PCM Pro-Boss GT-40 MP EFI - rpm Failures |
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PT Skier
Groupie Joined: June-03-2011 Location: Portugal Status: Offline Points: 66 |
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Posted: September-05-2013 at 1:07pm |
Hello,
I own a 1995 Ski Nautique with a PCM Pro-Boss GT40 EFI engine and this summer I started having some problems with inconsistent RPM at all speeds. While I'm driving I hear very slight and short (but constant) RPM breakdowns. It seems that the engine is having very fast hiccups. I barely feel any speed changes and the indicator on the RPM gauge varies only slightly but you can clearly hear that the engine is running inconsistently. Furthermore, I only have this problem while driving. If I disengage the shift mechanism I don't feel the problem when I advance the throtle. I replaced the HP and LP three years ago and I had my gas filters changed last month. Do you have any idea where I should start looking with my mechanic? Do you think there maybe be shortages of fuel delivery to the engine? Could it be a problem with the injectors? Thanks in advance! |
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Dreaming
Platinum Member Joined: May-21-2010 Location: Tacoma, WA Status: Offline Points: 1870 |
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Since you say Pro boss, is it throttle body injected? My guess is that you are starting to experience protec breakdown... If the "distributor" is sending an erratic signal, you would not get the proper spark timing.
If you're not sure about the Throttle body, some pictures of your engine would help. |
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21172 |
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Gt40 is multiport, no protec. It was still labeled pro boss.
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81nautique
Grand Poobah Joined: September-03-2005 Location: Big Rock, Il Status: Offline Points: 5778 |
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I would still go back and check your fuel pressure at the rail even though you've replaced the pumps before. I've seen a friend lose a gt40 once and then almost lose it again (just heads second time)both times the HP fuel pump was the issue. Don't run it hard if it's missing because it doesn't take long to melt them when they run lean.
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You can’t change the wind but you can adjust your sails
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Hollywood
Moderator Group Joined: February-04-2004 Location: Twin Lakes, WI Status: Offline Points: 13514 |
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Fuel rail pressure first. When's the last time you tuned up any of the ignition system?
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PT Skier
Groupie Joined: June-03-2011 Location: Portugal Status: Offline Points: 66 |
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I bought the boat in 2010, besides replacing LP and HP pumps, I didn't do anything with the ignition system. I will post some pictures of the engine later to clarify.
Thanks for your feedback!!! |
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Dreaming
Platinum Member Joined: May-21-2010 Location: Tacoma, WA Status: Offline Points: 1870 |
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Good to know... no wonder I am confused... did they label all the gt-40 motors "proboss" ? Is the TBI a 1994 only deal? Sorry for the thread jack |
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Hollywood
Moderator Group Joined: February-04-2004 Location: Twin Lakes, WI Status: Offline Points: 13514 |
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All PCM HO 351s are "pro boss"
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TRBenj
Grand Poobah Joined: June-29-2005 Location: NWCT Status: Offline Points: 21172 |
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Exactly. Carb, TBI and MPEFI... so long as it was HO, it was a Pro Boss. |
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PT Skier
Groupie Joined: June-03-2011 Location: Portugal Status: Offline Points: 66 |
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I've posted two pictures in the initial post of the thread.
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lewy2001
Grand Poobah Joined: March-19-2008 Location: NSW Australia Status: Offline Points: 2234 |
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Yep early GT40 with the sort after tubular inlet manifold and no FCC (Fuel Control Cell).
Like the guys said start with fuel pressure readings. And general tune up items plugs leads and dissy cap. A code reader may help if one of your sensors is playing up. At $25 this Ford Code Reader is worth having even for a one time use. |
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If you're going through hell, keep going
89 Ski <a href="http://www.correctcraftfan.com/diaries/details.asp?ID=5685" ta |
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gun-driver
Grand Poobah Joined: July-18-2008 Location: Pittsburgh, Pa Status: Offline Points: 4127 |
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If he hasn't tuned it up in the 3 years he owned it and we don't know when the PO last tuned it up, sounds like it could be an electrical miss.
This is all a guess not knowing how many hours a year he puts on the boat. I do like that fire bottle set up |
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PT Skier
Groupie Joined: June-03-2011 Location: Portugal Status: Offline Points: 66 |
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Could you please explain the meaning of "tuned it up"? I'm from Portugal and sometimes I have some difficulties understanding some words/expressions. |
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Bri892001
Grand Poobah Joined: September-27-2008 Location: Boston MA Status: Offline Points: 4947 |
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Tuned up typically means:
Spark plugs, distributor cap and rotor replaced. Sometimes replacing the spark plug wires since there is a performance problem. Fuel filter also. With a carbureted boat you'd also check fuel air mixture and accelerator pump adjustments. If you had a distributor with points (you don't with yours), you'd check dwell and timing too. |
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Hollywood
Moderator Group Joined: February-04-2004 Location: Twin Lakes, WI Status: Offline Points: 13514 |
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There are wear items on the ignition side that should be replaced. I'm a "if it ain't broke don't fix it" guy myself but now would be a good time for a cap rotor and plugs.
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PT Skier
Groupie Joined: June-03-2011 Location: Portugal Status: Offline Points: 66 |
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I'm confused, you are suggesting that I have a carburated engine? I always assumed it was EFI. See following pic. |
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bhectus
Platinum Member Joined: July-04-2010 Location: Gator Country! Status: Offline Points: 1809 |
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No, your boat is EFI, no carb. It could be something as simple as a faulty plug or plug wire. As suggested I would start by replacing plugs/wires/cap/rotor first and see what that gets you. It's easy, relatively inexpensive, and you can do it yourself. Just make sure you don't cross your plug wires into the distributor in the wrong configuration.
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'02 Ski Nautique 196 w/ 5.7 Apex bowtie - Sold
'87 Barefoot - sold '97 Super Sport Nautique - originally custom built for Walt Meloon '97 Ski Nautique '83 SN 2001 |
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Bri892001
Grand Poobah Joined: September-27-2008 Location: Boston MA Status: Offline Points: 4947 |
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No, no, no. My fault. I was just giving the full definition of a tuneup, or all the aspects I think of.
The piece about the points and the carburetor don't apply to you. Some might say that part of a tuneup is running fuel injector cleaner, which wouldn't apply to me since I have a carburetor. |
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PT Skier
Groupie Joined: June-03-2011 Location: Portugal Status: Offline Points: 66 |
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So, together with "fuel pressure readings, starting with the rail pressure" your post practically sums what all the guys are recommending: - Fuel pressure readings - Replacement of some of the ignition system components, namely: spark plugs/plugs wires/cap/rotor Do you think you could give me a hand finding the right tune up kit? I get very confused trying to understand the service manuals for the engines... One more thing, are these changes suitable to be performed with the boat on the water? Or should I wait 'till winter to do it off the water? Btw, the boat has now around 750hrs. I add around 40hrs each year. |
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bhectus
Platinum Member Joined: July-04-2010 Location: Gator Country! Status: Offline Points: 1809 |
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cap and rotor
plug wire set spark plug set - get the WL764 set (it is an option in the drop-down tab) I would recommend doing this on your own before moving to fuel-related issues only because it is an easy DIY project that requires very little mechanical skill. You can do it while the boat is in the water. If you are still having issues afterwards you can move to fuel system components. Where in Portugal are you? My mom lived there when she was a teenager and my parents actually just returned from there 2 weeks ago. They go every few years. I've visited many places in Portugal myself, I love it there! I really liked Cascais and of course the Algarve with all the topless ladies. :) |
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'02 Ski Nautique 196 w/ 5.7 Apex bowtie - Sold
'87 Barefoot - sold '97 Super Sport Nautique - originally custom built for Walt Meloon '97 Ski Nautique '83 SN 2001 |
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PT Skier
Groupie Joined: June-03-2011 Location: Portugal Status: Offline Points: 66 |
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Thank you very much for the support with the part numbers! Small world hey? I'm from Porto (in the North). I know Algarve very well and I know what you are saying about the ladies :D I've been in Cascais and Lisbon a couple of times as well. And now I'll tell you something funny, you know Carl deAndrade from White Lake Marine? He was born in Portugal :) in the Açores island!!! So I'll order the parts you mentioned and see how it works. Thanks a lot. If you ever show up in Portugal I'll be more than glad to offer you a pull in my Nautique :) |
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PT Skier
Groupie Joined: June-03-2011 Location: Portugal Status: Offline Points: 66 |
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Hello guys,
I just wanted to update you on my boat's engine condition. I have followed your advice and replaced spark plugs, s.p. cables, distributor cap and rotor. And you know what? The engine is running better than ever :) bhectus you were right, it was a funny DIY project!!! I found out that my mechanic (maybe not a very good one) had wrong spark plugs mounted and there was even one of them different from the others (at least the brand was different). I think the cables were still the original ones as well as the distributor cap and rotor. I would like to thank you a lot for your support. I will know create two different topics since I discovered two possible problems that I would like to have your opinion on: Rusty Distributor Rusty Exhaust Manifold |
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Bri892001
Grand Poobah Joined: September-27-2008 Location: Boston MA Status: Offline Points: 4947 |
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Congrats on the fix
I added this fix to the GT-40 thread and spreadsheet: http://www.correctcraftfan.com/forum/forum_posts.asp?TID=25584&PN=1&title=poor-mans-gt40-diagnosis |
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