Diamond Dave

Here’s a scenario:

I would first take it to MULTIPLE shops for repairs. Then over the course of a few years of missing the season over and over (not to mention a couple thousand dollars since none of them can figure it out) I would then Google the problem until your head explodes searching for the answer because the wife is busting your balls to fix that damn boat and won’t give it up anymore. After an exhausting search, you come across OSO like you did and post asking for help. You then wait for BUP to chime in like you have seen him do in SO MANY threads you ran across in your Google endeavors. OH WAIT! He’s been %$&#*@! banned so now what?!

So literally as I am typing this, I get a FB message and low and behold it’s BUP. Granted he’s two hours ahead of me which makes it what 12:30 AM his time? Anyways, he tells me he just got done working on boats and is super busy as usual. We shoot the **** a bit and he told me he went to peek on OSO for all the comments about him being booted off of here. Long story short, he wants you to know that your IAC values are off PWM percentage and you have a bunch of paint shedding within your upper portion of the gen 3 cool fuel. This shedding paint will be in the fuel rail and damper and all the fuel injectors. He wants to make it clear your IAC s are not with in spec for IDLE and off idle as well. Neither one.

Your welcome.

Edit:

You can PM me your credit card info (j/k it’s an inside joke from the BANNED thread) LMAO!

traumamed

I would second all of this. It sounds like an intermittent fuel delivery issue, and the most likely culprit in your setup is the paint contamination that has been mentioned. Also, with regard to the IAC, I didn't see that you mentioned the specific IAC brand/part number. I have experienced a faulty replacement from an aftermarket manufacturer, and I have heard of other people experiencing this as well. This is not specific to this engine or even the marine sector - it just seems like there are always a few defective new-in-box IACs floating around. It may be possible that the IAC replacement has now created a second issue. This may or may not be adding to the current issue, but could catch up to you later.

If there is one complaint I have about my 496s it is that they do seem to eat up IACs with some degree of frequency. So, kind of unrelated but (according to BUP-by-proxy lol) your starboard IAC may be on its way out as well.

jhonster

If it's popping & backfiring, its an ignition issue. Do you have coil over plug w/a crank sensor? Or is it a conventional distributor with a pickup inside the distributor? Scan data wont show you much unless it's an OBDII system, and even so....you'll just have a cylinder contribution test available and can see which cylinders are misfiring. Won't help you if it's a triggering issue. How many hours on the motor?

I'm sure what these other guys are saying is correct if tt's been an issue w/other Merc big blocks. You could still have good fuel pressure and a bunch of trash in the injectors if coatings are coming off the lines internally.