Rough idle and occasional hesitation and misfire
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URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=38330
Printed Date: November-24-2024 at 11:57am
Topic: Rough idle and occasional hesitation and misfire
Posted By: Keuka 95 GT40
Subject: Rough idle and occasional hesitation and misfire
Date Posted: March-28-2016 at 8:33pm
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'95 SN with GT40 experienced problem last summer and I want to fix it this spring. Boat will run great from cold start but after a few skiers I notice the idle will turn rough and it will hesitate on the hole shot (occasional misfire). My Dad also indicates similar symptoms occur after boat was run and then sits at the dock for for a few hours with motorbox closed (temperature related?). If our schedule only included skiing a few sets every morning and nothing else, we would never know this problem exists. Any clue as to what is causing this ?? |
Replies:
Posted By: Toertel
Date Posted: March-29-2016 at 7:41am
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If I remember right, this also happens to Paul Evaporation in the fuel line when hot and sitting. He vented it and it cranked right up? Zach, didn't you tell Paul to do that? ------------- 1994 Sport Nautique |
Posted By: 8122pbrainard
Date Posted: March-29-2016 at 8:47am
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Dan, This is from a previous thread where you asked the same question:
Do you have one of the EI conversions in the distributor? Depending on the brand, they are known problems causing the same symptoms you describe. The way the conversion is wired (ballast resistor or not) is also critical. "Vapor lock" has been discussed as well and strongly doubted it's a issue on marine engines. ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Keuka 95 GT40 wrote:Posted By: TRBenj
Date Posted: March-29-2016 at 10:50am
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Come on Pete, get with it! Gt40= multi port efi, not sure what you're thinking with the ei conversion and ballast resistor talk. Heat soak/vapor lock is largely overstated on carb'd engines, but it IS a problem on early multi port marine engines- such as this first-year, pre-FCC Gt40. Paul has had the same issue, and I've experienced it on an early multi port Mercruiser. I suspect that is what is going on here. I believe adding the FCC is the fix, there may be more info in the GT40 troubleshooting thread. |
Posted By: 8122pbrainard
Date Posted: March-29-2016 at 10:57am
Tim, Thanks for the help. Yes, you are correct and I need to pay more attention to what engine the OP has.  Without your knowledge and help, we'd be lost! ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: Gary S
Date Posted: March-29-2016 at 11:36am
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I have never experienced this problem with mine, I wonder if it's because my engine sits in a much larger vented compartment compared to a DD? I also wonder if the engine has a low pressure pump? It was my understanding when talking to a PCM rep that they added them to address that issue. Might be worth the effort to raise the engine cover when parked to see if it helps. ------------- 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: phatsat67
Date Posted: March-29-2016 at 11:41am
I think that's how we got it started fast Seb. I was probably several beers deep by then ha. I let Paul get gas all over his hands while I ran the key ha. One of my other theory's is that most people I've been around with 95s haven't always had vapor lock issues. I think when the high or low pressure pump hearings start to go a little south it creates more heat from the pump making the fuel temperature higher. |
Posted By: Toertel
Date Posted: March-29-2016 at 11:44am
So there ya have it, it's either beer and gas on the hand or buy and add the FCC (500USD cost for the FCC buys a ton of beer...just saying) ------------- 1994 Sport Nautique |
Posted By: Hollywood
Date Posted: March-29-2016 at 1:19pm
All GT-40s have a low pressure pump. You're thinking of the FCC, which was added after '95. Adding the FCC is "the" fix but Zach is saying a weak, dying LPP exacerbates the issue on boats without it. |
Posted By: Gary S
Date Posted: March-29-2016 at 2:34pm
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No I am not. I was told the low pressure pump was not originally in the system. It was added when PCM started having vapor lock problems. This was from the PCM rep I met last year at the Miami boat show. He said it was tough adding the pumps when in the engine was in the boat already. I wonder if there was a recall and some boats might not have a LP pump. My boat does not have a plug on the LP pump like many I have seen, it is hard wired. Wonder if it was added later? ------------- 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: Hollywood
Date Posted: March-29-2016 at 2:39pm
| The plot thickens. I have not heard of that before. You're way out of my league now. |
Posted By: phatsat67
Date Posted: March-29-2016 at 3:12pm
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All of the early stuff was hard wired gt-40 or not. The plugs were on the carter pump. The new pumps have non removable wires in place of the old style plugs hense the deutsch connector you see now days. Every pump I've seen on older boats is the plug on pump style even in carb boats. Gary, if yours has butt connectors and the pump shiny gold instead of black it's probably been replaced with a newer unit. If it looks hard wired and original it probably has 90 degree booted connectors on the bottom they push on to electrical nipple connectors. If not I'm lost |
Posted By: Keuka 95 GT40
Date Posted: March-29-2016 at 3:33pm
| Thank you all for helping me narrow down the possible solutions ! After double checking with the mechanic we use and our records, I can confirm the FCC was put in 2 years ago when we had similar problems. Mechanic says the high pressure pump would have been replaced when we did the FCC but the low pressure pump may not have been replaced at that time. Sounds like this might be the next step ? |
Posted By: Hollywood
Date Posted: March-29-2016 at 3:41pm
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absolutely BUT, there's other things you need to check first fuel pump relays are good that tube inside the FCC is not cracked ^common GT-40 problems |
Posted By: Gary S
Date Posted: March-29-2016 at 5:41pm
Yea Zach must have been changed   ------------- 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: phatsat67
Date Posted: March-29-2016 at 6:07pm
| Yep looks as if. They always painted them in the motor even back in the carb days. It's sort of a pain to hard wire them rather than use the plug. |
Posted By: Hollywood
Date Posted: March-29-2016 at 6:09pm
| Zack, you know alot about boats. You should work for a dealership. |
Posted By: tryathlete
Date Posted: March-29-2016 at 6:12pm
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I went through this methodically last year right after getting my 96 SS. I started by venting the fuel line at the Shrader valve (relays were both good) letting air out. I replaced the LPP and the problem went away. When they start to go, they act up by losing pressure when they get warm. There are other potential causes, but this solved the problem for me. |
Posted By: phatsat67
Date Posted: March-29-2016 at 6:33pm
| Don't accuse me HW |
Posted By: tryathlete
Date Posted: March-30-2016 at 4:35pm
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Yes it is a shi7 job to switch them to the Deutsch Connector. I was happy when finished. |