Engine cuts out intermittently

[BrokeMyCar]

Hi folks,

Started up my 82 SC to the smooth idle I get right after an oil change. Drove two blocks, then during a slow turn/gear-change the engine cut off! 0rpms, confusion, pulling over, and it starts again. So I park around the corner and go to the engine - the idle is smooth, no weird sounds. I get back in the car, and as I U-turn it cuts out again and restarts by itself.

Thinking it may be a warm-up issue I drove around for 15 minutes trying various revs, changing gears at different RPMS, turning both ways, etc... it seems solid. So I get on the freeway, accelerate through the gears and when rolling along nicely in 5th the engine cuts out again, with the battery light on. I press the clutch and roll out of into exit.

Once stopped, I start the car and fires immediately. I drive home, listen to the idle again, and go in rubbing my head. I figure it's got to be either fuel or spark, but don't know how to diagnose such an intermittent problem. I'll start with the fuel-filter, but I'm at a loss. Any ideas?

Babak

PS I just pulled the heater-blower and hose, that shouldn't affect this right?

[Driver Ed]

The only thing that I can think of that might be related to heater-blower and hose removal would be the vacuum lines going to the distributor on that side of the engine. If one or more is cracked or pulled off, then you can get weird symptoms like that. On my '82 SC, I had a vacuum hose problem and the symptom was that when I'd let off the gas, as when coming to a stop or shifting, it would stumble and sometimes stall. Cheap fix and easy to diagnose, so I'd start there.

Another possibility is electric. Make sure that the wires on the distributor and coil are all intact and solidly connected. An intermittent on the coil (either high voltage or low) could cause something like that.

[BrokeMyCar]

Thanks Ed, I'll check out the vacuum hoses. If the coil is dying would it manifest symptoms like this? Is there a check on the coil as well?

[Early_S_Man]

It is not likely that you did anything to the coil ... more likely choice would be the famous geen coax to the distributor. Check to see if it is cracked or discolored, first, then see if the AMP Junior Timer connector is properly seated onto the pickup coil Faston tabs, or at the pigtail junction -- only about 7" - 9" upstream from the distributor ... on its' way to the CDI unit.

If all seems well, then I suggest cleaning the connector and tabs at both ends of the pigtail [if equipped -- some cars have one continuous piece of coax from distributor to CDI] with Brakleen or 91% isopropyl alcohol.

If the coax going into the distributor is cracked, frayed, or discolored dark brown, then it needs to be replaced. Pelican part: 930-602-907-01-M14 ... $60.50.

[BrokeMyCar]

The coax looks ok, but I couldn't Ohm it out because mine is one that goes from the distributor to the fuses/ignition. Perhaps there's a point on the CDI that I can try, but I don't know it. So I wire-brush cleaned the end, put it all back together (including setting the distributor to TDC) and was going to re-time it when I discovered...

It won't start at all now! It cranks, but no start. Oil pressure goes up bit during cranking, and if I step on the gas it smells like gas through the exhaust. Looks like I need change the title of the thread.

I'm at a bit of a loss - does the gas smell mean my fuel pump is probably ok? How do I check for spark without an idle?

Thanks!

Babak

Bonus: I found this disconnected and wrapped wire above the fan, does it mean anything to anyone? Its two leads appear to be connected to ground.

[Bobboloo]

Warren has you going in the right direction. Your problem is surely electrical. In particular in the ignition circuit. You either had an intermittent short circuit to ground or intermittent open circuit of course now your problem is no longer intermittent.

Resetting the timing was not a great idea because you quite possibly now have two problems, circuit and or timing. If your motor was running fine but just cutting out momentarily then timing was not the problem. If it's possible set the timing back to where it was. (if it was marked?) Now you can focus on the circuit problem.

It's very likely that when you cleaned the connectors and adjusted the distributor that you triggered the failure mode by moving the wiring. Failure mode meaning short or open circuit. Go back and double check that everything is connected between the coil, distributor and CDI. Also check that grounds for the ignition devices are properly connected as well.

Now, turn the ignition to "on" but don't crank. Go back to the engine compartment. Do you hear a high pitched whine from the CDI box? If no then your not not getting current flow for the CDI and this is probably the problem. If yes then try to start the motor again. If it starts then you can proceed to troubleshooting the circuit problem.

If the motor is running at idle I would like to suggest a quick short cut to determining where the failure is coming from. Since your failure occured when you would take turns suggests to me that the G-force from the turn was moving the wiring just enough to cause the failure. With the motor at idle you can go to the engine compartment and gently move parts of the ignition wiring harness and probably locate where the problem is.

As for the wrapped leads if they are going to ground then ignore them. Just make sure they are wrapped so that they can't short circuit anything.

[T77911S]

the CD unit is going bad. mine started with very short off then on spurts. it may have even been a few weeks between the 1st and second time, but it eventually did it more and more. i put in an MSD unit for about $125. works fine last a long.......i hope.

[BrokeMyCar]

Great stuff to try, thanks folks! I must admit I'm a little lost on the acronyms. Could someone elaborate:

CDI?
MSD?
G-Force?

Babak

PS yeah, I'm kidding on the G-force

[T77911S]

CDI= capacitive discharge ignition (unit)
MSD= is the brand or company name of an aftermarket CD unit.

[Bobboloo]

CDI (Capacitive Discharge Ignition) unit is the silver finned ignition module that is attached to the left side of the engine compartment on the fuse panel. It triggers the coil to release the high tension voltage to the plugs.

MSD (Multiple Spark Discharge) is an aftermarket replacement part for the CDI.

G-Force I had a feeling I was going to catch some flack for that one.

I would suggest troubleshooting before running out and buying any parts. Thousands of dollars of good parts have been replaced by people running out and replacing perfectly good parts when the problem was only the electrical connection. Besides, if there is a bad part you need to determine which one it is before you spend your money.

[T77911S]

running out and just buying parts is bad, but pushing a porsche off the road at a stop light because it has been running fine for 2 or 3weeks is not fun either.
i was reluctant to replace the CD unit because it was so intermittant. i even thought it happened when turning a certain direction, then it seemed to be more heat related. i even bypassed the wires from the CD to the dist. and coil.

[BrokeMyCar]

I'm such a dope - the reason it wasn't starting anymore was that the dizzy was off by 180 degrees. Silly silly -

Anyhow, I took the CD unit out and took it through the benchtop test outlined here:

http://www.perma-tune.com/T-ignition-Porsche-911SC.html

and all the ohm specs were dead on. I didn't have a capacitance measuring meter handy. I checked the famous green wire and it Ohm'ed out well too. So I cleaned off all the terminals, even the ends of all the relevant fuses and the battery, and put her together for a ride. Fine, then 15 minutes later then it cut out again after a turn. Then again while idling at a light. And again while I was driving straight.

I drove home and let it idle while I pushed cables around with a stick, and it wouldn't cut out. Just as I shut her down though I noticed that a lead on the left chain-cover's thermic-switch was disconnected. That couldn't be it, could it? Any suggestions of other things to try? Any checks for the fuel system?

Thanks,

Babak

[Bobboloo]

It could still be the CDI. Sometimes the intermitent failure can be thermal related.

Do you know someone nearby with a known working unit you can swap out yours with just to test?

[Bobboloo]

I just noticed that the benchtop testing link you posted is for Perma-tune CDIs. Is your unit by any chance a silver Perma-tune? If so these are known to be very unreliable and buying a replacement Bosch or MSD CDI would be a good investment regardless even if the unit turns out to be okay. The blue Perma-tune CDIs are more reliable as well.

[BrokeMyCar]

The one I have looks gold-ish... perhaps silver? Here's the picture:



I can take a look at its model number tomorrow - do you happen to know what were the bad ones? Thanks for the catch!

Babak

[BrokeMyCar]

I should add that I'm using the blue Bosche coil...

Babak

[Bobboloo]

That's the problematic one. (Perma-tune that is.) Thermal related failures are the most common.

You can do a search but I think reliability of the available units rate are as follows from 1. most reliable to 3. least reliable.

1. Bosch
2. MSD
3. Permatune (all models except the older blue ones)

New Bosch units are ridiculously expensive but good used working units can be bought here on the board for about $100. The Bosch units can easily be repaired for more years of reliable service as well.

As for the Bosch blue coil more research would be a good idea. I've heard they do have some differences from the original Bosch coils. I don't know what they are but it would be a good idea to find out compatibility.

Hopefully Warren (Early-S-Man) will reply. No one on this board, possibly in the whole country, knows the early Porsche ignition systems better than him.

Do a search on Bosch CDI and Early-S-Man and you will find more info than you could imagine. Complete with schematics and currently available replacements parts for the units.

[BrokeMyCar]

Thanks Bobby- I started a separate thread on the various available units before I saw this message. Where do you think the Crane units fits into the reliability scale?

Also, do you know why people seem to also upgrade their plug-wires when they go MSD? I have recent Clewett's installed, and am a little reluctant to swap them out too.

Babak

[T77911S]

mine was also the silver perma-dume.
i think the blue coil is designed for conventional ignition systems.
i went with the MSD because of the price, about $125. you can also get one with a rev limiter for extra safety.

[Maxx1]

Good thread !!

I am having the exact same problem on an 82 930 with a gold Permatune. I was thinking it was a fuel pump or CIS problem and then stumbled across this thread in my search.

My car runs fine cold. When the oil temp hits 180 the idle will drop if I ease on the brakes. If I stop hard, the car stalls. If I turn hard, the car stalls.

Upon driving down my street, I noticed that high pitched buzzing began cutting in and out, then the car started bucking back and forth as if it were running out of gas? .... so maybe it is the ignition rather than the fuel!

I will check out the connections for starters and post what I find.