Why Can I Not Get This Car Over 24MPG?

[NVMyMPG]

UGH! I have done all sorts of work to my 87 LXi auto and just can not seem to get better then 24MPG in mixed driving. My buddy with his Hyundai loves to rum his 30 - 35 MPG in my face.
I have done:
New Plugs, wires, cap, rotor, vacuum advance, checked and fixed some vacuum leaks, new O2 sensor, punched out the plugged cat, and changed out the fluids both oil and trans fluid.

Car seems to run good. Not big on power but it gets there and back. No overheating, 189K miles. Only problem I have is the PFI light comes on from time to time. I get a 13 code from the computer which is a EGR code I believe. I have replaced the EGR valve with a junkyard one and checked for vacuum leaks and can't get the light to go away. I don't know what else to do but I thought Hondas got a lot better millage then this.

[derolph]

24MPG in mixed driving does sound low to me. Of course, the "mix" in your mixed driving is relevant. You've covered most of the checkpoints. Do you ever put fuel injector cleaner in your gas tank? If not, I would do that; alternatively, you could try the higher-strength fuel system cleaner.

What about the PCV valve? Have you checked it? Are your tires properly inflated? What about the air filter? And, the fuel filter?

[DBMaster]

A lot depends upon your driving habits. I got 26-27 out of mine in combined driving and I step on it hard and drive 80 on the toll roads around here. 32 is the best it would get on a highway trip. It got 35 prior to reformulation of the gasoline in 1995.

So, 24 may not be bad if all you are doing is stop and go.

[Legend_master]

When you talk abouts a Honda making good gas millage you to consider a lot of factors. Altitude, driving up and down hills, good bearings, proper intake flow, good gas quality, tire size....... How new is the Hyundai? Think about the advancements in PGMfi in the last 20+ years, that's the reason he makes better MPG.

[2oodoor]

Try doing a good clean and lube of the distributor centrifugal advance and set the timing a up 2-3 degrees over oem recommendation because you should have no complaints about power on take off. Lose any extra weight in the trunk tooEvery pound makes a difference,

[Dr_Snooz]

A code of 13 indicates a problem in the atmospheric pressure sensor circuit. If the sensor thinks you're at a different elevation level than you are, MPG will be impacted. We have a shop manual for download (http://honda.roadpwnage.com/manuals/pages/usdm-accord-1989-full.php) that you can use to diagnose the problem. It is for the 1989 model year and it might be somewhat different than the '87 you're driving, but you can try it. The troubleshooting procedure starts on p. 12-36. Run through the tests and report back what you learn.

[NVMyMPG]

Thanks for the replies. I have not advanced the timing yet. I forgot I also have replaced the fuel filter and air filters.

Thanks for the manual download. I will try working on the atmospheric circuit and see if I can get that back into line. maybe that will help.

Yes the Hyundai is much newer and I do expect it to get better millage then my 87 so you guys are right I am comparing apples to oranges there. But the point is that I expect the Honda to be closer to 30 then what I am getting. My mixed driving is more hi-way then city. I live 19 miles out of town. So my typical mixed trip would be 40 miles of minimal stops going 65MPH and 15 miles of city driving. I do this pretty much every day.

[Buzo]

I would monitor the output of my Oxygen Sensor using a voltmeter. Connect it to the output of the sensor and put it in the cabin where you can see it while driving. If it is continuously varying from 0 to 1 Volt, the mix is OK, but if it stays at 1V, then your mix is to rich. For instance, if it stays at 1 V in a stop light, but starts varying during acceleration, then your problem is at idle. Or the other way around. It won't tell you what to change to fix the problem, but it will narrow the problem. In my experience, 17 MPG means the sensor is always at 1V, 24 MPG you have only rich spots, 26-28 MPG, your reading is almost perfect (always varying).

Note: if want to try this using a digital voltmeter, make sure it is in manual range, otherwise it will continuously change scale from mV to V and it will be impossible to read.

[DBMaster]

^^That, I guess, is why my research a number of years ago indicated a preference for using an analog meter for the O2 sensors.

My car failed the emission test a number of years ago due to high hydrocarbons. I had no idea what could be wrong since it ran and accelerated well, returned normal fuel economy, etc. My mechanic said that unless the O2 sensors were REALLY bad they would not light up the check engine light. He used the voltmeter test and said they were "slow to respond." All I can say is that after he changed them (2 on the LXi) the car passed emission testing until I wrecked it. :(

[ecogabriel]

Code 12 is EGR-related, and to my knowledge there is no other code that is associated with EGR issues, so that is something you need to investigate.

As for the MPGs, I do not think your numbers are that bad, but that ignores how your driving habits are.
My wife got 18 mpg driving across downtown ATL back and forth to work. Traffic lights and heavy traffic meant lots of idling time; the same trip that on a weekend would take 15-18 min. it would take 40-50 minutes in the evening drive.
I would get one extra MPG on the same circuit. Because the "method" we use is count the miles between fueling to the top, I did the same calculation several times (I still do it every time I fill the tank full)

As for highway driving, I recently took the car on a 240mi. drive; with the reservations of a single drive, it averaged 30 MPG.
Car is auto and stock, but otherwise well maintained with less than 10K on spark plugs (platinum), wires, cap/rotor, filters, O2 sensor. Also, fuel injectors were bench cleaned and checked for spray pattern and flow.

Improvements in EFI systems including ignition (ours is pretty much mechanical/vacuum but without breakers) may account for the better MPG in newer cars.
I am pretty sure our cars would have been close to the top in fuel economy in their class and day; they are still pretty decent 20+ years since the last left the factory.

[DBMaster]

I had a code 12 about six or eight years ago. I was told that the EGR valve rarely failed so I spent a lot of time replacing the components in the control box to no avail. What happened was that the EGR would stick slightly about halfway open when vacuum was applied. It WOULD open all the way, but the sensor on top of it read that sticking as a faulty EGR valve. $140 later with a new EGR assembly and it was fine.

[Legend_master]

I actually always fill all the way up, just so I can keep track of my MPG. I can almost always tell when there is a problem just by looking at the data. I started using a free app on the iphone when I put the new Engine in, so this is since october.

http://img.photobucket.com/albums/v667/Legend_Master/1f9de617.jpg

http://img.photobucket.com/albums/v667/Legend_Master/d0eacbc5.jpg

The MPG dropped once I put A/C in the car. I have found it to be a little better if I only use the A/C on the Highway.

[derolph]

With my 88 Accord, I drove from my home (about 20 miles east of Columbus, Ohio) to Indianapolis, IN and back, in April 2003. The main route is I-70, which goes through both Columbus and Indianapolis. The trip was almost entirely on I-70; I live about 3 miles from I-70 and I was only off I-70, as nearly as I can recall, for about 10 miles in the Indianapolis area. On I-70, I was usually driving in the 65-70 MPH speed range. I got 38 MPG on that trip.

I"m sure my MPG calculation was accurate. I filled the tank at a gas station next to my entrance to I-70 in Ohio, I made the entire trip on that tank of gas, stopped at the same gas station back in Ohio, at the same pump, and topped up the tank just like I did when I filled before leaving Ohio.

I don't know what the MPG might be now on this car; I haven't calculated it for a long time. Since 2003, the distributor was replaced and I would like to have the timing checked and also confirm the spark advance mechanism is working right. Anyway, I doubt I can get 38 MPG with it now.

[2oodoor]

I am pretty sure the gas formulations have changed quite a bit since 03, even since 07. I was able to get 20 mpg on the interstate with my F150 in 07 and I am doing good to get 16 now, nothing has changed with the truck. I even use full synthetic in it now.
My Hondas, I always buy either exactly 10 gall or 5 gal, depending where Im at. I reset the trip odo every time. Whatever the odo says after about 10 min of driving with the low fuel light on, is what my estimated MPG is. For example this last 10 gal got me 248 miles which is 24.8 MPG round up 25 MPG.

Legendmaster is spot on with his idea. It is extremley benefical to collect data, lots of it and devote to it. You can use an app or just ues Excel spreadsheets. There are good tutorials for Excel, showing you how to enter formulas and achive desired outcomes with the data you collect. Patterns always emerge, especially visable when you convert data into graphs, which Excel does for you.

also, my Lxi has got 31 mpg on the black four lane, at 60-65 mph, that is with an automatic. Never gets better than 26 around town (usually 23) with mixed driving. That is bone stock, 25 year old cat etc.. and it isn't running quite right.

my lx, dohc, now for the past two months with a DFEV progressive Weber carb, no vac advance, timing set at 5 btc only that 24.8 so far is the best Ive got with that combo.
Even with a poorly tuned 38 Weber, it never dipped below 20 mpg.
For comparison sake...

[gyates93]

On a recent road trip from Kingston, Ontario to Halifax, my 89 lx with carb averaged just under 35mpg. It's bone stock without AC.. Are the carbeurated models known for having better fuel economy?

[derolph]

Are the carbeurated models known for having better fuel economy?I don't believe so. Generally, fuel injection yields better fuel economy than carbeuration.
Carburetor vs. Fuel Injection: Understanding the Pros and Cons (http://www.carsdirect.com/used-car-buying/carburetor-vs-fuel-injection-understanding-the-pros-and-cons). As i said in my previous post, I got 38 MPG with my 88 LX-i back in 2003.

[pickupman6]

Carbed cars have a higher final drive than the fi models, that is why on the highway they get such good mileage. You can do 80 in a carbed car and be running the "same" rpms as a fi car doing 70.

[derolph]

Carbed cars have a higher final drive than the fi models, that is why on the highway they get such good mileage. You can do 80 in a carbed car and be running the "same" rpms as a fi car doing 70.So, you're saying they are geared different. Can you provide a reference supporting that? I don't believe so.

I can find numerous other references besides the one in my last post confirming that fi usually yields better mileage.

[pickupman6]

Ok just to be clear I was talking specifically about 3geez. The fuelies final drive is 4.066 while the dx and lx cars final drive is 3.86 or something like that. If you don't believe me that's your problem do a search on here. I'm not going to waste my time trying to find the one thread that lists all the differences between the transmissions. But I did do a quick search so here you go. http://www.3geez.com/forum/showthread.php?t=44500&highlight=transmission+differences

[pickupman6]

Btw I used to have a carb trans in my car and could easily get 38 mpg, now I have an lxi I trans and the best I have gotten is 35. I don't need a reference to know there's a difference.

[kentwat]

Does the pgfmi light stay on all the time or does it come on after it warms up? I had that problem with mine. I swapped many egrs from junkyard and no change. I did the egr test in the manual going through all tests and it turned out to be the cvc in the black box. A little green disk looking thing that controls vacuum. No light after I changed it out.

Also when you say about mpg is this with the ac on? 26-7 is about what I get with the ac on. My car is an 86 with 5 speed and 318k. All stock without air I get 33 mpg if I keep the rpms under 4000 rpm. I get even better mileage if I keep it under 300 but that is very hard to do. Welcome!!!

[2drSE-i]

So, you're saying they are geared different. Can you provide a reference supporting that? I don't believe so.

I can find numerous other references besides the one in my last post confirming that fi usually yields better mileage.

Actually, they are geared different. And in many cases, carbed cars DO get better mileage. Why? I couldn't tell you. Maybe because these fuel injection systems are pretty basic, and the carbs (when running right) are very efficient. And if your basing your findings based upon what members on here have said, remember, there is no factual data supporting this. Heck, we had a member who based his fuel mileage on how many miles he could go on a half tank.

[derolph]

Actually, they are geared different.OK, I concede on that point.


And in many cases, carbed cars DO get better mileage. Why? I couldn't tell you. Maybe because these fuel injection systems are pretty basic, and the carbs (when running right) are very efficient. I think we need to keep in mind here that we're talking about early vintage fuel injected models. The 3rd gen Honda was the main time when Honda, like other manufacturers, was transitioning from carburetors to fuel injectors. And, why did the industry move completely to fuel injection? Because it is more efficient, and it got better each successive year. So, even if the early models with fuel injection were not more efficient that those with carburetors, subsequent improvements achieved that goal. Another point re: the 3rd gen Accords which I don't believe was mentioned in this discussion: the engines with carburetors were rated at 98 HP while those with fi were 110 HP. Also, driving habits and other factors (age and condition, etc.) vary from one driver to another and one car to another, which is clearly evident right here in this discussion.

Here's an article that explains it well: Why Fuel Injectors are Better Than Carburetors (http://voices.yahoo.com/why-fuel-injectors-better-than-carburetors-3223581.html)


And if your basing your findings based upon what members on here have said...What "findings"? My basic initial point in this discussion thread was that 24MPG seemed low and I stated I got 38 MPG during a trip consisting of mostly highway driving. I wasn't basing any findings on what members said here.

[Dr_Snooz]

The final drive specs can be found in the manual. Download it from the 3geez wiki.

[2drSE-i]

I think we need to keep in mind here that we're talking about early vintage fuel injected models. The 3rd gen Honda was the main time when Honda, like other manufacturers, was transitioning from carburetors to fuel injectors. And, why did the industry move completely to fuel injection? Because it is more efficient, and it got better each successive year. So, even if the early models with fuel injection were not more efficient that those with carburetors, subsequent improvements achieved that goal. Another point re: the 3rd gen Accords which I don't believe was mentioned in this discussion: the engines with carburetors were rated at 98 HP while those with fi were 110 HP. Also, driving habits and other factors (age and condition, etc.) vary from one driver to another and one car to another, which is clearly evident right here in this discussion.

What "findings"? My basic initial point in this discussion thread was that 24MPG seemed low and I stated I got 38 MPG during a trip consisting of mostly highway driving. I wasn't basing any findings on what members said here.

No one is arguing that carburetion is inefficient compared to FI; it's obviously true, in most cases. This not being one of them. That can be attributed to MANY things (Gear ratios, compression ratio, intake manifolds, crappy engine management, etc etc)

24 does seem low, but definitely not out of the ordinary, especially due to the age of the vehicles. I remember when I wouldn't average less than 30. Now, i'm lucky to get 24.

[g.frost]

I've had my (carb) stock DX manual since new. 26-28mpg in town, 34-36 hwy. All time record is 38 mpg once ( that's over 500 miles on a tank!) on a trip of all secondary hwy where I couldn't do over 60-65 mph. (hwy 20 from Grass Valley to Mendocino and back) Cruising at 65-75 mph will get 35mpg easy. You don't have to put an egg on the pedal to get these numbers in the carb manual. (...if it's running right)

[Dr_Snooz]

A code of 13 indicates a problem in the atmospheric pressure sensor circuit. If the sensor thinks you're at a different elevation level than you are, MPG will be impacted. We have a shop manual for download (http://honda.roadpwnage.com/manuals/pages/usdm-accord-1989-full.php) that you can use to diagnose the problem. It is for the 1989 model year and it might be somewhat different than the '87 you're driving, but you can try it. The troubleshooting procedure starts on p. 12-36. Run through the tests and report back what you learn.

You should do what this guy says.

[pickupman6]

Rofl! YES! ^^^ +1

[2drSE-i]

You should do what this guy says.

We are far more interested in internet conjecture!

[Dr_Snooz]

We are far more interested in internet conjecture!

:rofl:

Thanks! I needed the laugh.

[rocketman]

A few things . . . lighter engine oil . . . higher air pressure in your tires . . . turn off your A/C . . . advance your ignition timing until it pings, then go back a bit . . . and the BIGGEST factor . . . watch your driving habits. You will really improve your mpg by just driving like a little old lady. But how much fun is that? My '89 carb'd Accord has over 550k and I still get 25-30, using 20W50 but running a little advance on timing, tire pressure about 36 psi. If I put my foot in it a lot I go under 25, but I know why. Good luck! Rocketman