496 HO issues
 

Need help!!! 2006 35 Outlaw 496hos port engine having issues running. Boat will run perfect right off the trailer but after sitting in a cove for a few hours port engine will start but as soon as I put it under a load it just falls on its face. When given throttle, rpms jump all over and you hear and internal pop almost like a back fire. Boat has also done this after only running a few minutes so don't feel like it's a heat issue. Yesterday we coved out 6-8hrs after running about 20 minutes and it wouldn't run. Stopped scanned engines and then it ran fine all the way down the lake.

Things we have tried:
Scanned engine and no codes except for see below using Rinda TechMate Pro
Replaced spark plugs
Replaced IAC motor
Replaced fuel filter
Checked fuel pressure at idle and running 43psi
Compared outputs on both engines

When scanning I compared every single output and the only output that was not the same was the IAC % at idle. Problem port engine runs 20% at idle and starboard runs 0% at idle. Port ran about 50% at 3000 rpms Also, I did have a Map sensor code but it has since disappeared.

Anyone have this happen or have an idea what to look at?

Whats the battery voltage on each battery?

I would check your fuel injectors and rails. I am assuming 2006 motor so your cool fuel filter setup has been shedding all of its painted interior into the entire system for about 3 seasons now. Its very likely that you have clogged fuel system somewhere.

I just went through this same ordeal - Complete clean and refurb injectors, Clean and check fuel rails and new CoolFuel setups. Big expense but so is owning a 10k pound lawn ornament...

This is all advice given me own experience - you have not indicated Merc Alarm is screaming at you when you throttle up and it dies...so I am leaning fuel system.

I also had to replace my complete fuel system from the cool fuel and everything in between including the injectors. Find a merc. certified dealer and they can get all the parts under warranty and you just pay the labor. Do both motors at the same time. Even if its not the issue get it done because it will be a issue sooner or later. I was shocked they gave me thousands of dollars worth of parts for free. Merc. knows they sold a faulty system with paint on the inside of the fuel cool and it then peals off over time and clogs the rails, filters and injectors. The are doing the right thing so take advantage of it.

Imagine if only a knowledge source like BUP (John M) could dispense some quick advice on your issue given his overwhelming knowledge of this particular engine type? But alas....OSO needs to make that almighty dollar and since he has a marine mechanic business they gotta squeeze him for a membership.

I checked fuel pressure while having the issue and it was still 43psi but would not run.. It actually fluctuated a little higher when cutting out.. Up to about 47psi.. Would I still be seing the correct pressure during the issue if something was clogged up?

How old of a boat will they cover this on you think? Mine is a 2006 35 Baja

I did mine last year and it was also around the 2006 age.

Chances are yes because injectors can be clogged. Pressure is read before the injectors

Check your BUP...

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!

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.

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.