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Old 04-04-2011, 11:40 AM   #1
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Icon6 2000 Honda Accord V6 V-TEC - Horrible gas mileage

Ok, so before anyone asks, yes, I did a search before posting this, and I have researched this topic exhaustively, I am just getting desperate for help, so I decided to make my own thread.

A few weeks ago, I bought a 2000 accord v6 from a private owner I found on craigslist. The car is beautiful, fully loaded options, leather interior, 20" rims (light weight aluminum, none of that chrome crap), touch screen dvd player, etc. I got it for a really good price, and was pretty happy.

Obviously I should have done my homework on the car more, because I didn't learn until after the fact that these models are prone to a high rate of transmission failure (it's an automatic, and the first automatic I ever owned to boot). I had the car for about a week when the transmission basically died. I took it to a shop, and had the transmission rebuilt, and that's fine now, runs great, and smooth. My problem is this: Even before the tranny rebuild, the car is getting horrible fuel economy.

Average 12-16mpg at the most. Obviously, this is WAY off of what it should be getting.

I've looked around the forums here, and tried a multitude of things. First, let me mention symptoms, and then I will list off things I already tried.

Symptoms:

-Car occasionally stalls out after starting. Rarely, but it does. The fix for this involves starting the car and giving it gas for about 15-20 seconds, then it runs fine.

-Acceleration is unpredictable. Sometimes, if I try to floor it from a stop, it launches, and does so very quickly, then vtec takes over and the upper rpm ranges are quite nice. Other times, the car struggles, gives about 1/2 to 1/3 the acceleration of before, then vtec kicks in, the engine gets louder and a tiny bit faster, but not much.

-Poor fuel economy seems to be independent of how it drives. I've tested this by driving around never exceeding 3k rpm, windows up, a/c off, and have also tried aggressive driving, with a/c on at all times. There seems to be no difference at all in mpg between these. Yes, I am calculating the mpg correctly (always fill up to max and then 3 clicks, miles divided gallons purchased)




Ok, so these are the problems, and I am sure they are all related. Now comes the list of what I have already done to try to fix the situation:

-Replaced air intake with a proper short ram intake/cone filter

-Cleaned throttle body and idle air control valve thoroughly (was dirty, but didn't seem to make a difference in anything, not even the rough idle at start)

-Replace spark plugs. After consulting manual, found that NGK platinums were used, and that the V6 model requires a slightly beefier plug. Upgraded to Autolite double platinum plugs. Also saw no change at all after this. Old plugs were worn, but only to a degree that indicated they were just old. No oil or fuel on them. Plug wires are n/a because of coils.

-Replaced MAP sensor. This made no change at all, I am returning the new one and reinstalling the old.

-Plastic connector on throttle position sensor is slightly broken. Seeing as how they want you to replace the entire throttle body, I just zip-tied this on, and it has absolutely no wiggle at all to it. Multiple mechanics have verified that this will not cause a problem as long as it holds.

-Cleaned fuel system thoroughly with sea foam

-Wheels balanced/alignment, I do have one slightly bent rim on the front but it is very minor. Tires are at proper psi and even. Plenty of tread left.


I have not checked the o2 sensor yet, as it has not thrown any sort of code.

The only CEL I have gotten so far was an EVAP sensor, indicating an emissions problem. I have not traced the source of this, but since resetting the code, it has not reappeared.

I've read on some threads about a possibility of mechanical (cam) timing being off, but I have not checked that yet.

Any ideas?

I got fed up and went to a Honda service shop today, and the guy there was not much help after I told him the bases I already covered, telling me there is likely nothing that can be done about the poor mpg, and I just can't accept that for an answer. SOMETHING is wrong, and I need to know what it is so I can fix it. Price is an issue, but I will do whatever it takes to make this right, as long as I can feasibly afford it. (preferably under $500)

If anyone can give me something I haven't thought of yet, and it works, I will gladly PayPal you $20 for the trouble. I'm desperate. Help!
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Old 04-04-2011, 03:43 PM   #2
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Default Re: 2000 Honda Accord V6 V-TEC - Horrible gas mileage

Quote:
Originally Posted by DJApoc View Post
-Plastic connector on throttle position sensor is slightly broken. Seeing as how they want you to replace the entire throttle body, I just zip-tied this on, and it has absolutely no wiggle at all to it. Multiple mechanics have verified that this will not cause a problem as long as it holds.
But has anyone tested the TPS? Why is the connector broken? IIRC these V6s use a Speed Density system. The only way the engine knows what volume of air is coming into the engine is from a combination of MAP(engine load) and TPS(throttle position), with the O2s keeping the AFR in check. You also may want to pull the O2s and make sure they are still OK. I've had O2s bust and sound like tinkerbells, yet NOT set a code. Denso, Delco/Delphi and NTK brands are the only ones you should use. Bosch O2s are dogshit.
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Old 04-05-2011, 01:05 PM   #3
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Default Re: 2000 Honda Accord V6 V-TEC - Horrible gas mileage

It sounds like an air intake or exhaust issue. I would suspect O2s being bad, causing the PCM/ECM to dump too much fuel into the engine. However, that wouldn't cause the stalling out issue you described, unless the stalling out only occurs after the engine is warm (when the O2s are in closed loop mode and sending readings to the PCM). A clogged catalytic convertor can also exhibit similar symptoms, but the symtoms are usually more consistent. It can't hurt to have it checked I guess. Your best bet might be to have your exhaust air/fuel ratio checked to see how far off you are, which could clue a good mechanic in.
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Old 04-07-2011, 07:24 AM   #4
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Default Re: 2000 Honda Accord V6 V-TEC - Horrible gas mileage

Thanks for the replies.

I finally said to hell with it and took the car in to the Honda service department to find out what's going on.

After running full diagnostics and going over the car, and understanding what codes were thrown and why (short ram air intake install made a code, as did cleaning the throttle body and iacv) they claim to know 100% what is causing my problem...

My rims.

They are 20"s motegi wheels with a tire too big for my car (enough I had to lift the rear end 4 1/2 inches just not to rub fenders).

I'm shopping around for some 16" alloys now.

Does this sound feasible? I mean, I know it makes sense logically, and they also tell me the ethanol in our fuel hurts it by a few mpg too. Is Honda right, or were they just trying to get me out of their hair?

BTW they were nice and did not charge me for the diagnostics, despite quoting me $50 to do it beforehand.

EDIT: The car has NOT stalled out on a warm start since cleaning the iacv. This is no longer a symptom.

P.S.-Changing the wheels is not a huge deal for me, as I planned on doing it anyway, now I am just going to do it sooner. I could easily break even on some new 16" wheels with these 20"s. If THAT doesn't do it, I'm looking into o2 sensor. If THAT doesn't work... FML I dunno
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Old 04-19-2011, 09:16 AM   #5
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Default Re: 2000 Honda Accord V6 V-TEC - Horrible gas mileage

Ok, so I'm back with an update to my situation.

I took the car to the official Honda service department, and the most information I got from them other than detailed error codes was them telling me my 20" rims were causing the problem. That just HAD to be it. They were telling me that the P1457 code for the EVAP system was likely just a loose gas cap.

Well. Let me tell you WHAT. I replaced my rims with no change to my mpg. I put on stock size 16" aluminum wheels.

The Accord has a specific code for the loose gas cap. It's P1456. I DO have a leak SOMEWHERE in my EVAP system, and I'm going today to run a smoke test to see if I can find it.

I also did test my O2 sensors finally, and the upstream sensor seems to be dead, and it not returning anything to my multimeter, assuming we did the test right. We tested the downstream sensor in the same manner, and it read 13.5 ohms, well within the 10-40 range it's supposed to be.

I've read that the EVAP leak won't make the car run bad, and it DOESN'T run bad since cleaning the IACV, but would it be a potential culprit behind the bad fuel economy?

I also recently got a code P0420 about the catalyst system operating below threshold. I've done a visual and audible inspection on the cat, but it SEEMS as best I can tell to be fine. The car does not seem to feel like it has a clogged exhaust.

I DO KNOW for a fact that the car is running rich. You can smell fuel from the exhaust, and the exhaust is nice and black from the rich fuel mixture, as were the spark plugs I replaced.

Additionally, today I am removing my short ram air intake and replacing it with a stock intake system, just to eliminate it from the equation. Could perhaps that have some part to play? Perhaps not getting enough vacuum from the aftermarket intake? According to the program I analyzed the computer with while the car was running, the car maintains ABOUT -8psi at idle. Is this correct?

Should I just focus on the seemingly busted O2? Or maybe there is something else causing the car to run really rich which is what killed the sensor in the first place?

Looking for ideas.

Additionally, if the cat needs replacing, I can't afford to get an OEM one. Would a universal one modded to accept my O2 welded on there do the job just fine?
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Old 04-19-2011, 10:00 AM   #6
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Default Re: 2000 Honda Accord V6 V-TEC - Horrible gas mileage

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Originally Posted by DJApoc View Post
...Should I just focus on the seemingly busted O2? Or maybe there is something else causing the car to run really rich which is what killed the sensor in the first place?

...

Additionally, if the cat needs replacing, I can't afford to get an OEM one. Would a universal one modded to accept my O2 welded on there do the job just fine?
the upstream O2 is the one that matters. replace it and see what you get. try the "spark plug de-fouler" trick on the downstream O2 and see if that gets rid of your P0420. worked like magic on my wife's 4cyl. if it doesn't work, there are alternatives to OEM cats. we've been happy with the quality and fit of bolt-on Magnaflow standard replacement cats. you can find them for cheap on Amazon.com.

also, i feel pretty confident in saying that the after market intake wasn't doing you any harm. all the ECU knows and cares about in front of the TB is the the intake air temp. although it was still good practice on your part to eliminate it as a variable.

and i think you mentioned that you go three clicks when filling up... did you mean with the pump itself or when tightening the cap? overfilling the tank on the 98-02 model can cause liquid overflow into valves and lines in the EVAP system that are only meant for vapors. just FYI.
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Old 04-19-2011, 12:49 PM   #7
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Default Re: 2000 Honda Accord V6 V-TEC - Horrible gas mileage

Thanks for the tip on the Magnaflow!

I searched amazon and found this one

http://www.amazon.com/Magnaflow-5405...2000&carId=001

This should work, right? Amazon says it fits, but it looks like it would need to be welded on, but I assume any muffler shop can do this pretty easily, and it even has the slot for the downstream o2.
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Old 04-19-2011, 04:53 PM   #8
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Default Re: 2000 Honda Accord V6 V-TEC - Horrible gas mileage

Quote:
Originally Posted by DJApoc View Post
they claim to know 100% what is causing my problem...

My rims.

Does this sound feasible? I mean, I know it makes sense logically, and they also tell me the ethanol in our fuel hurts it by a few mpg too. Is Honda right, or were they just trying to get me out of their hair?
Well, while they are right that rim size and ethanol have effects on mpg, they are full of crap for saying that these two things are the entire cause for your horrible mpg. These two things can only account for maybe a 1-3 mpg drop (and that might be generous). Maybe if your alignment was terrible and your tires were pretty underinflated you would see a bigger drop but I'm assuming those two things are "in spec" enough to not be much of a factor.

This is the laziness that led me to never use my local Honda dealer.

Quote:
Originally Posted by hondamark35 View Post
the upstream O2 is the one that matters. replace it and see what you get. try the "spark plug de-fouler" trick on the downstream O2 and see if that gets rid of your P0420. worked like magic on my wife's 4cyl. if it doesn't work, there are alternatives to OEM cats. we've been happy with the quality and fit of bolt-on Magnaflow standard replacement cats. you can find them for cheap on Amazon.com.

also, i feel pretty confident in saying that the after market intake wasn't doing you any harm. all the ECU knows and cares about in front of the TB is the the intake air temp. although it was still good practice on your part to eliminate it as a variable.

and i think you mentioned that you go three clicks when filling up... did you mean with the pump itself or when tightening the cap? overfilling the tank on the 98-02 model can cause liquid overflow into valves and lines in the EVAP system that are only meant for vapors. just FYI.
Good info as usual. I'd say following this is your best bet OP.

And yes OP, any exhaust shop can fit and weld that on easily.
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Old 05-09-2011, 08:55 PM   #9
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Default Re: 2000 Honda Accord V6 V-TEC - Horrible gas mileage

I had a similar issue with my accord. 2000 v6. I was getting around 15 mpg. I replaced the timing belt. I bought the timing belt online from a honda dealer and found a discount for labor at my local honda so I had honda install the honda belt. I did all other labor. I did my valves, which later I was told did not need to be adjusted. I cleaned out the egr passage on the intake which is way easier than it sounds and I changed the spark plugs to stock new ones. My car is now getting 22 city 30 highway through normal driving. 400 miles per tank. I have 160k in it and it runs like new. I will also say to check for vaccum leaks as that will affect your starting. I did this throught the spraying of carburator cleaner while the engine was running but cold. If it is hot it could start a fire. Remember to do any maintainence when the engine is cold.

Thank you to these forums i spent 700 for the belt including labor and less than 20 for the plugs. The rest was labor. I am very happy now and hope something here helps others.
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Old 05-10-2011, 07:43 AM   #10
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Default Re: 2000 Honda Accord V6 V-TEC - Horrible gas mileage

700 for the belt?

If you had done it yourself, it would have cost you about $30.

I intend on changing mine soon too. The reason it cost so much is because it's basically easier to just pull the engine out to change the belt because it's so tricky to get at.

I've done a lot to try to fix all this so far, about to say "to hell with it" and just dump the lemon on someone else if I can't get it fixed for a reasonable price.

For some reason, my previous post update never posted, so I'll try to update now.

I took the car in to another shop to get things checked out in more detail. I'm also keeping closer tabs on CEL codes as they come up with a portable code reader.

Still getting P1457 (EVAP canister leak) and P0420 (cat below threshold).

Had the shop run full diagnostics on all sensors, and it turns out the O2's are just fine. EGR valve is fine. Checked the EVAP system and nothing is jammed up or leaking, but we did not run a smoke test on it since everyone keeps assuring me an EVAP leak won't impact fuel economy, although since I have a basic understanding of what it does, I don't see how it wouldn't.

I'm really beginning to think it may just be the cat. I'm going to change the timing belt anyway since all it will cost me is $30 and a saturday afternoon.

The mechanic at the shop gave me some BG 44k and told me to run that through the system, and now the worst MPG I get is about 17mpg. Problem is, I seem to get the exact same MPG on the highway. Something is definitely wrong, and getting the crappy highway MPG seems to tell me it's the cat, especially since after longer driving sessions the car seems to feel bogged down a bit for a few minutes, and trying to accelerate quickly doesn't go so well for about 5-10 minutes after getting off the highway.

So, I am pretty sure I narrowed it down, just looking for any other input...
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Old 05-10-2011, 07:22 PM   #11
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Default Re: 2000 Honda Accord V6 V-TEC - Horrible gas mileage

The cheapest I found for the timing belt(inside the valve cover) was 175 including water pump online. Also, there is going to be a tensioner in there that may need replacing. That was 100. So it was 175 + 100+425 labor = 700 which was good considering dealers were telling me over 1000. Honda calls for this belt to be changed at 105K. I was lucky and had it last until 156k. If it breaks it can do serious damage to the motor. while the belt was changed honda asks to do the water pump, it is in where the belt is.

Did you take off the intake manifold? That Egr port was clogged solid on mine and threw no codes, just bad milage. I used a screw driver and carb cleaner to clean it out.
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Old 05-10-2011, 10:21 PM   #12
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Default Re: 2000 Honda Accord V6 V-TEC - Horrible gas mileage

Hey Guys im new to the site..just bought a 00 3.0 and its funny first thread i see is about horrible gas mileage..Im gonna do a full tune-up on the car being i just got it..and timing belt and water pump also...and i pray to the good lord that it helps...because im getting about 21 highway..
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Old 05-11-2011, 12:58 PM   #13
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Default Re: 2000 Honda Accord V6 V-TEC - Horrible gas mileage

Well, I have just had it with this car, and decided to sell it to banish it from my sight.

Hopefully going to get into an older Civic, preferably an Si.

Thanks to everyone who tried to help.
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Old 05-11-2011, 01:21 PM   #14
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Default Re: 2000 Honda Accord V6 V-TEC - Horrible gas mileage

Sorry we couldn't help and that the problem never was fully solved.

As far as the EVAP code goes with mpg, it really doesn't usually affect anything. Hell, I had that code for a few months on my Accord because it can be a pain to find the issue sometimes. Finally had to fix it because of an upcoming emissions test.

Never affected how the car ran or mpg numbers. I haven't really heard of anyone else with an EVAP code see the drop in mileage you saw either.

Good luck with the car search!

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Hey Guys im new to the site..just bought a 00 3.0 and its funny first thread i see is about horrible gas mileage..Im gonna do a full tune-up on the car being i just got it..and timing belt and water pump also...and i pray to the good lord that it helps...because im getting about 21 highway..
Make sure you read into the other suggestions that were posted if the problem persists.
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