496 Eratic performance
 

First time out this year and the boat ran great at first. It's a 2004 496 Mag used to repower a 1992 Checkmate. After a short while the engine sounded a little different and I was unable to get over 3500 rpm. No alarms or indications of trouble on the smartcraft gauge. Back at home on the flusher the idle was unsteady, dropping from 720 to 630 and back up randomly. I pulled the separator/filter and checked the fuel in a jar. Looked normal, no water or debris. I pulled the in-line filter and it did have debris. Changed both filters and checked the pump inlet screen which looked pristine. Back in the water I idled away from the ramp for a few minutes and then tried to get on plane. The engine bogged twice severely for about 5 seconds and 1 second then came to life and ran perfect for several 5000 rpm runs. Back on the flusher the idle was fine for a few minutes then became unsteady once again. I don't know if I have fixed the problem or not until I get back out but any suggestions on other things to check would be appreciated. I'm going to order a scan tool this week so that should help.

Hey Nighthawk,

I have diacom marine software. If you feel like dragging your boat up I can scan it for you. You're not too far from me.

Dave M.

Just a wild guess here, but based on my recent experiences and those of others, it's either a boost pump crapping out, or your fuel injectors has gotten some junk in them....Verify your boost pump with a fuel injector pressure gauge off the fuel rail (38-43psi) first, if good I would then pop out your injectors and clean the inside with electrical contact cleaner via the small straw. I found small rusty colored granuals in 7 out of 8 injectors on the motor behaving very similar to yours AFTER having burnt out a boost pump last season via some bad ethanol gas. Otherwise you have a guardian situation and a sensor has crapped out.

Outstanding. If I continue to have trouble this weekend I'll PM you to possibly set something up. I trailer through La Plata pretty often on my way to Goose Bay etc.

Rusty colored granuals are what my in-line filter was full of.

How difficult are the injectors to remove?

Essentially they just pop right out like corks from the intake. First loosen and move aside a couple of things, then simply lift up on the fuel rail on one side until all four are free of the intake. Each injector you then "pop" out of the rail itself. Each is held in place to the rail by a clip ring. I left mine connected to the wiring harness since after i removed them, they were easy to flip and tap some residue out before blasting the inside with electrical contact cleaner (plastic safe). I did each one individually, then aligned and popped back in. I took a rubber mallet and used the soft rubber handle of a small hammer to ensure they were seated good, then did the four on other side. I plan to do the other motor even though I'm not having "noticeable" problems just to be sure all 16 injectors are operating at max capacity. I changed my in-line filters late last year after my ethanol related fuel issue last summer, as well as several seperators along the way as I was slowly purging my system of the bad gas.

Sounds easy. Thanks.

It does not like the rain!!!!!!!!!

I Know it is a tough crowd.

Ed

Hey NightHawk how's that 496 doing? I'm down to decision time within the next week. Leaning strongly to replacing my 454 with a 496 bobtail.

I've heard, somewhere on one of these boards that running the 496 on the hose will cause sensors to report errors also hard on the impeller due to the amount of air vs water. What are your thouhts?

Also how did you handle to fuel return line issue?

Thanks,

Never run any motor over 2500 Rpm's on a hose.