What would cause a car to not start when it's humid ?

[Cd]

I just tried out the multimeter with the settings I had above and it shows 12 .1 which I assume is volts.
Not running of course since its sprinkling out here now.
It also shows 12.1 at the fuse box ( both wires coming from fuse box )


EDIT. I was doing it wrong .12.1 amps are now showing at the starter .

[Cd]

I am getting current at the pump.
Reading is 11.88 and the picture in the chiltons guide shows 12.25 .

When I try a reading with the main relay installed , versus jumped , it goes to 0.10 for s split second then nothing.

I have the probes inserted into the fuel pump power supply connector.

[user removed]

12.1 at the battery compared to my Maxima that has not moved in 24 hours reading 12.45. The chilton manual reading of 12.25 is higher than your battery voltage. I don't think you are seeing any problem though as the volatge should be sufficient down to less than 10. Possibly older battery?

You are not reading any voltage with the relay installed versus bypassed? If so then the car should not start with the relay installed but start with it bypassed? That would be either the relay or the power source to swtch the relay.

The relay should have two different size wires, possibly a total of 4 wires (maybe more if it is multifunction). Check the voltage across the smaller wires, then across the larger wires. A relay is just a magnetic coil that works a higher power connection through a lower power connection. You may be able to take the cover off of the relay and actuate it manually. The relay should have power to the high tension circuit constantly. When actuated it should have basically the same current going in and coming out of the high tension part. The low tension part will have a voltage drop, not sure how much but the resistiance of the coil that moves the contacts together requires some power.

The relay is probably energized by the ignition switch. Anyway, if I understand your post it seems like the relay is not doing the job. What you need to do is check to make sure the relay is getting good voltage, enough to make it work properly. If you find it has good voltage then the relay is your prime suspect. You can even install a bypass and a switch to power the pump in an emergency, as long as you use the same circuit you have fuse protection. If you make a completely new connection then use an in line fuse for protection. If you have replaced the realy and nothing changed, the odds are you have an issue with the power getting to the relay to activate the coil inside of the relay.

regards
Mech

[user removed]

The purpose of a relay is to allow a low power circuit to engage a high power circuit. A great example is the starter relay which connects the battery to the starter motor. The starter can draw as much as 200 + amps of power, which would melt your ignition switch if that much power went through the normal ignition swtich. Basically the coil creates a magnetic field wich draws the points together to create the higher power circuit.

regards
Mech

[Cd]

I'm in the process of reading your posts right now, and i'll edit this if i miss something that is mentioned above, but i just wanted to mention that i did a very thorough testing of the original main relay on the car and it checks out fine. All terminals were checked for continuity. I bought a brand new main relay and it isn't getting voltage to the pump either, but i'd bet it will check out fine.

Regarding the battery voltage, it has been run down a bit with the car not starting.

[Cd]

[QUOTE=Old Mechanic;272979]

You are not reading any voltage with the relay installed versus bypassed?


Correct.

When i install the probes in the plug going to the fuel pump ( the red wire going to the yellow wire and the black wire to the black ) Nothing happens when i have the main relay installed, but i get juice when i have the main relay off and the circuit tripped.

I'll try again tomorrow just in case i did something stupid.

If so then the car should not start with the relay installed but start with it bypassed?

The car does not start with the main relay off ( circuit tripped ) and the fuel pump running. I have tried this several times.

That would be either the relay or the power source to swtch the relay.

With the testing that i just did that showed that the main relay is fine, im guessing it's the power source to the relay.


The relay is probably energized by the ignition switch.

So it indeed could be the ignition switch causing my problems. I used to have a wad of keys hanging on my ignition key and a guy warned me that this might be what the problem stemmed from, since it stresses the inside of the locking mechanism.

Anyway, if I understand your post it seems like the relay is not doing the job. What you need to do is check to make sure the relay is getting good voltage, enough to make it work properly. If you find it has good voltage then the relay is your prime suspect. You can even install a bypass and a switch to power the pump in an emergency, as long as you use the same circuit you have fuse protection. If you make a completely new connection then use an in line fuse for protection. If you have replaced the realy and nothing changed, the odds are you have an issue with the power getting to the relay to activate the coil inside of the relay.


regards
Mech
.

[user removed]

Basically that means you are not providing the power to energize the relay. This can be the power supply or the ground circuit to the relay. Use your volt meter to check the power supply and to check the ground circuit. Do this with the relay connected.

From the battery positive terminal to the positive terminal on the relay. If you read any significant voltage there is resistance in the circuit that should not be there. If you read no voltage it may indicate a ground problem or the circuit is OK. Remember voltage drop indicates the proper battery voltage is not getting to the point where it can activate the relay.

On the negative side connect to the negative battery terminal and to the negative side of the relay (on the part that is powered by the ignition switch, not the fuel pump power supply. Use a jumper wire with alligator clips if you can not reach both points without one. I usually use a jumper wire to the negative so it can not short out.

This is where a bad ground can be your issue, or a bad connection (probably a corroded plug in the harness). By going from the battery to the ground connection on the relay, your are checking the whole circuit. If either test shows a voltage drop, then you have to go to different portions of the circuit and isolate the bad connection.

The ignition switch would be my focus point in isolating the problem (assuming you find the place where the voltage drops occurs). The ignition switch is part of power supply.
The ground circuit is usually a black wire (but not always, best to get a diagram of the circuit-found on the internet) and print out the part you need.

Sorry if I missed any spelling-spell check is not working tonight.

regards
Mech

[Cd]

What a frekin headache !

I still don't get how that the slightest bit of humidity can kill a car when no moisture gets into the car at all.

( And if there is a problem...why does it only happen when its humid ??? )

Thanks for all the help.

[user removed]

"Circuit tripped" means you have made a connection that works without the relay in the circuit and the fuel pump works?

That can cure the problem temporarily but remember the fuel pump will run continuously, even with the key out of the ignition switch. Don.t leave it that way or it will kill your battery, but it should make the car drivable.

I have seen one Mercedes with 4 ignition switches replaced. The woman owned 100 vending machines and kept all of the keys hanging from the ignition switch. Once she separated all the vending machine keys from the key she used to start the car her problems ended.

regards
Mech

[user removed]

Originally Posted by Cd

What a frekin headache !

I still don't get how that the slightest bit of humidity can kill a car when no moisture gets into the car at all.

( And if there is a problem...why does it only happen when its humid ??? )

Thanks for all the help.

Oxidation in a connection is caused by moisture. As the connection gets worse failure will occur when the moisture content is at it's highest. The oxidation works like a sponge absorbing moisture which makes the resistance higher since pure water is an insulator.

While it is a headache, once you get the process down pat, you will never be in a position of allowing a similar issue to cause nearly the same amount of frustration. I have had some real nightmares, and it included a car my friend had rebuilt (collision damage) that would not start cold. After two dealerships wasted hundreds of dollars with throwing parts at the car in hopes of fixing it, he was going to junk it for parts, after selling it for $5000 and taking it back and refunding the customers money. He had a junked car out back that had the part needed to fix it sitting there. It just took me 14 hours to figure out which part it was, and 5 minutes to replace it.

regards
Mech