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Failing main relay?

 
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Old 07-10-2014, 09:28 AM
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Failing main relay?

So I bought a 91 Prelude, 2.1 ALB, 99,000 miles. Bought it off of craigslist almost 2 weeks ago. It drove fine for a few days, even went on a cruise or two with some friends. Before that, had to replace the alternator. Just the other day replaced fuel pump. Before replacing the fuel pump, a miss had started and has only gotten worse over the last couple days. Also, went to go start it to figure the miss out and it didnt want to start. So we push it in the garage and start looking at the fuel pump and main relay. Everything points to the main relay, but when we think about resoldering the points to fix it, it looks like it doesnt need it. There aren't any dry cracks or anything. The board just looks browned in spots. The cheapest I can find one is $100 so the smart thing to do would be to just replace it right? Well if thats not it, then thats $100 down the drain. Also, for the misfire; checked the plugs and they just look old. Ran a compression test and all the cylinders come up fine except for 4(I think). They all came up around 190 and 200 but the last cylinder came up around 150. Lower than the rest but that shouldnt cause a miss? Anything above 100 shouldn't even cause a miss. Also replaced distributor cap and rotor. So we have a mysterious misfire as well as a mysterious fuel pump/main relay problem. Help guys! Import Alliance is in two weeks. And I'm being pushed to sell my quelude if she isn't running better, which I really dont want to do. I know I probably need to baby her a bit more cuz she's all worn out right now. But the misfire is mind boggling. It started missing under low acceleration only. Now it won't start to test drive. It used to misfire in the low rpm's and then when you get to cruising speed its fine. Now its just getting progressively worse and barely lets you cruise. Then again, parked it until we could try to diagnose, then it wouldn't start.
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Old 07-10-2014, 12:14 PM
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Re: Failing main relay?

They have what's called an ignitor on the passenger side of the engine bay on the shock tower. Sometimes that dude gives up.
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Old 07-10-2014, 01:24 PM
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Re: Failing main relay?

Have you checked for spark and fuel when it doesn't start? If you have no spark, it's not the main relay. If you have spark but no fuel it could be the main relay, but not conclusively. There are other components involved (fuel pump, fuel filter, injectors, fuel lines, etc...).

Your main relay can still have a problem even if the solder connections look good. The components on the board can fail. But you should rework the solder connections even if they look okay. Sometimes a cold solder joint will look fine, but under heat it will separate just enough to break connection. It would suck to spend $100 on a part that you end up not needing, but if it's the original part it's probably going to fail in the near future anyway. So consider it preventive maintenance.

As far as the misfire goes, I have a few questions...Do you have any stored trouble codes? Do you know how to check for those? Have you replaced the fuel filter? Have you performed a complete tune-up (plugs, wires, cap, rotor, adjust timing)? You might also want to check the fuel pressure at the fuel rail. Then check the injectors. Also, since you just bought this car, how long did it sit with the fuel in the tank? Are you still running off the fuel that was in it when it was stored? You could have stale gasoline in there.
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Old 07-10-2014, 05:24 PM
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Re: Failing main relay?

I do NOT know how to check for STC's. I cannot solder so my father in law must do it. As for the tune up, so far we've done cap and rotor. That's all. Fuel filter and plugs are next. The wires don't look that bad at all. And the timing no. It was due for a timing belt and water pump check at 90. We're still kinda in the dark on whether or not they've been done but we have seen zero indication that they have so they're not much farther down the list. I also have a fist sized hole in my muffler. So muffler is right after belt and pump.
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Old 07-15-2014, 10:19 AM
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Re: Failing main relay?

Turn the key to ON and wait a few seconds. The check engine light should go OFF. iF IT DOESN'T THEN IT'S YOUR MAIN RELAY. That main relay sends voltage to your fuel pump after the check engine light goes out.
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b21a1 honda prelude, engine misfire, fuel pump, main relay, starting problem


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