This is an edited version of my first reply. The relay should go out 3 - 4 seconds after the ignition key is switched to on. You probably already knew this, thus the reason for your question. TO ANSWER YOUR QUESTION: The fuel relay may be the culprit. If the problem occurs after the engine has been running for awhile and then is OK when the engine is cold, that is a big hint that the circuit board in the relay is cracked. The cracking is a problem for the Prelude and occurs because the electrical current, running through the relay when the engine is on, heats up the circuit board a little. The repeated heating/cooling cycle eventually causes the board to crack. It can be easily repaired using a soldering iron. FUEL RELAY OPERATION: The fuel relay coordinates the electrical signal to the fuel pump based on the electrical signal from the ignition switch. The fuel pump relay also supplies electrical power to the fuel injectors. RELAY LOCATION: The relay is located in the passenger compartment, under the dashboard, on the left wall, just forward of the engine-hood-release-lever. It is retained by a single bolt and has a cable harness attached. Before removing or replacing, there's an easy way to see if the relay is working properly: by detecting three (3) clicks the relay makes, as the key is turned. To detect the three clicks, put your fingers of your left hand on the relay as you turn the key and you can feel the clicks; you might be able to hear the clicks, but "touch" is really the best way. RELAY TEST: Start with the engine "off" and the key out of the ignition. Put the key in. Turn ignition to ON (but not to START): Click 1 //// PGM-EFI light goes off: Click 2 //// You now turn the key to START: Click 3. If the relay is going through its 3 clicks, then the relay is fine -- don't replace it. NOTE: the 3 clicks occur with only two movements of the ignition switch. One of the clicks occurs without moving the ignition switch (when PGM-FI light goes out). There is another check that's easy also of the relay/fuel pump and it goes as follows: FUEL PUMP TEST: At a location that's quiet so you can listen carefully to the fuel pump, with engine and ignition switch "off", sit in the car. Since the fuel pump is located behind the drivers door, open the driver's door about 8 to 12 inches. Turn the key to the first position and you should hear the fuel pump come on for a 3 - 4 seconds as it "charges" the fuel rail at the fuel injectors. You might be able to hear it with the door closed too. The sound comes from your left-rear and sounds like an electric "hum" for a few seconds. The PGM-EFI light should go off after the fuel pump charges the fuel line and goes off. If no hum, the relay is not sending a signal to the fuel pump and the car won't start, or the fuel pump is bad (unlikely). If the car starts, and the light is ON, that may be a defect in a board component in the relay. Z-machine
A NEW QUESTION APPEARED IN THIS QUESTION'S HISTORY SECTION:I have an 87 Honda prelude where the PGM-FI indicator in the dash works fine when i start driving but comes on after a few minutes. Your post says this can easily be repaired with a soldering iron. Can you be more specific?
What, exactly, does the PGM-FI light mean?? ANSWER:THIS QUESTION HAS TWO PARTS: 1. What are the specifics regarding the soldering of the relay as a repair, and 2.)What does the PGM-FI light mean?FIRST QUESTION: The soldering-repair of the circuit board for the fuel pump relay is accomplished by pulling the relay out of the vehicle and using a 25Watt soldering iron with 60/40 electrical solder to heat up and RESOLDER ALL SOLDER POINTS. DO NOT let the iron stay on the joint for more than a few seconds because you can damage the electrical components from the heat which is conducted through the wiring to the electrical part. As you resolder each of the solder points, the solder should be shiny when done and be shaped like a "Hershey Kisses" candy. Don't lump a bunch of solder on the solder point or it will short out the components. If you have a "Solder-Sucker" device, remove the old solder first(heat and suck)and then put on new solder. I removed my solder first and then resoldered the connection points. It works fine now.SECOND QUESTION: The PGM-FI light is designed to alert the driver that the fuel system is improperly pressurized or that the fuel injectors have a problem. SOLUTION: With the car parked, and engine warmed-up, see if the light comes on. If it does, check the fuel injectors to see if they're working right. You can buy a doctor's stethoscope for cars with a metal stick-probe that you place on the injector to hear it clicking. You can also take a wire hanger, straightened-out; put one end on an injector and "listen" to the clicks by placing your ear on or near the wire. Don't stick the wire in your ear. You can also take a piece of rubber tubing, cheap cost, about 3/16" hole, and listen to it that way. The tubing can be purchased at any auto repair store for a dollar and it should be no longer than two feet long.DISCUSSION: The fact that the car still runs after the light comes on, doesn't necessarily mean it's the injectors, the fuel pump, or the fuel-pump relay that are to blame. It could also be due to a faulty sensor. If there is a problem with the injector(s), then you are going to have a problem with fuel consumption or imbalance in cylinder firing forces. The computer may try to compensate but I don't know if the computer would compensate by changing the good injector(s) as well as the "defective" one. There's also the fuel filter. If it's clogged enough to prevent the fuel from passing fully, that may cause a "running" problem. Finally, it's possible that an injector system may be clogged and need cleaning. Injectors are expensive ($50 each) and the replacement requires depressurizing the fuel rail. Z-machine