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=32987 Printed Date: October-08-2024 at 3:20pm
Topic: GT40 High Idle ProblemsPosted By: guitarist35jc
Subject: GT40 High Idle Problems
Date Posted: March-07-2014 at 11:51pm
With Spring coming soon, I've been thinking of a couple issues to be addressed when the season starts. In the last 2 years the engine has been out of my boat twice for non engine-related issues (long story). To be brief, since the engine went back in the boat last summer we've had issues with idle speed after the engine is warm.
Idle speed will consistently settle at 1100rpm once then engine is warm. When its cold, everything is fine. If the engine is shut down and restarted while at high idle speeds it seems to correct itself until the boat is put in gear and then put back in neutral. At this point it will usually return to the 1100rpm mark again. If you're lucky you may get another pass or 2 with normal idle speeds.
Has anyone else had similar issues? I've read of lots of people with the opposite problem with the GT40 (engine stalling, rough idle, etc) but not much on high idle problems. To the experts, what is the likely culprit? I am hoping its not a bad ECM, and don't think that it is since the problem started immediately after the engine was re-installed. Bad ground somewhere during the engine install? Vacuum leak? Trying to put some ideas together before the boat comes out of storage so I'll have an idea where to start.
Engine is a '97 GT40 EFI.
Replies: Posted By: Tim D
Date Posted: March-08-2014 at 10:51am
First thing I would check is the fuel pressure regulator. It's on the fuel rail at the back. When you're experiencing the high idle, pull the vacuum line off and see if anything changes. Electric fuel pumps run wide open, so at idle the regulator sends the extra fuel back to the tank. On the GT40, the return line is on the fuel control cell.
------------- Tim D
Posted By: guitarist35jc
Date Posted: March-08-2014 at 12:07pm
Makes sense, I'll be sure to try that when the boat comes out of storage.
Another coincidence is that we've had intermittent problems with the bilge pump not shutting off after getting the boat back last summer. Had to disconnect the battery just to get the pump to stop. Only noticed the problem one night when I went out to the driveway and could hear something running inside the boat as it sat on the trailer. I hate the idea of chasing electrical problems around, but I'm thinking that may be the case this year.
Posted By: guitarist35jc
Date Posted: March-08-2014 at 12:24pm
Additionally, I test drove the boat before picking it up from the shop last year as they replaced the transmission and i wanted to ensure no vibrations, etc. The tech was on board for the test drive. They had installed the fuel lines backwards (return line where the intake line should be, and vice versa). The boat died immediately on take off as it became fuel starved. Reversed the lines on the water and all seemed fine after that.
Any chance running the boat with reversed fuel lines could fry the fuel pressure regulator, or any other fuel delivery component? It was literally run for less than a minute in this condition.
Posted By: Bri892001
Date Posted: March-13-2014 at 1:13pm
These motors have an idle air control as well. Another thing worth checking.
Posted By: quinner
Date Posted: March-13-2014 at 2:32pm
Do you have perfect pass??
Check the routing of your throttle cable, be sure it is not under pressure against anything at any point.
Posted By: guitarist35jc
Date Posted: March-15-2014 at 12:40pm
No PP right now...some day though
Posted By: Bri892001
Date Posted: March-15-2014 at 1:23pm
Quinner makes a good point though. PP is one thing that can wind up putting artificial pressure on the throttle if it's not adjusted correctly.
But since your motor has been out and in a couple times, a pinched or misrouted throttle cable is also a suspect. Make sure the cable isn't somehow holding the throttle open. Like, disconnect it and see if the idle goes down to normal.
Even the 1100 rpms you're saying is the baseline when it's running well, is high.
Posted By: guitarist35jc
Date Posted: March-16-2014 at 1:22am
Baseline when running well is actually 6-800 rpm from memory...it only idles at 1100rpm once the engine is warm (usually after one or 2 sets if we're skiing, maybe 30mins cruising). I've had a couple other people mention the throttle cable also.
If it were a pinched throttle cable, or a cable not returning to normal idle position for whatever reason, wouldn't you see this problem regardless of whether the engine is warm or not? I'm hoping this isn't one of those annoying problems we chase forever and never really get to the source.
Posted By: Bri892001
Date Posted: March-17-2014 at 12:51pm
Although it's a different Ford engine, this video seems to really speak to IAC problems. He also gets into a pretty good explanation of why an idle may act up more after an extended high speed run. Worth a look:
Posted By: lewy2001
Date Posted: March-17-2014 at 8:57pm
It is not really a IAC motor on the GT40 engine it is a Solenoid that opens a piston allowing extra air into intake. It might just need a clean with some carb cleaner. I would also make sure the throttle body is fully closed when the idle is high. Another cause could be a air leak somewhere on intake or throttle body after the engine warms up.
Here is a video of IAC operation on a GT40.
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