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496 MAG difficulty starting

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    Member PDQH2O's Avatar
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    Default 496 MAG difficulty starting

    My 2006 Gen VI 496 MAG runs great from initial morning start, but after running a while at Mojave (~106* ambient temp), it is very difficult to start. It begins to fire right away, then immediately dies, almost like a sticky choke or vapor lock condition. Vapor lock is likely not the problem, but the symptoms are similar. The engine turns over and seems like it wants to fire, but idles really slow and dies again. Battery is fully charged. After several attempts it'll finally fire properly and run fine thereafter. No problems restarting after picking up a skier, i.e. shutting down and restarting within 15 or 20 minutes.

    Any ideas?

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    Quote Originally Posted by PDQH2O View Post
    My 2006 Gen VI 496 MAG runs great from initial morning start, but after running a while at Mojave (~106* ambient temp), it is very difficult to start. It begins to fire right away, then immediately dies, almost like a sticky choke or vapor lock condition. Vapor lock is likely not the problem, but the symptoms are similar. The engine turns over and seems like it wants to fire, but idles really slow and dies again. Battery is fully charged. After several attempts it'll finally fire properly and run fine thereafter. No problems restarting after picking up a skier, i.e. shutting down and restarting within 15 or 20 minutes.

    Any ideas?
    Check fuel pressure. I bought a fuel pressure test master kit, as I will use it on several other projects. It has a quick-coupler and large gauge to read tiny changes in fuel pressure. Anyway, you should have around 43 psi KOEO. However, the pump only runs for 5-7 seconds if there is no oil pressure. So, you will likely have to have someone watch the gauge while you are up at the helm turning the key. The reason I say check pressure first is - commonly, the fuel pumps go out on these setups. Additionally, if fuel pressure is good, you can then rule it out and move on to scanning the ECM for codes.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Thanks, Beer:30. Good information and logical steps to check out.

    Since it only has a problem starting while warm, and the HP pump was replaced 1.5 to 2 years ago, I would think the low pressure pump would be the more likely of the two. Yes?

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    Vapor Lock seems more likely at those temps...not as uncommon as you migh think..plus ck you ck valve at the tank...theses have a tendancy to stick...gotta love ethonal
    Last edited by DWeiss67; 08-10-2012 at 06:01 AM.

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    Plus something that might seem to be a fuel issue is usually electric...in your harness ck to make sure all the connections are 100% especially the purple wire...that connection above others ends more days...its to small of a gage for most applications...

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    DWeiss67 - Thanks for the help. The only part that points me away from V-lock is that the engine is injected, so the pump should compensate (I think) for any vacuum caused by heat. Got home and flushed the raw water system during clean up process used after any trip. Ran it to operating temp and turned it off. Restarted it about 30 minutes later, no problem.

    Going to do some additional testing, including a fuel pressure test on the system, as recommended by Beer:30, and both pumps if necessary. If that proves to be OK, I'll run the boat locally to see if I can recreate the difficulty.
    Last edited by PDQH2O; 08-10-2012 at 08:32 AM.

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    Quote Originally Posted by PDQH2O View Post
    DWeiss67 - Thanks for the help. The only part that points me away from V-lock is that the engine is injected, so the pump should compensate (I think) for any vacuum caused by heat. Got home and flushed the raw water system during clean up process used after any trip. Ran it to operating temp and turned it off. Restarted it about 30 minutes later, no problem.

    Going to do some additional testing, including a fuel pressure test on the system, as recommended by Beer:30, and both pumps if necessary. If that proves to be OK, I'll run the boat locally to see if I can recreate the difficulty.
    I've had this boat since Jan 2005. I've logged 300+ hours on it...MOST of that in 100+ heat. Including our first Hoover Dam run, when it was 116 ambient. We stopped several times up and back to dunk and cool off. I have never had a hard-start, no matter what the temp was.

    You should also, for good measure, have it hooked to a laptop or Rinda scanner to check for codes - and also see what the TPS is reading in the idle position.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Quote Originally Posted by Beer:30 View Post
    I've had this boat since Jan 2005. I've logged 300+ hours on it...MOST of that in 100+ heat. Including our first Hoover Dam run, when it was 116 ambient. We stopped several times up and back to dunk and cool off. I have never had a hard-start, no matter what the temp was.

    You should also, for good measure, have it hooked to a laptop or Rinda scanner to check for codes - and also see what the TPS is reading in the idle position.
    Great idea for laptop analysis, but it's a little beyond my current abilities. Looks like I have some homework to do. Checked out Rinda tools, lots of information and links to sift through.

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    Quote Originally Posted by PDQH2O View Post
    Great idea for laptop analysis, but it's a little beyond my current abilities. Looks like I have some homework to do. Checked out Rinda tools, lots of information and links to sift through.
    Yeah, I meant TAKE IT to a place that has the Rinda software (laptop). It is very comprehensive and shows every aspect of the engine control.

    I actually need to purchase either the software or one of their hand-held devices. I have the boat (PCM555) and also two RamJet (GM crate) motors with MEFI units. One Rinda unit will troubleshoot all of those ECMs.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Default Just lived through this exact scenario

    Load test your batteries . Cold starts are a cold battery .. Z. Warm starts on a shorting out bad cell mean once the battery gets hot and it was from you running it then the battery fail safe trips on and motor pukes .... I raised my hatch let it cool for a long while then it fired up to make it to shore. Now with that said your alternator can read accurate but it it's charging but the bad cell won't hold it then you won't have enought amps to sustain a start . Load test your batts

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    Bought a Actron Pro Fuel Test kit last week, tested today with the following results:
    Key on, engine off: pump spins up to 43 psi for about 3-5 seconds then drops to 40 psi as the pump stops.
    Key on, engine on: runs consistently at about 38 psi at idle.
    Rev to 1,000 to 1,200 rpm, psi remains steady at 39.

    Ran engine to ~165* for ten minutes, turned it off. Waited 15 minutes, started perfectly. Ran it for another 10 minute (to 165*) turned it off again, waited for 1 hour. Started again perfectly, no problem. I couldn't recreate the issue.

    More testing, maybe a trip to the shop later.

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    Quote Originally Posted by PDQH2O View Post
    Bought a Actron Pro Fuel Test kit last week, tested today with the following results:
    Key on, engine off: pump spins up to 43 psi for about 3-5 seconds then drops to 40 psi as the pump stops.
    Key on, engine on: runs consistently at about 38 psi at idle.
    Rev to 1,000 to 1,200 rpm, psi remains steady at 39.

    Ran engine to ~165* for ten minutes, turned it off. Waited 15 minutes, started perfectly. Ran it for another 10 minute (to 165*) turned it off again, waited for 1 hour. Started again perfectly, no problem. I couldn't recreate the issue.

    More testing, maybe a trip to the shop later.
    Could be a load of bad fuel?? First load of fuel for the seaon, I always load it up with Lucas fuel treatment. Then I just run the cheapest 87 I can find the rest of the season. Don't run any higher octane than 87. The engine timing will never optimize and it can make your transom a bit sootier. I alway run AM/PM 87.

    Also, if it EVER has an erratic idle, even occiasionally, you can check the IAC at the back of the intake. These motors are known for cooking the wires, causing IAC failure.
    Last edited by Beer:30; 08-11-2012 at 07:11 PM.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Quote Originally Posted by Beer:30 View Post
    Could be a load of bad fuel?? First load of fuel for the seaon, I always load it up with Lucas fuel treatment. Then I just run the cheapest 87 I can find the rest of the season. Don't run any higher octane than 87. The engine timing will never optimize and it can make your transom a bit sootier. I alway run AM/PM 87.

    Also, if it EVER has an erratic idle, even occiasionally, you can check the IAC at the back of the intake. These motors are known for cooking the wires, causing IAC failure.
    This was the third trip this season. The boat gets only 87 octane. This time was a fill up at Sam's Club in Bullhead City. The last trip was also to Mojave about six weeks ago. No problems at all on that trip. Ambient temps then were about 5* cooler. I typically do not use fuel additives except for Sta-bil at the end of the season. I've heard good things about Lucas products. Might be worth a try, not sure the injectors have ever had a cleaner through them.

    In running the pressure test, I connected the gauge to the schrader valve on the fuel rail. Is that sufficient or should I test each pump separately?

    Poked around the wiring on the intake manifold while the engine cover was off, but noticed no burned wires or anything else unusual. The engine idles smooth, but the IAC idea is interesting. Found some other marine boards with similar issues and fixes that include the IAC. Will take a closer look at the wiring and try Lucas additive for now to see what happens. Planning to get back out to Mojave in the next few weeks. Appreciate the help very much.

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    Quote Originally Posted by PDQH2O View Post
    This was the third trip this season. The boat gets only 87 octane. This time was a fill up at Sam's Club in Bullhead City. The last trip was also to Mojave about six weeks ago. No problems at all on that trip. Ambient temps then were about 5* cooler. I typically do not use fuel additives except for Sta-bil at the end of the season. I've heard good things about Lucas products. Might be worth a try, not sure the injectors have ever had a cleaner through them.

    In running the pressure test, I connected the gauge to the schrader valve on the fuel rail. Is that sufficient or should I test each pump separately?

    Poked around the wiring on the intake manifold while the engine cover was off, but noticed no burned wires or anything else unusual. The engine idles smooth, but the IAC idea is interesting. Found some other marine boards with similar issues and fixes that include the IAC. Will take a closer look at the wiring and try Lucas additive for now to see what happens. Planning to get back out to Mojave in the next few weeks. Appreciate the help very much.
    I don't see that you need to check both pumps independently. The schrader on top is exactly where you needed to test it.

    The reason I say check the IAC is it is the one controlling the AIR to the motor for start/idle. If it is not returning to the open position for start - the motor may not have enough air for the hot-start. If it does it again, crack the throttle an inch or two and see if it starts better. A motor needs three things to run AIR, FUEL, SPARK. It seems to have spark, fuel pressure seems good, so just make sure it's getting the air at startup that it needs.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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