Coolant gauge issue
 

Hello all, as always, thanks for any input. It really helps alot to get advice from fellow Z owners when fixing my car.

To make a long story short, I had a gas gauge problem. After figuring out my fuel pump housing was broken in half, I decided to jerry rig something up until CJM makes a billet top one.(pictured) It works great, and all the weight is not hanging on the electrical wires which is really all i wanted to fix( temporary). I had to make the housing shorter in order to fir in the tank.

Now im having issues, I have a fuel sending unit high input and fuel temp sensor high input engine codes. Im thinking it has something to do with my jerry rig. (this issue isnt my biggest concern as of now, ill wait to see if a properly made one fixes that issue) but any input would be appreciated on this matter as well.

The main problem, my coolant gauge is reading low constantly. The gauge worked fine until I did my jerry rig job on the fuel pump hosuing, but how does have anything to do with coolant? I'm going to ensure the theromostat is working properly after work today. Heres the weird part, when im driving the car, it reads 100% as low as possible, but when the engine is off, and just the electricty is on (engine not running) the gauge works fine.

Any help please :)

That's pretty good thinking. One of the first questions to ask when trouble-shooting is "was anything changed right before it happened?".

Just guessing here but, due to the timing, I'd be willing to bet 0.50 USD that the problems are related. If you can read electrical drawings, download the FSM and see if you can spot wires, harness, connectors, &c that the two circuits have in common.


Edit: Electric fuel pumps, especially those that are mounted internally, are not where one wants to jerry-rig or cut corners. Same goes for brakes and other "mission critical" or safety hazards.

Edit #2: It's possible that the fuel sensors and the coolant temp sensor have the same signal voltage source and a partial short in your jerry-rigging is pulling that source down. See the FSM to check.

:)
 

Thanks for your advice south ark. I have an update that may help trouble shoot the problem as well. When driving the car it stays on the lowest dot, but at idle it will heat up to normal operating temp. Once at that temp my ac stops working.. I'm thinking its a stuck thermostat and I'll check your suggestions as well.
The gas gauge has always been messed up, but it got stuck at half a tank instead of not reading anything

I would suggest waiting to check the thermostat - purging the system after everything is back together can be a royal PITA.

It still sounds a lot like a wiring problem to me. And, IMNSHO, checking wiring is a lot easier than purging a cooling system.

The AC thing has me scratching my head. I'd check the fuel sensors wiring (and then thermostat, if needed*) and see if fixing that problem doesn't magically fix the AC.

Edit: Actually, I'd check the temp sensor and wiring before checking the 'stat. YMMV

Sounds to me like you shorted the 5v ref. That's ref voltage is in parallel with basically all sensors. So you screw it up and all sensors that use it will be innacurate. Also some ac system now days are smart and will not run if they suspect t-stat issues (which is gained from temp sensor reading which also uses the 5v ref).

Even if you t-stat is stuck open it should still be able to get hot (it is after all summer). Leave it idling for a few hours in the sun if needed and then feel upper and lower hoses and check the gauge. If hoses hot and gauge cold well then you have an electrical issue.

coolant
 

Alright guys I went home and started tinkering with the car. I opened the radiator cap (cold start) and used a thermometer to get and idea of how hot/cold the coolant is. The thermostat opens at 170 degrees(according to FSM), and at about 165-175 I noticed the coolant level started to rise in the radiator cap. At idle the temperature maxed out around 190 degrees even with me holding the rpm at 2000 for like 2-3 minutes. So it appears the thermo is alright and the coolant inst over-cooling/heating and the fans work fine even with the A/C off. So it appears everything is in working order, however I thought the coolant temp sensor controlled the opening and closing of the thermostat but it appears it does it on its own without any input from sensors.
"CO-22
< REMOVAL AND INSTALLATION >
WATER INLET AND THERMOSTAT ASSEMBLY
Inspection
INFOID:0000000004491076
INSPECTION AFTER REMOVAL
1. Check valve seating condition at ordinary room temperatures. It should seat tightly.
2. Check valve operation.
• If the malfunctioning condition, when valve seating at ordinary
room temperature, or measured values are out of the standard,replace water inlet and thermostat assembly." from FSM.

There is a picture beside it that shows a person attaching a string to the thermostat and dropping it in boiling water in order to test its operation, and there were no electrical wires connected to the thermo so it must operate without any input from sensors.

So that would explain why the everything is working besides the gauge. Like you guys suggested it appears to be that temp sensor. (if i can find the damn thing)

As for the 5v ref, all my other gauges are working properly(oil voltage time etc). Could a short in the 5v still cause this?

Yes, the thermostat is a purely mechanical device with no electrical connections.

Any sensors/gauges that do not use the 5V ref would not be affected (oil pressure is a switch, voltage is referenced to ground, and the clock in the triple-gauge is a 12V stand-alone unit with internal time base). FSM will tell you which circuits use the 5V ref, but you may have to dig for it.


In any case, I still think the place to start looking is the fuel sensors wiring. Most of the symptoms you report point to that and nothing points away from it.

It appears that you don't know a lot about cars or electricity. See if you can find a friend/relative/acquaintance that can read a wiring diagram and operate a pocket VOM. He/she can probably identify the problem in just a few minutes. Without being able to lay hands on your car, it's difficult to trouble-shoot and we are just making (semi-)educated guesses.

Thanks
 

Yes I hate working with electrical stuff, I've never been great at it honestly. But I always try and figure it out. When I first got the Z I knew nothing, but I've never paid a shop to do any work for me and I've learned so much from it. It's frustrating trying to fix a issue but I love the feeling once I do figure it out. Anyways back to the point lol, I'll be doing the 5v test some time tomorrow. I just don't understand how I could've shorted anything on the fuel pump housing, I just stuck a bolt through the existing wholes to keep the bottom bucket and top part together. Never even touched the wires. I'll look up the circuit diagram to see what the 2 have in common.

Again, thanks for the help bud. :)

I am glad to hear that you are learning how to work on cars. It will save you a lot of money in the future and may get you out of a bind when the car goes into limp mode some moonless night on a deserted road. And it can be very satisfying. But sometimes you have to get some help or farm the job out to someone else. I was an electrician and instrument tech for a couple of decades and I would still suspect the wiring if I had done the job - feces occurs. Find somebody that knows a little bit about electricity/electronics and get them to help you trouble-shoot. Figuring out what is wrong should be pretty easy (fixing it may not turn out that way, but that's another thread).

I am not 100% certain that the problem is not somewhere else but am pretty sure the problem is related to what you did. If not the external wiring, then the internal wiring of the sensors. The timing is right and the symptoms seem to point in that direction. Maybe you shorted something out in the ECM or there is a wiring problem in the engine compartment.

And NEVER work on fuel systems, brakes, traction control, &c unless you know what you are doing. If you have any doubts, find someone that knows what they are doing to help.

PS: Disconnect the battery before doing any electrical work. You can find the procedure in FSM or many threads on this site. The same threads will usually tell you how to reset windows and other quirks that pop up when the power is killed.

:)
 

Hahaha hopefully that doesn't happen 😂. I'll double check the wiring for shorts and if I can't figure it out I'll at least pay Nissan the 100$ to diagnose the issue.

Thanks south ark! As I said before I really do appreciate the input.

as a journeyman level drivability/electrical diag tech for the last 11 years, up until this last year when finally leaving automotive to actually make a living so I can afford my own z and not fix everyone else, or in my case everyone else's corvette. Loved the work (once I got to a specialized role, no heavy duty, didn't have to do anymore engine R&R or trans etc,) hated the pay and the BS warranty times etc etc.. but I am fairly certain (I'm not there testing so I cant say 100% without a doubt) that you goofed on your wiring. Maybe you screwed up and wired something into the fuel tank pressure sensor? the multiple high voltage codes you have would re enforce my believe that somehow you have screwed up the 5v ref. and the timing of it too.

There you go, Wilson. You have two "electrical guys", one with general experience and one that specialized in automotive (it would be foolish not to listen to him), telling you the same thing. We can't be certain the wiring is the problem, but, it's the first place we would check.

I'll post back with my results !

Okay I'll be reading through the FSM today to gather as much info as I can and see if the two circuits have any common route. Both my codes are high input codes. I honestly think I know what is causing those codes though. When I depressurized the fuel lines I didn't unplug the fuse. I just unplugged the fuel pump and cranked the car. Yeah obviously that will throw a Cel and I knew that from the beggining, I just figured it doesn't matter and it'll be fine once I clear the codes. I bet that has something to do with the short or wiring issue. So basically, to test for the 5v reference I can use my multimeter at certain sensors and test for the 5v power supply?