The Stig

I just wanted to share my frustrating experience with the group. Hopefully this will help others if they run into the same issue. She's a 91 C4 with 170,000kms. She's a daily driver, so she can't be out of commission for more than a day or two. I know my technical limits so I have to take her to the shop for some fixes. That means lots of $$ in repair bills.

So the Hall Sensor fault (1234) comes up and the check engine light would come on once in a while. CEL led to engine hesitation between 2,000-3,000 rpm and occasional stalling. Gave the wire a jiggle, or engine would warm and light would go off.

Now the CEL light is on all the time. And hesitation is very prevalent. Engine will stall on first crank or until I apply some throttle to keep it ticking over. All made worse because it's -15 degrees C here.

So I started with the usual suspects and nothing to this point has solved the issue:

1. DME replaced
2. DME hard reset (unplug battery, etc)
3. Cleaned ISV
4. Misted the distributer/plug wires in the dark. (no arcing)
5. Changed both ignition coils
6. Mechanic checked engine ground strap
7. Changed all spark plugs
8. Changed all "resistors" in ignition leads (mechanic's suggestion)

I've hesitated changing the plug wires because its monstrously expensive to have someone do it (7hrs labour). Battery still strong, but a bit of corrosion on positive terminal, so I'll give that a clean.

Still have to check the rotors and caps on the distributor. Also hesitant to pull the trigger on a new distributor in case it's not the issue. Mecahnic thinks the Hall Sensor and/or dizzy is faulty.

Topping up my mechanic's Christmas bonus while chasing the ghost in the machine is no longer an option. I've decided to park the car and buy something cheap to drive everyday. I probably should have had a back-up car all along.

I'll continue to peck away during the winter until I can set her right. Love the car too damn much and I don't care about diminishing returns either.

I'll keep you updated on the search and take pity on my while I drive an appliance for the rest of the winter.

Happy Motoring!

Cliff

elbeee964

Wow.
Plug wires Are a nettlesome pain to route. (Best time to do it is when plugs get changed/valve gaps set.)
An entirely doable, straightforward DIY, should you go that route.

And if that DIY works, you regain superhero status in front of the mirror!

Wires - because my ignorance of such cryptic problems is only outdone by my impatience - would likely be the route I'd ponder next, too.
Good luck, sir.

bpras@msn.com

Two things you might try:

1. The coil wires. I think they can be checked with a voltmeter.
2. Water in the gas during cold weather. Doubt if it would cause a CEL but might be part of the problem. You might try one of the additives to remove the water.

tbennett017

So wait, I might have missed a detail, but have you replaced the Hall Sensor? Is that doable? Based on your write up that sounds like it was causing some of your headaches?

The Stig

Hall sensor can only be replaced if I install a distributor. New is $900+. Used is around $350. Still won't know if it will solve the problem.

I should get a local 964 friend to lend me his dizzy and swap it with mine to eliminate it from the equation. Already checked the Hall sensor connector and wire. They look ok.

The Stig

I'm dragging this up from the archives to bring it to a close. After much poking, prodding and replacing parts, my intermittent Hall Sensor fault is fixed.

It looks like it was a pooched distributor, specifically a pooched Hall Sensor itself. I ended up sourcing a used dizzy and put that in. My CEL problem has gone away. Time to pile on the miles again.

Hopefully this thread will help others.

Laker

congrats, Cliff...... I read this before and am surprised there are still no options for just replacing the Hall sensor, instead of the entire distributor.

The Stig

Cheers Laker. I'm happy with the result. Patience wins the day.

I too was surprised that you can't buy the sensor as a stand-alone part. I even contacted Bosch and they sent me an exploded view diagram of the replacement parts. Hall Sensor wasn't even noted in the picture. My mechanic said there were a lot of replacement parts missing from the diagram.

I had one dismantler quote me more for a Hall Sensor than for an entire dizzy. Pirates.

I'm going to keep the old dizzy just in case something else decides to pack it in.

jody stowitts

I don't get it. Back in Dec. '10 Hall sensor code popped up. That's pretty strong diagnostic evidence. What made you start looking around for other causes?

The Stig

Fair comment. Most of my research indicated that the Hall Sensor code pops, but it's not always the source of the problem. They don't break that often.

The only way to get a replacement is to buy a new dizzy. They run close to $1k new. I tried to source a new or used Hall Sensor while trying out the other known errors (cheaper fixes, see my list above). Hall Sensors are as rare as rocking horse ****. I wasn't going to spend big money, if there were easier, cheaper fixes.

I ended up parking the car for many months (other reasons) and searched long and hard for a reasonable priced used dizzy.

With 964s I think it's important to practice differential diagnosis. Especially when it comes to electrical problems.

JasonAndreas

Hall sensors don't go bad but the wiring and electrical connector to them can come loose on the distributor body itself.

Laker

JasonAndreas,
Are you suggesting something akin to the "Clock Re-solder" can be done to the connectors to the hall and all is good?

thanks

JasonAndreas

You'll have to work backwards trouble-shooting from the sensor itself but YES, there are no moving parts... Its been a few years but I don't remember seeing any solder joints, the pins were clipped into place.

Laker

Good to know- thanks

Mr.Spacely

Isn't the sensor just a glorified magnetic pick-up? Seems like a retrofit would be possible.