GT40 Sputtering Under Load

[INDpilotP]

My ‘99 Super Sport (GT40 EFI) was coughing and sputtering today when trying to accelerate under a load. First couple times was pulling a surfer out of the hole and after that was coming out of a corner pulling tubes. It loses a few hundred RPM then picks back up where it left off. Only lasts half to a second. When we were tubing we were going about 20mph but it refused to accelerate more until we straightened out and lightened the load.

Seems like it is losing pressure or something. I do hear one of the pumps run when the key is turned on. Any ideas?

[37tr3n5k]

The most likely cause of this symptom would be a fuel filter or bad gas. Before I started changing plugs, I'd add more gas to dilute potentially bad gas and change the fuel filter and run injector cleaner. If it is still doing it, I'd start with checking ignition coil, then plugs, then wires. I'm not sure if that year has a MAP sensor, but if it does, a failing MAP sensor will cause that. Once it's out totally, the boat will fall on its face and lose all power and throw a code. But this sounds like a fuel delivery problem.

One other thing- were you low on fuel? Some boats will starve themselves of fuel when the gas is sloshing around in the tank and the pump doesn't have anything to pull from... It happens from turns and starting from a stop.

[INDpilotP]

Thanks for the reply! I’m fairly sure it isn’t a low fuel issue, as it did the same thing full. Plugs, wires, cap, rotor, and fuel filter have all been changed in the last year.

[SilentSeven]

Open up your distributor and check the hall sensor. If it's all crusty and old, consider replacing the entire distributor. A new distributor has solved odd run problems for multiple members. Link below provides part numbers for low priced (non-pcm) remanufactured units.

https://www.planetnautique.com/vb5/f...e-replacements

[INDpilotP]

Open up your distributor and check the hall sensor. If it's all crusty and old, consider replacing the entire distributor. A new distributor has solved odd run problems for multiple members. Link below provides part numbers for low priced (non-pcm) remanufactured units.

https://www.planetnautique.com/vb5/f...e-replacements

I had it open the other day while I was inspecting the cap and rotor, and it is definitely old and crusty in there. I thought a new one could do good things but had a little sticker shock when I saw replacements on nautiqueparts for $550+.

Any these parts numbers are marine style replacements? Thank you for the info, going to give this a shot!

[SilentSeven]

I don't believe there is a marine version of the distributor. Yes - the $550 for the PCM version is a bit eyewatering. If you search, there's a good history of people using re-manufactured distributors without problems. The cap/rotor may be different; I'd be sure use the PMC version.

[SilentSeven]

Seems like not quite your problem but another insightful thread.

https://www.planetnautique.com/vb5/f...intermittently

[gun-driver]

No difference in the distributor, you can get one local or Rockauto for less than 100 bucks.
The last cap I got from a marine dealer was the same as an auto cap with a dab of silicone in the vent hole, so no difference just put a dab of silicone in the vent hole.

[JayG80]

I would check the fuel pressure first. I’ve had the loss of power issue before and each time it was a totally different issue.

1. bad pip hall sensor, the plastic piece inside the distributor broke and the sensor was out of alignment. I bought a Rock Auto distributor with cast gear and used my new pcm cap.
2. bad hose inside FCC. The 2.5” long hose inside the FCC suspending the high pressure pump had a small split. Diagnosed by low fuel pressure while running..
3. Broken baffle inside fiberglass muffler, centek fiberglass muffler baffle caused back pressure and power loss.

[phillik]

Just had the same issue on two different GT-40's. I wouldn't be surprised if it is in limp mode. (issue 1)
1 ) Was the oil pressure switch preventing power over 2700 RPM...just disconnect the wire if you know your oil pressure is good. The switch closed to ground until 5+ oil PSI
- Page 20 in manual

2 ) Was a long list of things from an engine sitting. We used the GT-40 service manual as a guide and didn't guess at problems. Started with fuel filter (dirty), regulator (couldn't keep psi), injectors (clogged to 60% flow. $25 per injector to get tested/cleaned). Then changed out the cap and rotor (diry), All plug wires were bad and brittle (cables from autozone were too short to get around the headers, purchased new ones for the GT-40). E-coil replaced (ohms out of spec). Spark plugs (was done due to sitting). There are some great videos on checking the sensors with an ohm meter. I purchased the Ford breakout box for the 60 pin connector to check them (overkill)

Manual:
https://www.planetnautique.com/Corre...e%20Manual.pdf

Sensor video:
https://youtu.be/hFmI-_B9IVs

Hope this helps,
Kyle

[INDpilotP]

Sorry for the delayed response on this. While I was troubleshooting I pulled the plugs and noticed on was wet after turning on the key and running the fuel pump. Checked my fuel pressure on the rail and found that it slowly fell off. Ended up pulling all the injectors and having them cleaned - haven’t seen the issue since.