2.4 ignition problem

jeff m · 07-18-2002, 08:50 AM

It's a 72 2.4T (MFI)

I have a permatune unit with a black coil.
The car starts, runs a while, then dies.
Common sense says it's the coil, which if not changed will take my permatune with it!
The coil is not all that old and should not be causing a problem.
Once the car stalled I put a timing light on an HT lead, no spark.
I then put a neon on the bk/yellow on the coil to check output of cds and also held a test lamp on Bk/purple, which goes to Tach via speed switch and the Bk which goes to input of cds (ground from points)

I got my wife to turn over the engine so I could check the flashing ground from points to tach and CDS. The engine started, (unexpectedly) I removed test lamp it stalled. Did it a few more times, it was consistant.

I decided to stop for a coffee and think about it , and my first thought was to post it here.

So that's a battery backed test lamp looking for a ground from the points, engine runs - remove test lamp car stalls instantly,

I will reclean the conectors and also check grounds but I would like to find the exact problem instead of just cleaning and re plugging the connectors etc, have the fault dissapear today and return at a less convenient time!

Thanks in advance
Jeff

pwd72s · 09:05 AM

Did you do a multitester test on your coil? The utimate solution? Most of the guys here seem to think that MSD is superior to Permatune...here's a link: MSD install...

jeff m · 07-18-2002, 09:10 AM

I tested the coil, it looks a little low on the primary, but not conclusive.
Also the fault is intermittant, runs then dies, that's why I was testing straight after stalling.

pwd72s · 07-18-2002, 09:20 AM

For a cheap quick try, I'd say try replacing the coil. I don't have the number right at hand, but weird as it seems, Ron replaced a Bosch blue coil with one he found at a local NAPA...because the guy behind the counter said it would work on a '77 911. It, and a new permatune unit gave him no problems...and he's now back in NY. Ohhh, lucky that I keep a sloppy work bench. Here's the box. Coil was bought at the Sweet Home, OR NAPA store, it's a Beck/Arnley. Part number 178-8009 and he paid $30.37 for it. We sent the original permaune to them for testing. Their response was that the unit was good. Did you check your points?

Early_S_Man · 09:34 AM

Jeff,

Unless your coil is leaking oil ... I doubt that it is a problem, which should be obvious from the following ...

Is the PermaTune unit a relatively new unit, or maybe one of the older blue anodized boxes? I have heard of many complaints about the quality control of newer clear anodized boxes.

I think I have an answer about the mystery of it working and running when the test lamp is connected ... and why it dies when the lamp is disconnected! Typically, there is a 100 Ohm pullup resistor connected bertween the input terminal from the Black/Violet wire to the +14 Volt supply. If that resistor is burned out, broken, or one of the wires is broken or has a cracked or bad solder joint where it goes to the circuit board (the resistor is a 5 Watt power resistor, and NOT mounted on the board) ... then the PermaTune unit will not trigger properly! Your test lamp is taking the place of the pullup resistor, and the unit triggers and runs properly while it is connected!

If you have basic electronics hand tools, a multimeter, soldering iron/pencil 25 Watts or under, and any electronics experience ... you should be able to fix this problem, assuming the PermaTune unit is no longer under warranty! The Permatunes are relatively easy to disassemble, and the cover and one side extrusion piece are all that would be needed to be taken off to test and fix this problem.

pwd72s · 07-18-2002, 09:38 AM

Jeff, I'm glad Warren came in here...he is THE electronics man of this board. I was just describing what was done to get Ron back into his Big, Big, Ride...

Early_S_Man · 07-18-2002, 10:08 AM

Jeff,

Unless you have a rather expensive digital multimeter (in the $300 to $400 range) ... they are not typically accurate below 1 Ohm resistance measurements! And, the primary side is not where 99.9% of the CDI coil problems occur ... it is the secondary that usually shorts out part of the winding.

It doesn't hurt to have a spare point set, coil and Bosch/Permatune unit as spares ... which I do have, and carry in the trunk! CDI-system components are not to be found out in the middle of nowhere, so you do need to be prepared in advance for ignition problems with the older cars! It doesn't hurt to have a spare spark plug cable long enough to replace #6, either!

jeff m · 07-18-2002, 12:54 PM

Thanks for all the help, it's just a little too hot at present.
I shall resume in the morning.

Jeff

jeff m · 07-19-2002, 07:10 AM

It's a bit cooler today, I'll be able to think, well maybe!
I removed the permatune unit from the car, it was not open circuit between b & C but I'm sure it was at the time I was testing with the test lamp yesterday.

I hope Warren is about.....

I have attatched below two pics of my permatune unit,
it seems to be filled with a "bakerlite type material"
Is this the type of unit you were refering to when you said it can be opened and the 100 ohm 5w resistor changed.

If I can get to the offending resister do you think replacing with a 10w res. would improve its life? or is a 10w resister to big for the space in the box.

Jeff

Early_S_Man · 07-19-2002, 11:05 AM

Jeff,

Unfortunately, no ... my blue anodized spare unit was mfr in 1980! And, there wasn't any potting compound used. I will make a note about clear-anodized PermTunes being repair UNFRIENDLY!!! I presume that one was made in Wylie, TX ... just outside Dallas?

The potting compound does complicate matters!

The resistor in my unit is clipped to a fuse holder clip attached to the screw holding that two-prong Faston ground terminal in place ... not far below the surface of the potting compound!

But, my assuption was that the resistor was OK ... just a bad solder joint or fractured wire was causing your intermittent problem. The 5 Watt resistor is only loaded to 1.96 Watts when the points are closed continuously, so that shouldn't have been a problem. A 10 Watt resistor would be a tight fit!

Early_S_Man · 07-19-2002, 10:23 PM

Jeff,

You can repair the unit without having to go into the potting compound! If you mount a 5 Watt 100 Ohm power resistor externally, such as glued to the relay panel/console with silicone sealant near the fuse block, then solder 18/22 ga wires to the resistor ... and connect one end th the fuse block, and the other end to the distributor wire with a piggyback connector.

jeff m · 07-20-2002, 06:16 PM

Warren,

That's exactly what I was thinking of doing, (no reason why it cannot be external)

Except that, it's intermittant, that is, I see the 100 across b & c when the unit is "cold" or not faulty!

That means I would have two 100 ohm resisters in parrellel (50 ohms until the fault reapeared and with the extra wattage it may not reappear.

I had this prob a few years ago, I had a spare permatune, put it in with a new coil (black), this is the one that is intermittant now.

So I thought I would get my old one which gave up completely and stick a 100 ohm across that one, I got it off the shelf took off the label which said "open circuit b & c" would you beleive I got 100 ohm reading!

I read as many of the early 911 problem posts as I can, it seems that many people have problems with permatune, or do you think it's expertise in many cases.
Although my car is pretty standard, it is a T and therefore perhaps does not warrent a Borsch unit. (cost)
What are my options other than permatune (new) if I am unable to repair it. Any other manufacturers.

PS my second permatune was not new, I bought it as a spare, so I prob got what I payed for (and deserved)

Jeff

Early_S_Man · 07-20-2002, 07:08 PM

Jeff,

Having two resistors in parallel part of the time won't be a problem! The points would still only be seeing a 280 mA load, and that is not going to dramatically shorten the points life!

I think your experience is typical, and, after having opened my spare unit and examined the wiring ... with the older, non-potted version, it is easy to see why the problem occured ... it seems to be that PermaTune used no discipline in the wiring, which is stranded 22 ga wire just routed point-to-point in a free form fashion. The wires are free to resonate or vibrate in sympathy to engine vibrations! Because stranded wire was used, it is more susceptible to breakage inside the insulation right at the point where solder wicking stopped ... I can understand how they got the reputation of being unreliable! Had a few wire ties been used to secure some of the wires together, or lacing cord ... this particular problem would never have occured!

Is your older PermaTune box a Blue anodized unit? if so, I think it would be fairly easy to replace the wiring with solid 20 ga wires like Bosch used, and eliminate one failure mode.

With the latest 'potted' units, I don't know what caused the problem ... perhaps just sloppy soldering!

J P Stein · 07-20-2002, 07:19 PM

I have an extra 3 wire Permatune unit that I removed when installing an MSD. F/S cheep......MSD is mo better if you can find a place to mount it.

jeff m · 07-21-2002, 06:56 PM

Warren
Thanks for your help, I'll go ahead with the external resister and post the results so that it may assist other poor souls.

By the way, don't ever reveal you home address on this board 'cos I'm sure some early 911 owner would kidnap you to fix their car.
Thanks again
Jeff

Joeaksa · 07-21-2002, 08:05 PM

Jeff,

Have you ever looked at a map of West Texas? Not much around San Angelo and Warren would see them coming for miles... and in that part of the world, if you move into town without a gun you are issued one...

Joe

jeff m · 07-26-2002, 10:55 PM

The external resister is in place, took the car for a short run seems fine.
A longer run sched for Saturday, optimistic, but WILL be taking telephone and the number of the flatbed guy with me!
Thanks Warren
Jeff