Mechanics

CAR WILL NOT START AT CERTAIN TIMES AND THEN SOMETIMES WILL START NORMALLY., WHAT CAN IT BE?

1996 Lexus ES 300 • 169,000 miles

I have replaced the electric fuel pump and fuel filter. After doing this the car started the first time. I then tried to start the car again. It would not start and has not started since. Previously My son called me to get the car at college when it would not start, I got there and started the car as normal and drove it home with no problems approximately a 70 mile trip. Once at home, I switched off the car and tried to start it again with no success, , I therefore replaced the electric fuel pump and fuel filter. I am not scratching my head as to what to do.
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Don1
March 3, 2012.



What's the symptom, sounds, etc. "Doesn't start" is as informative as "I'm in pain".

Caradiodoc
Mar 3, 2012.
The Car will crank but will not start. Where is the Fuel Pump Control Relay located on this car.I removed the relay cover and there was no relay where it was indicated on the underside of the cover, it was an open plug. What is the next step?

Tiny
Don1
Mar 4, 2012.
Why did you replace the fuel pump? Was it for this intermittent problem, or is this a new problem that started after the pump was replaced?

Oops. I reread your first post. What led you to the pump? Check for spark too. If it is missing, suspect the crankshaft position sensor or camshaft position sensor.

Most likely we are not going to find a stretched or corroded terminal in an electrical connector or a corroded splice because that would be more likely to cause a stalling problem while driving. Sensors very often fail intermittently by becoming heat-sensitive. They will stay cool when wind is blowing through the engine compartment but when the engine is stopped the heat migrates up into them. They will usually work again when they cool down, until they fail completely.

Most manufacturers have a way to turn the fuel pump off when the engine stops in case the car was in a crash that ruptured the fuel line. The Engine Computer knows the engine stopped by the lack of pulses from the cam and crank sensors. When one of those sensors fail, the computer may turn off the pump, injectors, and ignition coil. That's why you have to check for spark too.

To add to the confusion, some engines will run on just one of those two sensors as long as it fails while it's already running. It will not restart because the computer doesn't know which spark plug to fire first.

A failed sensor should set a diagnostic fault code but it might not turn on the Check Engine light. The light is required to turn on when the fault detected could have an adverse effect on emissions. The thinking could be "you can't have excessive emissions if the engine doesn't run". Regardless, checking for stored codes is the place to start. You can go here:

http://www.2carpros.com/articles/lexus-trouble-codes-obd1-1990-1995-code-retrieval-procedure

to see how you can read them yourself but this is for '95 and older models. All cars sold in the U.S. after that had the newer "on-board diagnostics, version 2", (OBD2) system that uses three-digit codes. Many brands display the codes in the odometer readout. I don't know if the procedure for getting the computer to spit them out is the same. The '96 and newer models all have the diagnostic connectors under the steering column and it's shaped like a trapezoid with two rows of terminals. If you find that on your car, you will most likely need a scanner to read the codes.

When a fault code is related to a sensor, remember that the code only means that's the circuit that needs further diagnosis. The problem is only caused by a bad sensor about half of the time. You have to check the wiring too. Also, a shorted sensor can kill the power supply for both the cam and crank sensors so no pulses will show up from either one. The computer typically shuts the power supply down to protect it. Once the short is gone, you have to turn the ignition switch off and back on to reset it. With both signals missing, the computer might assume the engine isn't even turning so it might not set a code. Each sensor should have three wires, and with the ignition switch on, one wire at each sensor should have 5.0, 8.0, or 10.0 volts. If it's missing, unplug them one at a time, cycle the ignition switch, then check if the voltage comes back.

Caradiodoc
Mar 4, 2012.