GT40: Hot Idle Loping
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=39512
Printed Date: October-06-2024 at 12:19am
Topic: GT40: Hot Idle Loping
Posted By: SteveHookEm
Subject: GT40: Hot Idle Loping
Date Posted: July-28-2016 at 5:07pm
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My GT40 has 340 hours. It runs like a Swiss watch from hole shot to full power and everything in between. Really runs great! Except after it warms up, we stop for a bit and restart. At that point, the idle is all over the place! Over 1000, down to almost stalling, back up and repeat. Very, very frustrating. And it seems to smoke some at this point too. It still has no hesitation and runs great at speed even when the idle is doing this. I have searched the forum, read the many threads about this. I found one promising thread that stated to replace the idle air control valve. Did that. No luck. Is this just going to be the way it is? Even my (very respected) repair shop here couldn't get this right. Any suggestions appreciated! ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=7890" rel="nofollow - My 95 Ski Nautique Diary |
Replies:
Posted By: Blamey
Date Posted: July-28-2016 at 7:44pm
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Did you read the poor man's GT40 diagnostic thread. I know they mention the ECM or Fuel relay as another possible cause. Any other issues with the boat? ------------- 96 Super Sport Previously: 95 Sport Nautique, 1980 Ski Supreme |
Posted By: gun-driver
Date Posted: July-28-2016 at 8:31pm
Failed Map sensor will cause the idle to oscillate and motor may stall according to the manual in the reference section  ECT, ACT or TP sensor fail will cause 800 instead of 600 RPM idle. |
Posted By: SteveHookEm
Date Posted: July-28-2016 at 11:27pm
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I'm not a mechanic. I wish I could do some of this myself but I have to rely on others. I did, however, replace the idle air control valve---and felt very proud of myself. It didn't fix it, but at least it's a new one. haha @gun-driver: is the map sensor something I can replace myself or does it require using special equipment (I likely don't have) to do it? If it requires putting any kind of computer to the engine after, I can't do that. I appreciate the help! I wish you guys were in Houston! I don't have anyone here that knows this motor other than my shop. Steve ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=7890" rel="nofollow - My 95 Ski Nautique Diary |
Posted By: gun-driver
Date Posted: July-28-2016 at 11:59pm
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Yes it's mounted to the front of throttle body, it has the vacuum line going to it. Pretty much plug and play. It would help you understand where things are and what they do if you look over the GT-40 service manual in the reference section. It's in the manual section at the bottom. There's a picture that points to all the parts and if you read the section called Theory of operation it gives you a simple understanding of what does what even for the non-mechanical minded. |
Posted By: SteveHookEm
Date Posted: July-30-2016 at 11:04am
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Looks like something I can do! PlanetNautique wants $259 for the Map Sensor. I hate to spend that much on something that may not be the cause. Any suggestions for a different source for the part? ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=7890" rel="nofollow - My 95 Ski Nautique Diary |
Posted By: gun-driver
Date Posted: July-30-2016 at 11:47am
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Ford or auto parts store Here's a picture with part number you could probably call ford to cross reference to current part number Called my local he said that part is NLA from Ford he gave me this number and said a Napa or other would be able to cross reference off E7DZ-9F479-A http://s256.photobucket.com/user/gun-driver/media/Mobile%20Uploads/image_zpsxxkb2zay.jpeg.html" rel="nofollow"> 
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Posted By: SteveHookEm
Date Posted: July-30-2016 at 1:10pm
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Alright! RockAuto Airtex model for $39.99! In the OEM part list, it shows the sticker part number and the part number the local guy gave you. Done. Thanks for the help. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=7890" rel="nofollow - My 95 Ski Nautique Diary |
Posted By: SteveHookEm
Date Posted: August-01-2016 at 4:02pm
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@gun-driver When you get a chance, can you pull back a little in your photo so I can see where this is located on my GT-40? I'm at home, boat in the storage so I'd like to know where to look when I get over there. It seems all I need is a flat head screw driver. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=7890" rel="nofollow - My 95 Ski Nautique Diary |
Posted By: gun-driver
Date Posted: August-01-2016 at 11:07pm
| Front passenger side of the air intake right behind the air cleaner, has a vacuum hose going to it |
Posted By: SteveHookEm
Date Posted: August-02-2016 at 3:11pm
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@gun-driver: Maybe I'm looking at a different service manual for the GT-40. I don't see a reference section or anything that says "theory of operation". I have the pdf file that I downloaded from here. The diagram that has the arrows pointing out the different parts is at the front of my manual and shows the MAP to be on the driver's side, front next to the EEC System Relay and STO/STI Connectors. It is shown in section 2A. Is this the same location you said to look? When the part arrives, I'm heading over to install. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=7890" rel="nofollow - My 95 Ski Nautique Diary |
Posted By: gun-driver
Date Posted: August-02-2016 at 6:30pm
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Yea that's not where it is on ours the rest is pretty close. Theory of operation starts on 2a-17 You may want to also check your fuel pressure regulator that just fixed rough idle/stall problem |
Posted By: gun-driver
Date Posted: August-08-2016 at 1:26pm
| Any feed back on if this was solved and or what was the fix???? |
Posted By: SteveHookEm
Date Posted: August-08-2016 at 4:17pm
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Hey, OK got it installed easily and tested on the lake Friday. It seems that the loping is gone! But I am now having some other issues pop up that never happened before. Starting then dying immediately. Then it starts fine. And sometimes idling at 1200-1300rpm. Not all the time. When it does come down to about 800, it's not all over the place anymore. When you put on the new part, do you need to do any other tuning to the computer to let it know? ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=7890" rel="nofollow - My 95 Ski Nautique Diary |
Posted By: gun-driver
Date Posted: August-08-2016 at 4:29pm
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No you don't have to do anything to the ECA. You may want to check your Fuel Pressure Regulator. One of the similar posts found his regulator to be bad causing fuel to migrate up the vacuum line (which shares the same line as the map sensor) causing erratic idle ( loping ) $20 at autozone Thanks for the follow up. We try to figure out these problems and a lot of times the poster never gives a follow up so we don't know if the recommended fix worked or not. |
Posted By: SteveHookEm
Date Posted: August-08-2016 at 4:36pm
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Fuel pressure regulator--do it myself or above my level? haha Do you have that part number? ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=7890" rel="nofollow - My 95 Ski Nautique Diary |
Posted By: Bri892001
Date Posted: August-08-2016 at 5:46pm
From another thread:
Not sure on difficulty. |
gun-driver wrote:Posted By: gun-driver
Date Posted: August-08-2016 at 6:00pm
| Easy peezy lemon squeezey |
Posted By: SteveHookEm
Date Posted: August-08-2016 at 6:05pm
I hate technical jargon. haha ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=7890" rel="nofollow - My 95 Ski Nautique Diary |
Posted By: SteveHookEm
Date Posted: August-09-2016 at 11:48am
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I'm guessing this is the one for a 1995 GT-40 as well. http://shop.advanceautoparts.com/p/carquest-by-bwd-fuel-pressure-regulator-21704/3463265-P?searchTerm=bwd+21704+or" rel="nofollow - Advance Auto Parts ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=7890" rel="nofollow - My 95 Ski Nautique Diary |
Posted By: SteveHookEm
Date Posted: August-21-2016 at 8:56pm
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@gun-driver I bought the part. Before I head over to install it, do I need to bleed the line? I don't have any special tools. The YouTube videos all show a vacuum bleed tool removing the pressure off the fuel line first. Also, what regular tools do I need to pull this? Is it connected with allen screws to the the three holes on the backing plate or flat or phillips head? Anything else I should know? Thanks for the help! ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=7890" rel="nofollow - My 95 Ski Nautique Diary |
Posted By: gun-driver
Date Posted: August-21-2016 at 9:08pm
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Take any pressure off the line by bleeding off through the schrader valve. If the boat hasn't been run in awhile probably only a pound or two in the system if any. IIRC it was a 3/16 allen head bring some absorbent towels because there will be some fuel that leaks out. I would blow out the vacuum line from the map sensor end in case there was fuel in the line. |
Posted By: cboland
Date Posted: May-27-2020 at 9:44am
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For future troubleshooting reference I want to mention that I also had an intermittent oscillating idle after the engine was warm. Thanks to gun-driver’s insights in the 3rd post up above, I replaced the MAP sensor and idle is now smooth. ------------- Bud 1999 Sport Nautique |