Coolant gauge issue

Wilson2608

On my way to work this morning both the fuel gauge and coolant temp gauge started working fine. So weird..

Im sure the gas gauge is still off due to what I had to do in order to get the fuel pump housing top and bottom to hook up right, but at least its reading.

Only issue now is I still have the CEL and the car tends to idle a little high. (1100 rpm) I think thats due to the fuel temp sesnor code.

Like I said before ill check the fuel temp sesnor wiring for shorts and post back!

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Stillen G3, z1 Intake Manifold, Stillen Headers, Z1 HFC's, Stillen Catback. 330whp 267 ft- lbs tuned at Z1 motorsports.

SouthArk370Z

Please get some help before you kill some electrical component(s) or start a fire.

But, yes, a decent multimeter and tools to access the wiring/sensors should be all you need. I'm guessing that the problem will be pretty obvious with a visual inspection.

I haven't looked at the wiring diagrams but the 5V reference that Jhill refers to may be internal to the ECM. If so, you will need to check it at the ECM (if possible). If the outputs from the sensors are out of spec (I'm betting that will be the case), the reference is probably not the problem. The 5V ref is just a possibility. I think (and it seems that JHill agrees) that the wiring/sensors is the most likely culprit.

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Jhill

You're pretty safe to check it as the ECM typically have their own resistor in series before the output and that is how they determine a dead short or open as the sensors operating is typically .7-4.5 so if it sees 0 or 5 it know there is an open or short. On sensors that have a sig return it's a little different and if you screw the ref up well like the saying goes garbage in garbage out. Before you even venture in this journey I would highly recommend you pull those codes and get the wiring diagrams that go with those systems. Without proper documentation you are just guessing.

SouthArk370Z

IF the person using the meter knows what they are doing. Even if the ECM is bullet-proof, I'd hate to muck around, short some wires, and put 12V where it doesn't belong (like inside the gas tank). If it were you doing it, I wouldn't be too concerned - I'm not sure OP has acquired the skills to do the job safely.

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Steering Lock Links - Search The370Z Bookmarklet - FSM @ NICOclub
Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

Jhill

Too true. I've seen so called master techs do **** that I still shake my head at. It can be scary out there.

Wilson2608

Both of you are obviously very knowledable about cars/ electrical work, and i basically know little to none about this kind of stuff. But im adament about doing the work myself for the purpose of becoming more educated. When my engine blew in my 300zx I took it upon myself to do a motor swap. It took me like 2-3 months, but eventually i got it perfect with no issues at all. And now i could do it in half that time, and thats the reason I want to fix this issue too. I will follow the procesdure in the FSM so I don't mess anything up and i'll let you guys know!

Thanks so much for help mates

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Stillen G3, z1 Intake Manifold, Stillen Headers, Z1 HFC's, Stillen Catback. 330whp 267 ft- lbs tuned at Z1 motorsports.

Jhill

Dumb ? What's this FSM everyone is referring to? Are you guys getting access to the wiring diagrams?

SouthArk370Z

Factory Service Manual. See link in my sig. Merry Christmas. The wire color codes are not always intuitive.

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Steering Lock Links - Search The370Z Bookmarklet - FSM @ NICOclub
Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

Jhill

Awesome, I can't download it on my phone but I will be once I get to my PC. My biggest worry about buying my z was getting future info if I have to work on it since I was an an ex tech I don't trust a lot of techs out there as there are a ton of bad ones and not being in the field any longer I don't have access to all data. So now I have my source. Thanks.

SouthArk370Z

You will probably like this, too: Ecm/bcm wiring diagram with pics (tech sheet)

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Steering Lock Links - Search The370Z Bookmarklet - FSM @ NICOclub
Mankind has progressed past the need for war but we haven't evolved that far. - NachoMahma

Jhill

So any updates yet? Curious as to what you find.

Wilson2608

I'm on vacation at the moment but it's keeping me up at night thinking about it hahaha. I will update sometime this weekend when I return.

__________________
Stillen G3, z1 Intake Manifold, Stillen Headers, Z1 HFC's, Stillen Catback. 330whp 267 ft- lbs tuned at Z1 motorsports.

Wilson2608

Alright so here's a long overdue update. I got back and my issue returned with both my coolant and fuel gauge reading low at all times. I took out the fuel pump and checked for shorts in the wires and there were none. I used my multimeter and unplugged the resistors to get a voltage reading to the sensors. (Fuel level sensor and fuel temp). I got a full 12v to the fuel sending unit and a 5v to the fuel temp sensor. So both seem to be getting their full amount of power. I did a resistance test on both gauges and the fuel level sensor failed. It's weird because I tested it right before I installed it the first time and it checked out okay. Funny how things break like that, I may of been to rough installing it idk. Anyways when I tested the resistance on the fuel temp I got 1.5, 1.6ohms. I need to dig in the service manual to check its specifications.

As for the coolant sensor I haven't really looked at it too much, I'm not throwing a code for it but I know it's not reading right. With my diagnostics tool plugged in it reads 130 degrees, but with my hand held thermometer it reads 180ish. So I know somethings up. When I turn the car off and just turn on the electricity it reads fine.

I'll update you when I find out more. HAPPY FOURTH OF JULY!!

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Stillen G3, z1 Intake Manifold, Stillen Headers, Z1 HFC's, Stillen Catback. 330whp 267 ft- lbs tuned at Z1 motorsports.

Jhill

Fuel temp sensor? I'm not sure what your referring to but I don't believe these have a fuel temp sensor, again not a Nissan tech but that would be pretty odd to have. Are you sure your not looking at a fuel tank pressure sensor? Also if your checking to see if something is pulling down the 5v ref then you need to do so plugged in otherwise if something was pulling it down and you disconnect to check 5v at the terminal you have just fixed your issue without even realizing it only to have the same issue once plugged back in. Looks like I am going to have to go through that manual when I get home and get a better idea what you are looking at.

Just did some googling and you are correct it does have a fuel temp sensor. That's actually kind of neat, never really paid much attention to that before.

Wilson2608

Yes I checked it while plugged in, I actually took the whole assembley out and tested it from there. I think I know what the issue is though, after switching the RIGHT resistance setting on my multimeter (noob mistake) i realized that my fuel level sensor is not broken. Once i pulled it all out i played with the sensor and raised it to the full position as i observed the gas gauge, it worked fine and the gas gauge read 3/4 a tank. (had a half tank of gas and we have 2 sensors so the avg was 3/4 a tank) I think what has caused my problems is my jerry rig. I believe its too short and the temp sesnor and fuel level sensor isnt even touching any gas in the tank when below like half a tank. I ordered a new one from courtesy Nissan parts for 350$ (opposed to the local dealships 450) so i guess i cant complain. I really wanted the billet topped one CJM is making but I can't wait any longer I need a legit non jerry rigged product in my car. I will keep you updated, the new part will be going in Thursday.

Again thanks to both of you for the input!

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Stillen G3, z1 Intake Manifold, Stillen Headers, Z1 HFC's, Stillen Catback. 330whp 267 ft- lbs tuned at Z1 motorsports.