jreifler

It never ends . . .

After replacing pretty much everything in the system last year, a (maybe) new problem has surfaced. Battery nearly died last week, and then finally did die today. Car cranked with effort this morning, but would not run for more than a few seconds. Fully recharged the battery, but no change. Strong, immediate crank, but then immediately died. Durametric shows Hall Sensor / 34 code.

So onto regular troubleshooting, and the car cranks and runs perfectly with lower ignition module disconnected. Also relevant - that lower coil was replaced last year with the broader overhaul, and then again a few months ago when it started arcing at the plug. So, I plug that recently replaced coil back up just for kicks, and it still arcs and runs rough. Whereas with the “new” coil, no arcing, but also won’t run.

The only thing I didn’t replace with the rest of the ignition system was plug wires. They looked like relatively new Beru wires, and the car ran amazingly once the other stuff was done.

So, with the symptoms around that lower coil, do we think it’s the plug wires? Surely 2 consecutive new coils aren’t both bad ? Maybe neither is bad ? But if it’s the wires, why would one of the coils arc, but the other not?

Goughary

Stock 964 coils are usually ok when new, but it's not uncommon for them to not be good when new. It's also not uncommon for them to crap out fairly quickly...

Also, it's not uncommon for them to last quite a long time.

Unfortunately - for this reason...the unknown and inconsistency, many of us change to 993 coils, since they are way more reliable.

Wires can look spot on perfect and be all kinds of problematic. If you don't feel like spending money right away on a new wire set, you can put a multimeter on each wire and make sure you have continuity from end to end - very often they are broken internally or the end have disconnected inside the boot, usually on the distributer side. This causes an arch and lots of glitchy problems. Also- the wires should measure approx 2ohm, but I'm not sure how important that is.

The actual hal sensor is in the upper distributer take a look at the wiring to the sensor under the dust cap in there. It is possible you have a bad Hal sensor. They are almost impossible to find new. I have a few somewhere, though i may have sold them, can't remember. But they are findable.

When you have the distributer cap off, check to see if the felt plug is in the center of the shaft on the distributor that the rotor sits on. This should be there.

There was a thread once that the plug on the outside to the Hal sensor gets loose and bounces around and causes running issues.might be worth throwing a zip tie on it to firm up the connection if you get to your last wit.


My guess is new wires and new coils will be the fix. Never hurts to do plugs, rotors and distributer caps at the same time. If the ones you take off look fine, just toss them in a box and keep them as spares.

Also - if you have a stock oem negative battery cable- the old school original braided type...replace that with a new one.

jreifler

Thanks for this, @Goughary ! I should have clarified that when I was chasing a misfire last October, I rebuilt the distributor (though not the hall sensor), replaced coils, ignition modules, ignition coil leads, plugs, crank position and knock sensors, DME relay, and 02 sensors. But as I mentioned, left the plug wires themselves alone.

Interesting to hear the coils are that finicky. I think I’ll go ahead and do plug wires in the spirit of fully refreshing this car, as I’ve done with everything else. Maybe now is also the time to do the 993 coil conversion . . . Pretty sure I’ve seen one before, but have a conversion DIY handy ?

systemsc

Typically the highest failure point, i.e. causes problems (radiated RF noise) for the Hall sensor, resulting in a no-start when testing either ignition system alone.

Goughary

Did you happen to remember to use thermal paste behind the ignition modules when you installed them?

There are a couple of threads on the 993 coil swap. One of them is mine i think...but if i did make one, i do the whole thing differently now.

Look for a thread that uses the original coil cage mounted in the same place. And then you just need a set of coil wires that are the correct 964 length, but with 993 ends on the coil side.
Somewhere in the thread you will find the specs.

964Luftballoon

Per Goughray's suggested. I posted this in the DIY 993 coil thread. I listed the wires and who to get them from. Hope this helps

https://rennlist.com/forums/964-foru...l#post16965394

jreifler

I didn't know to use thermal paste. Will make sure I add it when doing the conversion. Thank you !

It does! I found that thread last night, but thank you for linking !

I see FD has a kit now, which seems the hassle-free way to go.