Intermittent Engine Malfuntion
 

Hello all. I have a 2003 Mercruiser 350 MAG and intermittently it runs really rough. The rpm drops and sometimes it kills. I have replaced fuel filter, cap and rotor, and it has new wires.

I tested the fuel pressure and it fluctuates a lot. It sometimes jumps between 30 and 40 psi. Other times it runs between 37 and 38 psi. Even though this does not appear to be normal the engine seems to run fine even though it is doing this.

I assumed I must have a bad fuel pump until I observed the the malfunction while the fuel pressure gauge was attached. The fuel pressure actually jumped up to about 41 psi while it misbehaved. So now I'm back to square one. Even though there seems to be a fuel pressure anomaly I don't think it is what is causing the gross malfunction that seems to come and go.

I have come to the conclusion I need to read the error codes from the ECM module. So could anyone be so kind and give me some advice/direction how to get a reader cheap. I have seen the DIACOM software and it looks like it would work well, but is fairly expensive. I have a notebook PC so a software solution with a cable would be great. Actually, any solution to get the codes for under $200 would be great.

Thanks for any help,
Brian

I would suggest replacing the IAC muffler, they become restricted and will cause a low and rich idle condition.

As far as reading codes, if your not getting an alarm, you don't have any active codes.

Thanks Dave.

There is not any noticeable alarm. How are ECM alarms typically communicated to the driver. I don't think I have any indicator on the console.

The IAC was just installed new this spring. Also, the malfunction occures at high speed as well. So I doubt it is the culprit.

Thanks,
Brian