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Discussion Starter #1
My local test circuit is a 9 mile out and back on a dual carriageway/ divided highway. I try to keep the speed between 55 and 60mph.

There is a long gentle hill in the middle of the route and a hill at the midpoint where I turn on a ramp.

I did it a few times over the past 2 weeks in my new 2000 Insight and got 54mpg each time.

After a plug re-gap and valve lash adjustment, I got 60mpg with changing between 4th and 5th when needed.

I then did a lap while going only up to 4th gear only and cruising and got 64mpg.

I did another lap staying in 5th gear only (at speed) and got 62mpg.

It seems the car still needs tuning and corrective measures to stay in lean burn longer and not to charge the battery. Until then it seems that 4th gear cruising is the sweet spot for now.
 

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when i first bought my car, i thought that the car did not like 5th gear either. i later learned there were a number of factors that put drag on the engine that caused me to get better mpg in 4th then 5th. everyone is different, but maybe look into a couple things.
transmission fluid age(not that huge but if it has never been done it may be a good idea)
***clean the EGR spacer and its corresponding gasket on the intake manifold, use some carb cleaner and a punch or knife to help get some of the crap out. if you have any bucking it may be this or if not this, likely the egr valve.
*** pump your tires up to 50+ psi. youll be fine and the drag is much less.
fresh oil is always important, but im sure you know that.
im sure you know the concept of lean burn, but if it is hard to accomplish try and not watch your speed as much as your instant mpg on the FCD.
when you replaced the plugs, i assume they were the correct index. if not do so.
also, do you have your aero panels on the bottom? this can cause alot of drag at high speeds, or in general really.

you are getting good mileage on your trek, just a few things that may help, hopefully.

let us know of anything you do and any improvements.
 

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I can almost guarantee that your tires are 175/65r14 of some non-bridgestone make.
 

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in addition to the EGR cleaning, inflated potenza OEM tires and aero panels , can recommend also checking the 12v battery. a constantly charging deteriorated 12v battery was costing me 10-15 mpg. The battery was 5 years old only.
 

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Discussion Starter #6
Installed a new EGR (from a 2000 Accord 4cyl). The engine runs smoother and transitions to/from lean burn are smoother.

So thats it for now for engine work:

Plugs gapped, valve lash set, injectors cleaned, egr plate cleaned, new egr installed and efi ecu reset.

I did the test loop again and got 63.2 mpg in 5th and 66.2mpg in 4th. It seems consistent.

I also installed the clutch switch shorting switch. It helps control charging and assist nicely.

Now to get rid of the michelin x-ice 175-65-R14 tires LOL. I was able to order 2 Potenza RE92's locally but the dealers says they are back ordered in all NA.

I am heading to Memphis for the ZCAR convention so I'll try to get 2 more there if I am lucky.

Can anyone estimate the improvement of the tire swap?
 

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Now to get rid of the michelin x-ice 175-65-R14 tires LOL. I was able to order 2 Potenza RE92's locally but the dealers says they are back ordered in all NA.

I am heading to Memphis for the ZCAR convention so I'll try to get 2 more there if I am lucky.

Can anyone estimate the improvement of the tire swap?
Nailed it :)

Coming from a snow tire? 7-10 mpg seems reasonable.
 

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Installed a new EGR (from a 2000 Accord 4cyl). The engine runs smoother and transitions to/from lean burn are smoother.

So thats it for now for engine work:

Plugs gapped, valve lash set, injectors cleaned, egr plate cleaned, new egr installed and efi ecu reset.

I did the test loop again and got 63.2 mpg in 5th and 66.2mpg in 4th. It seems consistent.

I also installed the clutch switch shorting switch. It helps control charging and assist nicely.

Now to get rid of the michelin x-ice 175-65-R14 tires LOL. I was able to order 2 Potenza RE92's locally but the dealers says they are back ordered in all NA.

I am heading to Memphis for the ZCAR convention so I'll try to get 2 more there if I am lucky.

Can anyone estimate the improvement of the tire swap?
Make sure they put the potenzas on the front!!! Do NOT let them talk you into putting them in the rear.
 

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I cleaned the injectors and got 67mpg on the test loop.
You are getting serious if you have a repeatable test loop, but don't forget that the car is sensitive to a whole range of variables. Rolling resistance from the wrong tire will shorten your LB period. The car is also very sensitive to temperature and warmup period - never test until everything is thoroughly warmed up. In your location temperature should be fairly stable day to day for now but expect your MPG to drop fast when the weather starts getting cold.

A belated welcome to the club!
 

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Discussion Starter #10 (Edited)
Thanks to all. I read and tried to follow all of you input!

Focusing on the engine with ~ 140,000miI was able to increase performance by ~ 20%. Once I get the tires I'll hopefully put it back to where it should be. I may also try a new primary O2 sensor (NTK 24301) for completeness.
 

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Thanks to all. I read and tried to follow all of you input!

Focusing on the engine with ~ 140,000km I was able to increase performance by ~ 20%.

Only 87,000 miles - sweet! Many years of joy left there.
 

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Discussion Starter #12
Just drove 200mi mix of divided highway at 65mph and secondary highway at 50mph. I got 62mpg on the winter tires :)

I had to work hard last week to get 54mpg on a similar drive so a 15% improvement.
 

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Discussion Starter #13
I cleaned the primary (first) O2 sensor using a propane flame then reset the ICE's ECU.

Mileage stayed the same but it ran smoother and had more power on hills. Transitions to/from lean-burn were almost not noticeable and hills that needed electric assist were now easy w/o.

From my last experiments with an ECU reset, it seems to take ~ 50km of driving before it settles into a nice fuel efficient optimum.
 
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