Lets start with the fact that my 1987 Accord LX uses a proprietary fuel pump relay. Considering the age of the car and the possibility of in the future not being able to get another relay of the exact type I want to convert it to use a standard 30a automotive relay. I am currently waiting on a Honda Service Center Manual to arrive in the mail.

I am not 100% sure if the relay is bad, I get a brief spike of about 0.5v at the fuel pump when I turn the key. but then it drops to 0v dc after a split second. If this was a standard relay with a coil I would say the relay is bad, but with honda making a relay with what appears to be a couple of transistors and a mosfet with accompanying resistors diodes and capacitors I can't be to sure. From what I can tell the pump gets +12v dc and a ground wire. I check the black and red wire from the plug for continuity to ground but got NO continuity (possible bad ground from the fuel pump connector). I also check the solid yellow wire to ground and NO continuity (this should be correct).

Now the relay has 4 pins labeled FP (pin 1) + (pin 2) - (pin 3) IGN (pin 4) They are the size and shape of a standard male spade connector. If I connect the IGN (pin 4) to the coil of a relay (pin 85) and then connect the other coil pin (pin 86) to - (pin 3) that should energize the relay. I could then take + (pin 2) and put it on the switch of the relay (pin 30) and the go from the relay (pin 87) to the FP (pin 1).



I don't have the shop manual until next week but I wanted to get a start on trying to convert this to use a standard automotive relay for the fuel pump. I don't think the fuel pump goes through the ECU considering this is an ODB I system, and this is my first Honda from this era, so if anyone has any thoughts about this I would be grateful.

 

Is this for a fuel injected or carb engine?

 

2L 4cyl Carb

 

I was able to 100% verify that the black wire from the fuel pump harness does indeed connect to chassis ground. So the yellow power wire from the pump should go to the FP Pin (pin 1) on the stock relay.

 

I have an old pdf for an 86 accord that should be similar to your 87 relay, but the internals of the relay aren't clear. I'll guess Honda would have used a standard 4-pin relay if that was how it was wired.

Hopefully your manual is more detailed.

From what I can tell, it looks like the four wire colors are blk/yel, blk, yel, and blu. Using your pic and numbering.

1. Yel - Power out of the relay to the fuel pump
2. Blu - Also power out of the relay powering the coil and other items.
3. Blk - Ground (constant ground)
4. Blk/Yel - 12V coming from the ignition switch.

If you have a volt meter with that relay unplugged, check that the 2 blk has a constant ground. Also check that 2 Blu has or is missing voltage.

On the lower left of tthe original relay in your picture (I think) is a soldered relay on that board. A common problem on 90-97 accords is the solder joints would fail on one of legs of the relay. Take a close look at the bottom of the board for a cracked relay solder joint. If you can solder, you may be able to quickly fix that relay by reflowing the solder joint.

 

Okay I was able to verify that the FP pin (pin1) on the relay is indeed the power wire to the fuel pump. What you are thinking is a relay on the board I have is actually a mosfet or something similar with a heatsink. It's hard to tell from that one photo but there is no relay on the circuit board just a mosfet (see photo) 2 transistors and miscellaneous resistors, capacitors and diodes.




To sum up the Fuel pump harness has 2 wires, a solid yellow (confirmed to go to FP pin (pin 1) on the factory relay). And a Black with red markings( confirmed to ground to the chassis).

I'm not as limber as I used to be and I'm checking Pin 2 (labeled +) and pin 3 (labeled -) it's just hard to contort myself under the dash to check everything.

*edit I just check pin 2 and 3. Pin 3 is labeled - and there was continuity to battery negative AND battery postive. I have no clue what is going on there. It will be a week before I get a hard copy of the Honda Service Center manual so I think I'm at an impasse for now.

 

The pin 3 continuity reading is very strange on continuity unless you are seeing continuity to battery + through something else grounded through that wire. Best bet is to turn the key to the II position and test voltage on those wires.

I thought the green component from the first pic was a resistor. Now I see that it is a mosfet/transistor. That green mosfet has to act like a relay and send power to the fuel pump. I think the solder for those three legs is something you should inspect. The current required for a fuel pump is fairly large, so the heat/cooling cycle over 35 years could cause the solder to crack and still may be a simple fix to get the fuel "relay" working.

I see the relay is available online, so you can purchase a replacement. I haven't seen too many posts on here about the 86-89 accord main relays having issues, so a junkyard may be a cheap source for one as well. I'm cheap enough where I'd probably buy the equivalent mosfet and that capacitor and solder them in after doing some continuity tests on the board to ensure I understand the layout.

 

After more digging around under the dash I found out Pin 2 (labeled as +) has continuity to both negative and positive of the battery. It's the same for pin 3 (labeled as -). I was thoroughly flummoxed about this until my brother in law came by and noticed the fuse for the fuel pump is also used for the alternator. He thinks the diodes in the voltage regulator might have fried and created an open short. I'm not so sure since the fuse for the fuel pump / alternator is NOT blown. I will test everything again tomorrow when I have more light after I disconnect the alternator. I will also dig my transistor tester out of storage and test the transistors on the board. 1 is a NPN the other PNP and the large green one is an NPN power transistor capable of 30amps I'm going to assume the power transistor is what actually powers the pump. if any of them are bad I can just replace that component for less then a $.

I'm still waiting on the Honda service manual to be delivered next week. I will test more wires and replace the vacuum hoses this weekend while I wait for the manual to be delivered before I attempt much more on the fuel system. I also need to replace the belt in the stereo so the tape deck works again, and figure out how to get the audio from a bluetooth module into the stereo. That should keep me occupied over the next week. I'll update this thread as I find out more information on the fuel pump issue.