Absolutely abismal mileage!
 

My '87 gets absolutely terrible mileage. I've tried everything, i've even used a very light foot for as long as i could stand it. What is killing my mileage so much? I'll put it this way, a short (20 mile) free trip doing 70 used approximately an 1/8th of a tank. By my estimation that's NINE MILES PER GALLON!!! On the HIGHWAY. What is going on here? Keep in mind my lockup doesn't work so i'm running about 2500 RPM at 70, but there's no way that the lockup not working makes my mileage go from the 25-30 that most people claim to 8-12 that i have been getting. I think my PCV valve may need to be changed, can that do it? No i don't have a plugged cat. in case that would do it (in fact i have none at all). All the plugs are good, and the wires SEEM to be in good condition. The O2 sensor is also new. The EGR works fine although i get a code for it, i've tried cleaning it (moves freely) and swapping soleniods, no difference. Please help!

calculate your gas mileage, then we'll talk.

btw, gas gauges can be off you know. ;)

I'm just throwing this out ther, fuel filter or clogged/inoperable fuel injectors?

Yeah, don't go just by the gauge. Fill her up, record the mileage, drive at least 100 miles, fill back up, record the mileage, do some math. The more miles you drive, the more accurate your calculations will be. Anything will be better than "I drove for 30 minutes and my gauge moved 1/8 of an inch" though.

Also, a fuel filter can't cause bad mileage. You can't be using too much fuel if it can't get through the clogged filter. A bad injector, maybe... but lets make sure that you're actually getting bad mileage before guessing the cause of it.

That is a good point, but with gas the way it is now a days and my VERY limited income it becomes very difficult to fill her up the entire way. But i'll just have to pinch pennies for a while and try to get it. But it seems to me that before there was a time i had filled it up the entire way and only gotten 250-350 miles on one tank, which is closer to 20 MPG's i think but still not acceptable in my book. Maybe a bottle of fuel injector cleaner will help also? Or 2?

it could. have you checked your air filter? i hear those can mess with mileage too.

Yea my air filter is fine, i've also gutted my airbox. I'll have to save up the money to fill this fat bastard up! Lol

The other thing to remember, if anyone else has noticed, that when you fill it up, you get more mileage from full to half, then from half to empty.

It is just as easy to top it up from 3/4 to full than from empty to 1/4 tank. Plus it is better to keep it full, since that is what cools your fuel pump.

Ever had any MAF issues on that 87? I know they were very fruity about the MAF in 87-88 LG3... I have a friend that has been through several on his 3.0 LN7...

Not sure what the problem may be at this point..

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wouldnt that cause different symptoms?

Not always... I have seen them do some pretty funky things... Usually if the MAF is crapping out it will have a code 34, It can cause all sorts of issues...

It could be any number of things causing his low MPG's... Its hard to say what the issues may be...

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gas mileage
 

My 1989 sse is consistently averaging 19-20 mpg since I have owned it for a year.Bought the car after my fiancee recommended it and after doing research on vehicles.The many happy customer reviews that I came across in my research made me consider a Bonneville (87-91).Since owning it for a year I am now in the list of happy Bonneville customers.The car was bought for $750 and I put in $950 since owning it.I am amazed on how smooth and effortless the highway drive is.I love the car and would recommend it to all.The 3800 series 1 is on the Wards Top Ten List for best engines this century.It has good pick up and is durable.The sse has ground effects and is cool lookin.Long May the Bonneville Run.

Re: gas mileage
 

you musta got one of the good ones.

btw, is the offending vehicle throwing any codes?

Re: gas mileage
 

The offending vehicle has yet to get a calculated mileage and may not be offensive.

The only code i ever get is for an EGR problem, code 32. But i've checked and cleaned every part of the EGR system and everything seems to be in good working order so i don't know what the problem could be. The valve moves freely, the vacuum line is in good condition, and the soleniod works as it should.

This is very true, when I fill up the guage goes well over full. It takes forever to go down to 1/2, but 1/2 to empty is very quick. My bonne does 17-18 MPG all city driving.

My '91 SSE is stock and it has been getting 16mpg (combined) for several years. I can get it up to 20mpg with mostly highway driving and a light foot at the stoplights.

Alec, aren't you the one who has that walker O2 sensor? Maybe that's the cause for the poor fuel economy? Please eliminate any confusion here, for myself. If the ignition is weak, does the O2 sensor see that as a rich or lean condition? I always thought the O2 sensor saw that as a lean condition, and thus threw more fuel in. But that doesn't make a whole lot of sense.

Also, a gutted airbox doesn't necessarily mean a good flowing induction system. Do you have a new air filter in there?

I believe the PCV Valve can cause poor fuel economy, but I am not 100% sure. Just pull your's out and shake it. If it rattles, it's not an issue. The other test, is to pull the oil fill cap, and if it has a vacuum on it [possibly so much you can't even remove the cap] then it is also not functioning properly. If you do get the cap off, it's possible you could stall the engine due to the major crankcase pressure change.

It could also be a vacuum leak.. or the fact your EGR valve isn't operating properly, or the ECU isn't seeing it's proper use.

I will also agree with the fellow members, in that you should get your mileage tested via the wonderful testing, minus the fuel gauge. Hit me up on AIM tonight.. I have a few suggestions for you.

Yea i'm the one with the walker O2 sensor. My mileage improved after putting that in. All my plugs are very clean so it's not running rich (i don't think). It does smell rich out of the exhaust though but that could be the no Cat. thing. I'm not going to buy a new air filter for it until i just go all out and get the CAI so if that's it well then that's it. But i am going to start running E85 fuel in it. At $2.89 a gallon as of today, i can't afford regular anymore. Nice thing living in minnesota, we have LOTS of corn to burn. Lol

The alcohol in fuel may be attractive price wise but has less energy content. Interesting to see if the cheaper price will cover for less mileage? Weird that you should mention this since there was just an article in the local paper about ways to get the best mileage. #3 on the list was don't use alcohol blended fuel. Strange to see in a time when we need to stretch the available petroleum, and the alky helps that maybe, but on a personal note, it may cost you more? Alky does suppress knock better.

just anicdotal, but I get better mileage and performance with premium, than ethenol blend

and I ave found that I get better mileage on regular than premium. I have found I get the worst mileage on the ethanol blended fuel, I only tried it a couple times.

All pump gasolines have essentially the same energy, it's the alcohol that has less. Premium shouldn't yield better mileage, or performance for that matter, in fact the reverse should be true. All engines and conditions are different and if the engine is knock senstive, a higher octane may help. I don't know where you live but the best gas I could buy in Kansas was only 91 octane, close to what we have as mid-grade here. I had to be very careful on that stuff as the turbo. engine was very knock prone with it.

WTF?

all of our regular gas is 10% ethenol

I should have qualified that. On an engine tuned for 87 octane, premium offers no advantage over regular. Unless the timing is advanced to take advantage of the higher knock threshold of premium, the power output should actually be less, ar at least less responsive. I also said all engines are different and if high miles has created a lot of buildup, or maybe a hot spot in the chamber, premium fuel can help. For best output the engine should run close to the edge of knock, not beyond it, but close. Moving the knock point further away from the threshold, without adding timing or pressure to bring it back close to the edge, should not increase performance. It may feel smoother due to a more controlled (I can't say slower) burn. I experimented years ago between 87 and 93 octane in my stock engine and chip. It always "felt" snappier and would spin the tires more on 87 octane. Not an exact test of course, and conditions constantly change, but this switching back and forth went on for more than a month and several tanks of fuel. Some blending occurs out of necessity, but those were my results. The other thing I noticed was it started better on regular. It's easy to try different fuels and find what works best for you.

Sc here.. i know for fact that i run like shit on 89... in all standpoints

Uhh, yeah, pressure makes all the difference. :oops: Mine won't run well on that either. The statement about 87 and an N/A engine tuned for it is valid.

that has been the general consensus of the club

Well my car is NEVER going to get premium gas in it, or mid-grade for that matter. It is a beater and always will be so any way i can find to pinch pennies is worth it. The reason E85 is so much cheaper here is because we grow a LOT of corn, so it's really easy to cut down our gas usage. What i really should do is buy a diesel but i kind of... u know hate them. I have a friend whos dad just bought one to convert to vegetable oil though. Kind of a neat idea.

e-85 is for fuel flex vehicles only, it will corrode your fuel system parts because they are not designed to withstand the high alcohol content in e-85 which will eat right thru them

Well i got money today but gas also went up to 3 dollars a gallon, which means i have enough gas for 10 gallons. That's only a little over a half a tank. That's still not gonna help the mileage tracking... damn.

well, what you could possibly do is run the car out of gas, then put an exact amount of gas in <like 5 gallons or something like that> and then run it out again, and you have your fuel mileage.

Note: i recommend against this whole heartedly because you can quite possibly fry your fuel pump in the process.

It almost is out of gas right now, the needle doesn't even move off of the white line when you turn it on. So maybe i'll try that and get a close estimate. Oh and gas went up to 3.19 today.

but i MUST caution you, you run the risk of destroying your fuel pump in the process.

Yea i know. No big deal.