Boats For Sale:
Check Engine Light, Part 2 |
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Mpost 
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Joined: July-05-2018 Location: Monticello, MN Status: Offline Points: 329 |
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 Topic: Check Engine Light, Part 2Posted: April-12-2021 at 1:30pm |
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I posted a new thread for my reply so as not to hijack this one any longer with GT40 info
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84 SN Sold 98 SN Lund Pro V 1975 Alumacraft
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11112 |
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Posted: April-11-2021 at 4:35pm |
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I don't know if the colors for the switch wiring changed over the years, but in the 310 page manual they say tan/black wires for both switches and in some other PCM diagrams they say green
Maybe you or Marty or Gary S or any other gt40 owner can check and post what colors yours are. I see them with 1 tan/black wire from the oil switch to the temp switch, then 2 wires from the temp switch. One to the ECM (tan/black) and the other to the dash light (green) Looking at old threads, both tan/black and green have been mentioned for those wires. Kenny O could post what color his switch wires are too for the later non gt40 engines with the dash light. I think I'm losing my last remaining marble cuz I don't remember.
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MrMcD
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Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3750 |
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Posted: April-11-2021 at 1:22pm |
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Great break down Ken, I think most people are confused because many engines only have One Temp Sender and One Oil Pressure sender so when they find one and it does not fix the engine they don't look for the second sender. Your break down with the wire colors is the perfect answer for the rookie or experienced person trying to find the source of the problem. Now for the hard part, did PCM change wire colors over the life of the GT40? I don't know that answer.
KennyO, my 95 had the same issue 5 years ago, new temp and oil pressure sending units fixed it. I changed both not wanting to visit the issue again. They are not expensive and take little time to change them out.
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11112 |
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Posted: April-11-2021 at 9:53am |
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This gets confusing every time it comes up, but the oil pressure switch and temperature switch that only feed the trouble light on the dash both have the same color green wire
You can disconnect both and the engine will run just fine with no "idiot light" warning for the driver. The oil pressure sending unit has a light blue wire and it feeds the gauge on the dash. The temperature sending unit has a tan wire and it feeds the temperature gauge on the dash. A gt40 since it's computer controlled also has an ECT (engine coolant temperature sensor) that is one of the handful of signals to the computer for engine control. It has 2 wires going to it and strictly feeds the computer. The manual says a green/orange and a gray/red wire. I think they're in a wire loom with a 2 prong connector to the sensor Should be on the opposite side of the intake from the temperature sending unit on your gt40.. The temp switch on the GT40 is right where you say it is Marty, and maybe Kenny's is in the same spot or it's on the manifold. He should be able to say where. I think the discussions get tough because of terminology like switch and sender (sending unit) getting mixed up |
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Mpost
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Joined: July-05-2018 Location: Monticello, MN Status: Offline Points: 329 |
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Posted: April-11-2021 at 8:36am |
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Sounds like you already found the temp switch.
Quote " The water temp send has a green wire and the oil press send has a blue wire. Why do you suppose I still had water temp indication when I disconnected the sending unit? " On my 98 GT40 the temp sender is on the top of the water ciculating pump. ??? |
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84 SN Sold 98 SN Lund Pro V 1975 Alumacraft
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KENO
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Posted: April-10-2021 at 6:15pm |
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The switch does nothing at all except turn on the check engine light.
You also have a temperature switch that does an equal amount of nothing except turn on the same light. It'll have a green wire and a tan/black wire and should be across the intake manifold from the temperature sender. So, I think you already know your problem is that the oil pressure switch is bad.
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KennyO
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Joined: October-19-2020 Location: Georgia Status: Offline Points: 31 |
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Posted: April-10-2021 at 4:55pm |
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Thanks for the quick reply KENO. Had to wait for the rain to stop to get back out to look at it.
I disconnected the oil and water temp sending units on the motor. The water temp send has a green wire and the oil press send has a blue wire. Just found what I guess is the oil press switch t-ed in to the fitting for the press sending unit and it has a green wire. Didn't see that that other day. So, next step is disconnecting the oil press switch? I should still have oil pressure indicating? Why do you suppose I still had water temp indication when I disconnected the sending unit? UPDATE: I disconnected the oil press switch and the Check Engine light is now out. And to answer my own earlier question, yes I did have oil pressure indicated. So help me out, what does the switch do but turn on the check engine light? Seems like it is just an idiot light.
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1999 Sport Nautique
1988 2001 (sold) |
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11112 |
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Posted: April-09-2021 at 6:16pm |
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Going back to your Part 1 thread, did you disconnect the sensors(sending units) or the switches?
If you're not sure, can you post a picture of your oil pressure sending unit which probably has a switch tee'd into it. What color wires did you disconnect for each?
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KennyO
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Joined: October-19-2020 Location: Georgia Status: Offline Points: 31 |
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Posted: April-09-2021 at 5:49pm |
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I have a 1999 Sport Nautique with a PCM 5.8 (not GT40) with a check engine light on. I have been told it is either the temp sensor or oil press sensor. I am indication good oil pressure and temp never gets above 170. Today I disconnected the temp sensor while at idle and no change in the indicated temp (light stayed on). Then I reconnected the temp sensor and disconnected the oil press sensor. Oil press stopped indicating and the light stayed on.
Sound like a bad temp sensor?
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1999 Sport Nautique
1988 2001 (sold) |
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