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Discussion Starter #1
Hello. The car is a 2.0 75 with twin carbs. It uses a stock Bosch electronic ignition, the distributor pickup has 2 wires, it's the one with a VR sensor.
The car was running in 3 cyl so I've changed the plugs and then it ran on all 4, but at low rpm it was kinda hesitant. After 300 miles I parked it, and the next day it wouldn't start at all. I have fuel but no spark.
Checked all the wires, the coil has power, the distributor pickup works fine, new dizzy cap and rotor, new plugs, the coil is a red bosch (1 year old), plug wires 3 years old but seem fine.

I've checked the spark directly from the coil and the spark seemed strong, it was red but jumped like 2-3 mm. When I checked the spark from the dizzy it was super weak and could barely jump 0.5 mm. The spark is rhythmic so I figured the sensor work just fine. Checked the continuity between the engine and body and it seems fine.

What gives? What am I missing? Do I need a new distributor?
 

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A red spark is a weak spark. Are you sure that a Bosch red coil is suitable for your application?
 

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Discussion Starter #5
A red spark is a weak spark. Are you sure that a Bosch red coil is suitable for your application?
Not sure at all. The original Bosch coil would stop working when hot. The new one I've sourced from a parts shop who sells Alfa parts. When measuring it and comparing with factory specs I gotta admit it's way off (secondary winding 14k ohms, Alfa documentation said about 6-7k). But the thing is, the engine worked like a charm with it, for 2000 miles. Now this happened. I've heard that new bosch coils are kinda crappy, made in brasil. Could it have damaged something else? If so, what?

1611732


This is it.
 

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I don't know the details of your ignition as the 4 cylinder 75 was not sold here in the US. I am familiar with Bosch ignitions in V6 75's. The Bosch ignition module controls the charging of the coil by monitoring the current and the stock coil has a primary resistance of about 0.7 ohms. It is possible that the ignition module cannot work effectively with a coil of twice that resistance. But yours ran OK for 2000 miles so I would suspect the coil first. I successfully used an MSD Blaster 2 coil on my GTV6 and it is likely that it is a good choice for you.
The other possibility is that the Bosch ignition module is not working properly or that it has a poor connection in the 12V power or ground circuits.
 

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The Bosch red has a 1.8 Ohm primary circuit. There's a bunch of variation in Alfa's 75 manual, but I think the 2.0 75 should use an approximately 0.7 Ohm primary. Below is from the Euro service manual.

Given that the secondary resistance appears to be out of whack on what you've got anyway it's probably worth a shot to replace the coil? But do some digging to ensure that you get the right one, as Alfa appears to have fitted a whole bunch of different coils to the various iterations of the 75 (there are even more in the manual, but this is the one that specifically says "Alfa 75")

You don't happen to have the original coil and can snag the part number, do you?

1611737
 

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Discussion Starter #8
I have the original coil and I will try and use it when I get my hands on it (it needs to get shipped because I've left it in another town, stupid I know). My current coil has 1.5-2.0 primary and 14k secondary so it's double the resistance, whack, I knew that when ordering it because I have the same manual you've snipped. The problem I face is that no one here is specifying the coil resistances, this was the lowest ress coil I could find and the only reason I know the value is because it sais so on the label. The thing is, apart from this red model, not even Bosch specify the resistances which pisses me off like hell. When asking the guys at the shop about the coil resistance they looked at me like I was some kind of an idiot.

I might just order ALL coils on stock, measure them and pick the one I need. But God this rustles my jimmies because the values should be on the product page before ordering. I thought I got away with this red coil but it seems that it's not so simple.
 

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Secondary resistance is not important. As I posted earlier, an MSD Blaster 2 coil has the correct resistance and they are easily obtained on ebay.
 

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Discussion Starter #10
Ok so I've received the stock coil today and the engine still won't start. I doubt the ignition module went bad, they almost never go bad from what people tell me. All I'm left with now is a bad ignition module ground or maybe bad engine ground. Guess I'll have to dig deeper.

On a side note, are the Holley coils made in the USA? Because I have HT leads made in the USA and they seem to be pretty good quality ones.
 

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The ignition modules generate heat and they are installed on a heat sink with heat conducting paste between the module and the sink. They can overheat and fail if they are not installed correctly.
 
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