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Help with stalling 993

 
Old 02-09-2019, 09:47 PM
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Alfa40
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Default Help with stalling 993

Hello,

My early 95' 993 was parked in heavy rain for a couple of days and now stalls both during acceleration from a stop and normal driving speeds. At normal speeds, the rev counter goes crazy and the car begins jerking. It usually starts back up when I turn the key, but sometimes it just runs the starter and doesn't actually start until I retry 10 seconds later. Sometimes, the check engine light comes on, at other times it won't.

Cleaned the ISV 6k miles ago
Swapped DME Relay and battery ground strap with new OEM parts two weeks ago

I read about the immobiliser as a possible issue on this thread but always thought the early 993s didn't have this installed.

Any ideas?

Thanks,
Alfa40
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Old 02-09-2019, 10:44 PM
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Gbos1
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Bad gas?
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Old 02-09-2019, 10:54 PM
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Alfa40
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Is that actually a thing? I mean my last two fill-ups were at Arco, but there wouldn't be any gas sold in the US that would cause such issues, would there? I am sure I went with the highest Octane rating (which is usually 91 in California). Anyway, the tank is 3/4 full, so I won't be able to test this for a while.
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Old 02-09-2019, 10:54 PM
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Churchill
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Take the distributor caps and rotors off, clean and dry everything. Same with coil wires. When was the last time ignition wires were done?
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Old 02-09-2019, 10:55 PM
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Churchill
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Originally Posted by Gbos1 View Post
Bad gas?
None of the problems mentioned in this thread are caused by bad gas. Let's not send people out on wild goose chases.
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Old 02-09-2019, 11:13 PM
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Alfa40
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Originally Posted by Churchill View Post
Take the distributor caps and rotors off, clean and dry everything. Same with coil wires.
Will do!

Originally Posted by Churchill View Post
When was the last time ignition wires were done?
I had spark plugs, distributor cap and rotors replaced last July. I can't find any evidence of wire replacement in the service records, unless they were done together with the plugs (which were replaced regularly).
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Old 02-10-2019, 02:28 AM
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polluted air?

jk
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Old 02-10-2019, 09:58 AM
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If spraying a little DW40 or other spray oil lubricant on the wires and caps clears things up you probably need new ignition wires as the old ones are grounding out in the presence of moisture.
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Old 02-16-2019, 04:49 PM
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Ok, here's an update for anyone with similar issues: I cleaned the distributor rotor and caps and sprayed "Wire Dryer" on the spark plug wires and ignition cables (only those ends attached to the distributor). Looks like I didn't wait long enough for it to dry properly, which resulted in 3 or 4 violent stalls, which led me to bring the car to a local Porsche specialist right away. Interestingly, on its way to the mechanic, the car ran fine. The mechanic said he ran numerous tests and all systems run fine, he could not find a fault. Ergo, it seems as if the distributor contacts were the issue, but my failure to let the wire dryer dry off, ended up costing me the needless diagnostics.

Update one night later:
Back to stalling. Canít even leave the parking spot. What to do? Change caps, rotors and wires Ąjust in caseď?

Last edited by Alfa40; 02-16-2019 at 07:17 PM. Reason: Update
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Old 02-17-2019, 09:03 PM
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I posted a similar, though not as extensive and persistent, issue several months ago on a '95 C2. I got all kinds of ideas and suggestions and the issue resolved itself without my intervention. Lucky me.

One thing I haven't heard here is a possible faulty or clogged fuel pump or fuel filter--I believe that may have been my issue. (I am not the least bit mechanically inclined and I am a COMPLETE rookie/novice when it comes to air-cooled Porsches, so take my comments very lightly.)
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Old Yesterday, 08:46 AM
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ToreB
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Alfa40, I would like to refer to your other thread on this topic, and would suggest to have your immobilizer checked for solder faults.
I have seen many of these control units now, and they all have had serious problems that will disable the ignition without warning and any fault codes in any system, at any time and condition.
Cheers,
Tore
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Old Yesterday, 11:27 AM
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TheOtherEric
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The workshop manual goes through a bunch of tests that would be relevant here. Which of them did your shop do? Fuel pressure? Fuel flow rate? Ignition module signals? Etc. If they donít state each test and the results, itís fair to say you need a new shop (and a refund). Since they didnít solve anything, the least they owe you is a list of tests and results. Then see the shop manual and go from there. I wouldnít put all my money on rain as the culprit , although itís a good place to start.
Originally Posted by ToreB View Post
Alfa40, I would like to refer to your other thread on this topic, and would suggest to have your immobilizer checked for solder faults.
I have seen many of these control units now, and they all have had serious problems that will disable the ignition without warning and any fault codes in any system, at any time and condition.
Cheers,
Tore
He has an early Ď95 hence no immobilizer.
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Old Yesterday, 02:14 PM
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TheOtherEric, I am not sure of the situation in the US, but here in Europe, many '94 and 1995/1 models have the early version of the immobilizer system. I have repaired lots of them, and they all have the same type of fault.

By the way, such intermittent stalling problems are very time consuming and difficult to find. Ask me how I know. You have to be there when the fault is present, and even then it is very diffcult. The car can spring into life again under your hands, making it impossible to find the fault.

The thread starter is describing a typical case of a failing first generation 993 immobilizer. It is a 15-20 minute job to remove the driver's seat and take out the immobilizer to check this.

Cheers,
Tore
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Old Yesterday, 02:35 PM
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Originally Posted by TheOtherEric View Post
The workshop manual goes through a bunch of tests that would be relevant here. Which of them did your shop do? Fuel pressure? Fuel flow rate? Ignition module signals? Etc. If they donít state each test and the results, itís fair to say you need a new shop (and a refund). Since they didnít solve anything, the least they owe you is a list of tests and results. Then see the shop manual and go from there. I wouldnít put all my money on rain as the culprit , although itís a good place to start. He has an early Ď95 hence no immobilizer.
Hence another immobiliser than the later cars.
1994-95 993s with alarm do have an immobiliser incorporated into the alarm that is activated and deactivated simultainously with the alarm.
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Old Yesterday, 02:44 PM
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ToreB
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The early immobilizer is indeed tied to the door lock/alarm control unit, but these are two separate units. This early type also has a RF receiver, and upon receival of a valid key fob signal, it will turn on the ignition module power supply and send a signal to the alarm to unlock doors and turn the alarm off. The later and more common immobilizer will in addition to this also interact with the Motronic engine control unit to send a valid unlock code.
Cheers,
Tore
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