Spitfire Misfire on all 4 cylinders - '80 Spitfire

[wbdvt]

Hello,

I am getting a misfire on all 4 cylinders. I have tested each one with a timing light and can see the misfire. There is a new cap, rotor, wires, plugs, and coil. The ignition is an Allison XR-700. It looks to be original as there is an RCA canned transistor? mounted to a heatsink.

Is there a life rating on the ignition system? Anything else to look at?

 

[70herald]

The Allison is probably fine. I would start by trying a different rotor. Also make sure that all the plugs are reasonably clean and haven't been gunked up already.

 

[TR3driver]

No "life" rating, but they do sometimes die from old age.

Another thing to check first would be power and ground to the module. My Crane started acting up once because the ground connection had developed some hidden corrosion.

 

[foxtrapper]

What exactly do you mean by misfire and what exactly are you seeing via the timing light?

 

[wbdvt]

What I mean is that the timing light goes out briefly. I have also seen, via the Colortune, flame out in the cylinder.

 

[foxtrapper]

OK. Wasn't sure if you were meaning something like that, or seeing the timing jumping around, or crossfiring.

Because of where and how that box is usually mounted, it's real subject to poor grounding, and can cut out as a result. So like Randal suggested, check the grounding path well. A heck of a lot of people just run a bolt through the firewall with a nut on the other side, and that's a darn poor ground.

It's an optical pickup trigger. Have you ever wiped it clean? A distributor does get a little dirty inside over time.

Not sure what this transistor on a heat sink you mention is. Are you talking about inside the main module box? For I don't know of one that should be mounted externally with the Allison system. You sure you're not seeing the old points type condenser or perhaps a voltage dropping resistor?

I know you say you replaced the coil, does it match the Allison system? As in true 12V, or if it's a true 6V, does it have a voltage dropping resistor?

 

[TR3driver]

Not sure what this transistor on a heat sink you mention is. Are you talking about inside the main module box? For I don't know of one that should be mounted externally with the Allison system.

Although mine isn't that old, I do believe the earliest Allison ignition modules had a TO-3 style pass transistor mounted to the outside of the heat sink that forms the top of the box.

ISTR it also had the transistor insulated from the heat sink, meaning that any conductive dirt (or salt) buildup could cause problems.

 

[eschneider]

1) make sure the alison box is getting 12V with the engine running
2) make sure the allison grounds are clean and tight
3) make sure the engine-chassis ground is clean and tight
4) try a differnt rotor
5) try a different coil wire
6) double check the alison wiring - ballast needed?