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Old 04-09-2012, 10:51 AM
turbozinke turbozinke is offline
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Temp sending unit voltage

My boat is not running well 2000 Mastercraft 205V with a 2006 indmar engine. I pulled of the wire to the temp sending unit from the ECM and it only has 5V. Same with the oil pressure wire. I also only have 5V at the gauges (oil pressure, temperature, and fuel level don't work) How many volts should it have? I assume 12V

Thanks
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Old 04-09-2012, 11:16 AM
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JimN JimN is offline
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Originally Posted by turbozinke View Post
My boat is not running well 2000 Mastercraft 205V with a 2006 indmar engine. I pulled of the wire to the temp sending unit from the ECM and it only has 5V. Same with the oil pressure wire. I also only have 5V at the gauges (oil pressure, temperature, and fuel level don't work) How many volts should it have? I assume 12V

Thanks
How many wires to the temperature sensor- one, or two? If it only has one, you need to check the sensor with one yellow and one black wire if you want the one that reports to the ECM. However, the temperature sender only sees 5V from the ECM- it's the return voltage seen by the ECM that matters, from all sensors other than the knock sensor- (ECT, TPS, MAP) and the knock sensor basically acts like a microphone, picking up vibration from knock in specific frequencies and sending the signal to the ECM. The oil pressure sender shows resistance to ground and is for the gauge only.

Describe "not running well". Does it start normally? Does it idle smoothly? Does it stumble upon soft, or hard acceleration? (need to be specific) Does it not go above a certain RPM? Does it run smoothly, or rough, and at what RPM? Does it start normally, but not when hot?
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Old 04-09-2012, 11:49 AM
turbozinke turbozinke is offline
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THanks Jim!

Here's a pic of the wires. Two of them go to the temp sensor and the other one with a boot on it doesn't go anywhere? When I say running badly I mean that it doesn't idle and when you give it the gas you have to ease it on very lightly or it will die. When it gets revved up it runs fine. I had about 1500lb in the boat ran for 2.6 hours and used 25 gallons of gas, and top speed was 38mph. Seems a little excessive on the fuel consumption to me. Here's a pic of the wires running to the temp sensor
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Old 04-09-2012, 12:39 PM
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That's the right harness- does the exhaust smell strongly of gasoline? If so, check for codes. If you have a cheap code scanner, you can us it, even if it's only the metal piece with two prongs on the end. If you don't see any codes, check the fuel pressure. If the pressure isn't adequate, you'll starve the engine at higher RPM and the fuel won't atomize properly at any speed, so idle will be crappy, too.

You need to realize that a hull made for going on-plane will be very inefficient when it's loaded down with ballast. A hull is like a wing, inverted. If you add weight, you'll need to go faster just to go on-plane and it will require more fuel to go ANY speed. Weight adds drag and a planing hull is only efficient when the boat is on-plane. Also, look at the boat's weight capacity and make sure you don't exceed it. Where the ballast is located is probably as important as the actual weight. Optimize location and your economy will improve a bit, but don't expect it to not use a bunch of gas when it's loaded.
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Old 04-09-2012, 03:05 PM
turbozinke turbozinke is offline
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I don't think it is starved for fuel because it runs fine once it's revved up. I'm thinking that the ecm doesn't know what the true engine temp is and therefore the fuel mapping is incorrect. Is there not a specific amount of voltage that runs to the temp sensor? I read on another post that his is outputting 9V at 75 degrees at the gauge, but if i'm only inputting 5V then I can't output more that 5V. I only have 5.3-5.6 volts (constantly fluctuating) at the gauge. I put a cigarette lighter on the sensor and the voltage did not change at the gauge, just stayed 5.3-5.6
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Old 04-09-2012, 04:04 PM
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Originally Posted by turbozinke View Post
I don't think it is starved for fuel because it runs fine once it's revved up. I'm thinking that the ecm doesn't know what the true engine temp is and therefore the fuel mapping is incorrect. Is there not a specific amount of voltage that runs to the temp sensor? I read on another post that his is outputting 9V at 75 degrees at the gauge, but if i'm only inputting 5V then I can't output more that 5V. I only have 5.3-5.6 volts (constantly fluctuating) at the gauge. I put a cigarette lighter on the sensor and the voltage did not change at the gauge, just stayed 5.3-5.6
You can't know if it's not starving unless you check the fuel pressure and revving it without a load means. nothing. The control voltage to the senders is 5VDC, not 12VDC. Also, a lighter isn't going to work because it's not a sender- all it does is get hot when it's connected to DC voltage.

If you want to find out whether the ECM is seeing the correct resistance, check for codes or connect it to a diagnostic computer. Anything else is just guessing
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Old 04-09-2012, 06:24 PM
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While I don't have anything to add on the electronics part of this thread, 9.6gph in a 205V hull isn't right, with any amount of ballast at very, very max you should run 7 (granted, 2.6 hours is a pretty small sample size)
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Old 04-10-2012, 12:35 AM
turbozinke turbozinke is offline
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Thanks Jim. The boat ran fine once it was revved up even with a full load (10people) it was just hard to get it off of idle. I'll try to get a diagnostic computer on it tomorrow. I meant that I took the sensor out of the engine and put a lighter on it to heat it up just like the engine would, but I didn't get a change in voltage at the gauge. Do you know what the voltage is supposed to be at the gauge at 70 degrees for instance?
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Old 04-10-2012, 12:49 AM
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Originally Posted by turbozinke View Post
Thanks Jim. The boat ran fine once it was revved up even with a full load (10people) it was just hard to get it off of idle. I'll try to get a diagnostic computer on it tomorrow. I meant that I took the sensor out of the engine and put a lighter on it to heat it up just like the engine would, but I didn't get a change in voltage at the gauge. Do you know what the voltage is supposed to be at the gauge at 70 degrees for instance?
Yeah, I figured that out a little while ago. DOH!

Measure the resistance- that's what causes the return voltage to change. It should be above 10K Ohms- do a search here for this. A resistance chart ws posted. If you can't find that, google search for it.
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Old 04-11-2012, 10:33 AM
turbozinke turbozinke is offline
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I found the resistance chart and I think my sensor is good. I'm going to hook it up to a diagnostic scanner. Same as a car right? I found a plug by the ecm, but it wasn't the same shape as a car. Do I need a special adapter or am I looking at the wrong plug?
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