Here I share my story solving an issue with my Honda fit.



I bought a 2012 Honda fit LX manual (about 210,000 km) in July last year.

At that time, I knew nothing about cars.

I was happy with it because it had a very good appearance, and the seller claimed no issue at all.

However, my long frustrating journey began very soon.



The car drove fine in the city.

Several days later, when I drove my family to the mountain on the highway, it lost power completely when I was driving down a long slope and then accelerating again.
The car had no response to gas pedal at however I pressed it.

There was no light/sign showing on the dashboard. It felt like the gear was shifted into neutral but differently because it was still in gear and rpm did not drop quickly.

I was so panic you can imagine at this situation.

The speed slowed down from about 100 km/h to about 80 km/h. Then, suddenly, it response to gas padel again.

I happened only once.



I hoped this was just an unusual event.

But it happened again when I drove my family to another tourist place which is 3 hours away.

Still, it happened when I was driving down a long deep slope and then accelerating at the bottom.

It happened more than once. All were in a similar situation. I realized that the car did have an issue.

But it did not happen every time when I was driving down slope.

When we came back, I changed to another highway which is flat mostly. The issue did not happen.



I asked the seller. Certainly, he said no idea at all.

As I knew nothing about cars, I took it to a Honda dealer.

After an inspection and road driving, they found nothing wrong with the car. Only it felt weak on acceleration at high speed.

It cost me about $300CAD.

They recommended doing a valve adjustment which may cost around $1000CAD.

I had no idea of valve adjustment. I did not want it because it sounded like a big fix as it needs to take apart the engine.

I decided to leave it as it was because the issue never happened when driving in the city.

But I lost confidence driving this car from then.



In the autumn, I had to drive several times to a farmland about 1 hour away from the city.

The issue happened again. One or two times per trip, randomly.

One time, it happened on a relatively flat highway. This further confused me.

The car was still drivable as the issue happed mostly at driving down a slope. So, I did not need to stop the car as it could still maintain some speed even power was lost.

It never happened while accelerating.



The issue bothered me a lot. I decided to find out what's the problem.

At first, I wanted to figure out at what situation it would happen. If it was always random, I could not show it to others.

I concluded that it happened when releasing the gas padel (not completely) and then accelerating at high speed (over 100 km/h). Mostly I was driving down a long slope.

But one day, I left my car in the public parking lot. It was a hot day. In the afternoon, it stalled while idling after I turned on the air conditioner.

So, I did not use air conditioner. But the car stalled one or two times when I stopped or turned at a traffic light.

This time, it was a stall because the battery sign showed on the dashboard. I had to restart it.

This situation was new. I did not know what's the connection with previous issue.

But this happened even rare. Only leaving the car outside for a long time on a hot day I think.



I took my car to an auto workshop where I could talk to the mechanic and describe the issue in detail.

He said first you should check spark plugs. And it was time to replace spark plugs at this mileage.

So, I let him replace all the spark plugs. It cost me about $200CAD I can't remember.

Also, the transmission oil was changed.

The problem was still there.

Then he said it might be slipping clutch. Replacing clutch would cost about 2,000CAD and he did not have time to do that.

That freaked me out!

I came back and did some research on how to test slipping clutch. Finally, I concluded that it should not be a clutch issue.



I continue to search more on the web.

I believe it was most likely the fuel filter/regulator issue.

I called the Honda dealer to replace the fuel pump. They told me they can't do that because they must check what the problem is.

Damm. They had checked and found nothing.

Alright, I decided to do it myself. So, I ordered a fuel pump from eBay for $101USD and removal tools from Amazon.

On a snowy day, I replaced the fuel pump by myself following YouTube tutorial.

I did test driving. The problem was still there.

But I felt the car was more powerful at low speed. Maybe I was wrong.



I came to know a tool of OBD scanner which can tell me some parameters.

So, I ordered an OBDLink for $107CAD from which I can receive data on a laptop and view real-time graphics.

That began my days recording data.

I drove around frequently carrying this device, trying to catch the moment when the issue happens.

I did get the moments several times.

By analyzing the data, I still could not tell what was wrong. Everything looks fine to me.

This fit does not have fuel pressure data very unfortunately.

I compared the data with that from a Toyota. I found that the O2 sensor had a different response (opposite).

I did not know what the correct O2 sensor curve looks like. But I decided to replace it.

I bought a pair of O2 sensors (upstream and downstream) from eBay for only $75USD.

I took my car to the workshop. Let them replace the upstream O2 sensor for about $160CAD.

The problem was still there. The output curve looks the same as the stock one.

But I felt the car was more powerful even at higher speed. Maybe I was wrong.



Moving to summer this year. I needed to sell this car as I will leave the province.

I could not sell to someone by telling him of no issue with this car. I just could not lie.

So, I thought I must fix it eventually, or I would have to sell it at a very low price.

I started continuing my search, driving around, and analysis data,

I suspect the EGR issue as there was a 100% EGR ERROR at idling.

I ordered one from Amazon and replaced it which was a very easy job.

The problem remains. I returned the EGR.



I still suspected the o2 sensor because the car also felt weak on acceleration.

As the one from eBay was very cheap. I decided to buy a more expensive one for about $300CAD from Amazon.

This time I tried replacing it by myself using tools I bought ($60CAD).

I was easier than I imagined.

The problem remained. The output curve looks the same as before.

But I decided to keep the expensive sensor.



I thought I needed to check fuel pressure or vacuum leak.

For the vacuum and air intake, I believed they were unlikely wrong from the OBD reading.

So, I ordered fuel pressure gauge and wanted to check the fuel pressure.

It turned out that it was not easy to connect those fittings. And I thought that would be a mess if I did it.

So, I did not check any and returned the tools.



During that time, I changed back to stock fuel pump and there was not much difference.

I started to believe the fuel pump works fine and should not be the problem.

To verify that I thought a fuel pressure check was still necessary.

But I could not do it by myself. So, things stuck there.

I also suspect the ignition coils.

So, I ordered two but did not replace it because the work it needs, and the evidence is not strong.



I still needed a fuel pressure check to exclude the problem of fuel system. But I could not do it.

One day, I got an idea that I could check the power supply to fuel pump. I believe if the power was there, the fuel pump would be working.

Of course, measuring the voltage using a multimeter gave me normal reading.

But I know that could not tell the whole story because I could not keep monitoring the voltage by my eyes while driving, and the issue is so random and a short process.

I thought I could record the voltage signal using an analog-to-digital device and data logger.

Luckly, I have these devices.

I used a usb data acquisition (DAQ) device, making some wires connecting to fuel pump plugs, making software keeping receiving data from DAQ and save on the laptop.

I started driving out of the city carrying this system.

Not even out of the city, the issue happened while I was climbing uphill!

So, I turned around, drove back home, and looked at the data.

And I saw what happened: the power supply voltage dropped from 12V (should be but the DAQ range is +/- 5V) to 3V for about 1 second, back to 12V for less 1s, then dropped to 3V for 1s, then normal again.

At this time, I can confirm that the problem was caused because the power supply to fuel pump was cut off!



What will make the fuel pump power cutoff?

I did some search and came to a name called camshaft sensor, whose signal would affect fuel supply.

But replacing it might not be easy and I was unwilling to start.

I kept searching and came to names of fuses and relays.

The more I figured out the function of relay, the more I believed that was where the problem was.

So, I ordered 5 for $20CAD.

But they would come two days later, I could not wait and replaced the fuel pump relay with the one controlling rear window defogging.

I drove the car out of the city for several hours on the road I usually test driving.

The problem was GONE!

Finally, a several-bucks problem bothering me for a year was solved!

And I learned so much during the process: the deal, the dealer, and the car repairing.
The process is actually much longer than the description here, like the first time I tried to open and replace the fuel pump...


Stall while idling (some parameters are scaled for better viewing).

Fuel pump power voltage (+5V is the maximal range of the DAQ device).