Car only works when jumpstart?

[Fabunoz]

Hello I recently bought a nsx for very cheap and am running into issues.the car doesn’t start up unless I jumpstart it?went to autozone and battery/alternator are fine.battery shows 12.6 volts when turned off.car dash very dim and won’t crank but once I put jumper cables dash lights up and starts.I can drive car but once shut off will need jumpstart again.wondering what could be causing this issue?could it be fuel pump?fuel guage has been stuck on full since I bought it.or maybe a parasitic draw from a crappy job on aftermarket radio (doesn’t even work and radio unit moves on its own when car turned on)?please any help is appreciated and where to start thanks!!!

 

[drew]

Get new battery clamps ($10 at Walmart) and clean connections at the starter.

May also need a new ignition switch (electrical side, not key lock side). You can also clean and lube the existing switch too.

Fuel gauge pegged on F(ull) will need a VOM to diagnose. That would be quite a parts cannon to blindly fire away.

A cheap NSX is going to be very expensive unless you personally get down and dirty with it.

 

[Old Guy]

If you are jumpstarting from the correct jump start terminal in the engine compartment or you have strong jaws on your jump start cables that do a good job of squeezing the battery posts @drew probably has the answer. OEM Honda battery cable post clamps are notorious for being easily damaged by over tightening. This stretches and can tear the clamp metal with the result that the clamp no longer grips the battery post tightly. After I got my car, I discovered that with the bolts on the post clamp tightened to the max I could still twist the clamp loose off the post with my hands. That equals a bad electrical connection. Give your clamps a twist with your hand. If they move you have your answer.

Fuel gauge is a completely separate problem. Since you are a new owner who purchased an NSX that is obviously not pristine, find the button on the red banner at the top of the NSX Prime web page called NSX Prime Library. Open it and after prowling around you will find a link to a .pdf of the 1991 service manual. Download and start reading. In the electrical section of the service manual you will find details on the fuel gauge and how to diagnose where the problem might be.

 

[asylum]

12.6v does not mean it is good. Try a new battery.

 

[Old Guy]

A 12.6 volt open circuit voltage on a lead acid battery is probably just fine. For a conventional flooded lead acid battery typical guidelines suggest 90% state of charge (SOC) = 12.53 volts and 100% SOC = 12.64 volts. AGM batteries run a little higher and 12.6 volts would indicate a little over 80% SOC. The problem with these types of measurements is it depends on the quality of the voltmeter. A precision error of+/- 0.2 volts gives you a huge variation in SOC.

Battery voltage is an indicator of SOC. It is not necessarily an indicator of battery health. An AGM battery could be down to 12 volts which indicates a 50% SOC; but, could be successfully recharged to 100% SOC. The time to replace decision should be based upon a load test combined with battery voltage after a full charge cycle. If the battery post connections are in good conditions measuring the battery voltage while the starter motor is cranking is a good proxy for a battery load test.

 

[natcc99]

My car wasn't as bad as yours, but I had issues where I had to jump start my car on many occasions even after replacing the battery.

As mentioned in the above post, I ended replacing the terminals. My original ones looked okay, they were aged, but upon closer inspection, I noticed some corrosion was inside the cable.

After the terminals replaced and the corroded cable ends were removed, the car starts up without issues.

With that said, I suggest lifting up the car and remove the tray that holds the battery. Then, you will be able to have a good 360deg view of the terminals and cables.

 

[Old Guy]

This is what a dead NSX battery post cable clamp looks like. This shows that the clamping bolt was tightened to the max and I was able to yank it off the battery post without loosening the bolt.



The area circled in red shows where the clamps starts to stretch and ultimately the metal starts to tear. The metal appears to be copper with a tinned coating and copper is quite soft and stretchable.



If you do not over torque the bolts on installation the clamps will last just fine. I had a 2003 Honda Pilot with exactly the same clamps and they were just fine after 17 years. I do admit that the NSX battery is not exactly the easiest thing to work on which may make overtightening of the clamps easy to do.

If the clamps are not too far gone battery post shims may fix the problem. Installing a new battery ground cable is relatively easy and cheap. Installing a new positive cable is neither easy or cheap. You will definitely want to clean up and reterminate the positive cable.

 

[drew]

Nice write up @Old Guy

I can see "original battery clamps" being a concours checkbox in the future.

 

[Fabunoz]

Nice write up @Old Guy

I can see "original battery clamps" being a concours checkbox in the future.

Thank you old guy,drew,and other members for the help appreciate you guys .turns out was just messed up terminals swapped them out for 10 dollars ones from Autozone and starts up strong .will drive around and make sure it starts every time

 

[Old Guy]

Those would definitely be non OEM battery post clamps so somebody has been through this dance before you. Those are looking pretty bad. You need to get an AGM battery which are non venting and do not have corrosion issues (at least due to battery fumes).