Another MPG Thread

[kennyboi9o9of88]

I have a 91 NA and 3+ weeks ago I was getting 30mpg. I remember that night I was coming home from Riverside and pushing my car and when I got home, I let the car cool down for a bit before getting out. A few hours later, I was heading out to go out and when I started my car...I noticed it was idling horribly and the power is pretty much gone. I figured it was the spark plugs or the wires so the next day I changed my spark plugs and spark plug wires...apparently..the rubber on the spark plug wire had melted on the head. I scrapped it off and installed the new wires along with new plugs. Drove it that week and got 16 mpg. I changed back to the old spark plugs and replaced the air filter and am getting 20mpg. What's the culprit here? I was getting damn good gas mileage that day, but after shutting off my car and starting it up 3 hours later...it went down the drain. Any thoughts?

[Primera]

Wow, if your spark plug wires melted to your head that must have been some intense heat. In personal experience 2hours of 80mph hasn't even began to melt mine.
If I were you I would start checking some of your hoses, like the egr stuff. Could have easily melted one of those and set off those problems

[kennyboi9o9of88]

well the wire itself didnt melt onto the head, but the rubber above the coil melted. But yea i didn't expect that to happen but **** happens haha. What egr hoses should I be examining and should I just be checking if its properly functioning? I'll start checking that first. But the just yesterday I added some techron fuel injector cleaner and lets see if that solves some problems with the gas mileage.

[Medusa]

Is your engine overheating? How often do you check your temperature gauge?

And I would check all vacuum hoses, but especially the EGR.

Unless you have a blocked coolant passage...which would suck fat **** for you.

[kennyboi9o9of88]

So my dad checked the EGR for me and said it's still good. I replaced the top o2 sensor and I'm getting a small mileage gain. I'm gonna replace the bottom o2 sensor soon and hope the gas mileage goes back up to how it used to be. I was wondering could the catalytic converter be another reason why?

[Medusa]

Do you have a California MR2?

[Primera]

If it is clogged in some way it would drop power and gas mileage. Just pull it off and check it

[mattdouken]

so im guessing from what i have read so far, removal of the egr system gives you power loss and bad mpg?

[MRH]

I have averaged 20 MPG since day one. I drive nice most times, and hard others, it still ends up at 20, I'd love some 30 MPG. let me know what you do to yeld it!

-H

[Jason.MZW20]

Originally Posted by MRH

I have averaged 20 MPG since day one. I drive nice most times, and hard others, it still ends up at 20, I'd love some 30 MPG. let me know what you do to yeld it!

-H

It's very easy to achieve 30mpg on a properly tuned 5SFE. I never averaged 30mpg, but I did get 25mpg with spirited driving, which is 20 city/30 hwy. A steady foot will usually yield the best MPG. Constantly accelerating and decelerating kills your MPG because the ECU "primes" the combustion chambers by increasing injector duration to ensure adequate fuel supply on acceleration. Steady cruising allows the ECU to cut back on the injector duration and save fuel.

In the city, accelerate briskly and keep a steady speed. When slowing for stop lights/signs, don't brake at the last minute. When your foot is off the pedal, the ECU cuts the injectors, so allow the car to slow gradually. If you can time it to where you don't have to make a complete stop at a stop light, that also helps.

If possible, use the cruise control on flat roads and on the freeway. I usually set my cruise at 80mph, so the engine is turning 4000rpm and hills don't bog the engine. I still return 30mpg. I'm sure I could get 35mpg or more if I set it to 65-70mph.

I also set my ignition timing to 14 degrees and ran 87 octane (not 91). It pinged a bit if the engine were bogged (like 5th gear, low rpm + hill), but the combustion was hotter, making it more efficient. With 91 octane, it felt the same as 10 degrees on 87. It never misfired or detonated, likely because of the low cylinder compression on my worn engine.

[l.groves]

I was getting 23-24mpg then I put in a used turbo radiator and now I get a constant 26mpg city driving. I think the previous owner clogged up the old radiator with tons of fix a leak which put too much pressure on the water pump. It also freed up quite a bit of power. Oh yea- mine is a 94 with the original engine with 207,000 miles so far...

[Medusa]

I'm at over 208,000 and I'm getting MINIMUM 27 MPG average per tank, all city driving. And I'm a jackrabbit, I don't really cruise too often, I always roll with the windows down, etc. Pretty much most of the stuff that kills gas mileage. And I like to keep the engine revving.

If I'm on the highway, I see almost 40 MPG with t-tops off and doing a little more than 80 MPH.

[kennyboi9o9of88]

sorry haven't been on the forums lately, been busy.

yes, I have a california mr2

I haven't had the chance to replace the other o2 sensor. But I figure it might be the catalytic converter because when I had the car smogged, it failed cuz of the cat. So what my dad did was release part of the bold somewhere along the exhaust so the fumes escapes through that opening rather than through the exhaust which made it pass smog. I couldn't afford to get a new cat welded on so dont judge me . I'm sure it's time for me to replace the cat, but I'm sure the bottom o2 sensor needs to be replaced as well. I did notice there was somewhat of a small power loss compared to when I first got the car. But then again because of the cat the power was restricted in the beginning.

I missed getting 30mpg. Right now, I'm averaging 23mpg cruising on the freeway at 65-70 and being really light on the gas pedal on local streets.

Does anyone know how to check the cat or o2 sensors other than simply replacing them? I went to my normal smog place and the guy told me our cars don't have an obd port. Is that true?

[Medusa]

Yeah, we don't have a DLC. All we have is the diagnostic connector in the engine compartment, but that's not for hooking a scan tool up to. It's for using a DMM to troubleshoot electrical problems.