Out-of-spec distributor signal resistance in 930

[logician]

Hi,

I have an '86 930 with a PermaTune CDI unit. I recently did a static test on the distributor signal resistance, i.e. between pins 3 and 6 of the CDI connector. I initially measured 680 ohms with the engine cold. I then measured the resistance with the engine hot, and got a reading of 730 ohms. The Porsche spec for this resistance is between 580 and 700 ohms. The Permatune web site says that the resistance should be 600 ohms +/- 25 ohms. Permatune recommends that the distributor be replaced if this resistance is out of specification.

Question: has anyone else observed this resistance changing with temperature? Has anyone found that they had ignition problems resulting from out-of-spec distributor signal resistance?

While I have a 930, I think that SC's have essentially the same ignition system, so my question could be answered by SC owners also.

Thanks,
-Juan

[Early_S_Man]

Juan,

What kind of ignition problems are you experiencing?

Quite a bit of the rhetoric on the Permatune site is BS.

The pickup coil in your distributor is very fine copper wire, and the resistance will rise with temperature, but probably not as much as you measured. However ... I am certain that the test values Porsche uses are for moderate temperatures not to exceed 100°F, not elevated to 200°F++. So, I believe your pickup coil is within specs!

I suspect there is some corrosion present on the connector at the distributor cable junction to the engine harness, and also at the 6-pin connector at the CDI-unit. you can clean them with household vinegar -- alow to sit 2-5 minutes, then rinse with distilled water, and finally ... rinse again with 90% isopropyl alcohol. The sides of the female 1/4" Faston connectors can be crimped LIGHTLY with needle-nose pliers ... but, be SURE that there is still a gap present! After testing is complete, apply silicone grease such as Dow Corning 111, 112, or 4 to the comnnectors to prevent corrosion in the future.

If further problems persist, there is a $30 replacement green coaxial cable assembly to replace the cable that comes out of the distributor and makes a sharp bend to join the engine wiring harness. Problems with that cable are known to cause an intermittent miss or complete cutouts and loss of power. Good luck!

[logician]

Hi Warren,

Thanks for your quick reply:

> What kind of ignition problems are you
> experiencing?

I was experiencing intermittent engine shutoff while driving. Happens on a hot days. I suspect the CDI unit because the Tach goes to zero when the engine shuts off, even while the engine is spinning.

I swapped the Permatune for a Bosch unit in for one week, and didn't have the problem. Since the problem was intermittent, the fact that the Bosch unit never failied is not conclusive, although good evidence. I switched back to the Permatune today and waiting to see if it fails again.

I performed the recommended bench tests (including capacitance test) of the Permatune, and found everything within spec. I also measured the pin-1 (ground) to engine resistance on the connector and found it to be about .1 ohms. The only thing out of spec was the distributor signal. I have replaced the delay-time relay.

> The pickup coil in your distributor is very
> fine copper wire, and the resistance will
> rise with temperature, but probably not as
> much as you measured.
> However ... I am certain that the test values
> Porsche uses are for moderate temperatures not
> to exceed 100°F, not elevated to 200°F++. So,
> I believe your pickup coil is within specs!

So, I was hoping that someone else had taken the measurements and might give their data. Would anyone care to take some measurements and post their results?

The tech support guy at Permatune was pretty sure that the resistance should not increase by so much with temperature, and that high resistance indicates a problem. Why do you believe the distributor resistance is within spec, and that this is not a problem?

> I suspect there is some corrosion present on
> the connector at the distributor cable junction
> to the engine harness, and also at the 6-pin
> connector at the CDI-unit.

Actually, I suspected the 6 pin connector too. There is some possibility that pulling the connector off and replacing it may have scraped enough corosion off to allow the CDI to work better. I'm waiting to see if the Permatune will fail again.

Regarding the distributor cable junction, do you mean where the green wire goes into the distributor?

> you can clean them with household vinegar...

Thanks for the advice. I will clean the corrosion as you advise.

> If further problems persist, there is a $30
> replacement green coaxial cable assembly to
> replace the cable that comes out of the
> distributor and makes a sharp bend to join
> the engine wiring harness. Problems with that
> cable are known to cause an intermittent miss
> or complete cutouts and loss of power.

So my green wire is not the "pig tail" kind. The green wire goes from the distributor into the engine wiring harness with no additional connector. So is there good way to replace my green wire without replacing the whole wiring harness? Permatune sells a replacement wiring harness, but that costs more than $100. Also, do you know if I would have to take the distributor apart to connect the green wire, or does the green wire simply plug into distributor.

Thanks for the help!

-Juan

[logician]

Hi,

In reading the Porsche factory manual for the Turbo in detail last night, I see that it says that the distributor resistance measurement should be done with the engine at 0-40 degrees centigrade. It warns that the resitance measurement is affected significantly by temperature. Further, my mechanic also told me that the measurement was intended to be taken with the engine cold. Conclusion: it's not surprising that the resistance increased with the engine hot, and the Permatune tech support article should really say to take the measurement with a cold engine.

-Juan

[RoninLB]

Originally posted by logician
Hi Warren,


I was experiencing intermittent engine shutoff while driving. Happens on a hot days. I suspect the CDI unit because the Tach goes to zero when the engine shuts off, even while the engine is spinning.

-Juan

I went thru the same routine on a big ride..changed the Permatune and coil/problem gone..sent the suspected Permatune back to mfg/they said it was OK..had a shop check the coil/shop said OK..I didn't replace the originals and still use the newer ones..I want MSD/I don't trust Permatune, but that's my personal problem ......Ron

[Early_S_Man]

Juan,

That confirms what I thought.

I think that the fact the Bosch unit ran for a week without problems confirns that the problem is a fairly-well-known problem at high temperature with recent Permatune units! Whether the Permatune folks will acknowledge the problem is another matter! Is this Permatune unit still under warranty? If it is, you should insist that they test it at elevated temperatures in the 250°F range, or higher! I don't know what oil temperature range you have had when the problems occur, but temps at the relay/fuse/CDI panel can get pretty high because of a lack of air circulation and convective heating from the exhaust system to engine sheet metal.

[RoninLB]

Warren..my problem became more progressive/happening more and more..even on a cold evening with a 170deg eng. temp...I know that wierd things can happen in the Oregun mts./but WTF........Ron

[Early_S_Man]

Ron,

Hard to say for sure, since I haven't had the 'pleasure' of dissecting or repairing one of the high-temp-failure mode Permatunes ... but probably a bad solder joint, and they can be very tricky to find! Or nearly impossible ... with the new potted (clear anodized aluminum case -- potted with a black sealing compound) version Permatune has been selling lately!

On the 3-pin Permatunes ... there is one known failure mode that can be fixed fairly easily with an external 100 Ohm 5 Watt resistor, and it's discovery was pretty much a fluke here on the Pelican board!

But, the magnetic-pickup Permatunes are still an unknown area, mostly, but we are gaining more experience as each new problem turns up!

[logician]

Hi Warren,

> I think that the fact the Bosch unit ran for a
> week without problems confirns that the problem
> is a fairly-well-known problem at high
> temperature with recent Permatune units!

Actually, my unit is pretty old. I forget the exact date, but it was manufactured in either 1995 or 1997.

> Whether the Permatune folks will acknowledge
> the problem is another matter! Is this Permatune
> unit still under warranty? If it is, you should
> insist that they test it at elevated
> temperatures in the 250°F range, or higher!

The permatune guys were very nice when I talked to them on the phone and they did offer to test the unit if I returned it to them, even though the unit is out of warranty. However, they did not offer to replace the unit.

> I don't know what oil temperature range you
> have had when the problems occur, but temps at
> the relay/fuse/CDI panel can get pretty high
> because of a lack of air circulation and
> convective heating from the exhaust system to
> engine sheet metal.

Actually, the failure has occured at various times when the day is hot, usually when driving. It has also occured after the car was parked for 1 hour, although it was parked in the sun.

So one other interesting possibility is that the problem could be a result of a short in the tach or speed relay. Turns out that a short here will cause the engine to die. I'm not sure if the engine dies because the short kills the CDI unit, or whether the short causes the speed relay to trigger and shut off the fuel. Have you ever debugged this scenario? Do SC's have a speed relay like the Turbos?

Regarding the quality of Permatune, I get the impression that Permatune units are more sensitive to problems in the rest of the ignition/electrical system. Permatune says that. So perhaps a lot of the failures that are reported with Permatune are more related to other problems outside of the CDI unit. That being said, it would be nice if the Permatunes were designed to be more tolerant of other failures.

-Juan

[Early_S_Man]

Juan,

Yes, USA-spec SC's have a Speed Relay, and an intermittent failure could cause the Fuel Pump Relay to operate and cut off the engine. I don't think a fault in the tach or Speed Relay could cause the Permatune unit to cut out, though!

If you can live without a rev limiter for a few days, I suggest unplugging the Speed Relay for a few days ... just to be absolutely sure the Permatune is the sole source of the problem.

Yes, the Permatune units seem to be sensitive to electrical system anomalies, which is why I said there is a lot of BS on their site! They claim to be 'fail-safe' ... when nothing could be further from the truth! And, I have heard of lots of units sent in for testing ... that are returned tagged 'NTF' ... as in "No Trouble Found!" I would wager that all of their technicians do the testing at room temperature and never subject 'returns' to any form of vibration testing!

[logician]

Hi Warren,

> Yes, USA-spec SC's have a Speed Relay, and an
> intermittent failure could cause the Fuel Pump
> Relay to operate and cut off the engine. I
> don't think a fault in the tach or Speed Relay
> could cause the Permatune unit to cut out,
> though!

You wouldn't think so. However, for what it's worth, the Permatune guy said that a short in the tach wire would cause the CDI unit to fail.

Also the Factory manual debugging procedure for the ignition says to try disconnecting the tach and if the failure goes away, it's a bad tach. Don't know if the factory manual is implying that the bad tach would cause the speed relay to switch off the fuel pumps, or would cause the CDI unit to fail.

> If you can live without a rev limiter for a
> few days, I suggest unplugging the Speed Relay
> for a few days ... just to be absolutely sure
> the Permatune is the sole source of the problem.

Will the engine run with the speed relay completely unplugged, or would I need to jumper the fuel pump or other circuits. In the Turbo, the speed relay has something to do with the oxygen sensor as well as the rev-limiter.

-Juan

[gblumenstock]

"So my green wire is not the "pig tail" kind. The green wire goes from the distributor into the engine wiring harness with no additional connector. So is there good way to replace my green wire without replacing the whole wiring harness? Permatune sells a replacement wiring harness, but that costs more than $100. Also, do you know if I would have to take the distributor apart to connect the green wire, or does the green wire simply plug into distributor.

Thanks for the help!

-Juan"

I have the same problem. How do you add the pigtail into the harness. Is there a another new connector that I need?

GB


__________________

[Superman]

No, you will not have to do any wiring inside the distributor. The green wire (and also the pigtail replacement) just plugs into the side of the distributor. Original factory wiring connects the CDI unit to the distributor with a green coaxial wire. It's best to just replace the entire green wire, which means the whole wire that goes between the distributor and the CDI unit. It's surgery, but it's minor surgery.

There is a special tool (you can sometimes use a small piece of wire) that pushes down on the locking tab enabling you to neatly remove the 1/4" female spade connector from the rectangular, 6-pin block connector at the CDI unit. Unfortunately, I know of no source for replacement female 1/4" connectors that have the locking tab.

It's no more than a six-pack job, if you have the parts. You'll need wire (that can handle heat.....the factory green one cannot) the pigtail and one of those really really common Bosch 2-pin rectangular connectors. Like the one on the WUR or the AAR, or the cold start valve, or the........ They are sold separately, and you need it to connect with the pigtail.

[gblumenstock]

Please see new thread: "Replacing Green Distributor Wire."

GB

[logician]

Hi,

BTW, to follow up on the problems reported in this thread: I finally replaced the Permatune and coil. I did not replace the green wire. Haven't had any problems since, but since the problem was intermittent, I won't believe it until the car runs without problem for a month.

-Juan