John V

Hi folks,

My '81 has been sitting for a little over week. Its been pretty cold soI went to start it and no go. It was running excellent the last time I had it out so I suspect weak spark since fuel pressure is good and all other basics have just been done (t-belt, timing, cap, rotor, wires, plugs, filters etc..). It cranks good, almost catches but doesn't quite get there.

I'm leaning towards coil or plugs as the problem. I'm wondering if anyone has ever tried an Accel Super Coil in the early 928? (Same size, I beleive higher output and very sharp looking in chrome or hot yellow) Anyone know if it would be a problem for the electrical system? Also, whats everyone running for plugs? Any recommendations? Thanks in advance!

Best

Incendier

Funny you should mention this...I just pulled the Accel out and replaced it with a stock coil. It was a beautiful shiny chrome...

During the time the coil was good, I did not notice any increase in performance, but the engine ran fine. I note, FWIW, that the resistance across the coil input terminals is higher than the stock coil.

Also note that the Accel output terminal to the distributor is larger than the stock coil, and the stock wire does not seat fully into the Accel output.

Due to the recent failure of the coil (not total, just frequent variations in performance. Cause unknown.), I opted to go back to stock, as there was no apparent benefit to the hotter coil and I am concerned about possible effects of an aftermarket coil with the ignition control system. I don't know of any, but I'm not in the mood to risk it.

To quote Ed, YMMV.

James

Max

"Accel Super Coil" Stay Away, Stay Far Away fron this one.

There are very few Mfg. Co.'s that make coils and Accel is not one of them. They buy them (Cheap) and put their name on them. JMO but Accel bits big ones in the coil department.

Best to go with the stock coils unless you don't mind a little R&D and $$$.$$ (JMO).

Plugs? Bosch Plats for mine

HTH

Max

John V

that was easy... no super coil.

Too bad because I do think the spark output is weak. Anyone know how to test the coil to see if its output is to spec? Anyone else have this type of problem??

It could be plugs too...I had problems on another car with platnums and never went back. I'm using standard NKG's now. I've had this problem before and replacing or cleaning the plugs gets it to fire up no problem. Thats kind of why I thought a weak coil output could be conntributing to the plugs failure to fire.

John V

Okay, new info.

This is bugging me so I go home at lunch and pull a plug to check it. Its pretty wet. I clean it, connect the wire, ground the plug and crank the engine. No visible spark at the electrode. I pull the wire and insert a screwdriver and do a spark test at the wire, no spark. I pull the wire at the coil and and run a spark test right at the coil. First spark is good but subsequent sparks get weaker and weaker til... no spark. I kill the key and try again with same results... good initial spark then dies out.

Coil or something else??? Anyone?

Incendier

John:

Are you seeing adequate voltage at the coil terminals?

Just a check...this sounds like a super-bad coil IMHO.

It's worth the $50 or so to pick up a stock one (or the Niehoff (think I got that right) alternative, which is identical) just to eliminate it. Not like you won't need it someday, anyway.

Oh, and how new are your wires? I've lost coils before due to extremely high resistance from old, crunchy, dead wires.

Good luck.

John V

Wires are brand new. Anyway, I checked output right at the coil so the wires were out of the equation. I just called the local autoparts store and they don't stock the 928 coil (big surpise). Too bad on the super coil... they stock those for $36.00.

When I go home, I'll check the primary side, and make sure I have dwell but unless the the ignition module limits current, I can't think of what else it could be.

Best

dr bob

John:

Before you spend a bunch of time and $$ on this, consider what changes in a week, and what deteriorates with cold. (drum roll please...) It might be a simple battery problem. If the car has been sitting long enough for the battery to get a little low, combine that with the bunch of cranking you've done since, and you have recipe for weak spark.

Lift the ground strap from the frame in back and insulate it from ground to isolate the car from the battery. Check the water level in the battery, top up as necessary to get the level up so it just touches the plastic tube below the caps. Charge the battery with a good home charger overnight. Test the electrolyte density with a cheapo tester (under $2 at the bargain parts places) to see if the battery has much remaining life. Clean the terminals so they are shiny, apply a thin coating of Vaseline to them after they are reassembled. Reattach the ground strap to the rear frame. (another drum roll...) Start the car.

Cold weather helps identify a lot of weak battery issues. The battery itself has reduced output when cold. The oil in the engine and the rest of the driveline thickens in the cold, making the battery and starter work even harder with less. So it cranks slower, has fewer spare volts to make the ignition work, and you flood it in the process (see wet plugs reference) so it won't spark.


Start with the simple stuff if you can.


HTH!

Steve Cattaneo

John,

Ck. ballast resistor you have two 1st 0.35 to 0.45 ohms, .2nd 0.55 to 0.65 ohms. If you have a Wrong reading replace resistor. Coil resistance, plus terminal to coil wire feed hole, 0.33 to 0.46 ohms. Neg. terminal to coil wire feed hole, 7 to 12 ohms wrong reading, bad coil.

Pull off distributor wire, ck. Pickup resistance = 485 to 700 ohms wrong reading replace pickup or distributor.

Disconnect the tachometer (12-pin plug on instrument cluster or plug G on central fuse/relay panel. A bad tachometer can give you an ignition failure.
Dwell can only be checked if the engine is running.

There are intermediate steps I left out; hopefully it is not your control unit

Good luck
Steve C
The great white.

Joel Griffith

Your not alone John,my 82 928 is having the same problem, ran fine, went out of town for a week, came back to pull the the 928 on the ramps to work underneath, car turns over but won't start for the first time ever. Tested for spark and nothing! Battery hasn't been holding a charge lately so had it tested and it tested bad so I bought a new one.Guys at the parts store couldn't believe battery was for a Porsche, said it looks like a bulldozer battery!
Installed new battery and still won't start. Going the 928 shop manual route next and testing everything Porsche recommends, which pretty much sounds like what Steve C has outlined so we'll see what happens!
Thanks.
Joel

John Struthers

John V.,
All above sounds good. DrBob and the low charge/poor ground sounds about right and
Steve C.covered a lot of the loose ends.
Some other things to consider:
1. If the plugs and wires are fairly new resistance should not be a problem but back tracking through the secondary to primary ignition ciruit ...besides you state the spark gets weak off of the coil wire.
Coil failure, could be a 'partial' failure but that is usually a problem associated with heat/rising rpm's. The symptoms you describe could be coil failure, less than 12 volts charging the primary windings, bad ignition switch, bad ignition relay, bad ECU.
You could jump the relay/ecu - just for test or emergency movement-. If you start after jumping its not the battery/ground or coil.
I would check the rotor and cap again... remember the secondary windings dumps all of that voltage up the center terminal and to the rotor. Easy to check. As to the Accel Super Coil; no, the coil alone will not significantly alter HP, I think you would need to add a multi-strike ignition box with adjustable retard, go with a specialty distributor, and extremely low resistance plug wires. Street rodders are getting up to 14 more HP and 12 ft.lbs of torque this way.
You should get a noticeable boost in gas mileage however, if you widen the gap a bit-
you got a hotter, longer duration spark so use it for a more complete fuel burn-. If you want to clear the coil as the culprit simply swap it. Steve C. might know if you could swap a EFI Ford or Chev. V-8 coil.
Let us know and check the Nichols site.
John S. and Pattycakes

Max

Automotive Ignition and Fuel Distribution is a hobby for me, like R.C. and slot cars are to others. It sounds like the ones that have posted here have past Automotive Coils technologies 101, but for the few that have not taken this on yet, here are a few pages that I found to help out.

Coils Basics
http://www.fluke.com/application_not...AGID=1&SID=103
http://www.geocities.com/MotorCity/1715/basics.htm
http://home.earthlink.net/~jimlux/hv/igncoil.htm
http://www.vintagesaab.com/sonett/ss...l/HiPoCoil.htm

Suppliers/Mfg.

Like I said in my earlier post there are very few company's out there that make the actual coils. Some just buy what is called off the shelf coils and put their name on it. Some will contract the manufacture to make a coil to their specifications. I will leave it up to you to decide who does what and why.

As you can see there is not a link to Accel or Mallory, This is because they were bought by the H.P. Aftermarket Parts Giant "Mr. Gasket".
http://www.mrgasket.com/
http://www.msdignition.com/1msdcoil.htm
http://www.jacobselectronics.com/pro...itioncoils.htm
http://www.cranecams.com/ignition/intro.htm

The next step for your 928! Though a expensive proposition, the 928 would not only benefit from such a mod but it would be the logical next step. "Do we not evolve ?"
http://app3.internetwork-bosch.com/w...sp?mfacKey=SZS

My bet is on the coil or ignition module.

Mod. Ref.
http://residence.educities.edu.tw/so...topro-IMB.html

HTHS (Someone)

Max

Thom1

Hi John,

My guess is weak battery and/or dirty terminals. Next guess is to check the ground wires. Each coil has its own ground wire. See the following excerpt from one of my earlier posts for more ideas, and highly recommended maintenance:

When I was fixing valves, the most suspicious thing I found was a broken coil ground cable. Now that I am back up and running, there is no more starting problem. Here is what I did, and you can do: Yes clean the distributor cap and rotor contacts with a point file. Check or replace 2 coil ground cables. Check engine ground wire about a foot forward of firewall, and a foot deep on right hand fender well. Scotch Bright all male blades of engine compartment electrical connections. Cycle blades in and out several times to clean female sides. A small round file works on some round female connections. I sealed ignition wires and distributors with Coastal Ignition Sealer from Autozone. Check their condition before you pull all the wires – too much work. I saw an ignition wire tester at Autozone. Clean your battery terminals… Believe it or not, that can be the culprit.

Hi again John,

I went back through this post again, and have edited my response. Your 81 probably does not have 2 distributors, but probably has a coil ground strap. It should not be too much work to clean all engine male to female electrical connectors, clean ground contacts, clean battery terminals... that should all be done periodically anyhow.

I put in Bosch Platinum plugs this time, and cranking and performance are great. Platinums are reasonably priced too.

John V

Thanks for all the help folks... heres an update:

Dr. Bob, great thought on voltage and maybe its a contributer. Power at coil was measured at 11.1v (term 1(-) to 15 (+). when I checked Positive terminal(15) to chassis, I got 11.43. And when I checked at the battery, I get 11.97. Kind of surprising since the battery is less than 6 months old, I cleaned and replace most ground cables, alternator is brand new & I keep it on a trickle charger just in case. It cranks over good (no sluggish cranking at all). Still, I thought these values should have been higher? Any way, tried jumper cables just be sure but still no start.

Walt/Steve: I saw another tip site that recommended checking dwell (with dwell meter)while cranking to test the primary side (pick-up) signal. It worked (it gave me a reading). I was getting between 30 and 50 degrees dwell while cranking which according to the site- should be enough to trigger the coil.

Balast resistors checked out.

Steve: Coils resistance... I'm confused. the manual says primary is from term 1 to term 15 (which is the + & - screw lugs). I think thats correct. But, your post and the manual diagram shows primary from + (term 15) to coil wire feed hole (term 4). If I go your (and manual graphic) way, I get 8.6k Ohms (no good). If I go by what the manual text says, term 1 to 15 (+ to -) I get .6 Ohms which is still high (normal = .33-.46 ohms), but appears to be more in the ball park. Secondary side appears correct at 8.6K ohms (term 4 to 15). (manual says 7k-12K ohms is normal).

Please chime in here folks... I'm still thinking bad coil even though the voltage is not where I'd like it. The coil resistance is bad (albeit, borderline) but the most telling symptom for me is the weak spark at the coil output (without the coil wire). I've done that spark test lots of times and normally you get a nice loud CRACK with a white hot spark that will jump a good 1/4" or more to ground. I'm not getting anything like that even on the first discharge which is the strongest.

Steve Cattaneo

John your right the manual diagram at page 28-13 illustration is wrong. Primary resistance test is from 1 to 15 + to -.

Secondary resistance test is from 1 to 4 + to wire feed hole.

We have new information, that spark test that you do all the time may have damaged the coil or control unit. By doing that test you shocked the system. Ck manual at page 1A –28.62. CHANGE THE COIL


. GOOD LUCK
Steve C
The Great White