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Old 03-20-2018, 11:07 AM
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Failing Main Relay Causing Performance Issues - Do You Believe?

Most main relay issues are black and white. The car either runs or it doesn't. However, I noticed something over the past 24 hours that has me wondering about some performance issues. This may be the key to undiagnosed problems.

Believe it or not, I've never had a main relay issue with any Honda I've ever owned. My first trial by fire with the infamous Immobilizer Unit was over the past couple days. My first 6th Gen Accord as well. During the process of figuring out what was up, I swapped the main relay to no avail. After figuring out that the immobilizer unit was the culprit and getting the car started, I decided to leave the new main relay connected even though it was unnecessary.

During the test drive, I noticed that the car seemed to be running smoother. I have noticed a very slight hesitation or misfire during the month that I've owned it..especially in gears 1, 2, 3. The idle was perfect and there were really no other symptoms. Just the slight hesitation when under load. With the new relay, the car seemed to be running noticeably smoother. For experiment's sake, I came home from the drive and put the old relay back in. The hesitation seemed to return when I took it back out for a ride.

I'm thinking that since the main relay controls both the fuel pump, ECU, and other key parts, a relay that is failing / fluctuating in voltage, etc. could totally cause some of these phantom hesitation and other performance issues. Issues that could be blamed on distributor / inner distributor parts / plugs / wires / etc.

I've swapped back and forth twice and am going to swap a third time to be absolutely sure. But it seems that an even slightly failing main relay can cause these issues.

Has anyone else dealt with this issue? Or come to the same conclusion? It really seems to be the case.

Last edited by PSYCHIC-TOMATO; 03-20-2018 at 11:14 AM.
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Old 03-26-2018, 12:20 AM
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Re: Failing Main Relay Causing Performance Issues - Do You Believe?

Not I. The two times my main relay failed on my 6GA was the black and white "it works or doesn't work" situation you mentioned.

Interesting theory though.
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Old 03-26-2018, 01:12 PM
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Re: Failing Main Relay Causing Performance Issues - Do You Believe?

Originally Posted by CDsDontBurn View Post
Not I. The two times my main relay failed on my 6GA was the black and white "it works or doesn't work" situation you mentioned.

Interesting theory though.
Yeah, mine was intermittent. and now that I quit switching the old one
back and forth, the lag / hesitation is completely gone. That was also days
prior to me replacing the plugs and wires. So the only change made to the
car was the main relay. Period. It's electromagnetic. I think when the voltage
/ power gets squirrelly due to fuel pump voltage dropping as well as other reallllly
important controls..like the ECU. I think when that happens, these cars start
to act like this.

In fact, there are a lot of frustratingly undiagnosed Honda / Accura problems
that have smptoms like this but have never deen actually diagnosed.
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Old 03-27-2018, 04:17 PM
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Re: Failing Main Relay Causing Performance Issues - Do You Believe?

My main relay went bad about 2 years ago, replaced it with another OEM HONDA.

My symptoms were:
1. On a cold start, would take several tries for the relay to kick in and engine to fire up.
2. Sometimes after driving, car would take a few tries to fire up
3. Car shut off while driving 3 times

The 3rd time was when I knew for sure, Main Relay was bad. Replaced it that same week. After replacement, no issues at all.


I think the main cause of the undiagnosed issues is the Main Relay and ECU. Hard to say because you would really need to scrutinize the ECU to see if it is the solder connections going bad, like the main relay and LED odometer display, or if it is a component(s) on the circuit board that starts to fail.
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