2002 SAN GT-40 engine missing

[intrlaz]

So i hadn't run the boat in a few weeks, flushed it once during that time on the trailer at idle for a few minutes.

Yesterday we dropped it in, she started right up. I pushed the neutral switch and gave her a bit of gas, but when i dropped back down to idle rpm's one or more of the cylinders were not firing. I could easily tell by the sound. The engine continued to miss at any rpm level. Turned the engine off, then restarted and still missing.

I brought the boat back to the house, let it sit for maybe 30 minutes, then restarted and all cylinders were firing (at least from what i could tell by the sound). So again I attempt to put in neutral and give some gas, same problem as before and reverted to missing at any rpm.

I have new spark plugs installed, and looked to see if the plug wires had any nicks in them. Did not notice anything. By what I have read on the forum, my next step would be fuel pressure?

Thanks for any insight you guys could give.

[DanielC]

RE: 2002 SAN GT-40 engine missing

Checking the fuel pressure is a good idea, and if the fuel pressure is good, when the priblems are occuring, you can eliminate that as a cause.
I do not know how many hours are on the boat, but if they are getting high, the secondary ignition system might be a cause. Did the new spark plugs help, or have you not gotten a chance to run it yet? If the new plugs helped, the distributer cap, the rotor, or the plug wires might be a cause for the miss.

[intrlaz]

RE: 2002 SAN GT-40 engine missing

I believe the boat has less than 400 hours. The gauges were replaced before I purchased the boat and the perfect pass is not operational.

The boat ran fine with the new plugs before the misfiring started. The distributor cap is a possibility. I had the boat serviced several weeks ago, and the shop replaced the cap for free with a used one they had sitting around the shop because the old one was badly corroded.

I will report back with fuel pressure results

[WakeSlayer]

RE: 2002 SAN GT-40 engine missing

Assuming you verified the plug wires were installed per the firing order. It is possible that between replacing plugs and then the cap that a couple got crossed. Worth looking at.

[intrlaz]

RE: 2002 SAN GT-40 engine missing

Okay so I finally got time to do some testing. First I unhooked what I believe were the oil pressure sensor and the temp sensor. Both were near the oil filter and I am told they could be causing the problem if faulty. No go here. Next I tested fuel
pressure. It was consistently above 30 psi, near 40 at idle. Any further recommendations?

[TravisFling]

RE: 2002 SAN GT-40 engine missing

I would also reco double checking the wiring to the cap. Easy mistake to make. I would replace cap, rotor, etc. too.

[intrlaz]

RE: 2002 SAN GT-40 engine missing

Also double checked the wiring order. New rotor next I guess

[intrlaz]

RE: 2002 SAN GT-40 engine missing

Did some more testing this afternoon. Ran the boat from an external fuel tank. Same issue not firing all cylinders. I also noticed that near idle fuel pressure at the rail is about 39 psi, but drops to 32-34 at higher rpms. Could this be part of the problem?

[intrlaz]

RE: 2002 SAN GT-40 engine missing

More updates. I started the boat this morning and it was running on all cylinders at about 1k rpm. I let it sit for several minutes to see if it would cut out. It did not, so I pulled the throttle back to idle and the cylinders cut out again. The engine would not return to normal firing at any rpm.

Also, I checked spark at all of the plugs and it looked strong. I took the cap of the distributor and it looked clean, but then again I'm not really sure what it should look like. I did notice the part that the rotor mounts too was very rusted.

[intrlaz]

RE: 2002 SAN GT-40 engine missing

No ideas? It would be greatly appreciated.

[bobchris]

RE: 2002 SAN GT-40 engine missing

clean the battery conections something is messing with the electronics and the ignition system, low voltage, weak current to sensors or coil. check the alternator for proper output voltage, check the belt make sure it's properly tensioned,

[DanielC]

RE: 2002 SAN GT-40 engine missing

The fuel pressure should be lower at an idle, and go higher as the engine load increases. It is hard to impossible to load the engine running it in the driveway.
This is how I check my fuel pressure:
http://planetnautique.com/index.php?...&start=100
This check is done with the key on, engine off. You should have fuel pressure on 39 +- 3 psi. Disconnect the wire at the test port, that makes the fuel pumps run, in my second ppicture. After supplying water to the raw water pump, start the boat. The fuel pressure should drop, with the engine at an idle.
If you have not already done so, download the GT-40 service manual from this site.

[intrlaz]

RE: 2002 SAN GT-40 engine missing

Thanks DanielC. I will try the pressure test like you suggested with the engine off. I have the service manual.

Batteries are new, belt is new and has proper tension. I will check alternator.

[bobchris]

RE: 2002 SAN GT-40 engine missing

CLEAN CONNECTIONS?

[intrlaz]

Re: RE: 2002 SAN GT-40 engine missing

CLEAN CONNECTIONS?

very clean. in fact, I just had a second battery installed with new wiring. I guess it never hurts to check the connections on the motor side to make sure