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Discussion Starter #1
2l TS in my 73 Berlina- all stock short of Volvo MAS

so recently i had two issues develop
-tach would cut out under heavy load ie floor it, seems to disconnect
-car stalls until warmed up, then sometimes would stall even after warmed coming to a stop

Replaced one coil after it literally melted, spewing its guts onto the inner fender months ago, before any issues started
been fine

other coil is one that came with conversion ( I didnt do this =, was already converted when I bought it and was the main reason I bought it)

Today I disconnected the older coil ( that goes to top dist ) and starting issue went away, but no tach feed.

Swapped connectors from one to the other, and tach came back and works as it should, starting is much better.
Lil gas to get going but then idles and adjusts until warm on its own.
didnt change the coil wires, only swapped connectors

Coil wire from old coil to top dist came apart at coil end when I tried to remove it
I rebuilt it with a new connector.

So yay it works, but I dont fully understand the system and curious as to
A) did I screw up before and connect them backward?
B) is my older coil not long for this world
C) are my new wires crap and I need a new coil wire thats better built?

Also does it matter which coil feeds the tach?
I read the dist are dumb, so does it really matter which coil they are wired too?

Sorry if this too broad, just trying to get a handle on how it all works, whats important and whats not

I do have an extra set of compete coils w modules (used) to test as needed

Appreciate the feedback
 

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447 Posts
2l TS in my 73 Berlina- all stock short of Volvo MAS

so recently i had two issues develop
-tach would cut out under heavy load ie floor it, seems to disconnect
-car stalls until warmed up, then sometimes would stall even after warmed coming to a stop

Replaced one coil after it literally melted, spewing its guts onto the inner fender months ago, before any issues started
been fine

other coil is one that came with conversion ( I didnt do this =, was already converted when I bought it and was the main reason I bought it)

Today I disconnected the older coil ( that goes to top dist ) and starting issue went away, but no tach feed.

Swapped connectors from one to the other, and tach came back and works as it should, starting is much better.
Lil gas to get going but then idles and adjusts until warm on its own.
didnt change the coil wires, only swapped connectors

Coil wire from old coil to top dist came apart at coil end when I tried to remove it
I rebuilt it with a new connector.

So yay it works, but I dont fully understand the system and curious as to
A) did I screw up before and connect them backward?
B) is my older coil not long for this world
C) are my new wires crap and I need a new coil wire thats better built?

Also does it matter which coil feeds the tach?
I read the dist are dumb, so does it really matter which coil they are wired too?

Sorry if this too broad, just trying to get a handle on how it all works, whats important and whats not

I do have an extra set of compete coils w modules (used) to test as needed

Appreciate the feedback
Pin- I have followed your project through the posts here and am frankly amazed that it runs as well as you say using a Volvo MAF. Still don't understand how that works as the connectors and the functioning parts within are different, but guess the proof is in the running.
Sounds like the intermittent tach signal is a connector/wiring issue- do the usual checks and remedies for continuity and pin to socket tests for that, and no I don't think it matters which coil you get the signal from as they both fire simultaneously. However IIRC there is a dedicated tach signal wire in the harness close to the ECU, orange/? stripe, maybe. I am assuming you have a factory wiring harness for the original Motronic ignition and injection setup or some part of it, Volvo MAF notwithstanding.
Why not substitute your known good set of coils/modules and see what happens ?
IME the stock setup with all original pieces makes for an amazingly dead nuts reliable, seamless system that works well in all circumstances- just as designed. From what I have seen Alfa 75 twinspark parts are still around and not too costly because many folks just want the motor and will discard the original Bosch system for carbs.
A couple of tips on this or any EFI conversion: 1.) you can't have too many grounds!, 2.) you can't have too many grounds ! I grounded separately the cylinder. head, the block, the alternator housing, the ECU case, and the exhaust system- the oxygen sensor likes this if you have one. Unnecessary ? Maybe, until something doesn't work, or worse, works intermittently. :)
 

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Discussion Starter #3
ill try swapping out the older coil. its not hot, previous one that melted was crazy hot, new one cool as a cucumber. fwiw. ill also dbl chk grounds. Had guru go thru n cleanup all the grounds and check draw, its super low. Big brake kit on the shelf, vasilating on installing in Berlina or buying vented version from CA n holding this one for 67 Super. First world problem I know. Not much else to do on the car other than drive it...
 
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