Search results

  1. C

    350 Mag MPI intermittent rough running.

    Will work on the computer scanner Saturday. I had the injectors overhauled 600 hours ago, every time I checked the TPS numbers, they have been normal. Vacuum leak, I agree is a possibility. Looked for one before, could not find one. For emissions, does this have much? There is no cat converter.
  2. C

    350 Mag MPI intermittent rough running.

    I changed the MAP sensor and the engine runs much better, but the problem was not completely solved. I have never been able to troll between 600 and 1,000 rpm. Now I can run at 700 or 800. During a half hour sea trial the high idle issue did appear once, but it was not as dramatic as before...
  3. C

    350 Mag MPI intermittent rough running.

    Also I noticed that the engine appeared to be running very rich, when the problem occurs. Thinking that a temp sender may be faulty so perhaps I may replace the MAP sensor.
  4. C

    350 Mag MPI intermittent rough running.

    Okay, will check that. Also the fuel pressure reading was 44 psi at all times, so that is good.
  5. C

    350 Mag MPI intermittent rough running.

    So connect the meter to the two center wires on the DLC, and there should be a voltage signal of some sort?
  6. C

    350 Mag MPI intermittent rough running.

    Good progress today. No loose or chafed wires that I could find. However when I compressed one of the IAC hoses, the engine smoothed out and went to idle. I tested the connector and found with key on there was 13 volts to the IAC valve, so possibly a sticking valve. A year or two ago I...
  7. C

    350 Mag MPI intermittent rough running.

    350 Mag MPI Horizon, s#OM675521 I checked the fuel pressure a few months ago, was 46 psi or whatever the spec is, can check again. Will test the DLC connector with a meter, good idea, thanks.
  8. C

    350 Mag MPI intermittent rough running.

    That is the first thing I did, about a year ago. I also changed the linkage to make sure I was getting full pressure on the throttle body plate. Another clue: Yesterday I partially warmed up the engine, running rough. Then I restarted and the rpms went to the correct 600 and the motor was...
  9. C

    350 Mag MPI intermittent rough running.

    This engine is FWC, has 1900 hours, but I have rebuilt the heads and replaced the timing chain set. Recently it will often start out running rough, and the idle will shoot up to 1,300 rpm. If I shut the engine down and re-start, often the engine will run correctly again. However the problem...
  10. C

    350 Mag MPI question on 555 relay fuse blowing.

    Thought I would give an update on what caused the problems on my engine. Primarily the newish coil had some sharp edges on the aluminum portion of the bracket. This abraded the wiring harness that was just above it, eventually shorting the wire the was connected to the 20 amp fuse. Second the...
  11. C

    Alarm Going Off for Mercruiser 350 Mag MPI

    Impeller could be weak, causing low water pressure. The Merc Guardian system is reducing your RPMs to 2,500. Best to get a code reader.
  12. C

    350 Mag MPI question on 555 relay fuse blowing.

    Thanks for the recommendation. I have the old coil, there was nothing wrong with it. This weekend I will do some testing with my ammeter, and swap some parts. Will try to determine what is causing the circuit overload.
  13. C

    350 Mag MPI question on 555 relay fuse blowing.

    A year ago I pulled the IAC cable off while the engine was idling. An hour later a 20 amp fuse blew. This fuse powers the fuel injectors and coil. Twice since then the same fuse blew, and today it blew twice more while out in the ocean. It tends to blow just after increasing RPMs to cruise...
  14. C

    350 Mag MPI Horizon died at sea, cannot find the problem.

    Ran the boat for 35 miles on the ocean this Sunday, engine was reliable. Generally I clean the contacts inside the distributor 2x/season with a soft stainless wire brush in a Dremel tools. Otherwise corrosion builds up. This is an older boat where all the water drains into the bilge. I have...
  15. C

    350 Mag MPI Horizon died at sea, cannot find the problem.

    The Fuel Injector fuse was out, thanks for the professional help. I did not know there were fuses under the cover... Charging system worked excellently today. On the day the engine died, upon starting the boat the idle was too high, ~1100 rpm. I unplugged the IAC connector, engine died, but...
  16. C

    350 Mag MPI Horizon died at sea, cannot find the problem.

    Thanks, I will check those. Are they glass fuses or mini blade fuses?
  17. C

    350 Mag MPI Horizon died at sea, cannot find the problem.

    I will be back at the boat on Friday, and will check the cranking voltage. Any idea where the 12 volt injector fuse is, if it has one? Looking at my schematic, I see that the two light wires in the coil connector are parallel. Will check the voltage there as well.
  18. C

    350 Mag MPI Horizon died at sea, cannot find the problem.

    12V injector fuse, I will have to find that, did not know it existed. Swaped in a used cap and rotor, no change. For the coil, put the probes on the white and pink wires? Connector has a pink plus two light colored wires. Starting voltage was back up to 12.7 volts, I have a Blue Sea digital...
  19. C

    350 Mag MPI Horizon died at sea, cannot find the problem.

    We had been running for an hour, engine appeared to be running well. Engine just stopped. Checked for spark, nothing from the coil wire. Also battery voltage was low. Engine has 1800 hours on it, coil and both fuel pumps replaced 500 hours ago. 2006 (?) model, s#OM675521. Was towed 15 miles...
  20. C

    Recommended anti-seize when assembling drive and transom shield?

    What are recommended anti-seize compounds to use?
Top