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Old 05-24-2018, 01:53 PM   #7 (permalink)
Cyborg ECU
California98Civic's Avatar
Join Date: Mar 2011
Location: Coastal Southern California
Posts: 6,297

Black and Green - '98 Honda Civic DX Coupe
Team Honda
90 day: 66.42 mpg (US)

Black and Red - '00 Nashbar Custom built eBike
90 day: 3671.43 mpg (US)
Thanks: 2,373
Thanked 2,162 Times in 1,465 Posts
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.
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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