So screwed ... There goes our Summer

[oceanbu]

10 hours ago, Imracin68j said:

UPDATE:  So I had a crack in the port manifold.  I replaced it, excited about going out today.  The boat was cutting out really hard under throttle.  At idle it sounds normal.  Do I have to remove the entire floor board to get to the fuel pump?  Anything else I can check before I take apart the boat? Do things get caught in the fuel pump?

 

Did you end up being able to find an ETX CAT manifold?

[Imracin68j]

I did, I was hoping my problems were over.  I'm thinking it's fuel, which probably got the manifolds hot

 

[boardjnky4]

It should be steady.

[Imracin68j]

Got a 2008 VLX with a drop in fuel pump.  This fuel pump is not available anywhere.  Can I rebuild this one?

Part: 3020516-1
or 3020516-2

[ORMailbuboater]

Bakes Online Fuel Pump Gen 3 Malibu       Bakes online shows the pump you reference.  Do not know if it is in stock.  Give them a call.  

[Eagleboy99]

Here ya go bud!  Buy two!    https://www.greatlakesskipper.com/millennium-boat-in-tank-fuel-pump-3665-01-malibu-high-flow-3020525

[Imracin68j]

That I've fixed or changed thus far.  backfires and stalls when I give it throttle. 2008 VLX.  Hate this summer. 

New fuel pump - PSI is normal
New cap and rotor
New crank trigger
cleaned out throttle body
change port exhaust manifold. 
New batteries

I'm out of ideas. 

[formulaben]

Fuel filter.

[Sparky450]

Crank shaft sensor??

[MadMan]

A faulty throttle position sensor or MAP sensor can cause this.

[hawaiianstyln]

Billy, on FB Malibu/Axis Owner page you had mentioned you bought your cap and rotor at Autozone or NAPA (can't remember)?  Could it be possible you bought the wrong HVS cap or accidently crossed the wrong plug wires going into the HVS Cap?  Did you buy new spark plug wire set as well?

[Steve B.]

Fuel injector?

[Imracin68j]

Or is there something different in the wiring? 

Mine looks exactly like this:  https://www.summitracing.com/parts/ado-12679524

[Johnwayne]

Maybe wires crossed or timing out of spec

[Imracin68j]

Changed:
 

Spark plugs
Cap and rotor 
throttle body
coil
fuel pump
batteries
right side manifold.

Compression and leak down check out. 

Backfiring around 3000 rpm
 

[MadMan]

I don't have any direct experience with this throttle body, but I have successfully used many other GM parts.  I'd say go for it.

[ahopkins22LSV]

To anyone trying to follow this and help or follow as you have the same issue:

I just moved all of these topics to the Maintenance, Tech and Troubleshooting forum then merged them all into the original thread. So please keep all conversation to this thread now so anyone in the future who may have the same issue can follow one thread and not 5.

[justgary]

Thanks, @ahopkinsVTX.  I was kind of avoiding the multiple threads....  To the OP, it's the same group of people that read these threads, so starting a new one with every new thought doesn't mean new people will read it, it only frustrates the ones who do read them and try to respond.

I would not change the throttle body unless you know for fact that the original one is bad, which is very unlikely.  A visual inspection should confirm that the butterfly is not loose, etc.

Potential causes of backfire off the top of my head include (and others have mentioned these, and you have checked some of them):

• Hung injector
• Improper fuel pressure
• Improper timing advance; ECM and ignition module under distributor collaborate on this
• Worn distributor bearings
• Throttle position sensor
• Crankshaft position sensor
• Poor compression
• Crossed plug wires
• Bad plug wires - I would go ahead and change them; get quality ones with good boots
• Bad spark plug
• Bad rotor/cap
• Carbon buildup on valve tops (less likely in a boat due to engine load, but possible)

Note that most of these are spark related, not fuel.  A timing light could tell you a lot about your spark, and two timing lights could tell you even more.  If you use the first light on #1 and everything looks good, you could use a second light at the same time on the other cylinders to make sure they all stay where they are supposed to relative to #1.  You can do this with one light easily enough, but you don't see the difference in spark patterns that way.

If you don't catch the spark misbehaving, I would focus next on the injectors.  It's easy enough to pull them and have a look.  If you have a shop locally that can test them, that's probably a good idea.

P.S. On thinking about it more, you have cats, so you have a closed-loop control system.  You might find that spending a few hundred on a MEFI reader (I'm not talking about just a code reader, you want data and plots) would help you quickly pinpoint the problem.  The plots will show you spark advance (that you can verify with a light), injector pulse width (that you can verify with an oscilloscope), engine load, throttle position, and all the other fun stuff.  Your system might not be going to closed loop mode due to a faulty temperature sensor, for example.  If it is not in closed loop mode, don't expect it to run well under load.

[justgary]

Thinking even more about it, I would go ahead and clean/test or change out the temperature sensor that goes to the ECM.  It's easy to do, and could be the source of your troubles since it could keep you from going to closed loop mode.

[oldjeep]

34 minutes ago, justgary said:

Thanks, @ahopkinsVTX.  I was kind of avoiding the multiple threads....  To the OP, it's the same group of people that read these threads, so starting a new one with every new thought doesn't mean new people will read it, it only frustrates the ones who do read them and try to respond.

I would not change the throttle body unless you know for fact that the original one is bad, which is very unlikely.  A visual inspection should confirm that the butterfly is not loose, etc.

Potential causes of backfire off the top of my head include (and others have mentioned these, and you have checked some of them):

• Hung injector
• Improper fuel pressure
• Improper timing advance; ECM and ignition module under distributor collaborate on this
• Worn distributor bearings
• Throttle position sensor
• Crankshaft position sensor
• Poor compression
• Crossed plug wires
• Bad plug wires - I would go ahead and change them; get quality ones with good boots
• Bad spark plug
• Bad rotor/cap
• Carbon buildup on valve tops (less likely in a boat due to engine load, but possible)

Note that most of these are spark related, not fuel.  A timing light could tell you a lot about your spark, and two timing lights could tell you even more.  If you use the first light on #1 and everything looks good, you could use a second light at the same time on the other cylinders to make sure they all stay where they are supposed to relative to #1.  You can do this with one light easily enough, but you don't see the difference in spark patterns that way.

If you don't catch the spark misbehaving, I would focus next on the injectors.  It's easy enough to pull them and have a look.  If you have a shop locally that can test them, that's probably a good idea.

P.S. On thinking about it more, you have cats, so you have a closed-loop control system.  You might find that spending a few hundred on a MEFI reader (I'm not talking about just a code reader, you want data and plots) would help you quickly pinpoint the problem.  The plots will show you spark advance (that you can verify with a light), injector pulse width (that you can verify with an oscilloscope), engine load, throttle position, and all the other fun stuff.  Your system might not be going to closed loop mode due to a faulty temperature sensor, for example.  If it is not in closed loop mode, don't expect it to run well under load.

Unfortunately in these newer engines a timing light doesn't tell you much more than that your plug is firing.  The cam angle needs to be set by viewing the value via Diacom

[oldjeep]

Are you getting any codes?

[Fman]

Ever consider taking it to a marine mechanic for a diagnosis to help troubleshoot?  What is your time and frustration level worth?  You are also replacing parts that are not the solution to the problem.

[justgary]

1 hour ago, oldjeep said:

Unfortunately in these newer engines a timing light doesn't tell you much more than that your plug is firing.  The cam angle needs to be set by viewing the value via Diacom

That was exactly my point.  He doesn't really know that his plugs are firing properly.  This is either fuel or spark, but probably not both.  Hard to continue without knowing which one to tackle. 

[oldjeep]

1 minute ago, justgary said:

That was exactly my point.  He doesn't really know that his plugs are firing properly.  This is either fuel or spark, but probably not both.  Hard to continue without knowing which one to tackle. 

He has a modern MEFI boat, it would be throwing misfire codes like crazy

[justgary]

9 minutes ago, oldjeep said:

He has a modern MEFI boat, it would be throwing misfire codes like crazy

I guess we could say that for his current backfires and stalls also....