97 SN, loss of power, top speed, rough idle

[skiflyer45]

Hi everyone, I'm having some issues with my GT40 and need some help figuring this out to avoid the stealership.

Here are my symptoms in the order they began:

1. Intermittent and slight momentary loss of power (rpm) at any speed (felt like bad gas)

This progressed into:

2. Momentary loss of power (RPM) at any speed (see video - http://youtu.be/z9eSgtXrSi4 )
http://youtu.be/z9eSgtXrSi4

3. Intermittent Loss of top speed - This became progressively worse from not being able to go over 35., then 30ish, now high 20's. When at driving it feels like the boat wants to go faster and occasionally surges but the bogs back down.

4. Rough idle - it will idle fine then suddenly sound like the engine is dying or seizing and the rpms will drop...this is the same symptom as when driving just at idle (see video - http://youtu.be/bcirxCtgV1M )
http://youtu.be/bcirxCtgV1M

5. I don't know if this is related or not.... and these two issues have only occurred once each independently.

1. Both batteries died....I saw the volt meter on dash slowly creep down over 2 minutes or so and the boat died in middle of lake. Switched to battery 2 and same thing. Recharged system and everything was fine. Batteries are charging and at proper voltage.

2. Boat would not start...there was no power to anything like there was no battery connected. When turning the key the battery gauge would move very slightly (as if hitting the dash). Tried a few times and all the sudden it worked again as if nothing was wrong

---

I have tried the following:

1. Checked anti-siphon valve (OK)
2. Changed fuel filter (NEW)
3. Changed little tube inside FCC, had a tiny crack, however I may have caused it removing the FCC/filter (NEW)
4. Checked and cleaned screen at fuel pickup
5. Added Seafoam
6. Checked for water in fuel (OK)
7. Fuel pressure at idle was 34, when RPMS went down (power loss) the pressure would surge to 38-40 then back to 34. It would basically bounce between 32-38 when the engine sounded like it was seizing. It seemed like the seize occurred before the pressure went up, almost as if the pressure was compensating to prevent the engine from dying. If that makes sense. (***I have not tried it under load, will do that Wednesday)
8. I visually inspected and pulled plugs/wires. (OK, from what I can tell, they are 6 month old)
9. I individually pulled the plugs of cylinders 1,2,3 (one at a time) and started the boat...it ran the same? (I don't know what that means and if I did it correctly but I got zapped so I quit - I will try this again when someone can give me some good direction on how to test this properly please. This part also seemed very confusing to me that the engine would run the same with plugs removed of a cylinder...But again, I probably did this wrong.
10. Changed low pressure fuel pump
11. Changed plugs
12. Changed cap/rotor

After all the replacements...its ran better but still a iloss of power at speed, generally not over 2700rpms (no engine light)....as if running over weeds or something.

---When I tested it tonight battery 1 ran down to about 10 volts with the engine running...when I switched to battery 2, i immediately felt a power surge and small increase in speed. I think this is electrical?

Any advise would be greatly appreciated and sorry for the lengthy post.

[ski4evr]

Not sure is the whole problem is electrical, but if you are discharging your batteries, the alternator would be my first replacement. I am assuming you have fuel injection. If your alternator dies, so does everything else when the battery drains. You should be around 14.4 volts at the battery terminals with engine running. If not, it is not charging. good luck

[SilentSeven]

Read the service manual for the motor, it may help with some ideas. Here's a few things to look into:

- no run over 2700 RPM is limp mode. The manual describes causes.
- when the boat idles at 800 RPM, not 650 RPM (looks like 800) on the video, the manual says its due to one of 3 sensors not reporting correctly. Check these 3:

Throttle Position
Electronic Coolant temp sensor
Air Charge Temp Sensor

If you're pulling plug wires and not getting any RPM change, you may have wires installed incorrectly. When you changes the cap, you may have gotten a couple reversed. Check to make sure you have the leads to the correct ones on the disti cap. Incorrect wiring can cause poor idle and loss of power.

Does it smell gassy? If so, your surge at speed might be due to the coolant sensor reporting the engine "cold" and thus the mixture is rich. Incorrect plug wires could also contribute to the gassy smell.

Re the alternator - agree with the above it's likely not the root cause. Simple test is to pull it and have it bench tested at a local auto parts store. What did you mean when you 'everything was fine' after the recharge? Did the boat run problems go away too? If so, this is a good clue.

Fuel pressure will surge up and down as the vacuum in the motor changes. I think you are OK there.

To safely pull plug wires and not get zapped, you can get a tool that will let you grab the leads and remove / install. Maybe $10 or so at the auto parts store.

[skiflyer45]

Update.

The electrical issue is fixed....it was a lose wire. However the other problems still exist.

- I did a compression test and results were good.
- Changed the in-line fuel filter
- Replaced high-pressure fuel pump
- Double checked wires and they are on correctly

[SilentSeven]

If you're still stuck, this may be your next step.

My boat is running better with a refreshed distributor and the price was much lower than expected.

http://www.planetnautique.com/vb3/sh...yone-seen-this

http://www.planetnautique.com/vb3/sh...r+part+numbers

[skiflyer45]

FIXED!

Thank you for that SilentSeven. That was 100% what the problem was. You saved me hundreds $$$. Got a rebuild distributor from NAPA for $100 ish. Nautique part would have been $525.

[SilentSeven]

Glad the suggestion worked. Interesting - are those scores on the inside of your hall effect rotor? (last pic) Was there runout in the bearing or was the center shaft in OK condition? Also, how many hours are on your boat?

Certainly seems to be a pattern that the trigger sensor on these vintage boats is a (more?) common failure point.