Potential ignition problem
 

Hello Pelican members,

I have a 1983 3.0 motor i recently rebuilt with new steal head studs, Euro Spec Mahle Nikasil cylinders, rebuilt heads, new springs, etc. Basically the entire top end is new including a new Euro spec Airbox with the larger diameter intake tubes. Basically this US spec engine has all Euro spec parts. Anyways I am starting to think this car is cursed. When I first got the car, before I rebuilt the engine, it had a stumble under load. It would then quit. You would let it sit a few seconds and it would start right up and run until it would get warm again. I determined it was the CDI box that was failing and installed a new MSD 6AL ignition box plus a coil blaster 2 coil. Turns out this fixed the problem.

Fast forward a few months, the car was running fine. I decieded to adjust the valves and change the oil. Anyways, when I opened up the valve covers a head stud fell on the ground. Anyways, I took the engine out and rebuilt the heads and changed the dilavar head studs with steal ones. I put the engine back together and started it. It took me about 3 months to rebuild the engine as it was my first one. Rebuilding the hydraulic tensioners was a pain because I had to source new ones becuase somebody had modified the original ones into solid ones. Don't ask me why somebody would do that.

Anyways, I also had problems with the clutch fork (pin broke) so basically I had to take out the engine twice after the rebuild. After the first start up it ran quite well. I had it idling for about an hour changing RPMs to seat the engine per se. I then drained the oil changed the filter. I found no metal shavings. Having done this i felt confident I could actually drive it on the street.

I took it out and it drove beautifully. It pulled harder than it ever had, really came alive after 3k RPM. However, this is where things took a turn for the worst again. When ever the car would fully get to operating temperature it would start to stumble at anything over 2.5k RPM. I did the usual checks, I checked fuel pressures and they are within spec, I checked for vaccum leaks and I did find one. The big o ring underneath the throttle body was perished. I replaced that and concluded I have 0 vaccum leaks. I was 100% sure this would fix my stumble. Note, this only happened when the car fully reached operating temperature. Unfortunatley the problem remained. I then proceeded to check fuel injectors. They all give out a spray/mist triangle pattern so I think they are all fine. This is where I started to get desperate, I was running out of things to check and running out of ideas. I decided to replace spark plug wires since mine seemed a little old. Anyways, this did not fix my problem either. While i was there I checked my rotor. I took it out and it looked like it had melted. I thought I had found my problem so I bought a new one. Drove it around again and it also melted it within 20 minutes. After researching a bit I figured that since I had installed the MSD 6AL I needed to use a resitorless rotor. I was so excited I thought I had figured out my problem. I bought a resistorless rotor and the car ran almost perfect. It had a slighy stumble very high on the RPM range. I was happy since I rarely rev it that high.

I was on a cruise last weekend when I stepped on the brakes and I had no brakes. I pumped the brakes (not the first time I run out of brakes and probably not the last either) and I managed to stop. Thankfully i was 1/2 a mile from my yard. I limped home and the engine started missing and sputtering again. Anyways, it turns out my front right caliper had seized. I didnt notice and it got so hot hot it boiled the brake fluid. Anyways, I thought the engine started sputtering because the brakes were still dragging (Wishful thinking I know). I rebuilt my brakes with new seals, pistons, pads, flexi hoses. Relatively cheap and easy job thankfully. I took it ouf for a cruise and the brakes work beautifully. However, the engine now sputters and misses. Before I changed the rotor it would only do it when it got to operating temperature and at higher RPM, now it does it hot/cold high/low RPM. I don't know what to do anymore. I am so lost that I don't know whether to check fuel or spark. If I had to guess I would say its an ignition problem. Whatever the failing component is, has gotten worse. Any suggestions would be greatly appreciated.

I am especially interested in people familiar with the MSD 6AL ignition box. I dont understand why my car was running well pre engine rebuild with the rotor with the resistor and after the rebuild it only runs with a rotor without a resistor.

I have also adjusted the air/fuel mixture on the fuel injection head. I have also also changed the O2 sensor.

http://forums.pelicanparts.com/uploa...1629718150.jpg

You said you ran a fuel pressure test. Did you run the complete test for system and control pressure hot and cold?

Hi Walt,

My control pressure are as per below:

Disconected WUR 20PSI.

1 minute: 30 PSI
2 minutes: 40 PSI
3 minutes: 43 PSI
4 minutes:46 PSI

Warm Control pressure: 54 PSI (Takes around 10 minutes, I know my heater element is lethargic)

I also rebuilt my WUR. I had to unclog the micromesh with acetone. I also did the adjustable modification to it.

Check your green wire from your distributor, make sure it isn’t frayed, cracked or damaged. I think that there are two wires coming out of the green wire and that if they get hooked up wrong the motor will run, but not run right. It’s been a while since I had the issue, I’ll see if I can find the post and get you more information.

Edit: your signal and your ground wire could be backwards, see post below from Henry.

Hi, I just checked and it is severely damaged. If thats my issue I will be the happiest person on the planet. Hope i didn't damage anything else. I drove it less than 100 miles though.

Read this for replacing the bad part of the green wire that is usually at the dizzy.
http://forums.pelicanparts.com/porsche-911-technical-forum/795232-distributor-green-wire-loose-frayed.html

Many thanks, replacement green wire has been purchased plus the connector. Thank you for the write up, helped a lot.

I think you could just stick with a solid rotor. I’m not sure if the stock rotor with the resistor serves any purpose with the MSD.

Another recommendation is to fuse the connections to the MSD, this will protect the circuitry from surges or shorts, etc.

Hello everyone, my high RPM stumble is fixed. Thank you for your help. It was the green wire.

That’s great! How does it feel to be the happiest person on the planet?

I'm going to piggy-back on this post since it's recent and some MSD experts on it.
I have a race car with a 3.0L and installed an MSD a few years ago. Did one track event and then the car sat for two years. Now, I have no spark. I did the coil wire, jumper wire test and nothing. Swapped coils, nothing. Question: I turn the ignition on, the MSD light come on for a few seconds, then flashes a few times then turns off. Is that normal? I don't recall from a few years ago. I thought it stayed on. Any ideas?
Thanks for the piggy-back post.

Go to NAPA and buy an ECHLIN rotor without a resistor. No more MSD melting rotors.

Wow! MSD's melt rotors? I don't mind buying a new rotor but not sure that is the issue. Since the coil test for spark showed nothing, the coil is not alive. I saw a friend, at Sonoma Raceway today, (vintage races) and he suggested checking the coil for 12 volts. I'll try that. Seems to make sense. I may still pick up the new rotor.
Thanks for the feedback.
Here's a shot from the track. My contribution to the thread...

http://forums.pelicanparts.com/uploa...1633218757.jpg
http://forums.pelicanparts.com/uploa...1633218757.jpg

CDI systems, e.g. MSD, Bosch, don't have "12 volts" on the coil primary pins. A CDI system sends a pulse signal to the coil to produce a spark.

Steps
Adjust points.
Check continuity from points to msd
Check 12vdc to msd when the key is on
Check continuity from msd to coil wires.
Chrck ohms on coil. 33?

3.0 liter SC motor.......
 

The 3.0 liter SC motors don’t have point ignition distributor.

Tony

Tony is right but check the distributor first

https://rennlist.com/forums/911-forum/1093507-distributor-pulse-generator-fault.html

Well, I have an update. Yes, the coil had no 12v going to it (as you state), but it did make me find the problem. I decided to trace the wires from power to the MSD box. Then, I noticed a large red power wire hanging near the starter motor. Since the car was sitting for quite a while, the starter was sticking and I removed it to free it up. Then, forgot to reconnect the MSD wire to 12v from the starter terminal. Since it's a race car, I turned all the switches on and it fired right up. But, died within a second or two. I have an adjustable warm up reg. so will try and adjust. Seems like it's not doing anything.
Thanks for all the input. I did get me going in the right direction.

It might be the rotor this time.

I took a day off from it but did more testing today. The WUR has 0.00 ohms which is not good. So, I took it off and took it apart. The WUR is part number 0438140 033. Which some sites say, this is for Porsche 911 3.0. Other sites don't show this number for a '78 3.0. Also, the resistor inside is 21R (ohms) but some sites say it should be 24 to 26 ohms. I can only find one resistor for a WUR, on Earth (in Australia), and it's 21 Ohms. Not sure if this is the main problem but it must be contributing to it.
I'll research more and probably start a new thread that's focused on "this" issue.
Thanks for the feedback.