GT40 intermittent rough running
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=27323
Printed Date: November-26-2024 at 7:58pm
Topic: GT40 intermittent rough running
Posted By: cgofort
Subject: GT40 intermittent rough running
Date Posted: August-05-2012 at 5:19pm
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I thought I had this whipped. I replaced all plugs and wires after finding one wire broken. I had also replaced fuel fileter Yesterday was first day to water test. Boat ran great for 30 minutes. All of sudden, loss of power! Engine sounded poor,like was missing. Rough running, and rpm wouldn't go over 2500. In neutral, would rev high but still sounded off. If I pulled a plug wire at distributor, it sounded same. I wanted to get some feedback- should I replace the cap/rotor? Not sure which way to proceed. What symptoms are common for fuel relay? After boat sat for 1hr, it ran great for about 45 seconds, then went back to rough- loss of power Thanks for any suggestions and feedback Charles |
Replies:
Posted By: cooperlacy
Date Posted: August-05-2012 at 11:29pm
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Was the red light on the top of the dash lit up? If the engine overheats or loses oil pressure (less than 5 psi), it will go into "limp-home" mode which will not allow the engine to run above 2700 rpm. What were your temperature and oil pressure readings when the boat lost power? The following is taken directly from the PCM GT40 EFI owners manual (page FM 4,5): "In the event of a water temperature overheat (200°F or higher) or loss of oil pressure (below 5 PSI), engine operation will noticeably change. The ECA will alter the injector timing sequence, the engine will run rough, and engine speed will drop to 2700 RPM. Below 2700 RPM the engine will run normally, but not above. The engine will remain in this Speed Limiting Operation Warning (S.L.O.W.) mode as long as the cooling/ oil pressure problem exists. After the problem is corrected and water temperature or oil pressure returns to normal, the ECA will automatically allow the engine to resume proper operation. The ignition switch does not have to be turned off to reset the system." Has the boat always run well up until this point? Cooper |
Posted By: Bri892001
Date Posted: August-06-2012 at 2:54pm
| One of the most basic things is to check the antisiphon valve on the top of the fuel tank. |
Posted By: cgofort
Date Posted: August-06-2012 at 4:59pm
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Hi Cooper, There are no alerts / alarms to signify SLOW mode. The issue can be quite volatile, meaning rough running/clear/ rough in just a span of seconds. On the antisiphon valve, can someone point me to the part? i did a search on nautiqueparts.com and came up with nothing. Is this a replacement or clear /repair? thanks! Charles |
Posted By: Bri892001
Date Posted: August-06-2012 at 5:03pm
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I'm pretty sure they call it check valve. I think this is the antisiphon: http://www.nautiqueparts.com/checkvalvefuel.aspx" rel="nofollow - http://www.nautiqueparts.com/checkvalvefuel.aspx Could be worth calling to double check. It can be cleaned or replaced. Up to you and how bad it is. |
Posted By: guitarist35jc
Date Posted: August-07-2012 at 12:11am
| I just solved a similar issue with our boat. I'd pull the fuel pickup tube right out of the tank. The filter at the end of ours was completely clogged to the point that fuel stuck in the tube couldn't drain back out once it was out of the tank. |
Posted By: cgofort
Date Posted: August-21-2012 at 1:04am
| So far parts replaced:distributor cap and rotor, plugs and wires, fuel pump, fuel relay. Issue STILL exists, but I have more awareness. The boat runs great cold, but after 5-10 minutes, it starts acting up. Once it acts up, it's done. I docked the baot, put trailer in water, and by that time it ran fine to put on trailer. Would a faulty coil cause this kind of symptoms? |
Posted By: cgofort
Date Posted: August-21-2012 at 1:05am
| Fuel pressure was 34-32 |
Posted By: cgofort
Date Posted: August-21-2012 at 2:50am
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i uploaded some videos to you tube, maybe someone with a good ear can recognize here is video of it running rough, under full throttle.I show gauges which appear normal http://www.youtube.com/watch?list=UL-88dGr4ahl0&feature=player_detailpage&v=-88dGr4ahl0 Here is video going from stop to full throttle: http://www.youtube.com/watch?list=ULI7fK8-ntZXo&feature=player_detailpage&v=I7fK8-ntZXo Here is video of engine running in neutral, then putting in gear: http://www.youtube.com/watch?v=Nh9Dzv5KlYk&feature=player_detailpage You can tell I don't know how to embed video! |
Posted By: lewy2001
Date Posted: August-21-2012 at 10:36am
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That engine sure sounds like it is not running on all 8 cylinders. Have you checked your plug leads to the firing order. You may have inadvertently swapped a couple while replacing plug wires. If the firing order is correct. I would then remove the plug leads one at a time. This will isolate what plugs are firing and any that are not.(The engine will run rougher when you remove a good firing plug lead) Check quality of spark you should have nice fat blue spark at plugs. I also heard a couple of noises I did not like the sound off. I could just be damper rattle in gear due to the rough running at low rpm. Get back to us once you confirm the above. ------------- If you're going through hell, keep going http://www.correctcraftfan.com/diaries/details.asp?ID=2999" rel="nofollow - 89 Ski <a href="http://www.correctcraftfan.com/diaries/details.asp?ID=5685" ta |
Posted By: Bri892001
Date Posted: August-21-2012 at 1:45pm
here is video of it running rough, under full throttle.I show gauges which appear normal Here is video going from stop to full throttle: Here is video of engine running in neutral, then putting in gear: |
cgofort wrote:Posted By: Bri892001
Date Posted: August-21-2012 at 1:49pm
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I think Lewy is on the right path as usual. That is a perfectly timed miss, which to me, suggests an ignition problem. Definitely sounds like a cylinder not firing. I'd be checking for mixed up spark plug wires and wires not completely seated on the cap or plug. |
Posted By: cgofort
Date Posted: August-21-2012 at 2:08pm
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I really WISH the cables were in incorrect order, but because I'm no expert wrench, I numbered all the plug wires and the respective connection to the cap. All of those are aligned. What gets me on this issue, it runs flawlessly for 10 minutes, but then once it heats up, it starts to go bad. Would a failing coil produce this sort of situation? Video was taken yesterday. What is odd, i turned the boat off to get trailer and load it. In the time that took (maybe 10 minutes) the engine started smoothly. I can post that video. Can someone give me hint how to embed the video so i'm not just showing links? Thanks, Charles |
Posted By: Bri892001
Date Posted: August-21-2012 at 2:13pm
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cgofort (or name not give as Pete would say, When you are looking at the video in Youtube, press the "Share" button, this will serve up the direct link to the video, so copy that link. Sometimes, the link you'll be watching it through is from a subscription, featured video etc. Those links often don't work. You want that "Share" link. Then, take the link and put in between these {tube}http://youtu.be/I7fK8-ntZXo{/tube} Now, replace the squiggle brackets { with the square brackets [, and you've got it. Coil is possible? I'm not familiar with that one really. Relays are another strong possibility. |
Posted By: Bri892001
Date Posted: August-21-2012 at 2:14pm
| Also, do you have a Fuel Control Cell, FCC? |
Posted By: cgofort
Date Posted: August-21-2012 at 2:21pm
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Thanks for the direction on embedding videos. Here's the boat yesterday during trailer load, right AFTER earlier videos: To answer above question FCC: yep, it has FCC. I replaced the filter there. I've owned the boat almost 1 year. Previous owner replaced low pressure fuel pump before I got it (allegedly). |
Posted By: Bri892001
Date Posted: August-21-2012 at 3:07pm
This doesn't necessarily sound like a typical failed fuel tube insside the FCC, but did you check the fuel tube inside the FCC for good measure? |
Posted By: lewy2001
Date Posted: August-21-2012 at 10:30pm
Charles I would check fuel pressure when the engine is running rough. This is so you can rule out fuel supply being the cause of intermittent problem. Next I would check the quality of spark at plugs when running rough if you can get an idea of the nice fat blue spark when it is running correctly to compare it would be good. It could be the TFI module or coil firstly I would clean all the connections to both and then test. The code reader may be a real help here and at their price probably cheaper than any part you are going to replace. http://www.amazon.com/Equus-3145-Ford-Digital-Reader/dp/B000EW0KHW" rel="nofollow - GT40 Code Reader   ------------- If you're going through hell, keep going http://www.correctcraftfan.com/diaries/details.asp?ID=2999" rel="nofollow - 89 Ski <a href="http://www.correctcraftfan.com/diaries/details.asp?ID=5685" ta |
Posted By: cgofort
Date Posted: August-24-2012 at 1:24pm
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Latest update: I took boat out last night with the fuel pressure gauge. It was consistent at 38PSI even during the rough-running period. I don't think this is fuel related. Same characteristics: runs great first 10 minutes, then when warmed up, it will start to sputter. If boat sits / cools down, it runs good until warm again. I sprinkled water on the exhaust manifold during poor running period. Water evaporated real fast on the front and back manifold, not so quick on the middle. Makes me suspect those aren't firing. I haven't performed TFI test yet, I lack the hardware and a little nervous on complexity. I'll planned to take the weekend and run more test on the water, will post any findings. charles |
Posted By: cgofort
Date Posted: September-05-2012 at 3:34pm
| I couldn't figure it out, and was done throwing parts at it. I sent the boat over to local marine shop. After 2 weeks, they believe it is related to the computer. Will see. |
Posted By: Bri892001
Date Posted: September-05-2012 at 3:42pm
Keith's post in Poor Man's GT-40 Diagnosis does sound similar:
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Posted By: storm34
Date Posted: September-05-2012 at 4:04pm
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Nice posting guys! Good info here. ------------- |
Posted By: phkemp
Date Posted: September-05-2012 at 6:57pm
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Check this thread, even though you don't think it's fuel related. Unless the shop already has you up and running. Even if they do...change this $1 part. The tiniest little crack in this house can shut you down, it did with me this summer. It's the short house from the top of the high pressure pump in the FCC. Several members here had major running problems that were fixed when this hose was replace. Even if you are back up and running, replace this anyway. Call Skidim for the part. Consider preventative maintenance. http://www.correctcraftfan.com/forum/forum_posts.asp?TID=27375&title=pcm-gt40-58l-efi-abrubtly-barely-runs ------------- 1997 Hydrodyne Grand Sport Elite PCM GT40 5.8L EFI, 310 HP Hybridized with Big Air Wake Tower and Bimini |
Posted By: cgofort
Date Posted: September-18-2012 at 8:11pm
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solved!!! This would be a very tough issue to identify unless you're super with electrical diagrams and know what you're doing. Short answer: corrosion in the fuel injector harness caused the injectors to OHM out, making them shut down. Injector harness was testing at 30 OHM, should be no more than 12 OHM. Mechanic cleaned harness and replaced corroded connectors inside the harness. Boat works great! Of course, this took a long time to track down, mechanic swapped the ECM, distributor assembly, cleaned injectors, etc, etc so after 3+ days of labor charges, it's finally fixed, just a huge punch in the wallet. Glad to have it back, and hope this will help anyone in future. |
Posted By: Gary S
Date Posted: September-18-2012 at 8:43pm
You gave up but since you were paying your mechanic thought he could throw just as well as you  . I would be embarassed to charge someone to learn on their boat.I guess I'll just keep my carbed old beater.Glad you got it back,but if you can't do it yourself you'd better find another mechanic before you need one again  ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1711&sort=&pagenum=1&yrstart=1966&yrend=1970" rel="nofollow - 69 Mustang HM SS 95 Nautique Super Sport |
Posted By: pamedida
Date Posted: July-19-2021 at 10:55am
| Thank you for taking the time to document this issue |