1986 454 Magnum stalling issues

[alldodge]

Your saying everything is good, yet it still dies after 10 minutes. The motor needs air, gas and spark to run, so at least one of these is not working.

In your post 10 you said

Update, I had the same problem and ran the fuel line to a 2 gallon gas can I brought along. The boat ran like a champ. So what should my next step be?

So you have proven your running out of gas. As Bondo and others stated stated

The system consists of the tank, the vent, 'n line, the diptube, the A/S valve, 'n the fuel line to the motor,.....

It's restricted somewhere,....

It will run fine from a 2 gallon gas but dies when reconnected to the tank. SO your issue is where the fuel line connects to the tank or parts of the tank. These parts consist of:
Anti-siphon valve
Tank pickup tube
Tank Vent line

You said the anti-siphon valve is good and so is the vent line. The only thing left is the pickup tube. The tube is where the gas line connects to the tank

 

[isp184dude]

I think what happened is when I ran it on the 2 gallon tank I didn't run it long enough the first time. Yesterday when I switched it out it still died on the 2 gallon tank. I also ran it with the gas cap off and it still died. Checked the pickup line and it seemed fine. Maybe something shorting out? Coil? Ignition module?

 

[alldodge]

OK, then you need to find out which one of the 3 you do not have when it dies

 

[isp184dude]

Last time it backfired when it died, makes me think it's some kind of timing spark issue maybe?

 

[isp184dude]

Here is what I have done so far

1. replaced fuel pump and anti-siphon valve
2. Checked fuel pressure, it was good
3. Checked tank pickup tube, clear.
4. Ran the boat with the gas cap off, still died after about 10 minutes
5. Ran the boat on an auxiliary tank, still died.

Here is the interesting part. The last time it was on the water it would die, I would wait a couple of minutes, and it would start right back up and run for 10 minutes then die. Before it would die and then keep dying right away. The last time it backfired a bit. It also dies after 10 minutes instead of about 30. This one is stumping me. Could it be any of these?

1. Coil
2. Distributor cap and/ or rotor
3. ignition module
4. bad ground somewhere?
5. shift interrupter switch?

Thanks for all of your help. I really appreciate it.

 

[alldodge]

I would say something is getting hot, and its getting worst (going from 30 minutes to 10 minutes). I would lean toward the coil, ignition module, distributor pickup, tachometer.

Have you tried removing the tach wire yet?

 

[isp184dude]

No but I will try that. Grey wire on coil right?

 

[achris]

Right.

 

[isp184dude]

Ok I put new cap, rotor, ignition module, and a new fuel filter. There was also a ground wire in the back of the engine that was just hanging there. Maybe that was part of the problem? I grounded it and checked the timing. I'm headed back out on the water tomorrow. Wish me luck!

 

[isp184dude]

Forgot I put a new coil on as well. It seems to be idling better. It would idle around 500 then suddenly jump to 700 before. Now it is purring like a kitten around 550.

 

[alldodge]

A loose or disconnected ground can cause all kinds of issues. Hope it fixes your issue

 

[isp184dude]

Thanks for all of your help, the boat is running great now, I think the fuel was bad among some other things. Happy boating!

 

[isp184dude]

Hi everyone,

I took the boat out again yesterday and it did the same thing, ran for about 15 minutes then dies. I can get it to restart but it won't go above idle. I did run it almost wide open during that 15 minutes and the oil lines were pretty hot. Just to review the things I have done:

1. replaced fuel pump and anti-siphon valve
2. removed all fuel and put in new
3. checked gas line for leaks, none found
4. checked pressure and fuel flow from pump - all is good
5. replaced distributor, rotor, and ignition module
6. replaced coil
7. checked timing and timing advance

I guess I'm thinking something is getting hot and shorting out since the next day it will run fine cold. Could it be the ignition amplifier (Thunderbolt IV), carb, or vapor lock? Or maybe something in the wiring? Thanks for your help.

 

[camalot]

You need to find out whats stopping the engine from running, next time the engine dies turn off the ignition remove the flame arrestor and get someone the move the throttle. Look for gas spraying into the carb, if no fuel sprays then it's fuel delivery if fuel does spray it has to be spark.

I would check your ignition switch as well.

 

[alldodge]

Hi everyone,

I took the boat out again yesterday and it did the same thing, ran for about 15 minutes then dies. I can get it to restart but it won't go above idle. I did run it almost wide open during that 15 minutes and the oil lines were pretty hot. Just to review the things I have done:

1. replaced fuel pump and anti-siphon valve
2. removed all fuel and put in new
3. checked gas line for leaks, none found
4. checked pressure and fuel flow from pump - all is good
5. replaced distributor, rotor, and ignition module
6. replaced coil
7. checked timing and timing advance

I guess I'm thinking something is getting hot and shorting out since the next day it will run fine cold. Could it be the ignition amplifier (Thunderbolt IV), carb, or vapor lock? Or maybe something in the wiring? Thanks for your help.

From this list your telling me you don't have a problem. A motor needs fuel, air and spark and you have all three so there is no issue. The one in particular I notice which have been asked a couple times is in bold. You have good flow and good pressure yet you do not say how much pressure you do have, and if it stays at that pressure as the rpms are increased.

What is the pressure?

 

[isp184dude]

The pressure is at 4 psi when idling and does rise when you throttle up to about 7. Trust me it's frustrating when it dies in the middle of the lake and you have no idea why. Can I run a jumper wire from the battery to the positive side of the coil to see if that helps? It may be something somewhere in the wiring. It is a 30 year old boat

 

[alldodge]

That's different going from 4 up to 7, most pumps will go from the higher to lower as rpms increase.

You can run a jumper

 

[isp184dude]

The boat ran great today for about 3 hours then died again, was tougher to start this time than last. I disconnected the grey tach wire from the coil and ran a jumper from the positive side of the coil to the battery. When I dies there is fuel squirting in the carb when you throttle, it acts like it isn't getting fuel. Could it be vapor lock? It wasnt that hot today, 84 degrees. When I ran the jumper the reading was 14 on the amp gage instead of the 12.5 to 13 I usually get. Any ideas?

 

[NHGuy]

Did it start when jumped? Next time it dies, quickly take the flame arrestor off, shoot a burst of carb cleaner in there and see if it starts. If it does you have a fuel problem, likely inside the carb.

 

[isp184dude]

Thanks I'll try that. It died after I ran the jumper wire, so im thinking more and more it's a fuel issue. I'm just stumped as to why it would run for a few hours then die