83SC ran great; now no start, just crank

dfk911sc · 12-12-2009, 03:27 PM

Fellow Pelicans, I'm in a bind. I know you like people who help themselves 1st. I have, much reading troubleshooting and damage to my checkbook. here's the backround: 83SC - all work performed by a local P-car mech approximately 2.5 years before, engine upperhalf rebulld and reseal, new spark plug wires, vacuum lines ect...the car is garaged and driven regularly. Has been solid till now. The car was just in 5 months ago for an oil change and "once over" and given a clean bill of health. last week went out to go for a drive...no start, engine will crank great.
the PO installed a Perma-Tune CDI (the coil was replaced by my mech when the engine work was done). I have verified that the fuel pump is working. There was no spark.
I had verified 12 vdc into the CDI with the ignition "on", the distributor is sending 4-5vac to the CDI when cranking, I checked the CDI unit with the tests from Perma Tune Technical Support for Porsche 911 SC
with the exception of: Pin 1 to Pin 5 = 220uF to 250uF, This reading requires the use of a meter capable of reading capacitance (I don't have an LCR meter).
I then attempted to check the Perma-Tune coil with the info I found here: Pri winding 0.03-0.06 ohms, Sec winding 600 ohms, I didn't know how different a Bosch coil is from a Perma-Tune. The Perma-Tune was reading Pri 0.7 ohms Sec 9.46 Kohms. I assumed I had a bad coil. Got a new Perma-Tune coil and checked it Pri 0.7 ohms Sec 10.79 Kohms, still no spark. I took the plunge got a new Perma-Tune CDI ($$)

Installed it and hoped for happy motoring...not so. the car just cranks. I checked for spark out of the coil, good strong blue. I pulled a plug wire and checked for spark - weak dull orange. I have lost my helper for the day so I'm back at it in the am. I'm leaning toward a bad distibutor cap or rotor, I have pulled them and nothing looked obvious so I cleaned the contacts and reinstalled. Same result. Am I headed in the right direction or should I flatbed it to my mech? Any help or advice I'll try Thanks in advance for you collective wisdom.

ossiblue · 12-12-2009, 03:30 PM

Have you checked your points/point gap?

dfk911sc · 12-12-2009, 03:39 PM

Ossiblue, I don't think this has pionts everything I've read say its a magnetic induction for the acv signal to the CDI box, did I misread? I'll check again. Thanks

BLEW911 · 12-12-2009, 03:45 PM

No points on the SC.

john walker's workshop · 12-12-2009, 03:54 PM

is the fuel pump working? you have some sort of spark. you have air, so.....

dfk911sc · 12-12-2009, 04:04 PM

JWW, with the key in "on" I can press the air flow sensor plate up and hear the fuel being pumped. Plus with all the cranking and the air box open the garage smells like a gas can. I guess I can assume that the fuel pump is operational when the key is in start position. I have changed the fuel pump relay just in case, is there another check? TKS

Jim Williams · 12-13-2009, 05:13 AM

With all that smell of gas, you might pull a sparkplug and see if it's too wet to fire.

lyonsfin · lyonsfin's Garage

I had a similar occurrence when I was changing my interior light and blew the fuse it shares w/the O2 sensor. Once I replaced the fuse started immediately. It is shared w/ courtesy light and trunk light.

Josh

w21055 · w21055's Garage

Quote:

Originally Posted by lyonsfin

I had a similar occurrence when I was changing my interior light and blew the fuse it shares w/the O2 sensor. Once I replaced the fuse started immediately. It is shared w/ courtesy light and trunk light.

Josh

Josh points out a common issue, same thing happened to me. Need to check that fuse as well.

Phillip

spsfiend · 12-13-2009, 08:07 AM

A couple months ago my car would crank but not fire up. Turned out to be the Crank speed sensor. I ended up replacing both the top dead center and speed sensors and fixed the problem.

If this ends up being your problem, I read (after I replaced mine) that bosche essentially makes the same part for BMW but they are half he cost of the "Porsche" cables. Just do a search for the BMW part numbers.

Good luck.

Gerry

Howard M · 12-13-2009, 08:13 AM

Double check the rotor, especially the condition of the imbedded resistor.

Howard

rhogg · 12-13-2009, 08:16 AM

+1 on the crank sensor. You can test its continuity to see if its still good. Worth checking out if there are no other obvious causes. In my case, on a different car, it just needed a cleaning.

psalt · 12-13-2009, 08:43 AM

There is no crank sensor in an 83 SC. Replace the plugs if you soaked them in fuel while cranking with no spark. Replace the cap and rotor and recheck the spark at the plugs.

dfk911sc · 12-13-2009, 11:41 AM

thanks to all, here's an update. Josh & Phillip, all fuses checked. the car has been "modified" as it is an RoW. the O2 sensor and much of the circuitry has been removed previously (no control boxes or wiring to the sensor) But it has been running well since this was done. Rechecked the spark this am, had to hook up the battery maintainer last night, have blue spark at plug wire #4. Checked the fuel pump relay socket for voltage in "on" and "start" key positions, all good. I have not pulled a plug to check for fuel soakage. Going to get a cap and rotor, just to have. At this point any parts not used will be kept for spares. I'm in too deep to quit now. I'll pull a plug and update. Keep the sugestions coming as I'm really stumped.

dfk911sc · 12-21-2009, 08:34 AM

Update: again thanks to all. Pulled plug #4 all looked good, after going over all the fuel pressures and numerous electrical checks again, I decided that for my sanity I would have to concede. Had the car flatbeded to my Mech. After several days at the shop he called me and informed me that the new factory sealed Perma-Tune CDI box was BAD! It seams that the box was internittent, sometimes good spark, sometimes weak spark and sometimes no spark. Even when operating with good spark it was not a long enough of a duration for the car to run.

The moral of the story being "just because it's new, doesn't mean it works".

Thanks again to all.

Superman · 12-21-2009, 09:19 AM

As John advised, keep it simple. Pull the center wire from the top of the distributor and, using insulated pliers, hold the end near the engine case while an assistant cranks the starter. You should have a snappy blue arc. If so, then your problem almost has to be fuel. If the FP is running, then I would check the dome light fuse and perhaps the frequency valve relay under the seat. At least, if there is a snappy blue arc, then you know your ignition system is working.

Superman · 12-21-2009, 09:23 AM

Oops. Didn't see your last post.

In my humble opinion, Permatune is the worst of the CDI box alternatives. Lots of guys swear by MSD but I'm a factory Bosch fan. In my experience, nothing else is as reliable. Sure, they can go bad but it's uncommon. Look around and you will find guys willing to sell the ones they have in their garage. Prices can be pretty good between private parties. Substantially less than a new MSD or Permatune. I've gotten them for $50 or $100. $200 is still fair for a working box, IMHO. Heck......$300 is fair, for what you're getting.

ruf-porsche · ruf-porsche's Garage

I would have replaced the perma Junk with a rebuilt BOSCH unit. Do a search for Perma Junk. I think that you should submit the bill from your mechanic back to Perma Junk. After all if they had a decent product you wouldn't had needed to have the car tow to the mechanic.