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HF POOR FUEL ECONOMY

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HF POOR FUEL ECONOMY

Postby wspangle » Thu Apr 20, 2017 11:45 pm

I recently changed out the SI transmissions in my 90 HF for an HF transmission to get better MPGs. I was getting around 35 mpg with the SI trans, and now with the HF trans I'm getting a whopping total 36 MPGs.
Yes, it has the 8 valve D15B6 in it with a true HF trans (at 70 I'm at 2,225 RPMs). I have already done a complete tune up to the car before the swap. There is no check engine light on and the car is running great, just not getting the economy I was expecting.

Anyone have an idea?
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Re: HF POOR FUEL ECONOMY

Postby 4drSpankR » Fri Apr 21, 2017 10:37 am

How many miles on the engine? Best I got out of my HF (when stock) was 46mpg and that was at 178K miles.
1991 HF - previously '90 B18A1 now '97 B18C1
1989 Si - running parts car/gone
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Re: HF POOR FUEL ECONOMY

Postby Dave_Darling » Fri Apr 21, 2017 11:03 pm

What kind of shape is the motor in?

Did you drive in a lower gear with the new trans than the old? Drive at about the same RPM as you had before?

Lots of stop-and-go city driving?

Many things can cause lower than expected fuel economy.

--DD
"Mango Bango", 1990 CRX Si -- Sold on 10/01/11, with over 227,000 miles.

VTEC is Honda's "select a cam profile on the fly" system; VTECH is a crappy phone.
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Re: HF POOR FUEL ECONOMY

Postby wspangle » Sat Apr 22, 2017 12:34 am

The engine has around 166k and I'm driving the exact same route everyday that I was with the old transmission, which is about 10 miles in town and to miles on the interstate at 70 mph. I am driving at lower RPMs, but that is because I went from an SI trans to an HF trans.
This car should be getting at the very least 40 MPG.
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Re: HF POOR FUEL ECONOMY

Postby 4drSpankR » Sat Apr 22, 2017 9:21 am

The biggest factor for me in getting higher MPG's with an HF engine was my foot. Because the engine is so under-powered, I found myself aggressively stepping on the pedal just to get up to speed. As soon as I regulated myself my MPG's got a lot better.

Proper tire pressure, stop and go driving, oil change intervals and overall maintenance are all factors, just like not tromping on the gas pedal. It all adds up, you'll get there. Just might have to change a few habits! :-)b
1991 HF - previously '90 B18A1 now '97 B18C1
1989 Si - running parts car/gone
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Re: HF POOR FUEL ECONOMY

Postby wspangle » Mon Apr 24, 2017 1:35 am

I'm just thinking there might actually be a problem. I thought it might be the car had the wrong ECU, but I checked it and it is a pm8-h030. The car is timed properly, tuned up, correct tire pressure, etc.

I wouldn't think that my driving habits alone would drop the MPGs that much. I drive somewhat efficiently.
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Re: HF POOR FUEL ECONOMY

Postby 4drSpankR » Mon Apr 24, 2017 6:46 am

I didn't either. I filled up at the beginning of the week and drove it how I normally did, which got mid to high 30s'. Next week I filled it up again and drove more cautiously and way more conservatively and my MPG's shot up to mid 40s'.
1991 HF - previously '90 B18A1 now '97 B18C1
1989 Si - running parts car/gone
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Re: HF POOR FUEL ECONOMY

Postby mossin_90 » Wed May 03, 2017 1:43 pm

did you reset the ecu unplugging the hazard fuse?
I would not bother removing the battery terminal, my ocd won't let me. lol :bounce:

make sure injectors and fuel filter are clean.
'90 CRX DX_5sp
"Maybe it's better that way... memories can be terribly painful, being able to forget is a great blessing"
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