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BG1772
08-16-2010, 03:37 PM
Thinking I may have a faulty fuel pump. Does anybody know what the fuel pressure for the LTR 330 motor should be?

kal_dude
08-17-2010, 12:52 AM
35 to 45 psi

BG1772
08-17-2010, 08:23 AM
Thank you! I have 40 psi, so my problem must be elseware.

mtajpa
08-17-2010, 07:38 PM
Check for loose connections they will cause pump to operate intermitantly. If you can have someone drive the boat and feel the connectors from the pump to main harness if they feel hot the are not making good contact.

BG1772
08-18-2010, 12:42 PM
Check for loose connections they will cause pump to operate intermitantly. If you can have someone drive the boat and feel the connectors from the pump to main harness if they feel hot the are not making good contact.

Thanks for that tip. I'll check that out.

BG1772
08-20-2010, 03:28 PM
Forgive my ignorace. I've looked around in the posts, but I can not find the answer to this question. What is the round "puck" on top of the fuel pump where the line that goes to the motor attaches? Is this a filter / water separator?

mtajpa
08-20-2010, 10:50 PM
I believe it is the pressure regulator. Mine only has a single line to the fuel rail.

BG1772
08-21-2010, 09:58 AM
Thanks. Thought that might have been my issue, but it was not. A friend has a spare fuel pump assembly, so i borrowed it off of his. Back to the drawing board.

mtajpa
08-21-2010, 02:47 PM
What is the actual problem?

falconjeter
08-21-2010, 03:12 PM
check the inlet screen on the fuel pump, if it gets restricted it will cause this.

BG1772
08-23-2010, 09:21 AM
Sorry for the slow response, been away from the internet for a couple of days.

Problem started with a weak hole shot and then proceeded to loss of top end speed. Changed out the fuel pump and cleaned / replaced the filters. The problem did not go away.

I have not resolved the issue as of now, but I am failrly confident that I have the solution. A mechanic friend has the diagnostics software to read the computer on our boats. He loaned me the software and cable. I ran through the system and found that the Throttle Position sensor appears to be failing. My understanding is that the TPS at Full Throttle should be putting out approximatley 5.0 volts. However, at Full Throttle, my TPS is only putting out 4.18 v. Going to give that a try.

Jeff d
08-23-2010, 11:33 AM
A mechanic friend has the diagnostics software to read the computer on our boats. He loaned me the software and cable.
Whoa! Is this something you could rip a copy of? Does the cable look like something fairly common or very specialized?

BG1772
08-23-2010, 11:38 AM
Unfortunately, no. The cable is specialized and has a "sentnel key" in it that contains the license for the software. The software is pricy ($579), but if you get a couple guys together it is worth it. I am actually a part owner in the one my mechanic friend has.

It is really cool what you can find out about your motor. The boat computer keeps track of some interesting statistics. One of the tables shows you how many hours the motor has run at 0to 999 rpm, 1000 to 1099 rpm, etc...

BG1772
08-23-2010, 09:25 PM
Just got back from working on the boat. I was incorrect on the voltage for the TPS. Full Throttle is only 4 v for the TPS, so mine was within tollerance. No idea what else could be the problem. I'm open to suggestions if anybody has any.

Here is what I have done so far (not in any particular order)
1. Changed fuel pump
2. Cleaned fuel filter in tank with carb cleaner (it wasn't too dirty to begin with).
3. Checked grounds (main battery ground and ECM Grounds).
4. Drained Tank and replaced fuel.
5. Changed whatever that puck is on top of the fuel pump. I thought this was a fuel pressure regulator, but found a maintenance document that showed the fuel pressure regulator on the fuel rail.
6. Tested TPS.
7. Changed spark plugs.
8. Tested fuel injectors.

Does anybody know if there is a second fuel fitler hidden somewhere that I am not seeing?

mtajpa
08-23-2010, 11:09 PM
Any chance the flame arrester / air filter is plugged, pcv valve plugged. Easy things to check.

Would a bad knock sensor be possible? It would retard the timing causing poor performance for sure? Check and make sure the wire to it is plugged in. On my LTR it is actually the port side block drain and has to be removed to drain block.

BG1772
08-24-2010, 08:15 AM
I have checked the K&N filter - it is clean. I've run the engine with it off and get the same results.

I've not checked the PCV Valve.

I don't know enough about the Knock Sensor, but it is for sure something worth testing.

I was reading last night in a troubleshooting manual about how the TPS and the MAP sensor work together to tell the computer how frequently to pulse the injectors. So, I am wondering if the MAP sensor could be causing the issue?

mtajpa
08-24-2010, 10:22 PM
Knock sensor I believe controls the timing to some degree. I know if its disconnected it won't run well.

Probably a good time for JIMN to chime in I'm sure he can help.

BG1772
08-25-2010, 07:43 AM
Last night I got my wife to go down to the boat with me so she could drive while I ran diagnostics. Here are my latest findings.

Key is in the run position, but the motor is not running:
Throttle Position Voltage at Wide Open Throttle (WOT) is 4.18 v. and throttle percent open is 100%.

Engine Running:
Throttle Position Voltage at WOT is 3.88 v. and throttle percent open is 88%.

MAP Sensor Voltage at Key in the Run position, but engine not on: 4.97v.
MAP Sensor Voltage with engine on and WOT: 5.0v.

If I understand troubleshooting the TP and MAP, it sounds like both devices are working properly. However, I am completely stumped on why the TP does not show the same results with the engine running as when the key is in the run position. These findings would make sense why I have lost top end speed. Any suggestions?

BG1772
08-25-2010, 07:44 AM
Knock sensor I believe controls the timing to some degree. I know if its disconnected it won't run well.

Probably a good time for JIMN to chime in I'm sure he can help.

How do you test the Knock sensor? I verified that the knock sensor is still connected.

mtajpa
08-25-2010, 07:19 PM
I believe it sends a resistance/pulse value to the ECM. But I am guessing at this point does your LTR have the NorthStar ignition system(no distributor)? Coil Packs?

Below is an article on Knock Sensors.
http://www.wellsve.com/sft503/counterp_v4_i4_2000.pdf

You might PM JimN as I am sure he can help if he sees this post.

mtajpa
08-25-2010, 07:35 PM
Check this link it is the GM MEFI marine manual.

www.pleasurecraft.com/manuals/L510004.pdf

BG1772
08-25-2010, 09:57 PM
I believe it sends a resistance/pulse value to the ECM. But I am guessing at this point does your LTR have the NorthStar ignition system(no distributor)? Coil Packs?

Below is an article on Knock Sensors.
http://www.wellsve.com/sft503/counterp_v4_i4_2000.pdf

You might PM JimN as I am sure he can help if he sees this post.

Yes, my motor has the northstar ignition with coil packs. Thanks for passing on the links. I'm going to check them out now.

BG1772
08-25-2010, 10:10 PM
Check this link it is the GM MEFI marine manual.

www.pleasurecraft.com/manuals/L510004.pdf

This looks like a great resource. Thanks for posting!

JLMax16
08-03-2012, 09:27 PM
What ended up being your issue?

BG1772
08-04-2012, 08:14 AM
My problem ended not being anything with the engine; it was instead the exhaust silencer that was causing the problem. The inside of the exhaust silencer is separated by a "shelf" that runs horizontally along the distance of the silencer. Something caused this "shelf" to come loose on both ends (although it was still attached in the middle). When the engine ran at lower rpms (under 3000) there was not enough exhaust and water coming from the engine to affect the loose material. However, once the engine was above 3000 rpm the water and exhaust pressure would push the shelf down and cover the exhaust ports out of the silencer, which caused the engine to choke out. Once the engine was down below 3000 rpm, the pressure would relieve and the path out of the silencer would open.

I considered replacing the silencer. Then I considered repairing it with fiberglass. Then I decided that I would use a 3" hole saw and cut a hole in the area that was blocking the output of exhaust. Problem was resolve immediately. The engine is a little louder now, but not significantly.