Ok so I've been fixing cars for a few years now and have a pretty good basic knowledge of what it takes for a vehicle to run. My 93 4cyl camry crapped out today on the highway from what it turned out was a worn out distributor cap. At the same time the check engine light came on which has never been on before. I found out by checking for spark at the end of the plug wires (very weak) then at the coil where it was real strong. So I put in a new cap and rotor on the side of the road and was off and running with the check engine light still on.

When I got home I read the codes which there were two 12 and 24. 12 is no rpm signal from the distributor to the ecm. I cleared the codes by removing the efi fuse AND by disconnecting the battery for a little while. The code 24 did not reset but the code 12 keeps resetting after the engine is running for about 5 seconds.

My question is how is my engine running as well as it is if it doesn't know what my rpm is and why then does my rpm guage on my cluster work? doesn't the ecu need this info to calculate when to set off each injector pulse?

UPDATE: Instead of spending all kinds of time diagnosing where I was loosing the NE or G signals from the distributor I figured I'd pull off the cap and rotor to take a peak at the sensors and to my surprise I found one of them had come apart sending thin copper wire shrapnel all over inside my distributor. There are 2 magnetic sensors within the distributor and I'm guessing that one is for the injector pulse (the one that didn't blow up) and the other is for acurate timing advance (the one that is gone). so untill I replace the distributor I may not be getting the gas mileage I was used to. Kind of weird that this happened at the same time that the distributor cap failed. I'm thinking maybe because the rotor was sparking out against this sensor instead of the cap because the pins inside the cap were so deteriorated. If anyone has ever ran into this before please don't be shy and let me know.