How to get better gas mileage for a 3rd gen

927 Views 40 Replies 11 Participants Last post by Sam91, 2 mo ago

Sam91

Discussion Starter · 2 mo ago

Ok guys so I have been driving my 1991 si alb to and from school for the past 2 weeks. I haven’t really been that happy with my gas mileage. So for this week I drove 4 days to school. The mileage is 7.8 miles to get there. After 4 days of driving a total of 15.6 miles a day my gas tank is down to half a tank. Should I be getting better mileage than that? At half a tank I have to refill it since it likes to die when braking. I am hoping to fix that this week. If my calculations are right I am getting around 10-12 mpg. And I am not even driving it hard. My car has 183,000 miles on it. What should I start replacing to get better mpg?

Thanks Sam

Also I can see the gas gauge move when I drive it. When I floor it I can definitely see it move.

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MommysLittleMonster

· #21 · 2 mo ago

This is going to seem like a dumb ask, but are you letting the car "warm up" a lot?

Additionally, what shape is the rest of the car in? Is the transmission working okay? What kind of driving are you doing in those short trips? A lot of stop and go in cold weather will ruin any mileage you get.

Those plugs look pretty good to me, the porcelain is nice and white/tan and not super dark and sooty. The grounding strap shows a nice heat range line a little more than halfway down the ramp, and there isn't any deposits left behind.

For reference:

Automotive tire Light Product Font Auto part

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Sam91

Discussion Starter · #22 · 2 mo ago

MommysLittleMonster said:
This is going to seem like a dumb ask, but are you letting the car "warm up" a lot?

Additionally, what shape is the rest of the car in? Is the transmission working okay? What kind of driving are you doing in those short trips? A lot of stop and go in cold weather will ruin any mileage you get.

Those plugs look pretty good to me, the porcelain is nice and white/tan and not super dark and sooty. The grounding strap shows a nice heat range line a little more than halfway down the ramp, and there isn't any deposits left behind.

For reference:
View attachment 33072

I am letting the car warm up for like 2-3 minutes. The car is in pretty good shape for 183,000 miles. It doesn’t burn oil. The trans works great. I am doing country driving to school and back.

When I came back from getting gas on Friday I was beating on it a bit. And ever since then I might have fixed my problem. My gas gauge hasn’t really moved in the last 2 days of driving like it normally does! I guess it just needed some full throttle to fix it. Maybe an injector wasn’t perfect. I will keep you guys up to date on my next fill up and see what MPG I am getting.

Sam91

Discussion Starter · #23 · 2 mo ago

Ok guys well I just checked the coeds and there aren’t any! So I guess my car has decided to fix itself. I still have the ALB, and the below half a tank problem. But I think it is now magically getting better gas mileage!

1funryd

· #24 · 2 mo ago

Sam91 said:
Ok guys well I just checked the coeds and there aren’t any! So I guess my car has decided to fix itself. I still have the ALB, and the below half a tank problem. But I think it is now magically getting better gas mileage!

No, its not fixed, its telling something is about to fail.
This was a warning shot.

Mechanical things do not fix themselves, they get worse and most average people do not understand how basic mechanical stuff work.
You still need to triage your problem.
But from history, its usually the O2 sensor that is causing the issues.

Sam91

Discussion Starter · #25 · 2 mo ago

1funryd said:
No, its not fixed, its telling something is about to fail.
This was a warning shot.

Mechanical things do not fix themselves, they get worse and most average people do not understand how basic mechanical stuff work.
You still need to triage your problem.
But from history, its usually the O2 sensor that is causing the issues.

But then why did it get better?

1funryd

· #26 · 2 mo ago

Sam91 said:
But then why did it get better?

Sam, because it is working again.
Mechanical and electrical all fail at some point, and when you start having issues, that is a huge indicator that your parts are now beginning to fail.

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Sam91

Discussion Starter · #27 · 2 mo ago

1funryd said:
Sam, because it is working again.
Mechanical and electrical all fail at some point, and when you start having issues, that is a huge indicator that your parts are now beginning to fail.

That is crazy! I guess I will be prepared to replace an O2 sensor someday.

1funryd

· #28 · 2 mo ago

Sam91 said:
That is crazy! I guess I will be prepared to replace an O2 sensor someday.

Its not crazy its normal.

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luzer

· #29 · 2 mo ago

Your issue with the car not using fuel below half a tank is one of two things. Either a previous owner swapped a fuel tank from an S model (dual carbs) or the baffles have rotted away inside the tank. The only way to fix either problem is to replace the tank.

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JimmyRay

· #30 · 2 mo ago

When I run 87 octane gas I only get 22 miles per gallon. 240 miles to a tank of gas.
When I run 93 octane gas I get 29 miles per gallon. 310 miles to a tank of gas.
When I run 110 octane gas I only get 15 miles per gallon. 160 miles to a tank of gas.
But if I run 90 octane with 0 ethanol in it I get 35 miles per gallon. 380 miles to a tank of gas.

So I have been putting nothing but 90 octane in it and love the gas mileage. I run 93 octane gas for 2 and a half years. Wasted so much money.

I was like you and going through an entire tank of gas in 1 day. I was getting 7 - 10 miles per gallon. I bought the Denso O2 sensors off of eBay or RockAuto and didn't pay much for them. Fixed my issue.

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nailbender

· #31 · 2 mo ago

Before I went too far on buying parts, I'd be trying to figure out why the engine is wanting to die while braking hard. That's not normal. Especially with a half tank of fuel.

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Sam91

Discussion Starter · #32 · 2 mo ago

luzer said:
Your issue with the car not using fuel below half a tank is one of two things. Either a previous owner swapped a fuel tank from an S model (dual carbs) or the baffles have rotted away inside the tank. The only way to fix either problem is to replace the tank.

Well I think it is the fuel pump strainer. I think it could be clogged up.

Here is a video that a guy made:

Sam91

Discussion Starter · #33 · 2 mo ago

JimmyRay said:
When I run 87 octane gas I only get 22 miles per gallon. 240 miles to a tank of gas.
When I run 93 octane gas I get 29 miles per gallon. 310 miles to a tank of gas.
When I run 110 octane gas I only get 15 miles per gallon. 160 miles to a tank of gas.
But if I run 90 octane with 0 ethanol in it I get 35 miles per gallon. 380 miles to a tank of gas.

So I have been putting nothing but 90 octane in it and love the gas mileage. I run 93 octane gas for 2 and a half years. Wasted so much money.

I was like you and going through an entire tank of gas in 1 day. I was getting 7 - 10 miles per gallon. I bought the Denso O2 sensors off of eBay or RockAuto and didn't pay much for them. Fixed my issue.

How much is a gallons of 90 with no ethanol? I might have to go that way.

Now I am getting awesome MPG but I think I might still replace those O2 sensors.

Thanks!

1funryd

· #34 · 2 mo ago

Sam91 said:
How much is a gallons of 90 with no ethanol? I might have to go that way.

Now I am getting awesome MPG but I think I might still replace those O2 sensors.

Thanks!

Again, it never fixed itself.
That is newbie speak for not doing proper diagnosis.

If it stopped working properly and the starts again, that is called an intermittent issue.
That is a massive indicator that certain parts are going bad sporadically.
Which means, replace it asap. Do not wait for it to break cause it can cause other issues along the way.

Reactions: 1

Sam91

Discussion Starter · #35 · 2 mo ago

1funryd said:
Again, it never fixed itself.
That is newbie speak for not doing proper diagnosis.

If it stopped working properly and the starts again, that is called an intermittent issue.
That is a massive indicator that certain parts are going bad sporadically.
Which means, replace it asap. Do not wait for it to break cause it can cause other issues along the way.

I know, I am just saying that right now I am getting very good mpgs. I will fix it maybe this week coming up since I have spring break.

luzer

· #36 · 2 mo ago

Sam91 said:
Well I think it is the fuel pump strainer. I think it could be clogged up.

Here is a video that a guy made:

That can certainly cause a fuel issue, but it doesn't explain why your problem only happens when the fuel level gets below half a tank.

Reactions: 1

diaboliq380

· #37 · 2 mo ago

You need to do some research to evaluate if you need to do a complete overhaul of the motor. Otherwise, you can test and tune until you get some results. Sounds like you are fairly new to auto mechanics. Nothing is better to improve a cars condition then to take components apart and clean them. Systematically.

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Sam91

Discussion Starter · #38 · 2 mo ago

diaboliq380 said:
You need to do some research to evaluate if you need to do a complete overhaul of the motor. Otherwise, you can test and tune until you get some results. Sounds like you are fairly new to auto mechanics. Nothing is better to improve a cars condition then to take components apart and clean them. Systematically.

My engine is fine. It doesn’t burn any oil and has 190 psi for compression. I was planning on just testing stuff out. I am 16 years old and I have been working on cars since I was 14. I mostly work on older cars from the 60s and 70s. So I am a lot more experienced with those. And my grandpa who helps me knows more about the older stuff too. I probably will take stuff off and clean it.

blazeaglory420

· #39 · 2 mo ago

When I first got my 88 with over 300k miles I was getting roughly 15mpg. After spending a couple Gs and replacing every gasket down to the head gasket, cleaning and polishing the intake system, changing plugs and wires to NGK, fixing any exhaust leaks, doing a valve adjustment, alignment, new tires and control arm bushings, short ram intake(basically just took off everything on the intake to the filter Haha), replaced seals/ bearings on distributor and CYL sensor, replaced 75% of hoses with better gas line hose replaced timing belt and water pump, I started getting 28 to 30mpg with about 25 city mpg. So basically get to scrubbing!

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blazeaglory420

· #40 · 2 mo ago (Edited)

If I remember correctly you had much rust in your trunk area? If so I would definitely check the fuel pump and tank because once the rear of these Preludes start rusting, it doesn't stop. But I'll send you a link for many videos from a really good Prelude fixer upper Haha.

But 1funryd is right tho. Internment problems seem to "fix themself" but they usually come back worse. If the car feels like it wants to die when braking that could be an additional problem and the bad gas mileage is something different. Car dying when braking and this is a long shot but maybe a possible alternator and or serpentine belt issue? Is your battery good? Are you getting the proper voltage from your alternator? Is the belt in good shape? It could also be the 02 sensor(s) needs to be cleaned or is going dead. Have you tried cleaning the intake and throttle body? When's the last time you replaced the fuel filter? But maybe something is happening in your gas tank when you brake and it's affecting the fuel pump? Rusty tank and pump causes all kinds of problems

This person's YouTube page has all kinda self help Prelude videos

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