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Cd 12-01-2011 09:34 PM

What would cause a car to not start when it's humid ?
OK guys, I have a puzzling problem with my '93 Civic DX :
Like clockwork, my car will fail to get electricity to the fuel pump when there is even the slightest bit of humidity out.
If there is even a single dark cloud on the horizon, the car will fail to start.

If i turn the key to the ACC position ( the second click of the key before the third click that starts the car ) the fuel pump does not come on. When i remove the main relay and trip it, the fuel pump comes on fine.

The main relay is a brand new unit.

I have replaced the fuel pump with a brand new pump

The distributor might seem to be the problem, since the car has very weak spark, but this doesn't explain the way the fuel pump acts by not coming on when i turn the key.

I am replacing the distributor this weekend regardless.

The only other thing i can think of would be a short in the ignition switch wiring. I posted about this problem on a honda forum about a week ago, but only got one response, so im posting here too just for the hell of it.

I was told that the ignition switch could be tested by checking the main dash lights that come one as you start the car.
They all check out fine, so i'm puzzled.

user removed 12-01-2011 10:42 PM

Dirty bad connections on the battery cables. Bad grounds. Bad connection in the fuse box. Sometimes what you are facing is one of the most difficult electrical troubleshooting problems possible. Intermittent loss of a connection.

In extreme cases I have run a test light circuit to the fuel pump power lead. If you have no light when the pump should have power you know it is in the power circuit to the pump. If you have a light but no pump you know it's in the ground circuit.

Once you establish which circuit is failing you can move the test light connection back alone the power circuit until you lose your power. This is if the problem is in the power circuit to the pump.

If it's the ground circuit then you need to use a DVOM to test for a voltage drop along that circuit.

Your bad connection will be where you lose the test light in the power circuit, or where you see a significant drop in voltage in the ground circuit.

Most common problem I have seen in Honda's is the ground wire from the engine to the chassis is either missing or has a bad connection, corrosion at either end. Could also be a bad ground at the fuse block. Use the DVOM (digital volt ohm meter) to check from the battery to the various places, like engine, body dash, steering column, etc.

Also pay close attention to the ignition switch. Not sure about Honda's but Nissan's were notorious for bad electrical parts of the ignition switch. So bad I can almost remember the Nissan part number, even though haven't worked on them in over 10 years.

I think it was a 48750 E7705 for the Z cars.


Diesel_Dave 12-02-2011 09:25 AM

My dad had starting problems on his Chevy pickup when it was humid outside. He'd take off the distributer and clean off the points and it would start. Eventually that didn't work anymore. Turns out he had a cracked coil. Most of the time it was fine, or at least good enough so that clean points would make up for it.

Cd 12-02-2011 12:38 PM

Thanks guys.
I suspect a short in the wiring in the steering column, just because problems always seem to appear in the hardest possible place to get to eh ?

I'm going to change the entire distributor this weekend, as well as the battery cables and grounds.

user removed 12-02-2011 04:31 PM


Originally Posted by Cd (Post 272769)
Thanks guys.
I suspect a short in the wiring in the steering column, just because problems always seem to appear in the hardest possible place to get to eh ?

I'm going to change the entire distributor this weekend, as well as the battery cables and grounds.

If you KNOW those parts are bad, or have reached the limit of their life expectancy then replacement is not a costly hit and miss guessing game.
Part of being a professional in business is to treat the customers money the same way you would treat your own.

A cracked distributor cap could be your problem, but before I replaced the distributor, it would have to have excess play in the shaft, or a bad ignition module, or other issues that made replacement the best solution. Bad ignition modules are usually heat related, but if a bad cap is the issue you should be able to see evidence of moisture inside the distributor.

Intermittent problems are seldom solved by throwing parts (read money) at the problem. Testing circuits for voltage drops starts at the battery terminals. Hook one end to the negative terminal (of your DVOM) and measure the voltage drop to parts of the engine and body of the car. If you see more than .25 volt (with systems operating) then you are on the track of the problem. Moisture can be added to the equation by spraying a mist of water on the car or engine with a hose, but don't drown it, just a light mist will do.

Lets say you have a bad fuel pump. If so you will show with a test light, which can be made out of two 20 pieces of wire, two alligator clips (preferably insulated) and a peanut light bulb. Hook the clips to the terminals on the fuel pump and if it does not come on and you have a strong light, then you KNOW it's the pump or corroded connections at the pump.

I always had a very hard time when a customer accused me of a hit and miss repair with no regard to their cost. Proper diagnosis is not hard, usually just tedious. Wiring is a lot like plumbing and on older cars the diagnoses are fairly simple.

I had customers ask me why I replaced the water pump when I did the timing belts on a 84-89 300 ZX, especially when the water pump was not leaking. I told them if the water pump failed it would destroy the timing belt and possibly the engine. That was why we learned the hard way and replaced the cam seals, cranks seals, tensioner, and the timing belt as a part of the job. It was a systematic approach that gave them the best chance of not having to go into that system for the recommended 60k miles between replacements.
Seen to many bent-broken valves, holes in pistons, and pieces of piston skirts coming out in the oil drain pan.


Cd 12-02-2011 08:36 PM

Thanks again Mech, I really appreciate the advice.

I will try the testing that you suggest.

I changed the fuel pump because it seemed to show all of the symptoms of a dying fuel pump that i had read about. Same with the main relay.

I had previously changed my cap and rotor, as well as installed new wires, but i still have weak spark, so i thought "what the hell", i might as well replace the whole thing.
At least that would hopefully help with the weak spark issue that i am having.

It's been raining today, and there is moisture in the air.

Is it a bad idea to change the distributor if there is dampness in the air still ?

( If extremely mild humidity can kill a car dead, i thought it might be a good idea to ask before i change the part with dampness still in the air. )

user removed 12-02-2011 09:04 PM

Actually since your issues are dampness related it would be best to see if you can resolve the weak spark issue in the same conditions when it occurs. Just be careful you don't get ZAPPED! :eek:

What is your battery voltage reading both running and with the ignition off?

Engine to chassis ground could be the weak spark. Check for a voltage drop from the positive battery terminal (part on the battery itself) to the connection where the big cable meets the starter. The check for a voltage drop from the engine itself to the negative battery terminal.

Voltage drops of over .25 volt indicate there is additional resistance in the circuit that is not supposed to be there, Just take the leads and go to the parts and touch them with the meter set on volts (not ohms, it could fry your meter or blow the fuse). Think of a voltage drop as a plugged plumbing pipe and you have low water pressure. Starting at the battery, as long as it reads about 12.5 volts (not running) and 13.8 to 14.2 running. Then go to the first place the main battery cables go where there is a connection. The voltage should remain the same. If the voltage drops you have probably isolated your problem especially if it is more than .25 volt. Unintentional added resistance in the circuit reduces to power available to the electrically driven components. Low battery voltage can really make things go crazy, all kinds of stuff not working properly. The battery may be the problem, or the pathways electricity need to do the job could be the problem. It's usually at the points where things are connected to other things, especially in areas where corrosion is a problem.

Keep me posted and I will see if I can walk you through it. Believe me I have been there and done that, including buying cars that were partially submerged and fixing them so they could go another 10 years, but that topic could take pages.

I have had people get mad at me for not tackling these types of jobs, because there is no way you can estimate the unknown, just plug away and isolate the area where the problem is. You start at the battery and work outwards, fuse block, grounds. Remember the engine to chassis ground which is usually just a wire that runs from the valve cover to the radiator support. If you don't see one the put one on. The volt meter will show you it needs one if you just touch the engine and a bolt on the support that is plated. Scratch the bolt head to make sure you have a good connection. If you see a voltage reading from the negative battery terminal to the engine itself, you know there is not a good ground, add the ground (even a simple wire with two alligator clips, or just the bare wire ends under two bolts and eliminate the voltage reading it might fix the weak spark.

I'm not going anywhere and there are others here who know just as much, so you have the advantage of our common experience. When I was 16 it took me week to figure out plug wires could be bad, the second time it took about 5 minutes. Stupid graphite core wires!


Cd 12-02-2011 09:49 PM

Again and again thank you !
I'll try and do some testing this weekend unless its raining ( no garage )

Of course i will have new questions that pop up since i have a voltmeter, but have never done testing with it.
i'm not even sure how to conduct testing with it actually. ( I will do a quick review online to see how it is done.

I should add that my engine to chassis ground wire has been modified. I snapped the bolt that holds the valve cover on and so i have it attached to a something ( metal ) on the block itself and leading to the chassis.

user removed 12-02-2011 10:20 PM

That ground should be fine but it's easy to check it. With the car running one lead on the negative battery terminal the other on the engine metal, No voltage it is OK.


Cd 12-03-2011 09:56 AM

Mech, this is the DMM I will be using.
I lent it out and no longer have the manual.
I'm not making sense of all the settings on this thing. It is currently set to ' 20 ' on the ' DCV ' section ( just below the \' back light \' button .
The leads are plugged in to the \' V ? mA \' and \'COM \' outlets
( the black lead being plugged into the \' COM \' outlet of course.
Digital Multimeter Manual

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