Engine shuts down

[crimedawg]

Ok, here is the situation:
When I bought the car last month, the PO said he was frustrated and could not take it anymore. His mech. could not help him with it and he let the car go at a very good price.

Occasionally, while driving or idling, the engine will just shut down. The PO had replaced the CD with a permatune and thought that fixed the prob. It didn't. So once every once in a while (once a week to once in a six month period of time) it will do this. Well it did it to me (several times) today for the first time. Both at idle and at speed. When it shuts down, I still have gauges with the exception of the tach. After waiting 30 seconds up to 5 min. it fires right back up and runs like a champ. If it does not start right up the tach will not move. It also backfired through the exhast. I was able to check the coil wire at the cap when it failed to start and did not get a spark. The coil is a permatune which is very new. All fuses are ok and relays are ok. It appears to be an ignition only issue but I am not sure where to start. While cranking the engine with the coil wire off there was no spark, and then all of a sudden spark. I insert wire in cap and it fired up and got me almost home and did it again. Please advise a starting point. Thanks in advance

[Mookster]

Intermittent problems are a pain in the butt! Don't ask me how I know.

Don't throw parts at the problem. Diagnose the problem not the symptoms.

Look for common issues when the vehicle stalls, speed, idle, braking, RPM ranges...

That being said start simple.

1. Exchange the fuel pump relay with the ac relay and see if this is the issue. Clean the fuel pump relay connections with a small round wire brush. Replacing the fuel pump relay is not a bad thing anyway.
2. Check the transmission to chassis ground strap. Clean the connections at both ends.
3. When the car doesn't start do you hear the fuel pump whine? (key just past half but not starting the vehicle is a good test to listen for the fuel pump whine). If there isn't a whine electrical is most likely the culprit
4. Old spark plug wires can be a bad thing. At night start the vehicle and see if you see arching off the spark plug wires. Mist a little water on them if needed. If you see arching, I suggest replacing the spark plug wires. Search other threads for recommondations if you need to replace them.
5. Permatune boxes have a bad wrap when they get hot. FYI. I would suggest going back to the Bosch CD unit or exchange one with a friend to see if this is the issue.

Starting point. Keep us informed. Good luck.

[livi]

While on the fuel pump topic, I would add, make sure the ground wires at no 1 intake are tightly connected. It would probably not be an intermittent symptom but still. My car started to stumble and finally just stop after I adjusted the valves. I could not hear the fuel pump as described above. The whining sound was gone. Turns out I had disconnected this ground wire for better access on left intakes and screwed it back on too loose. Took me two hours to find out and 10 seconds to fix.

[crimedawg]

thanks for the suggestions - keep them coming.

Mook - I was lucky enough to have the PO with me in the car when the problem hit. He said he would rotate the relays for the fuel pump and ac and fog lights, and after doing so, it would start. It did not work today. His mechanic said this was a coincidence and he had checked all the relays, fuses, and cleaned the connections - replaced the CD unit, which then failed and was replaced again under warranty. As for when it occurs - well it did it today at idle when relatively cold and at speed (5th @ 75 mph) and no bumps. The wires and ground are excellent starting points. It appears the original wires are still on it. Would a bad coil wire cause intermitent kills without the wire being distrubed (as in hitting a bump)? Also, I don't think I have heard the fuel pump humm, but I will check tonight when I get home.

livi - thanks for the input. I will check the ground connection. Again, would it just fail sporatically w/o aggitating it?

[Mookster]

I have never had a coil go bad on me before...not to say it's not possible it's going bad. I can say the 2 P-cars I have owned, both of them needed fuel pumps. My bet it is the check valve on the fuel pump. I am not sure on your vehicle if this is internal or external.

The price of a new coil is not cheap. The people on this board will recommend cheaper coils..use the search button. It is your friend.

The goal is not to throw new parts at the car in hopes to fix the problem but to diagnose the problem.

Once you resolve your problem, if I may suggest, you being the new owner of the vehicle and unsure if you have the owners prior records, things you should do: Buy Wayne's book 101 projects for your 911. It is a blessing and a curse.

Base line tune up:

1. Replace the rotor cap and plugs ($7, $5, $12 ($2 x 6)
2. I would replace the fuel filter ($25)
3. Replace the transmission to chassis ground strap ($18)
4. Adjust the valves (DIY $35 for the gasket kit, shop est $350)
5. 4 wheel alignment
6. Check brakes and rotors
7. Refresh the brake fluid(1 hour labor and materials $10)
8. Replace all the vacuum hoses ($30 for the pretty cloth covered hose.) est 12-15 ft.
9. Replace the negative battery cable ($15-$20)

Our host can hook up with these parts

The things mentioned will save a lot of aggravation and AAA towing in the future.

Again, start simple and keep us informed.

[DW SD]

Do you have an ohm meter to measure for continuity across the coil windings next time it dies?

Since it backfired, I'd assume it might be dumping raw fuel and not getting spark (like you experienced). I'd be focusing on the coil first and permatune amplifier even though it is new.

I have a used black coil from an 84 to 89 car, but I don't think that is the right one for you.

[crimedawg]

The first week I had the car, I replaced the cap, rotor, and plugs.

When I pulled the coil wire from the cap last night, the connector disconnected, leaving the wire bare and the connector in the cap. Remove it and put it back together and it still started. The original braided plug wires are on it. I will replace the coil wire immediatley and plug wires soon. And I agree, need to find the problem instead of throwing money at it with parts.

So, why would it shut down with no spark, the rest of the electrical still working, with apparent fuel delivery (exhuast backfire) and then just start right back up after waiting a period of time? Would a ground strap really do this? Its acting like a breaker switch that resets itself, if that makes sense.

I tried to listen for a "humm" at the fuel pump last night but was unable to hear anything, and it still fired right up.

I do have an ohm meter, but I need to be lucky and have someone with me to crank while testing.

Any and all suggestions are appreciated. Thanks

[DW SD]

i'm thinking your coil may be shorting from heat. It cools and then you have continuity again.

Check that the coil has continuity through each set of windings, when it is dead.

Doug

[targa911S]

"I "piggy backed" a Bosch unit on the permafail and when it shut down I would just switch boxes. "

easy test. The issue only seems to occur when the unit is hot, so by the time you get it to the bench, it will have cooled sufficiently to not show the failured area.

[RANDY P]

Check for a failing harness to the CDI. A test light plugged into the +12V main lead while you move the harness around will tell you if the copper is failing.

I had a bad Permatune out of the box that would intermittently quit, and got progressively worse during the 1st 3000 miles I owned it - it would get hot then die. Tach would go dead flat - as it did it.

Get rid of it.

rjp

[crimedawg]

Is there a way of testing the CDI unit (permatune) to see if is ok, or do I need to wait until this problems strikes again and then test. How to test? Is it going to take some special equipment that only the mechanice would have? Thanks for the great advise, I really do appreciate it.

[DW SD]

any chance you've searched on "permatune"? I believe there are many posts about intermittent issues. I believe I've read about test procedures, too.

Doug

[targa911S]

Originally posted by targa911S
"I "piggy backed" a Bosch unit on the permafail and when it shut down I would just switch boxes. "

easy test. The issue only seems to occur when the unit is hot, so by the time you get it to the bench, it will have cooled sufficiently to not show the failured area.

try this.

[crimedawg]

I emailed Permatune to inquire if they had an answer to this issue and this is the response I received. Has anyone tried the method described. It appears that Permatune is side stepping the fact that thier unit may have issues - it is a grounding issue.


"Sounds like an ongoing ground loop problem. I have seen this many times
where the mechanic overlooks the simplest things. In one case, a car had
been to the top 4 Porsche mechanics in the city and finally came to us
in a last ditch effort. I found a bad battery ground wire using our
trouble shooting guide in about 30 seconds. The car has run perfectly
ever since. I know of at least five cases where a Porsche was purchased
at fire sale price due to ongoing ignition problems that the new owner
fixed with a $2.00 ground strap after contacting us.

Below is a link to the trouble shooting guide for the 911SC. Perform the
ground circuit check exactly as it appears in the guide, do not skip
sections and perform the operations in the order given.

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

If you want to send us the unit to check it out, let me know before you
ship it.

Best regards,

Lonnie"

Thanks for the suggestions, I have spent a couple of hours gleaning the information on this site regarding the "permajunk/permadoom/permaturd/ect" and it now my understanding that I shoud look at using it as a wheel chauk or paper weight. BTW - I have the silver unit not the blue.

Bret

[targa911S]

Standard answer from them. "It's a ground thing" .

[2.7RACER]

crimedawg,
In your first question, you have part of the answer.
Quote "I was able to check the coil wire at the cap when it failed to start and did not get a spark" unquote.
Check the condition of all the wires to the Permatune unit. You are looking for any old crispy wires particularly at the connectors.
Remove the connectors and clean the tabs on the permatune unit.
Check the 12 volt power and the ground wire.
Anything under 12 volts is not good enough.
Check the wires at the distributor and coil. Again remove clean and replace if suspect.
Original wires to the Permatune, distributor and coil should be replaced. 26 or 27 year old wires if not failing yet are getting ready to fail. Replace 'em.
Try another primary wire from the coil to the distributor. At least check the one you have.
If all wires check out OK, I think Mr Permatune is history.

[Early_S_Man]

Bret,

While the tests in the referenced page are valid to find high-resistance grounds, some cautions should be noted -- not all digital multimeters are suitable for making low resistance tests below 1.0 Ohm, and there have been suitable analog meters made by HP, Fluke, and other mfrs for at least 60 years ... called milliohmmeters or Wheatstone Bridges that are perfectly suited for this type of low resistance testing! High-resistance grounds are a valid concern, but they are pretty rare ... much more rare than silver Permatune failures in summertime temps! There will usually be intermittent starter engagement issues if there is a high-resistance ground cable problem! Lonnie's usage of the term 'Ground Loop Problem' is highly unusual, and not really appropriate for discussions of DC power circuits!

Lonnie has never, to my knowledge, I repeat, NEVER acknowledged a heat problem with their units, and I know of one case where they tested a comfirmed intermittent 'silver-cased PermaDevil' 3-pin Permatune and sent it back tagged 'No Trouble Found' ... it was later sent to me for further evaluation. The car from which the silver Permatune came had no problems due to high-resistance grounds! I am convinced that Permatune technicians never test units returned from the field under heat lamps or at elevated temperatures! Lonnie used to post on this board, and I challenged him to address the temperature problems many, many Pelicans have had with the silver permatunes ... his response was that their 'lab' had an autoclave!!!

I tested the intermittent unit under heat lamps during an extended bench test while monitoring the case temperature adjacent to the Permatune emblem. Over several hours ... I moved the pair of heat lamps closer and further away while monitoring for missing output pulses with a pulse error detector. In every case, when the alarm went off and missing pulse failures were happening ... the case temperatue was above 190°F -- a not-so-unusual temperature under the hood of a 911 engine in the summertime!

Does the PO still have the Bosch CDI unit? Is he willing to find it and give it to you so can return it to its' rightful place in your car?

What I suggest at this point is the following:

1. I would emphasize that the body-to-transaxle ground strap probably does need to be checked ... and then removed and cleaned with a wire brush at both ends [mounting location at body and transaxle, too] ...

2. The magnetic pickup assembly should have a resistance of 600 Ohms, +/- 10% at room temperature. Disconnect 6-pin cable from CDI unit and measure the resistance back through the green coax cable towards the distributor and pickup coil with digital multimeter set on 2K Ohms range. Leave test leads connected and set multimeter to 20 Volt AC range ... crank over engine and look for 1 - 3 Volt trigger signal. NAPA sells a replacement pickup assembly for around $30 ... if your tests are indicative of a bad pickup coil.

http://www.napaonline.com/masterpages/NOLMaster.aspx?PageId=470&LineCode=BA&PartNumber=1800144&Description=Distributor+Pick-Up+Assy



The electrical connections in your engine compartment go through a heat cycle every time your car is used. Expansion and contraction occurs every time, and any corrosion present may cause a change in the connection when the connectors cool down from normal operating temperatures!



My basic position is still the same as that posted in the following thread ... regarding cleaning electrical connections!

Ignition Troubleshooting??????

[crimedawg]

Ok, finally had the opportunity to work on the car this weekend. I decided to do one thing at a time and see what happens. The first thing I did was remove the connector on the permatune to check for dirt/grime/wear. After being satisfied that good contact was being made, I replaced. I tried to start and now nothing. Before, it would start but die intermittently. Pulled coil to cap wire and now no spark, ---- until the key is released, I get a short spark blast. In fact, when trying to start, it actually tries to start when the key is released. Permatune website troubleshooting says ignition switch start circuit issue or distributor signal. Does this sound accurate or is permatune failing to acknowledge thier issues?

[targa911S]

permatune....get rid of it. Find a used Bosch unit on ebay or from a friend. It will save you any more grief. Just forget the Permaturd.

[Early_S_Man]

That does sound like a worn ignition switch issue.

I suggest monitoring the Voltage present at the CDI connetor during the starting cycle. Pull the connector, connect test leads to Terminal #15 and a good, solid ground.