Honda CRX Forum banner
1 - 20 of 24 Posts

·
Registered
Joined
·
3,549 Posts
Discussion Starter · #1 ·
Symptoms of a faulty main relay:

Problems starting the car, usually after a short run (when the interior is warm), though in some cases, the car may fail to start at any time. A classic time for the problem to occur is at the gas station, or if you park for a minute to get something from a shop. If the car is parked for a long period, the interior usually has cooled enough for the joint to make contact again, and you won't notice a problem. As the cabin temperature is a major feature of this problem, it might appear worse on cold or rainy days when you have the heater running to clear the windows etc. Extremely cold temperatures can also cause the problem to be more apparent.

FYI, The Main Relay controls five circuits:
Battery
Ignition
Pump
Injectors
Starter

Reason why car won't start:
The main relay wouldn't fire up the fuel pump due to the soldering cracks on the Relay PCB.
Cracks would appear over time and can be re-soldered, or you can buy a new one from the dealer. Im cheap, so I'd fix it. LoL

Here's a closeup of a bad main relay solder joints:



MAIN RELAY LOCATION:
On most Honda's the main relay is usually located under the dash on the drivers side,
in or near the fuse box area and due to its size is quite easy to find.

MAIN RELAY REMOVAL:

The steps below show removal of the relay from a right-hand drive 88-91 CRX, however the steps are exactly the same for the left-hand drive model.


Tools Required:
Cross-head screwdriver.
10mm Socket.
Extension bar for above.
Ratchet for above.
10mm Ring spanner (preferably ratchet type).

1. Remove the hood lever with a 10mm socket and extension bar. There are two bolts, the bottom one is being removed in the picture. When the bolts are out the level will fall out of the way.



2. Remove your fuse box cover to gain access to the coin holder. Now remove the coin holder - spring it open and you will see two screws at the top and one at the bottom. When the holder is out of the way we can see the top of the relay.



3. The bolt securing the relay is well hidden, you can access it from the directly above the hood lever. The bolt is impossible to see unless you get your head in the foot well so just use have a feel for it.



4. A ratchet spanner greatly speeds up removing the relay although it is possible with a normal ring spanner but it will take a few minutes. DO NOT try to use a open-ended spanner as you will probably round the bolt! Only use a ring-spanner if you do not have a ratchet one!



5. With the bracket loose we can now lift out the relay. Along with the bolt, the bracket is hooked with a tag so you may have to wiggle it a bit to free it off or it might just lift straight out.



6. The relay will now lift out - it is fitted with a long lead so you can easily get into the connector, and unplug it.



Re-installing the main relay back in is the reverse of removal, however getting the bolt
back in can be a little tricky. Remember to slot the notch on the relays bracket back into
the hole on the car as this will hold the relay in the exact position for the bolt to go in.


MAIN RELAY REPAIR:

Repairing your main relay is very simple, and requires only a few tools:

- Soldering Iron, powered around 25w is fine.
- Good Quality Solder.
- De-soldering tool - pump style, braid or de-solder station if you are lucky.
- Stiff toothbrush
- (Isopropyl Alcohol) cleaning Solvent

1. Bend back one of the retaining clips and lift up one side of the relay, then repeat with the other side.



2. The relay should now be free from the housing. ( lifted out )



3. Slide the relay PCB board from the housing. Note that it only fits one way.



4. Now you have to remove the old solder from the board. I recommend you only de-solder and re-solder one connection as a time as there is a chance some of the components may fall out the board inside the relay requiring it to be dismantled.



5. Now re-solder the connections making sure you use enough heat to fully flow the joint - compare your joints to the picture. They should have a shiny finish. If the finish on your joints is dull, you are probably using a poor quality solder, or not enough heat.



6. Next you can remove the flux from the board. This isn't strictly required, but it's nice to finish the job properly. Spray on plenty of Alcohol solvent and use the brush to remove the flux, you may need to do this a couple of times to get rid of it all. This will make a bit of a mess.



The relay can now be clipped back into its housing and reinstalled to the car.
 

·
Registered
Joined
·
3,864 Posts
The Main Relay should be called the Main Fuel System Relay so as not to be misleading. The only function of the main relay is to power MPG-FI engine control system which includes the distributor, injectors, and fuel pump. The only relationship to the battery is that's where it's power comes from. There is no connection between the MPG-FI system and the starter.

Mike
 

·
Registered
Joined
·
173 Posts
I don't feel it's misleading...just sayin'. The "main relay" in most Honda's is the Main fuel system relay. And it doesn't "control" the battery or starter. But there are connections to BOTH at the main relay. And it's PGM-FI. :wink:
 

·
Registered
Joined
·
43 Posts
Ok let me reiterate this it is not the Main Relay, but it is the Fuel Pump Relay. Because of misleading threads like these I wasted time and money buying the "main relay" when I was supposed to be buying the "fuel pump relay."
 

·
Registered
Joined
·
2,457 Posts
The only issue I have is once you have it out, I along with MANY other people, just zip tie it back in place since it is such a pain in the butt to get to.
 

·
Registered
Joined
·
3,549 Posts
Discussion Starter · #9 ·
KevinEF7 said:
Is there a part number difference between the Main Relay and the Main Fuel Relay

I wouldnt mind buying this new just to have as a backup
You dont really have to buy a new one per say, just resolder all the joints and it will be as good as new. The same goes for any other 20+ year old electronic piece.
Solder joints tend to crack over time due to differences in temperatures and constant vibrations.
 

·
Registered
Joined
·
57 Posts
Hi Robb,

Thanks for the great writeup. Is it really necessary to remove all of the old solder? Can't you just use some flux and re-flow the existing solder, adding more if necessary?
 

·
Premium Member
Joined
·
1,896 Posts
While replacing all the solder on the relay will bring it back to life, it(the solder) hasn't gone bad, it has just separated from the board. I have found with great success that you can simply "Re-Float" the solder that is currently on the connections. The process is very simple if you have a shop heat gun.

To do this:

1. Open the Main Relay to expose the connections, and place it in an upright and flat position.

2. Next, get your heat gun to temperature, and using a small, sweeping circular motion, move your heat gun across the connections, they will slowly liquefy, and you can tell by seeing the solder become very shiny and "wobble" or move with the motion of the air from the heat gun.

3. Once you have all connections "Re-floated", let it cool to room temperature before putting it back together, it's going to be hot to the touch.

This is very simple to do, and every bit as effective as removing and re-soldering, I have one in my car right now that I re-floated in 2003, so it is a very high quality fix. I have done dozens of relays for friends over the years, so I just wanted to offer up another, cleaner and easier solution to this problem, take it for what it's worth.
 

·
Registered
Joined
·
3,549 Posts
Discussion Starter · #18 ·
tonyguns said:
While replacing all the solder on the relay will bring it back to life, it(the solder) hasn't gone bad, it has just separated from the board. I have found with great success that you can simply "Re-Float" the solder that is currently on the connections. The process is very simple if you have a shop heat gun.

To do this:

1. Open the Main Relay to expose the connections, and place it in an upright and flat position.

2. Next, get your heat gun to temperature, and using a small, sweeping circular motion, move your heat gun across the connections, they will slowly liquefy, and you can tell by seeing the solder become very shiny and "wobble" or move with the motion of the air from the heat gun.

3. Once you have all connections "Re-floated", let it cool to room temperature before putting it back together, it's going to be hot to the touch.

This is very simple to do, and every bit as effective as removing and re-soldering, I have one in my car right now that I re-floated in 2003, so it is a very high quality fix. I have done dozens of relays for friends over the years, so I just wanted to offer up another, cleaner and easier solution to this problem, take it for what it's worth.
Well, if you want to repair a main relay,from what I read, new solder doesnt have lead in it so its not that great as an old stock oem main relay.
This is also a problem with new electronics that dont last as long anymore !
 

·
Registered
Joined
·
500 Posts
Use Rosin core 60/40 solder, the thinnest you can find. Removing all the old solder is a good idea if you have a solder pump (below), but not 100% necessary AS LONG as you add new solder.

 
1 - 20 of 24 Posts
Top