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Old 03-29-2018, 11:43 AM   #1 (permalink)
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Hello from the PNW with a 98 Civic EX

Hello!

I picked up a Civic EX automatic with ~190k miles, as something of an EmergencyINeedACarRightNow purchase.

I suspect it had been sitting for some time as it ran horribly rough, but it had had a new O2 sensor installed, just over a month or two prior.

When it was running horribly, it was getting around 32 MPG. Not too bad I thought.

Then I did a tune up with a new cap and rotor (both Standard Motors), new NGK V-Power plugs, and NGK plug wires. I also replaced the valve cover gasket. I figured with how much better it was running, the economy would have gone up.

Fuel economy took a dive down to ~28 MPG. I figured the ECU had to relearn timing and fuel metering.

A month or two ago, I posted about the undesirable fuel economy at Honda-Tech and it was suggested that I should inflate the tires to a higher pressure. I inflated them from ~30 PSI to ~35 PSI. The economy went up to ~28.5 MPG.

It was still running rough, so I adjusted the timing and got it fairly close. Economy dived down to an average of ~25 MPG for that week. Granted there was a lot of idling when I adjusted the timing. With a coworkers help, and his really fancy timing light, we were able to get the engine timing to be spot on, and it runs very smooth. It's almost nice to drive around town, but still rough on the highways (the tires are terrible Les Schwab tires). The economy on that tank was down around ~24 MPG. When I fuel up tomorrow I'll have a complete week on the current timing. And that average was 25.7 MPG

So, I'm not looking to hypermile, but I'd like to get decent economy out of this car! At ~24 MPG, I might as well be driving a a turbo Subaru!

Hopefully I can get some suggestions to get this car running better!

SC


Last edited by Smithcraft; 03-30-2018 at 02:20 PM.. Reason: Add the most recent MPG average.
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Old 04-26-2018, 10:43 PM   #2 (permalink)
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Quote:
Originally Posted by Smithcraft View Post
Hello!

I picked up a Civic EX automatic with ~190k miles, as something of an EmergencyINeedACarRightNow purchase.

I suspect it had been sitting for some time as it ran horribly rough, but it had had a new O2 sensor installed, just over a month or two prior.

When it was running horribly, it was getting around 32 MPG. Not too bad I thought.

Then I did a tune up with a new cap and rotor (both Standard Motors), new NGK V-Power plugs, and NGK plug wires. I also replaced the valve cover gasket. I figured with how much better it was running, the economy would have gone up.

Fuel economy took a dive down to ~28 MPG. I figured the ECU had to relearn timing and fuel metering.

A month or two ago, I posted about the undesirable fuel economy at Honda-Tech and it was suggested that I should inflate the tires to a higher pressure. I inflated them from ~30 PSI to ~35 PSI. The economy went up to ~28.5 MPG.

It was still running rough, so I adjusted the timing and got it fairly close. Economy dived down to an average of ~25 MPG for that week. Granted there was a lot of idling when I adjusted the timing. With a coworkers help, and his really fancy timing light, we were able to get the engine timing to be spot on, and it runs very smooth. It's almost nice to drive around town, but still rough on the highways (the tires are terrible Les Schwab tires). The economy on that tank was down around ~24 MPG. When I fuel up tomorrow I'll have a complete week on the current timing. And that average was 25.7 MPG

So, I'm not looking to hypermile, but I'd like to get decent economy out of this car! At ~24 MPG, I might as well be driving a a turbo Subaru!

Hopefully I can get some suggestions to get this car running better!

SC
If it helps, my 04 Civic isn't getting the mileage (while hypermiling no less!) that many others are able to get while driving like they are at the races. I'm getting an average read of 30-31 mpg. I'm not sure what my issue is either. I've got the engine and transmission running much better than when I bought the car. I'm not going to get wrapped around the axle about it, but it IS annoying. Best of luck my man.
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Old 04-26-2018, 10:54 PM   #3 (permalink)
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If your MPG dropped AFTER you had your rotors changed check to see if they were installed properly (a major red flag to this is wheels being hot to the touch after drives, poor coasting ability, and hearing metal rubbing against metal when driving slowly with the windows down). My Civic's MPG went down from high 30s (prior to modding) to around 30-31 due to the caliper dragging.

A couple other things could be:
- Bad tire alignment (requiring more effort on the part of the car to drive straight)
- Old fluids (transmission fluid, oil, brake fluid, etc).

A dragging emergency brake could also be a possible cause. So could short trips on a cold engine combined with high speeds and little coasting.

Are you monitoring fuel economy with a Scangauge? It could be miscalculated too, unless your low MPGs were from a tank refill direct calculation.
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Old 05-24-2018, 12:50 PM   #4 (permalink)
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I didn't have the brake rotors changed. I replaced the rotor in the distributer.

The alignment hasn't been changed. I strongly doubt that the ebrake started dragging when I did the tune up.

I compute the MPG by filling the tank and then dividing the miles driven by the gallons put into the tank. I used the same procedure, before and after the tune up.
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Old 05-24-2018, 01:23 PM   #5 (permalink)
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I would bet that 28.5 MPG is about what an AT 1998 Civic EX is expected to get in the city? What kind of driving are you doing? Lots of stop/start city stuff or a combination of that with longer freeway trips?

How do you know the timing was close? Which mark on the crank pulley did you use for judging? And did you jump the ECU while setting it?

Have you done wet and dry compression tests? Checked for exhaust gasses and/or oil in the coolant? 190,000 miles is a lot of miles and you don't know that much about the vehicle history... leaking valves, rings, head gasket... all would sap power and undermine fuel economy.

I'll keep tabs with you and see if I can advise other stuff too.

Hey, you have the Honda factory service manual for the 1998 Civic? I do. I'll share if you want. Free, of course.
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.



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Old 05-24-2018, 01:39 PM   #6 (permalink)
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The exciting part is that it was getting ~32 before the tune up, with the same route to work. Granted it was undriveable on the freeway at freeway speeds, whereas after the tune up, it is pretty much driveable on the freeway.

I adjusted the timing, and apparently had it very close. Then my timing light said "F*** YOU! I'm outta here!" Then I had a coworker (ASE certified) with his fancy timing light help out, and it was running quite well after that. MPG went down to 24. [edit: It's hard to see the timing as the cruise control line, and the power steering line cross right over the timing mark on the inside of the pulley. I don't know which timing mark my coworker used.]

The economy had been slowly creeping up, so I decided to do an end run around the ECU and just reset it and then do an idle relearn. I hoped that by going to the default values, it would go back to getting ~32. The ECU had a different plan in mind, and the MPG has been floating around ~27 since then.

I have a scan of the factory manual. It's not as nice as the Subaru factory PDFs, but it's useable.

Last edited by Smithcraft; 05-24-2018 at 02:24 PM..
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Old 05-24-2018, 02:53 PM   #7 (permalink)
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Since the tune-up and timing setting seem to have precipitated a 25% reduction in fuel economy, I have to think something was not right in the servicing. But since the car was not running well at freeway speeds, well, you have possibly more than one set of problems confounding any "read" on what is the cause.

Suspect the timing. Your car is probably identical to mine on the timing setting. On the crank pully are several timing marks. You want the white one. It sets the timing to 12 degrees BTDC. But before you do that, you have to jump the ECU under the passenger size dashboard. If you don't, you cannot get it truly correct. The ECU will be actively compensating as you work with your timing light. It will look right on the pully and be wrong in reality. You have to jump the ECU. You did jumped it?

The timing marks are wicked difficult to see. And you have to see them directly through the "V" shaped viewer on the timing cover or you will not get the timing right.

BTW, you got the Honda service manual? It is full of important detail. Nearly 2000 pages or something. I have a good PDF copy I can send to you via gmail. I do that for folks on this site from time-to-time. File is clean and safe. PM me if you want it.
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.



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Old 06-07-2018, 09:46 AM   #8 (permalink)
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Yes, I followed the instructions in the FSM for setting the timing. Dang kick panel won't go back on right, but it's not something I'm worried about.

I had the timing very close while doing it myself, but it's a bit of a reach to adjust the distributor and check the timing. Having my coworker sight the timing mark while I adjusted the distributor worked out great.

Generally, when you get a car running better, the economy should improve. Why it doesn't with this one, is what's irritating to deal with.
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Old 06-07-2018, 10:17 AM   #9 (permalink)
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Quote:
Originally Posted by Smithcraft View Post
... Generally, when you get a car running better, the economy should improve. Why it doesn't with this one, is what's irritating to deal with.
How you drive has a big effect. But a big part of your frustration might be due to expectations of higher economy and the fact that it is an automatic. The EPA 2008 rating formula, which is more realistic for most drivers, rates the 1998 4 speed auto EX at 24 city, 31 highway, and 27 combined. Your car is more or less running as expected. Modding will help. Start by pumping to max sidewall on the tires. And there are some low-prifile and cheap mods you could try too.
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.



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Old 06-07-2018, 12:07 PM   #10 (permalink)
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I drive my car the same way now, that I drove it before the tune up.

That doesn't relate to the loss of MPG after the tune up.

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