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gt40 EFI HELP |
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Don W 
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Joined: April-23-2019 Location: ga Status: Offline Points: 30 |
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 Topic: gt40 EFI HELPPosted: April-26-2019 at 6:27pm |
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I have a 97 Nautique GT40 EFI. It cranks right off but shuts off after a few seconds. I took off the MAP sensor and it idled fine. Put on a new MAP sensor- same problem. take it off and it runs fine. I had the computer replaced a couple of years ago. Hope it's not related. Any ideas would be appreciated. Don W
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DON W
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tryathlete
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Joined: April-19-2013 Location: Lake Villa, IL Status: Offline Points: 1796 |
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Posted: April-26-2019 at 7:32pm |
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Poor Man’s GT-40 troubleshooting guide
Sounds like low pressure pump is acting up but help yourself the the wondrous guide linked above! |
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tryathlete
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Joined: April-19-2013 Location: Lake Villa, IL Status: Offline Points: 1796 |
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Posted: April-26-2019 at 7:34pm |
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You can probably keep it running if you keep the ignition key in the start position a few seconds longer. It’s complicated but the guide will set you free.
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tryathlete
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Posted: April-26-2019 at 7:36pm |
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Forgot to mention the most obvious.
KILL SWITCH |
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Don W
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Posted: April-26-2019 at 7:48pm |
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Thanks guys. I should have mentioned that I checked the kill switch and fuel pressure- its 40 psi plus-also changed plugs. I will spend some time on the poor man's guide for sure! In talked with the tech at skidim and he is baffled too. said it sounds like electrical.
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DON W
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tryathlete
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Posted: April-26-2019 at 7:55pm |
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Try my little trick of holding the ignition key in starter engaged position for about three seconds after it kicks. If it stays running....
I replaced my LPP and ignition switch to solve the exact same issue. Slow failure of the LPP seems to be a difficult one to solve. I too had 40 psi at the rail/Schrader valve but my pump was somehow sucking air. The ignition switch might be a very cheap fix for you. Once I got past the issue, never had another problem in 3 years. |
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Don W
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Posted: April-27-2019 at 9:46am |
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I will give it a shot! Thanks! I replaced the pumps about two years ago and I can hear them cycling. I never thought about the ignition switch.
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DON W
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 10641 |
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Posted: April-27-2019 at 10:20am |
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Color me a little confused here.
If the boat runs with the MAP sensor unplugged how can the issue be the keyswitch or the kill switch or even a fuel pump for that matter? You say it runs fine with the sensor unplugged, Is that idling in neutral or driving it around on the water that it runs fine? More info would be good. |
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KENO
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Posted: April-27-2019 at 11:09am |
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Since this is an EEC-4 system with no O2 sensors it has a lot (but not everything) in common with the automotive EEC-4 system with O2 sensors and if you were to google the problem in the automotive world you can find lots of issues like yours and lots of reading.
Or click on the link below link The unplugged MAP sensor will richen up the fuel mixture It could be lean due to another sensor causing the computer to want to lean things out and unplugging the MAP sensor compensates, You say your fuel pressure is good, but there is a lot of input from the sensors to control fuel to the injectors. Maybe this will help, maybe not 
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tryathlete
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Posted: April-27-2019 at 1:40pm |
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Look where the light’s best. Corrosion on the multi pin connector at the ECM, TFI, MAP and other easy stuff. The ignition switch fix on my SS really didn’t offer itself up with a lot of troubleshooting logic, but it was part of the fix for my start and then stall issue.
The intermingling of sensors as KENO points out can add some extra time to the fix. Many on the auto threads have reported board related ECU issues as a fix. I hope that’s not your issue as you state, given the $$$$ and limited availability. I’m trying to upgrade every 4-5 years to keep ahead of the grim reaper NLA scenario. I wish PCM would somehow own this a bit more to help those in need, but we help ourselves fairly aggressively on CCF. Lots of really bright folks like KENO and Lewy to help get us through the dark nights of despair. |
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Don W
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Posted: April-27-2019 at 8:06pm |
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Well I tried holding the ignition key longer and that did not work. I checked all the breakers and they are good. I do have power going to the MAP sensor. I then pulled out the pcp valve and it cranked right up and idled fine. I have found the valve and will get it tommorow< I have not driven it yet but I hope this will fix it. I guess taking off the MAP sensor allowed the engine to get the air it neededs for combustion is the only thing I can figure. Many thanks for the input!
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DON W
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tryathlete
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Posted: April-27-2019 at 8:11pm |
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You mean the PCV valve was clogged? Sheesh. Glad it’s a cheap part. I always change those out when I do any plugs or filters.
Nice job! |
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KENO
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Posted: April-27-2019 at 10:30pm |
I checked with this guy and he thinks you'll still be looking for the problem tomorrow, but at least you'll have a new PCV valve  |
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KENO
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Posted: April-27-2019 at 11:30pm |
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Carnac seems to think that the first thing you did, removing the MAP sensor let air into the engine downstream of the throttle body and the second thing you did also did the same thing.
If you think about it, there's something whose job it is to do that normally. That would be the IAC valve. He thinks you should look at the IAC valve to find the real problem. Strictly a guess on his part
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KENO
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Posted: April-27-2019 at 11:45pm |
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The manual calls it the ISC BPA solenoid.
That would be the Idle Speed Control Bypass Air solenoid |
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MrMcD
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Posted: April-28-2019 at 2:03am |
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Nice Work Carnac!
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tryathlete
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Posted: April-28-2019 at 2:10am |
KENO CARNAC, electromechanical WIZARD!!!! |
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KENO
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Posted: April-28-2019 at 8:17am |
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Way to early to be saying anything yet
It was just a thought based on Don's description. Carnac could be screwed up, but it seems logical |
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tryathlete
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Posted: April-28-2019 at 8:22am |
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Logic prevails—usually—-with the GT40
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Don W
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Posted: April-28-2019 at 8:54am |
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Thanks so much! I'm betting its better than a guess! Will update as soon as I can get the pcp valve
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DON W
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Don W
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Posted: April-28-2019 at 5:03pm |
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Okay. with great embarrassment I must start over. I get confused with all the different valves and sensors. When I started having the problem I called Skidim and Vince suggested I remove the IAC valve- (not the Map sensor) I did and the boat would stay cranked. So I put on a new IAC valve and it would not stay cranked. I checked to make sure I had power going to the IAC and I do. I Then removed the PCP valve and the boat stayed cranked. I replaced the PCP valve today and the engine again shuts off after a few seconds. So, I am back to square one- except that I now know the difference between the Map sensor and the IAC. Apparantly I am not getting air for combustion. Any other ideas?
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DON W
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Don W
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Posted: April-28-2019 at 5:07pm |
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And if its not getting air for combustion why does it crank to begin with??
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DON W
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Don W
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Posted: April-28-2019 at 7:50pm |
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OKAY!! The boat is fixed. I put fresh gas and a lot of sea foam and injection cleaner in gas. I took the hose from the manifold to the pcv valve off from the manifold end and the boat stayed cranked and ran about 2000 rpm.. I let it run for about fifteen minutes and then put the hose back on and it stayed cranked- until i put it in gear. Repeated the process and reved engine a good bit and then put in gear and was able to run it around the lake. It ran great and when I pulled into the dock I turned it off and cranked it several times and it did fine. I have no idea why. I appreciate all of your help. I've had this boat since 1998 and have had very few problems until recently. I had to have the computer replaced two years ago.$$ It is Loping a little at idle- should I be concerned?
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DON W
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KENO
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Posted: April-28-2019 at 9:47pm |
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Well good that it's "fixed" hopefully it stays that way.
The idle lope seems to be one of those "no extra cost" options that comes with the GT40. It just pops up at some time in it's life for a lot of people. Do a CCF search for "loping idle" or just click on the link below and you'll have lots of reading link |
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gt40KS
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Posted: April-28-2019 at 9:47pm |
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Loping ... a familiar term when associated with the GT40. Loping or commonly referred to as rolling idle, unfortunately is one of those things about our engines that sooner or later will plague a lot of them. What causes the issue?? Well, that's the $2 question. We've identified probably a dozen different possible causes ranging from a faulty IAC to the PIP sensor. and sometimes it's even a combination. I spent quite a bit of time and replaced many parts chasing mine. Hope yours is quick and painless. Then again, it could be nothing and go away by itself.
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JCCI
1995 Ski Nautique GT40 |
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Don W wrote: