on, no stall. Prior to the toggle switch it was still possible to get a stall at 12 volts.
My question now:
New brown wire from the battery hooks to a 50 amp toggle then continues as the new pink wire to the coil. The gages and warning lights piggy-back onto this pink wire and is fuse protected. Is this enough fuse protection or should there be another fuse in-line with the ignition coil?

[ari]

Although i found different ways to reduce voltage drop, the symptoms were reduced but not eliminated. I got my hands on a used Marelli coil and determined that this was the problem. Different sources convinced me that it's not likely a coil problem. A coil is either functional or non-functional. Not true. This proof shows that coils can go bad at operating temperature. I wired up the ignition switch back to normal and its voltage drop does not affect the new unit. Dave, you're right, when you're troubleshooting it's always the last thing you try that solves the problem

[spider2081]

Ari
Great to hear your car is finally running as good as it looks. Enjoy a smooth top down summer.
Dave

[Saleen13s281]

I had the same problem !! Thanks to this post I saved alot of diag. time ! I had high resistance in the switch connector this is a fun car !!