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Discussion Starter #1 (Edited)
Hello Everyone
This is my first post on this site / forum. I’ve been a lurker here for some time now. Im not no mechanic by any means but i do like working on my car and saving money. So here is a little background to my accord and the problem im having. Sorry in advance if this is a long post.

2004 honda accord v6 ex sedan automatic. Mileage 130xxx

I purchased this car maybe 5 years ago from a guy on CL. Car checked out good and drove really good for its age. I was a new driver and never really paid attention to it. Just did little maintenance to it like change oil, change air filters, top up fluids, those kind of stuff. I do 85% city driving and hardly would use highways as my job was near by. As time went by, i noticed my car becomes sluggish to accelerate. When i take my foot off the gas, it bogs down. It picks up speed okay but ive seen videos of other people accord picking up speed way faster than mines with less effort. Its like its struggling to go faster. I have to press the pedal all the way down 100% sometimes to even get some speed.
I noticed I was getting really bad mpg. It kept on dropping even with the new parts installed. According to my calculations i was getting 11-12 mpg!! I had started reading up online what i can do to remedy the situation and did these things below. I didnt do them in the order below.

  • Cleaned out the throttle body and map sensor and later then I installed a used low mileage throttle body from another honda and new map sensor
  • installed reman fuel injectors
  • changed spark plugs and coil recently (more on these)
  • changed air filter
  • installed new egr valve
  • installed new pcv valve
  • installed both pre cat o2 sensor
  • increased tire pressure to 40psi
And thats what I remember right now. Im not sure what to do 😕. There are no trouble codes coming up. BTW A mechanic friend had changed out the timing belt, pump and pulleys around 105xxx miles. Ive never done a valve adjustment to it. My fuel trims are in the positive and its terrible. I checked out the spark plugs today and they are burnt and smell like gasoline. They were only change maybe 5000 miles ago, gapped at .44.
Can anyone help me out. These are my fuel trim at idle and 2500 rpm
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Discussion Starter #3
I have to change them out soon again. But im afraid they will get to this point soon again if the problem isnt fixed
 

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A lot of city type driving = a lot of carbon build up. Start with a top end cleaning where the mechanic injects / sprays a commercial carbonize cleaner, then take it on the hwy. & floor it several times.
 

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I recently did a piston soak on my ‘03 2.4L to address oil consumption. Well, it didn’t do anything to help oil consumption but it does feel like it restored some pep off the line. Previous it felt a bit “loaded” when accelerating and I used to comment that it feels like it lost compression since new.

I used BMW Fuel Injection Cleaner Concentrate (82140428376) with an overnight soak. You can find the procedure on this board.


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Discussion Starter #7
I use to use fuel system cleaners and they worked well. I could of felt the car drove a bit better. I remembered using techron, redline, liqui moly & bg 44k. I’ll give the bmw f.i. cleaner a shot since i saw my pistons were not looking good.

Guys thank you all for the suggestions. I appreciate it a lot and will use them.
Looking back at my first post. The main problem i have is my mpg. What do you guys think is causing my car to get 11-12mpg?
 

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Discussion Starter #9
I should of clarify that part a little better. What i meant was sometimes i press the pedal all the way down bc it feels like it goes nowhere when im half way pressing it. But i really don’t drive with a heavy foot. I try to granny drive it so i don’t have to go fill up gas every other day. The low mpg was already there
 

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To me it seems like too much backpressure on the exhaust. I suspect the Catalytic Converter downstream may be clogged or the mufflers internally collapsed. Another place to look is the brakes, make sure you do not have one dragging. Easy to check, jack it up and spin the tire.


The sparkplugs are showing signs of glazing, high temperature in the combustion chamber. You say you changed the EGR valve, are the passages clear as well.

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Discussion Starter #11
I think you might be on to something. My engine does seem to running hot, is that why my fans coming on often to try to cool it down?

By downstream cat, are you referring to the 3rd cat?

I checked the tires last week and theyre spinning good 🙂

Right now, NY is having some rainy days so im waiting till it eases up then im going to check and clean the egr area if they need it. The passages are located inside the intake manifold right? Its that long metal piece ?
 

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The O2 sensors may be suspect. Downstream cat would be the 3rd cat, but technically they are ALL downstream, and the maniverters would be exposed to more heat. If you don't have a remote camera, get one. Pull each O2 sensor before the cat, stick the camera in and check for a nice honeycomb shape. It will be obvious if it is melted.

The release side of the EGR passages are in the intake manifold. They are little holes located by each cylinder's intake runner. When you pull the cover on the intake manifold, they are right up top. There is wavy tube inside the manifold close to the throttle body, that one can also clog up.

Unbolt the intake manifold and clean everything you can with throttle body cleaner and a rag. I have noticed MPG and power improvements from a thorough cleaning.
 

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The 3rd cat has no sensors, if it has melted or damaged in some way that could cause excessive backpressure. The EGR's job is to lower the combustion chamber temperature, if the passages are clogged then the exhaust gases never make it to the intake. You remove the top plate and clean all those passages, if it is like most I have seen several are completely clogged.

The fans are supposed to run, they should not be running after you turn off the key. If they run then that is a cooling system issue.

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Discussion Starter #14
I will be looking for an endoscope cam on amazon tonight. As soon as i get it, I will check the cats out and get back to you guys.

Also something you guys should know is about 2 months ago my exhaust pipe that attached to the 3rd cat got separated. It was loud as hell. So since there were no sensors on that cat. I told the exhaust shop guy to take the cat out and weld a piece of pipe in. The honeycomb inside that cat looked good to me. I didnt Notice any difference with the car afterwards.

On a side note, Can a bad fuel pump or regulator cause the injectors to pump more gas than it should? I know for sure the injectors are good bc i replaced them with reman. I got from ebay. I never tested the fuel pressure. So maybe i should do that. What do you guys think?
 

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Nothing wrong with those fuel trim values.

Park at the top of a gentle slope. Put it in neutral with engine running. Coast down the hill. Does it coast along or come to a quick stop?

Go for a drive at speed for a few mins then stop gently without brakes. Put in park. Get out and check brake rotor temps (don’t touch!!)

Betting you have a dragging brake or brakes on the rear.

Or jack each rear wheel up and spin by hand. Both should spin with little effort.


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How, exactly, are you calculating your mpg?
 

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Discussion Starter #17
Im filling up until the pumps clicks the first time. Then drive until the gas light comes on. Most of the time i get 200 on the trip odometer. Then i divide that by 17 gallons. Which gives me 11-12 mpg. I know the car has a 2-3 gallon buffer zone after the light comes on. So if i divide 200/15 gals, i still 13 mpg. 😕

We get ethanol mix gas here year round so its not the gas. Also i try to stick with shell, exxon/mobil, or bp regular. Once in a while I’ll use the premium.
 

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Nothing wrong with those fuel trim values.

Park at the top of a gentle slope. Put it in neutral with engine running. Coast down the hill. Does it coast along or come to a quick stop?

Go for a drive at speed for a few mins then stop gently without brakes. Put in park. Get out and check brake rotor temps (don’t touch!!)

Betting you have a dragging brake or brakes on the rear.

Or jack each rear wheel up and spin by hand. Both should spin with little effort.


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Ill report my slope findings back tomorrow. Thanks 🙏
 

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Im filling up until the pumps clicks the first time. Then drive until the gas light comes on. Most of the time i get 200 on the trip odometer. Then i divide that by 17 gallons. Which gives me 11-12 mpg. I know the car has a 2-3 gallon buffer zone after the light comes on. So if i divide 200/15 gals, i still 13 mpg.

We get ethanol mix gas here year round so its not the gas. Also i try to stick with shell, exxon/mobil, or bp regular. Once in a while I’ll use the premium.
Where does the 17gals come from? Is that what the pump reads or theoretical tank capacity?. Use the actual pump reading, nothing else.


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