454 mag not running right

[Husqy510]

My buddy is currently in Big Bear with his 2000 Shockwave which has a 454 mag. He just called looking for help because it's running terrible. He replaced the fuel filter and said he can hear the fuel pump turn when he turns the ignition on. He said it fires up but then stalls right away. He reached out to the local mechanics but they're booked 4wks out

Any ideas? Are you able to plug a scanner into it?

 

[HBCraig]

My buddy is currently in Big Bear with his 2000 Shockwave which has a 454 mag. He just called looking for help because it's running terrible. He replaced the fuel filter and said he can hear the fuel pump turn when he turns the ignition on. He said it fires up but then stalls right away. He reached out to the local mechanics but they're booked 4wks out

Any ideas? Are you able to plug a scanner into it?

Is it carbureted? I have a 454 Mag that did a similar thing. If it is carbureted he might need to replace the accelerator pump. I had to do it on mine.

 

[Husqy510]

His is fuel injected. Thanks for the reply, though

 

[JayBreww]

Loose ground?


Sent from my iPhone using Tapatalk

 

[Racey]

If he hasn't touched anything and the problem just came all of a sudden, start with the basics, Battery Voltage, Spark Plugs, Cap & Rotor, Plug wires.

 

[D19]

What Racey said plus the fuel filter

 

[liquid addiction]

Not sure if they have the same type of fuel pump as the carbureted, but there is a check valve inside the pump that gets gummed up. Or oil pressure switch.

 

[SS-C]

nope, his IAC actuator/valve went bad.

 

[guest hs]

Start with a fuel psi test.

 

[Icky]

If he replaced the fuel filter and didn't prime then he possibly isn't getting fuel.

 

[lbhsbz]

nope, his IAC actuator/valve went bad.

IAC doesn’t matter above I....which is where the problem exists.

 

[sintax]

Start with a fuel psi test.

my thoughts, check the psi at the rail

 

[SS-C]

He said it fires up but then stalls right away.

Yes, This is a text book description of what happens when the AIC fails.

 

[SS-C]

I meant to say IAC valve, but you all new that... Lol

 

[DRYHEAT]

If he can get it to fire in neutral and bring it just off idle and it runs it’s the IAC most likely.

 

[Husqy510]

Thanks for all the quick replies. I sent him a link to this post and he's trouble shooting it.

 

[Racey]

If it fires and sounds fine then stalls i agree with looking at fuel psi.

If it's the IAC he should be able to crack the throttle and it should stay running.

The IAC for all intents and purposes just acts as a controlled vacuum leak, which does the same thing as opening the throttle blade a slight amount.

 

[Mandelon]

It isn't just the altitude? Other wise Spark Plugs are cheap. They seem to just fail sometimes. Worth checking.

 

[Husqy510]

No, not the altitude. He's run this boat almost exclusively at big bear. He was asking about plugs, but i told him I've never had plugs fail in a stock application, but you're probably right. Too cheap not to at least try it

 

[guest hs]

It should still run fine at that altitude just a little down on power which the next size pitch on his prop will help that. Gen 4-6 BBC don’t usually have problems with spark plugs like the gen 7 496 Merc. Engines.

 

[Mandelon]

My 496 worked great one weekend, then the next weekend it ran like crap. A couple bad plugs was the culprit. Happy to find it was a cheap fix.

 

[707dog]

is this the year efi 454's that had the vapor lock issue??

 

[Shlbyntro]

is this the year efi 454's that had the vapor lock issue??

It's very likely but with the description of how poorly it's running before it dies, I'd be more apt to believe it is a failing fuel pump or fuel contamination if it is a fuel problem. A fuel problem does sound to be the most likely culprit though

 

[Husqy510]

Thanks again for the replies. He's going to throw a FP Guage on it tonight

 

[707dog]

It's very likely but with the description of how poorly it's running before it dies, I'd be more apt to believe it is a failing fuel pump or fuel contamination if it is a fuel problem. A fuel problem does sound to be the most likely culprit though

gotcha... with this new fuel it doesn't take long to funk up the fuel system, filters...ect had a buddy who chase that vapor lock deal seemed like every trip he was ready to drill a hole in the boat and send it to the abyss. did some kind of bypass or drain back deal and never had a issue again.

 

[guest hs]

Its not going to vapor lock in Big Bear

 

[sintax]

Its not going to vapor lock in Big Bear

wouldnt think so, esp not on a cold engine.

I've never dealt with water in the fuel before, but i'd expect it would never fire? This seems to fire and quit, which seems like supply issue

 

[Shlbyntro]

Water wouldnt neccesarily make it completely not run. Sometimes it will cause the engine to run very poorly but still run, like on 3 cylinders instead of 8.

Fuel when poured into a clear cup should be absolutely clear and about the color of white grape juice. If it is cloudy, there is water in it. If it is darker like apple juice or piss then the fuel is going bad.

See if you can get access to a spark checker and a fuel pressure tester. 454 mag should be somewhere in the neighborhood of 40psi fuel pressure. Might as well knock out a compression test and replace the spark plugs now to get it out of the way.

Post whatever pics you can. Keep us posted

 

[Husqy510]

So he put a FP guage on it last night and it made 10lbs, so today he'll replace the pump. Thanks for all the help, hopefully he'll be on the water with his family by lunch

 

[Husqy510]

He's back on the water having fun with the family, but he said it doesn't idle well.

 

[guest hs]

Does it have a VST tank ?

 

[Husqy510]

Does it have a VST tank ?

Yes it does

 

[guest hs]

Make sure the diaphragm in the vst hasn’t ruptured it will dump raw fuel down the number 8 intake runner and will cause a rough idle.

 

[SOCALCRICKETT]

Make sure the diaphragm in the vst hasn’t ruptured it will dump raw fuel down the number 8 intake runner and will cause a rough idle.

Been there, done that. Those vst systems are a pain.

Sent from my SM-G981U using Tapatalk

 

[Husqy510]

Make sure the diaphragm in the vst hasn’t ruptured it will dump raw fuel down the number 8 intake runner and will cause a rough idle.

Thanks, apparently its running terrible again, maybe that's the problem.

He really appreciates all the suggestions