Hello Pelican: GoodBye CDI?

[docpardue]

I will point out that this is first thread, I originally touched on this issue in a prior post, and I believe that I read as much as possible before having to reach out

[docpardue]

The next thing I will point out is that I am by no means a Master Mechanic, by trade I am an Investment Broker, but nor am I a complete moron in the garage. I have had several newer BMW's, and have enough knowledge that I am willing to accept the challenge of learning the issues of ancient Porsche's. I also realize that if I want to be able to sustain my desire to race in SCCA, and any other form of racing, I need to be able to fix things myself. My budget can't afford anyone else to. Now to how I ended up with this car. I bought my car from a friend, who doesn't remember how he build some of it, it is a 1967 Porsche 912 w/ 1983 911SC 3.0l complete with Bosch CDI, I believe manual fuel injection. 1975 911 hubs, and brakes. The hull with mostly carbon fiber, the tranny is a 915, and thats what I have learned about it thus far. My friend is much more knowledgeable about the auto than I am, but seeing that he sold it to me, to leave the hobby I need to learn so I can quit taking his time. He was an ASE Master Mech in the local Porsche dealership here in Nashville. I bought the car from him for 4k. and since then have replaced the battery, the fuel cell bladder, both inter constant velocity joints, boots, and torque bolts. These issues have pretty much followed one, after the other since I bought it.

My newest issue is that when I try to start the car. I blow a 5Amp fuse that is direct lined to the CDI. The car will turn over and then run for a millisecond, blow the fuse and die. I have tried this progression with a 5,8,10,and 25amp fuse. Each gives me a little long life, but yet it still blows, and then the engine cuts off. This problem literally......Blows!!! The annoying part is that it began right after I did my replacement of the CV Joints, and then while I had the car on the jack stands I chose to put in FrostKing liner, and carpet to quiet down the car. The frost king did have a foil like top, but I was careful with wires during this install. My car is louder than most 912's due to my 3.0, and it doesn't help my oilcooler is aftermarket and placed in my rear seat space. Regardless, I pulled my newly installed sound barrier, thinking that maybe I effected my ground by doing this... That didn't help, just made my hull sticky. Oh well its gonna be a racecar so it doesn't have to be quiet. Then I traced my wires. No nicks, breaks, burns, etc. Then checked my CDI, opened the box, I don't see any carbon flash, and everything looks fine. Yet I still have a fuse that blows.

At this point I am at a loss. I am considering replacing with a MSD 6A, and Blaster coil. I would prefer not buy parts I don't need if I am missing something as a "rookie" mistake, but if I am not I want to know is the MSD a good choice? I've read about the Bosch CDI, the Perma-tune, and the MSD. The CDI seems the best of all options other than mine is not working, which I'll admit if it's just bad luck for me, its lived a long time. The Perma-tune seems like a good option if it were reliable, Even though I have read with the swap to digital they are better, they still seem a bit of a loss cannon for a car this 40+ years old. This lastly I read mixed opinions about the MSD. Some say it's an upgrade, others say the multi-spark til 3k is a novelty. After my overly analytic explanation these are my true questions:

1. What am I missing? Is there something simple I overlooked?

2. If replacement seems in order, what is the best choice?

3. If the MSD is the best choice and the placement is indeed in order, why do people mount them on the dash?

[docpardue]

[docpardue]

[wwest]

Use a garden hose to run cool water over the CDI box while revving the engine up and down....

It's impossible to diagnose a failure of your CDI, although it seems to be blown according to your description. An experienced electronic repair will be able repair it. You need to supply them with the circuit diagram, which are available on the internet. However, not all components are available new, so in case of a repair some technical creativity is needed. That will cost time and money.

I think, the best solution is a replcement for the CDI. The MSD is an option, but there will be other alternatives. Perhaps some other Pelicans are willing to shine theire light on this subject. At least that will be the cheapest solution for your problem.

BTW: Did you replace your coil? Is it old and could there be a short in the primary winding, explaining the high currents? try an other coil to be sure the ignition unit (CDI) is the cause. And check your wiring!

Otto

[Bob Kontak]

Originally Posted by wwest

Use a garden hose to run cool water over the CDI box while revving the engine up and down....

The box don't last but a second or two before the fuse blows, Willard.

How can he cool the box off when the damn thing don't run for but a second?

[wwest]

I assume the CDI "runs" (1Khz "hum") until the engine is started and a bit thereafter. Pre-cooling, cooling, the CDI case (heat sink) might prevent the fuse blowing. We then know that some component inside the CDI is heat sensitive.

Op needs to also measure the input voltage right at the CDI connection. Voltage, voltage spikes, can be dramatically higher back in the engine compartment vs at the battery itself.

[Ayles]

I have a 6 pin CDI tested to be working. I'd let it go for $450 shipped (unless you require intl shipping).

[ajwans]

Firstly, stop. The fuse is there for a reason and replacing it with a higher current rating fuse is asking to trash whatever it's connected to.

Contact Ingo <3.6@cox.net>who will steer you right on repairing or replacing your CDI.

andy

[Bob Kontak]

Originally Posted by wwest

Pre-cooling, cooling, the CDI case (heat sink) might prevent the fuse blowing. We then know that some component inside the CDI is heat sensitive.

This feels like more of a short to ground. But worth a try to cool. A second or two, I don't think the hose is gonna do it.

Something more profound than an electrical gizmo with stripes on it getting hot.

[RWebb]

I agree with the above posts. Someone may well have shorted you, and you definitely want to go long on the grounds.

Also inspect all connections going to the box - pull them apart so you can check out the fundamentals; don't just look at the outside of the connection and think you can use trend analysis.

[LEAKYSEALS951]

Okay,
Here are my newbie $0.02 suggestions. Repeat- I am a newbie. take it for what it is worth.
I just went through this with my car.
You sir, have a short. It is either from the CDI itself or the wiring supplying it.
Here is your $600 (permatune) or $way more (bosch), or $300(MSD al)question.

Is it the wiring?or is it the ignition itself?
Imagine dirty harry. He says "well... do you feel lucky? punk?
If you do, install your ignition of choice and pray the there isn't a wiring fault.
If you do not, test each wire for continuity. Don't assume anything. Research your wiring diagram. Your car also appears to have custom wiring. understand what got "redone" and how it affects your system. My car had a good power supply, but the wiring harness in the engine bay was all cracked and such. The + and - leads to the coil were shot. Who knows what else.... Teach yourself what each supply wire does, and test/examine it to make sure if it is good. The MSD on the dashboard appears to be the NASCAR equivalent of the Ignition mounted in the rear seat of a porsche. A good place to put an ignition outside of the heat and vibration of the engine compartment.
Once you have "proved" your wiring to the ignition good... then install your replacement. I (you may have seen my cheesy post) went with a MSD streetfire- a cheap alternative to the MSD 6al. I'm not suggesting it..BUT... If nothing else- it is SO cheap,it is disposable, so theoretically, you could use it as a sacrificial lamb to ensure the CDI was the culprit. If the car works.. then you know it was the ignition module itself- therefore you could always rebuild your CDI- and ditch the streetfire, but if it blows, then you know that there was a wiring problem.
I would also like to add... my most important lesson in life came form a guy named"mustang bill." He said (and I quote)..Mustangs generally work, until someone messes with them...At the time I was asking him about a broken heater in a girlfriends mustang... He said... dont make me walk out there and tell you what is wrong with it... He did walk out... and from a distance of 20 feet said- " boy, there is an aftermarket radio in the dash- that is you problem.. start there... " and he walked away. I got under the dash, looked at the ass end of the radio. and sure enough, whoever installed the radio knocked loose the wires to the heater control panel. The fact that this all happened after your CV joint replacement echos the yoda like wisdom of mustang bill.... something either you did (or the previous re-wirer) might have caused this. Not intentionally, but it did.

You car it a beaut btw!
Good luck
Ron

[docpardue]

I can't hear the "Humm" from the CDI. I will inspect the grounds, and track the wires again.

As for the CDI, thank you for the offer, but I don't think I intend to go that route again. Do any of you guys have a MSD?If so, can you tell a difference?

Also Otto, I didn't try the coil, I'll get the Fluke out.

Why would the temp of the CDI Box effect the fuse?

[docpardue]

Leaky, Thanks for the response. I did read your post, and honestly it perked my interest in the MSD. I will use this weekend to inspect my system again, and test all my grounds. How do you your MSD, and what is the difference between the Streetfire, and the 6?

[Bob Kontak]

Originally Posted by docpardue

Do any of you guys have a MSD?If so, can you tell a difference?

Why would the temp of the CDI Box effect the fuse?

I have MSD. 12 years now. One box, one coil. No issues ever. Don't install it on the dash like the legitimate twin NASCAR MSD boxes. That stuff is way out of our league AND the DIY guy that does it is a wanna be.

wwest is thinking if something is getting hot in your box and then blowing your fuse. Therefore, cool the box, delay the fuse blowing, then you isolate the problem to your box. Makes sense but your blow is too fast.

Disconnect your CDI box. "Start" the car. Does the fuse blow? That's what I would do.

Get your multimeter and plug into the CDI box connector - on the wires side, not the box side. Find if anything goes to ground that should not.

[LEAKYSEALS951]

My streetfire has been perfect to date for my daily driver use. Looking at your rig, I think the 6al might have a little more gusto, but the streetfire works for me and got me on my feet again. I do notice a little "less" throttle reponse from the streetfire. That could be psychological, but I am so happy that the car works, I dont care. Like my post said, the streetfire is so cheap, it is disposable, so you could thoeretically try it, and if it works, later go to MSD 6al and gap your plugs to max. I think both would work for you well. Im am sure you have seen the MSD 6al mounted in other people's engine bays. Since you have all that fancy stuff in the rear of your seats, you could mount it anywhere. Also, in my post, some guy had the MSD programmable unit. You might want to look into that as well for racing puposes...If I had to do it again, I might have gone that way. I dunno... I just didnt feel comfortable gambling$600+ on a permatune when my car itself could have been the culprit. Good luck!
Ron

[Bob Kontak]

I put mine under the driver's seat.

Chill on maxing out the plugs first step. Do it gradually. 0.060' gap will find limitations in your secondary system pronto.

[LEAKYSEALS951]

Agreed ^^^ I said that wrong.

[Bob Kontak]

I would go 0.40 first from 0.030 then step it up .005 at a time. Given OP's interest in racing, I would work it to the max as I know I am leaving several ponies on the table with my 81 still gaped at 0.030".

Nice to not have to hassle with the late night "light show" under the engine lid.