OK this is kind of a I think I know but what do you think question. My' 74 914-4 carborated conversion, with MSD Ignition runs great for about 30 miles then the tach starts acting up. When coasting with the engine in gear and turning, the tac drops out reading 0 RPM until I give it gas. The engine backfires and comes back to life. I can drive as long as I'm giving it throttle but if I stop with clutch in the engine cuts out. It will immediately restarts with the key, and runs but the condition seems to get worse.

I had the Battery bench tested and it tested good at 475Amps but slightly low for voltage. So, I think it's a bad Alternator, or could it be the MSD acting up or Voltage regulator. Maybe a week Coil? What do you think?

........I may be wrong? .....I'd try the weak coil
have it tested (among other things,distributor)

Good idea and easy enough to do, hope it is the coil. could be too weak to handle the MSD output or could be the alternator not charging the system to handle the MSD maybe.

[quote name='struckn' date='Nov 10 2011, 05:27 PM' post='1569777']
[quote name='Drums66' post='1569755' date='Nov 10 2011, 04:34 PM']
........I may be wrong? .....I'd try the weak coil
have it tested (among other things,distributor)

[/quote]


Updating post. I cecked and cleaned the contacts in the voltage relay, looks new. Noticed that there is a magnetic pick up under the distributor cap, points were removed. The MSD information says that their units will not work with a magnetic pickup? Also the System does not have the PN8910 Tach Adater called for. Note, this was originally a fuel injected 1.8 that now has the dual EMPI Carborator kit installed. It is using the stock Bosch Red Coil and stock VW Plug Wires. I think I need to install a MSD Coil and MDS Plug Wires. Plus I think I need to remove the magnetic Distributor sensor and replace with stock Points. I do not see a typical vacuum advance system on the distributor or know if it is required. I'm wondering how the car can run normally for approximately 30 minutes before the tach starts acting up just be for the engine begins running ruff and then everything cuts out. It's almost like an onboard computor senses something and kills shuts down the ignition?
Can an MSD do that? One last note I just bought the car and did not set it up this way so I'm de-bugging someone elses work.

Take pics of that dizzy and post here. You may have a empi 009 with the empi pickup sensor. The empi sensors are know to fail, so much so the local bug house won't sell them.

OK Thanks, here are pics of Dizzy cap on and coil wiring, Dizzy cap off, and Battery wiring to positive post?

Cut and Past to my phoito bucket link.

http://s1210.photobucket.com/albums/cc411/...E%20914%20PICS/

Wondering? If the empi sensor failed would the car still run at all?

Thanks
Doug

Not the empi one. Maybe Pertronix or hot spark? That coil is not stock, neither is the dizzy. Personally I would get the msd unit out of it for now, just put the red wire from the pickup on coil+, black wire to coil -, tach wire on -. The only problem I can see with doing it that way, is we don't don't what coil you have. If it is not internally ballast type, it can burn up the pickup. I have seen symptoms you described once on a friends vw bug. He hooked up the coil backwards, but it was pretty obvious after 20 minutes, as you couldn't touch the coil it was so hot.

OK Thanks. The Coil does have Bosch written on the top not sure which one it is other then it is Red, not Blue. I'm thinking the sensor is Petronix too, as I've installed one on a 68 AMX I have. Looks the same. Interesting that the dizzy isn't stock. I'll disconnect the MSD and check the wiring to the Coil then see if it runs OK.
I'll also regap the plugs that I have set at .040 gap to the spec gap which I think is .028.

Thanks again,

Doug

Pick up a blue coil too... we have put red ones in our cars for temp fixes and they have never run correctly. Pull the MSD, get a brand new comp-u-fire electric ignition for the distributor and a blue coil. Plug and play and off you go.

Good luck!

Update. Talked to MSD Tech. Told him I did the Check to see if the MSD is working and it failed to produce a spark when ignition is on and Coil wire at dizzy end s held 1/2 inch from a ground source while the white MSD wire pulled of of Coil is touched to ground then lifted. No Spark, Bad MSD or Coil. He also confirmed that the sensor in the dizzy, which is a two wire, is a Pertonix and is not a magnetic sensor so it can be used with an MSD Unit. I also removed the Coil from its Bracket and it is a Red MSD Blaster 2. I disconnected the MSD from the coil and plugged the Dizzy's Pertonix's wires on to the coil. Tried starting the engine and still no fire. So next thing is I have a old Coil I'm going to use to see if it fires up. If it does I'll Buy a New Coil and then retest the MSD.

Don't use that coil with the Pertronix module. It will fry it without a ballast resistor.

Thanks, didn't think of that. I have a Petronix's Igniter Coil in another Car I can use
to see if it will fire?

I got it running. The problem I had was my MSD took a dump. I'm thinking I don't need it as it has Pertronixs under the Dizzy cap and a MSB Blaster 2 Coil. Coil turned out to be good. Here's the wierd thing, after I figured out the problem I ran it with only the ignition and Pertronixs wired to the Coil. I then plugged in the Tac wire to the Coil and it ran good for about 1/10th of a mile and then completely shut down.
It wouldn't restart, so I disconnected the Tac Wire from the Coil and she fired right up and has run fantastic ever since? I'm leaving the tach disconnected. I'll use my ears instead to. My guest is I might need the MSD PN8910 Tach Adapter if I want the tach to work with this set up. I'll call Tech Support for confirmation next week.