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  #1  
Old 02-24-2015, 12:26 AM
pkreusch's Avatar
pkreusch pkreusch is offline
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Boat: 2000 Gekko GTR22 (but I'm a MC owner at heart)
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A little help for a poor Nautique soul....

I got this buddy who cant seem to figure this issue out with his PCM GT-40 engine. I know you guys out there in MC land could give a hand to a poor unfortunate nautique soul (other than the obvious issue of not owning a MC).... Here is a very detailed description of the issue...My comments in red. Goood luck!

Long standing symptom/problem prior to servicing engine. Running warm up to 190 at idle after a few slalom passes. But in the pass would go down to 170s. Then climb after dropping skier and lining up for another pass. Been like that for a while. Did all the usual; new thermostat and gasket, checked all hoses, checked trans. cooler, checked all ports in thermostat housing, checked intake under hull and so on. All good. Conclusion; flow problem due to old manifolds (1200hrs). Plus old hull huger muffler was going bad..developed a crack.

Other than temp issues, boat ran smooth as butter. (remember this)

Time to replace manifolds and risers. Sent to shop and the following was done. (Some items added to job just for maintenance.)
1. New Exhaust manifolds, risers, gaskets and ss fasteners
2. New Hull hugger muffler
3. New exhaust hoses
4. Replaced fuel filter-FCC filter
5. Installed a new inline fuel filter, never had one before
6. New thermostat/gasket
7. Oil change and filter
8. Transmission fluid changed
9. New cap and rotor
10. Cleaned flame arrester
11. Tank drained and 5 gal of fresh mid grade added.
12. Clean and grease rudder and rudder port
13. Shaft packing
14. Bilge cleaned


Received boat back. Started and idled normal. Backed off of trailer. Short run to dock at idle speed. Parked boat. Few hours later test ride. Seemed ok at first. Seemed to run as normal throughout power range. But within a few minutes, idle was stuttering. Range between 1000-2000 as throttle was pushed up, it stuttered and struggled a great deal. Continue pushing throttle and at 2500rpms, it gave a mostly normal response on up to WOT. Some slight stutters detected but barrely noticeable compared to the 1000-2000 range. Back down to 1200. Boat surged between 1500 and 2000. Up and down, up and down. Continued this until throttle was repositioned. Idle still stuttering. Left boat sit for a couple hours. Seemed to run slightly better but within minutes repeated all above symtoms.

Day 2, added 10 more gal of mid grade gas and test ride results were the same.

Following has been attempted or found to be normal when checked. After some but not all, a test ride was done with the exact same symptoms as above;

1. Removed new in line fuel filter, checked tank pickup and fuel line. (test ride..no change).
2. Both HP and LP pumps prime as normal with key turn.
3. LP pump tested with normal flow/volume and pressure. All connections appeared normal and were reseated. (test ride..no change)
4. Fuel pressure gauge shows 35psi at idle and 41psi at WOT
5. FCC opened and full of fuel to the top. No water. All connections appeared normal, hose intact, and psi did show as normal with gauge at WOT. (test ride..no change)
6. At idle removed vacuum hose from Fuel Pressure Reg on rail. PSI jumps to 41psi when vacuum hpse removed. Reattached hose and normal psi at idle-35 and 41psi at WOT. (test ride..no change)

All symptoms have stayed exactly the same for every test ride. Over several days of lake testing it seems that the issue arises when boat is up to temperature (160). Seems there are no issue run from a cold start and running up through the power band. 100% normal operation. Smooth as butter. Once boat is at temp, the issues at idle (stuttering) and between 1000 and 2000rms (struggling, running rough, losing power) are present. At 2500rpms it catches and runs close to if not normal to WOT.
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  #2  
Old 02-24-2015, 08:20 AM
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paco_06 paco_06 is offline
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Efi or carb? Sounds like choke is not properly adjusted if it runs well cold but not warm.

Also you mentioned changing cap and rotor button. Points or electronic ignition? All the above sounds more like an ignition problem. Maybe out of time a little due to something being moved during tune up. Also check advance springs in distributor.

Back to carb if not efi, air screws may need adjusting also.
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  #3  
Old 02-24-2015, 09:25 AM
Double D's Avatar
Double D Double D is offline
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Boat: 2008 X14, w/ LY6 400HP w/ 1.22 Ratio Tran
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My questions also. Since you didn't mention the year its hard to determine if the GT-40 is Carb, Throttle Body or Full Injection. My brother had a 99 SN with a GT-40 and that sucker was great. Only issue he had was a high idle once in while. But, back to why I am even commenting;

I know we're probably talking two different animals and this will be no help, but your symptoms sound similar to mine in my 1994 Prostar with an Indmar 350 CI with TBI. It would be normal until it got to temperature and then it would struggle on the low end and in idle, it would pulsate up and down constantly. Sometimes even struggle to stay running and get started.

Long story short, and after throwing some money at it, I was able to watch the TBI injectors into the carburetor. One of them was sputtering and every time it did the idle would drop. After switching wires the problem followed the wire. After checking all wires and GROUNDS, the problem was still there.

My Answer: MEFI-1 Computer, Injector Driver Failure.
My Solution: Run both injectors off one driver (since the system was designed for a 4-barrel with four injectors, and I had two) which was confirmed with Indmar
Outcome: Problem was gone and I am still running the boat that way.

Someday I will have to update the Computer and this solution may not work for your friend, but it could tell you the computer could be bad...

Good Luck!!
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  #4  
Old 02-24-2015, 09:29 AM
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Spork Spork is offline
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Quote:
Originally Posted by pkreusch View Post
I got this buddy who cant seem to figure this issue out with his PCM GT-40 engine. I know you guys out there in MC land could give a hand to a poor unfortunate nautique soul (other than the obvious issue of not owning a MC).... Here is a very detailed description of the issue...My comments in red. Goood luck!

Long standing symptom/problem prior to servicing engine. Running warm up to 190 at idle after a few slalom passes. But in the pass would go down to 170s. Then climb after dropping skier and lining up for another pass. Been like that for a while. Did all the usual; new thermostat and gasket, checked all hoses, checked trans. cooler, checked all ports in thermostat housing, checked intake under hull and so on. All good. Conclusion; flow problem due to old manifolds (1200hrs). Plus old hull huger muffler was going bad..developed a crack.

Other than temp issues, boat ran smooth as butter. (remember this)

Time to replace manifolds and risers. Sent to shop and the following was done. (Some items added to job just for maintenance.)
1. New Exhaust manifolds, risers, gaskets and ss fasteners
2. New Hull hugger muffler
3. New exhaust hoses
4. Replaced fuel filter-FCC filter
5. Installed a new inline fuel filter, never had one before
6. New thermostat/gasket
7. Oil change and filter
8. Transmission fluid changed
9. New cap and rotor
10. Cleaned flame arrester
11. Tank drained and 5 gal of fresh mid grade added.
12. Clean and grease rudder and rudder port
13. Shaft packing
14. Bilge cleaned


Received boat back. Started and idled normal. Backed off of trailer. Short run to dock at idle speed. Parked boat. Few hours later test ride. Seemed ok at first. Seemed to run as normal throughout power range. But within a few minutes, idle was stuttering. Range between 1000-2000 as throttle was pushed up, it stuttered and struggled a great deal. Continue pushing throttle and at 2500rpms, it gave a mostly normal response on up to WOT. Some slight stutters detected but barrely noticeable compared to the 1000-2000 range. Back down to 1200. Boat surged between 1500 and 2000. Up and down, up and down. Continued this until throttle was repositioned. Idle still stuttering. Left boat sit for a couple hours. Seemed to run slightly better but within minutes repeated all above symtoms.

Day 2, added 10 more gal of mid grade gas and test ride results were the same.

Following has been attempted or found to be normal when checked. After some but not all, a test ride was done with the exact same symptoms as above;

1. Removed new in line fuel filter, checked tank pickup and fuel line. (test ride..no change).
2. Both HP and LP pumps prime as normal with key turn.
3. LP pump tested with normal flow/volume and pressure. All connections appeared normal and were reseated. (test ride..no change)
4. Fuel pressure gauge shows 35psi at idle and 41psi at WOT
5. FCC opened and full of fuel to the top. No water. All connections appeared normal, hose intact, and psi did show as normal with gauge at WOT. (test ride..no change)
6. At idle removed vacuum hose from Fuel Pressure Reg on rail. PSI jumps to 41psi when vacuum hpse removed. Reattached hose and normal psi at idle-35 and 41psi at WOT. (test ride..no change)

All symptoms have stayed exactly the same for every test ride. Over several days of lake testing it seems that the issue arises when boat is up to temperature (160). Seems there are no issue run from a cold start and running up through the power band. 100% normal operation. Smooth as butter. Once boat is at temp, the issues at idle (stuttering) and between 1000 and 2000rms (struggling, running rough, losing power) are present. At 2500rpms it catches and runs close to if not normal to WOT.
Sound like possibly a engine coolant temp sensor issue reporting inaccurate temps to the ecm also Fords are known for having the TFI ignition module in the distributor crap out when warm and will cause studdering issues.
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  #5  
Old 02-24-2015, 09:56 AM
pkreusch's Avatar
pkreusch pkreusch is offline
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Join Date: Mar 2008
Boat: 2000 Gekko GTR22 (but I'm a MC owner at heart)
Location: southeast
Posts: 55
Thanks for the GREAT replies and so soon! I knew there were great guys on this forum!! Unfortunately, it was late, and I lost my first post late last night when I took too long to get back to the page. Forum booted me off and I lost all the info I had written. Bleary eyed and frustrated, I re-posted what I could remember.

OK, answers.....
Year - 1997
Fuel injected
Electronic ignition

Thx. Paco, but it's not the choke. I'll check the timing and dist. springs. Good suggestions. Our first impression is electrical hence posting in the electrical portion of the forum.

Thx. DD, Not TBI. We think it could be associated with any one of the myriad of components talking to the ECM.

Thx. J.Mc, I owned a PCM in my old 1980 MC and had the module crap out also. We will check. We also thought one of those coolant/engine sensors talking to the ECM may be bad. At present, I don't have the wiring diagram, my buddy is working on that today. We need to get the testing procedures and go ahead and test them.

Thx again to all and any other suggestions or experiences, keep um comin'!
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  #6  
Old 02-24-2015, 10:17 AM
Shaun R's Avatar
Shaun R Shaun R is offline
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Boat: 2011 X25
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Posts: 1,749
Check the resistance on each injector and make sure it's within spec. If one is going bad, it will not only cause power loss but lean that cylinder out and raise engine temps.
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  #7  
Old 02-24-2015, 10:36 AM
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thatsmrmastercraft thatsmrmastercraft is offline
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Boat: 1977 Stars & Stripes
Location: St. Paul, MN
Posts: 17,508
Did all the work cure the temp issue?

You might do a little checking for a vacuum leak. Spray around intake manifold base, lower and upper with a can of carb cleaner while the engine is idling. Best results are obtained when the engine is cold.
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  #8  
Old 02-24-2015, 10:39 AM
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east tx skier east tx skier is offline
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You're probably on the right track. It seems like most issues with the PCM GT-40 are fuel pressure or delivery related. Bit it MIT be something different based on your symptoms. You mentioned the hose in the FCC. Are you talking about the little horizontal hose inside the housing? Hopefully, you checked that to make sure it isn't damaged/worn. Also, while not entirely typical of all of your symptoms, you may also want to check the antisiphon valve on the fuel feed line from the gas tank. They get gummed up and can lead to issues both at idle and underway. While we are on the fuel lines, you might try to rig something up to run it off a gas can to rule out the possibility that the fuel lines have degraded over time (I don't think this is too likely).

Sounds like the temperature issue was solved, but if not, make sure the raw water strainer is on tightly. That is a very common culprit for temp spikes.

Lastly, check this out. This is the GT-40 troubleshooting spreadsheet. Some of your symptoms have been shared by people with distributor isssues You might also check with the good people at correctcraftfan.com or Jody at Florida Inboards. Very knowledgeable when it comes to this engine.
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Red 1998 Ski Nautique, PCM GT40, 310 hp, , Acme 4 blade, Perfect Pass SG/Zbox.

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Last edited by east tx skier; 02-24-2015 at 10:50 AM.
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  #9  
Old 02-24-2015, 11:13 AM
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chriscraftmatt1976 chriscraftmatt1976 is offline
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I worked on nautiques for years, and that GT-40 is a great engine. GL with the fix.
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  #10  
Old 02-24-2015, 11:53 AM
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east tx skier east tx skier is offline
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Quote:
Originally Posted by chriscraftmatt1976 View Post
I worked on nautiques for years, and that GT-40 is a great engine. GL with the fix.
I love mine.

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