its a 730 ecm on a speed density 350 -5 speed and i am having a random misfire at idle. I have replaced everything and just now noticed that the cap was scored on one side like the rotor sliced it up. it is right after cylinder 6 post. I have replaced everything else and still hear the misfire every once in a while when its idling. I tried to tune it but i just put the stock 305 chip back in and it runs better... Do i need a new ECM? by everything i mean, dist, cap, rotor, plugs, wires, pcv valve, air filters, intake manifold and runners, coil (MSD blaster), ICM, IAC, MAP, Knock sensor, O2 sensor, everything!!!

The reason i think i need a new one is because the speedometer is not working but when i datalog it shows the vehicle speed, what the speedo should say but it's pinned at 0mph...

 

With the previous distributor cap being scored, check the distributor base plate.

The base plate is what the cap screws down too. They sometimes come loose from the distributor body which causes all kinds of issues. See that it is still secure to the distributor body.

While there check that the star wheel on the distributor shaft is still tight on the shaft. They too have been known to come loose.


For the malfunctioning speedometer, it is driven from the ECM. It may be the ECM, but it can also be a bad wire, connection at the instrument cluster, or the speedometer itself. IOW: I'm not going to tell you to buy an ECM and see if it fixes it.

However, if you can borrow one or get one for low cost then it will help in troubleshooting. And maybe fix the problem.

RBob.

 

I will check that tomorrow, the pickup coil is what you are talking about no? that thing is solid on there... i think. Ill check it out. I replaced the cap and rotor today and it seemed to help, but i'm still getting a random misfire, noticing it only at idle. is there a way or a shop that can test the computer?

Thank you for your help RBob. You = da man!

 

ps i was poking around with a test light and a multimeter but apparently i dont know how to test for a short to ground or short between two wires... any suggestions