The car in question is a 1986 Ford Taurus which is the primary transport for my elder daughter (hereinafter referred to as Elder Ottlet, or EO), and the curious incident is that it refuses to start at night. During the day it’s as reliable as one can expect from a car its age; but at night—nothing. It cranks over fine but refuses to fire.
After several futile attempts to figure out what was going on, I had her take it to the mechanic who cares for my car. He was pretty skeptical, especially when it started right up the late afternoon. But the next evening he was in the shop late (he runs a contracting business out of the same office) and happened to try it at about 10 pm. It refused to start. He checked it then&there and determined that it wasn’t getting fuel. Since replacing the fuel pump on that model is expensive, we decided to replace the fuel pump relay first. That didn’t help immediately, but a night or two later EO (in a whimsical mood) decided to give it one more chance. Wonder of wonders, it worked! And there was much rejoicing—for about a week. Then it went back to its prior shenanigans. This leaves EO without reliable transportation after dark, which is not an acceptable situation for either of us (especially since she frequently gets off work between 9 and 10).
At this point, there seem to be two options: as the old saying has it, “jack up the radiator cap and drive a new car under it,” or replace the fuel pump. For reasons that are far too convoluted to go into here, the former is not feasible; and while I could probably afford the latter, I’d hate to shell out that much on such an elderly vehicle without some assurance of success. So like many others before me, I turn to the Dope for counsel. Has anyone experienced/heard of this sort of behavior? The mechanic has been fiddling with cars for over 20 years, and is completely baffled. (At one point he suggested changing the clock so that the car would think it was earlier in the day. I think he was joking.) Or could it be something small, obscure, and not overly mechanical, such as a leaking vacuum hose? Any and all advice solicited and gladly accepted.
My first guess would be spark plug wires and dew (or the humidity that accompanies dew). The next time it actually does run after dark, pop the hood in an unlit area and see whether you have blue lights running up and down the plug wires. If you do, replace them. (You might want to replace them on general principles, anyway.)
The cranking may be misleading you to think that the problem is fuel and not electricity, but the starter motor can crank until it self destructs while the fuel system is in perfect shape if no spark is getting to the cylinders
Sounds like condesation inside the distributer cap (were all the plug wires originate). Usually held on with a metal clip on each side. Take it off, spray it lightly with WD-40 and put it back on. Let us know what ends up working.
Another vote for condensation on the plug wires or in the distributor cap. I had a car that wouldn’t start early in the morning due to condensation.
Here’s what I did until payday, when I could afford parts:
Try placing a 100-watt light bulb under the hood in the evening. The heat from the bulb will keep the engine compartment drier than normal. Then see if the car consistently starts later that night or early in the morning. If so, either replace the plug wires or always park where there’s a convenient electrical outlet.
I use the same bulb trick on my motorcycle in the winter. A 100w bulb in a droplight will make it possible to crank in cold weather. It will probably work here also. Good call, JCoM!
Why did he stop at partial diagnosis? If a car isn’t getting fuel, testing can be done to find out why. It’s fairly easy to check for voltage to the fuel pump, the presence of which would eliminate the fuel pump relay from consideration. While occasionally one has no reasonable option other than replacing a suspect part, that’s not the case here. Doesn’t give me confidence in his ability.
If it had been a faulty fuel pump relay, the fix would have been immediate and (barring the very rare chance of getting a defective new one) long lasting.
Get a can of starting fluid (ether). Next time the symptom occurs, squirt some into the air intake (pop loose the top of the air cleaner, or simpler and quicker one of the finger-sized air hoses that goes into the air intake boot). If the car starts and runs for a few seconds on ether, it’s a pretty sure bet it’s lacking fuel. Try it several times. If it consistently starts and runs briefly on ether, then dies and won’t restart without ether, it’s a definite – lack of fuel in the cylinders.
The next step is to check for fuel getting to the engine. There’s a test valve in the fuel rail for this where pressure can be tested, and one can disconnect the fuel supply line between the fuel filter and the fuel rail to check for volume. If fuel is not being delivered (or not enough volume and/or pressure of fuel), the suspects are the fuel pump, the fuel filter, and the electrical signal to the pump (which relies on one or more relays, a fuse, various wiring connectors, and sometimes the ECU). If fuel is getting to the engine, the signal to the injectors is about the only possibility. It relies on the ECU, which relies on certain inputs (e.g. voltage on particular circuits, signals from particular sensors).
But sometimes it’s easier than that. Usually you can hear the fuel pump run for a few seconds when the key is turned on. Verify you can hear it during the day. Then next time it acts up at night, pay careful attention to whether or not you can hear it. If you don’t, the fuel pump isn’t working. Tap a test light into the power wire to the pump and see if it lights. If it does, the pump is bad.