1997 7.4 Bravo 1 dies after 30 minutes...starts after sitting, dies again

[DownByTheRiver]

I've got a carbed 97 7.4 B1 (0k282280) that's giving me fits. After running flawlessly for 30 minutes, it stalls out very quickly. If I let it sit for a few minutes, it'll fire back up and run at low rpm, then die again in another 5 minutes. Oil pressure around 50, temp around 150 or so.

It's done this twice, and after the first time, I replaced the coil, cap and rotor with new units. I figured it was a good time for a tune up, but obviously, this did not help. I can't determine if this is fueling or ignition related, so any help would be appreciated. I've read everything from the check valve in the tank to the ign module. Until it stalls, the engine is singing along at 3700 rpm with no issues.

 

[Rick Stephens]

Sounds like a fuel system plugged up. Filter(s) and Anti Syphon valve would be the first place I would look.

Rick

 

[DownByTheRiver]

Man you guys are fast! Thanks for the reply.

I'll look into getting the valve replaced, fairly cheap and easy.

I did forget to mention that the separator was clean and full of only fuel. It was then replaced with a new one.

 

[Rick Stephens]

Pull the Anti Syphon valve and check it out. See if it actually is the problem.

Also can be the fuel tank vent. If your engine dies, and you open the fuel filler, does it gulp air?

 

[DownByTheRiver]

Is it more than coincidence that it sputtered out and died at almost the exact same operating interval both times?

I'll have to check the fuel filler next time I have the pleasure of a half 7.4 power/half sea tow power boat trip.

 

[Bondo]

I can't determine if this is fueling or ignition related,

Ayuh,.... Welcome Aboard,.... Bring a tool kit with ya, when it dies,...

Pull the flame arrester off the top of the carb, 'n pump the throttle,...
There oughta be a couple of streams of gas bein' shot into the throat of the carb,....

Pull the coil wire outa the distributor cap, hold it 'bout 1/2" from ground, 'n turn the key,.... is there spark,..??

 

[alldodge]

I'm thinking fuel related.
How old is the fuel pump and when was the last time the lube was checked in the seawater pump housing?

 

[DownByTheRiver]

Thanks fellas, I appreciate the advice. I have a very trustworthy and knowledgeable marine mechanic that's currently backed up, but may be able to check her out this week...I'm just trying to get the jump on some things. Bondo, I did hear some sizzling as I was trying to start it back up, so that could've meant fuel was being sprayed. On the next stranding..err trip, I'll be sure to test the fuel and the fire. I did find a troubleshooting guide for thunderbolt V ignitions, so it'd be worth it to test that out as well. AllDodge, the service records are on the boat, so I'm not sure about the seawater pump lube. I do know the temperature has never been over 150 that I've seen.

Some back story on the boat: it was owned since new by a friend (FRIEND :lol up until last year. He's an older man, who had the money and time to take care of the boat very well. Unfortunately, it wasn't used a ton, and it spent the majority of its life on his dock lift. It's only seen ethanol-free fuel from marinas, as its never been trailered. It's a 1998 Donzi 275 that had 108 hours on it when I purchased it last month. I was wary of a boat with such low hours, and I seem to be finding out this is somewhat justified. The 50 and 100 hour services were done, but almost a decade ago for the 100 hour service. I tested the compression before I bought it, and got back readings of low-122 high-135.

I actually had this same problem with a Datsun 280z with a Holley swap last year. It would vapor lock because the electric fuel pump was taking a dive. It'd sit for 10 minutes and start right back up. Changed the fuel pump, never happened again. That was an electric pump though, so this mechanical one may not share the same "qualities of failure". The first time this happened, I watched the RPMs fairly quickly drop off from 3700 to about 3000 when it stalled. This last time, I was running around there, and as soon as the lever dropped to neutral, she stumbled and died.

 

[DownByTheRiver]

Finally got a chance to run the boat the other day, with all my tools and the mechanics' tools onboard. Naturally, the boat ran like a sewing machine.

We ran the boat full bore for an hour and a half, with the throttle down the whole time, taking waves, hard cornering and really running it through the ringer. Didn't even flinch.

At this point, I'm at a loss because it didn't skip a beat. I'm going to go ahead and replace a few items, like the vents and check valve, but other than that, I can only wait for it to fail again.

 

[DownByTheRiver]

UPDATE:

Took another long ride today, about 2 1/2 hours. After all that time of running great, as soon as I pulled back into the channel, she died. I tried and failed to start it back up, got a short tow, and took it out of the water at the marina. I tried jumpering the coil to the battery with zero success. Next, I checked the carb, and got nothing. I then disconnected the fuel line at the carb into a bottle, and nothing once again. I'm going to replace the anti siphon valve and the fuel vent (screen is missing on outside) and then check the pickup and tank. If I find trash in the tank, what's the best way to go about cleaning it out? I've got about 50 gallons of gas in there.

 

[alldodge]

Some have put a hose in to the tank and connected to an electric fuel pump and filter, then start circulating the fuel thru and back into the tank. There are companies that do this just don't know if one is in your area.

 

[lihartke]

I just had this problem or seemingly so. It led me to: replace water/oil separator(was told gas was bad), rotor,caps,and plugs then noticed coil sparking/arching replaced that then noticed the engine tried to turn over when I just slightly pushed in the key(didn't turn it) so, I replaced the ignition switch. It always ran great for at least 8 mins. Gave up when it stalled after ignition switch replacement and took it for diagnosis. They said it was the ignition sensor. They replaced that and ran it for 1/2 hour on water/ 1/2 hour on land. So I think they found the problem. The boat ran fine and would just die out as if when it warmed up it was shorting out and shutting off. Hope that helps. I know it's not an expensive part for you- mine cost $400. Send donations if it helps

 

[HT32BSX115]

UPDATE:

Next, I checked the carb, and got nothing. I then disconnected the fuel line at the carb into a bottle, and nothing once again. I'm going to replace the anti siphon valve and the fuel vent (screen is missing on outside) and then check the pickup and tank. If I find trash in the tank, what's the best way to go about cleaning it out? I've got about 50 gallons of gas in there.

Howdy,

The best way is to remove the tank and drain/flush. If you cannot do that, put the boat on a trailer, expose the top of the fuel tank and remove the fuel gage sender.

Then get a long piece of clear vinyl hose (3/4, 7/8, 1" diameter) hose and put a short piece of PVC pipe on each end with a valve (a 3/4-1" ball-type gas valve from Home Depot etc works great) on the "other" end.

Use this hose as a siphon and have a helper on the other end with the valve that can switch containers when they get full using the valve to stop the flow while switching.

Use the end in the tank with the short piece of PVC pipe (12"-24" or so) to use as a "Vacuum" to suction out all the fuel, water and/or debris in the tank.

If the gage sender hole is at the back of the tank you need to jack the bow up a little and you'll get most or all the debris and water out of the tank.

The fuel pickup and anti-siphon valve is also at the back of the tank. remove BOTH and inspect or replace them.

Now having said that, if you suspect vapor lock, you can probably mitigate the problem by running your bilge blower continuously. I installed 2 of the inline-type bilge blowers in mine. and usually run them all the time.

Let us know what you find!


Regards,


Rick