Expert: Sean Halliday - 11/10/2008

Question
QUESTION: HI,
I HOPE YOU HAVE SOME ADVICE THAT WILL HELP. I'VE GOT AN 88 NOTCHBACK 5.0. IT IS BEING TEMPERMENTAL FOR LACK OF BETTER DESCRIPTION. THE CAR DOESN'T WANT TO START AFTER THE SUN GOES DOWN. I'M PRETTY SAVY WITH MUSTANGS I'VE WORKED WITH THEM FOR ABOUT 16YRS SO I'M NOT CLUELESS AND HAVE BEEN RUNNING IT DOWN PATR BY PART
WHEN I SAY IT WON'T START I MEAN IT WILL TURN OVER BUT WON'T RUN. I HAD A FULL DIAGNOSTIC SCAN DONE ON IT LAST WEEK AND NOTHING CAME UP THAT WOULD KEEP IT FROM RUNNING. THIS PROBLEM ONLY HAPPENS @ NIGHT AND EVERYTHING SEEMS TO WORK RIGHT UNTILL I GET TO THE FUEL PUMP RELY SWITCH. WHEN I HOLD THE RELY IN MY HAND AND TURN TYHE KEY YOU DON'T FEEL THE RELY CLICK ON. BUT IF I WAIT TILL THE NEXT MORNING AND I'VE HAD THE LUXURY OF SITTING ALL NIGHT TRYING TO START IT & IT WON'T HAPPEN AS SOON AS THE SUN IS UP YOU CAN GO. WHEN THIS IS HAPPENING IGN MODULE CHECKS OUT SPARK IS GOOD IT HAS A NEW FUEL RELY SWITCH BUT SEEMS NO POWER IS GOING TO THE SWITCH. I'VE HEARD STUFF ABOUT THE TPS CAUSING THIS BUT I JUST USED A SNAP ON SCANNER TO GO THROUGH IT WITH NO PREVAIL . @ THIS POINT I JUST DON'T KNOW WHAT TO CHECK NEXTxjvj6

ANSWER: The tps will not cause this.If you are getting a good spark,then its got to be fuel.How about the fuel pump ?Did you try that?I dont understand why it does this in the dark as there is no reason for this unless you have some sort of solar alarm or other cut off wired to a similar component which kills the ignition at night.Install a new fuel relay and have the pump wired direct from a 12v source to test as you turn the key.

---------- FOLLOW-UP ----------

QUESTION: THANKS ALOT FOR YOR HELP, JUST A SMALL QUESTION. IS THE WIRING FOR POWER SUPPOSED TO SUPPLY THE FPRS TO POWER THE PUMP FIRST OR THE OTHER WAY AROUND? BECAUSE THE RELAY SWITCH ISN'T GETTING POWER WHEN THIS HAPPENS. IF THE PUMP HAS BECOME FAULTY WILL THIS EFFECT THE FPR, IS THERE ANY KIND OF CIRCUT THAT WOULD CAUSE A DROP IN VOLTAGE TO CAUSE THESE TO SIMULTANIOUSLY FAIL AT RANDOM
SURE APPRICIATE THE HELP
HBSefeur

Answer
When you turn on the key,the first thing to activate is the fuel circuit and the relay will click.On most cars there will be a 2 second amount of fuel supplied to start the engine usually much more than normal, then when the engine fires the main relay acts as normal and will run as long as the key is on.It should be live at all times when the key is on and engine running.If there is no power to the relay,the pump will not work.There must be 12volts to the relay and 12volts from it when the engine runs or the key is turned as you start the car or crank the engine.There is a relay,fuse and starter or ignition switch and thats it,after that there is the fuel pump and fuse for that.No reason for both to fail and im pretty sure you have a bad relay or fuse,extremely unlikely but possible short in the wiring.Check the ignition switch as well for 12volts to the start system.