Gas Mileage

john266 · Post by **john266** » Wed Nov 05, 2008 7:11 pm

I am just curious to see what everyone's thoughts are on this. My Beretta sees alot of highway driving, and was wondering if there is anything that will help improve my gas mileage. Right now I'm getting around 25 mpg (250 miles to 10 gallons). Does anyone have an opinion on the best/most efficient spark plugs for the Beretta (3.1)? The guy who owned my car before put copper Autolites in it, and Im wondering if my mpg will improve if I put a set of Bosch Platinums or something in it. I've gone through many steps to improve my gas, including Sea Foam, good alignment, etc., etc. Any thoughts?

Money pit Beretta · Post by **Money pit Beretta** » Wed Nov 05, 2008 10:51 pm

This just what I did for my old 3.1: Good plug wires(lowest ohm's for the longest wire), AC Rapidfire plugs,coils with more power, K&N filter on a CAI, new cat and I used a Flowmaster muffler(just use what you like best as long as it flows better than stock). Also I used Slick 50 for the engine and the stuff they make for the auto trans. Don't try to use synthetic oil, I did and ended up with leaks on such an old engine(almost 200K at the time). You can buy a stock replacement K&N, but the stock set up doesn't flow very well(they are about 45 bucks VS something like $150 or so for the CAI with a cone K&N). I had the best sensors that I could buy(everything) and a ignition control module that cost me $180. This was all in the name of power, but does give the best MPG also.

john266 · Post by **john266** » Wed Nov 05, 2008 11:57 pm

Right now I've got new Borg Warner wires on it, and a short ram intake (just put a cone filter on the stock hose). Does it make a difference if I leave the air charge sensor out of the intake setup? I've been driving for 10K miles with the sensor just hanging....doesn't seem to hurt anything. I was considering either the AC plugs or the Bosch single Platinum plugs. I cut the stock muffler off and replaced it with a glasspack, and since I already have a leaking rear main seal, I'm sticking to conventional 10W40 with the Lucas additive (b/c of low oil pressure at idle). I guess for now all I need to do is change the plugs and see what happens.

Red_Bra_Black_GTZ · Post by **Red_Bra_Black_GTZ** » Thu Nov 06, 2008 7:42 am

it goes without saying that proper tire pressuse and proper driving habbits will increase mpg.. i am finding it hard to believe that the 6 cyl only gets 25 mpg... or is it the high engine mileage that has lowered it to 25 mpg...many, many years ago, the GF on a road trip busted 55mpg with the quad 4. little miss light foot...

john266 · Post by **john266** » Thu Nov 06, 2008 12:22 pm

heck if I know, what kind of MPG is everyone else getting out of the 3.1?

Post by **Cliff8928** » Thu Nov 06, 2008 1:24 pm

25 MPG is probably about right for a V6 with the 3 speed auto with the 3.18 ratio. I know with the 5-speed, my old 2.8 got over 30 once. I might be able to squeeze 25 out of the 3400.

john266 · Post by **john266** » Thu Nov 06, 2008 5:11 pm

I could get 28-29 MPG when I had the wheels you see in the picture below on the car. I took them off and put the stockers back on with a new set of tires to get a better ride quality, and I guess the heavier weight of the steel wheels knocked the MPG down. I'm driving it on the interstate all the time, and with that 3-speed auto, I'm taching at like 3100rpm, which I would imagine would eat some gas...lol

wicked-irocz · Post by **wicked-irocz** » Thu Nov 06, 2008 6:30 pm

yeah, the 3 speeds definately lose some mpg to the manuals or 4t60-e's. The slower you go the better mileage you will get down to about 55 mph.

Money pit Beretta · Post by **Money pit Beretta** » Fri Nov 07, 2008 11:58 pm

I've got BW wires too. Was the filter that you put on a K&N? Yea, I also had a leaking rear main seal in my 90GT. On the IAT, I'd think it would be better for MPG if it was in the intake. Not sure how you would do that with your set up. My CAI only had one hole and I put the IAT in it(put a K&N looking small filter in place of the PCV tube,but I don't think you should do that). Sounds like you need a CAI anyway with the extra power you want(you will have to do some cutting to get it to fit). I had a 3T40 4 speed trans, what do you have a THM125C?

john266 · Post by **john266** » Sat Nov 08, 2008 2:02 am

As far as I know its a TH125 (mine has 3 speed with torque converter lockup). As for the IAT, I was thinking of just cutting a small hole out in the stock rubber intake tube and putting it in that way.

Asylum · Post by **Asylum** » Sat Nov 08, 2008 8:59 am

Just as a point of reference so you get some idea about just how inefficient that ancient 3.1 is, I got 23.9 mpg with my 3500/3t40 and 3.73 gearing over 7 hours on the way back from Albany NY at 3400 RPM the entire way.

And it runs 14.20's

Depending on what your plans are with the car, it might be worth looking for a 3400/3500.

Even the hybrid option is worth considering, however a complete swap is likely cheaper at this point.

As far as the mounts, I have both and there is some minor vibration at idle, but under load it is negligable.

As for the other points DON'T put platimum plugs in that engine!! AC Rapidfires are fine.

The IAT sensor is another issue that draws a bit of controversy.

I have had mine laying around the engine compartment for 8 or 10 years now with no noticable ill-effects. In fact I am of the opinion they really don't do much.

However there are those who tend to disagree.

Money pit Beretta · Post by **Money pit Beretta** » Sat Nov 08, 2008 3:48 pm

Asylum is very right, you should always use AC plugs. The thing on the IAT is that it is ok where you have it. It will work fine there,but you have a speed density system for the 3.1. It uses the IAT and MAP to calculate incoming air mass. That controls all fuel and timing maps. So, it is best to have it in the intake pipe. It's just what I've read, Asylum and others have real world testing, so it's up to you on what you want to do. A 96 3100 has a MAF(the 3400 also has one), this is a big change and it's better(something to think about if you want to do a swap). I miss my 3.1's low end TQ every day. The newer engines have all their power in the mid to top end.

1988GTU · Post by **1988GTU** » Sat Nov 08, 2008 5:05 pm

Make sure your brakes are not dragging (especially out back) and be sure all proper maintenance is done using known good manufacturer parts (AC DELCO, DENSO..... NOT BOSCH AUTOLITES VALUE CRAFT DURALAST)

Then, if you're really into getting that extra mile per gallon, figure out what kind a driving you do the most. For most it's highway (55+ MPH) for others it could be city. If you do a lot of highway traveling, you can swap to taller tires, but KNOW it will throw your speedometer off (not into your favor) . Don't go wider tires, just go taller. It may even rub some if you hit speed bumps or turn with the wheels fully locked.
Make sure your oxygen sensor is working properly too. Denso is a good brand to use for that part.

Mr. Beefy · Post by **Mr. Beefy** » Sat Nov 08, 2008 10:55 pm

Well just to give you a "city" comparison(cause I only drive locally with stop and go 45 mph roads) The last time I filled up my Corsica was on Oct 17th. milage(on the cluster but not the car) 72, 945, currently sits at 73,201 and has just a hair below 1/4 tank. The reciept tells me it was 13.1 gallons and it was on empty when I filled it up. So.... I should easily be able to get 300miles out of that 13.1 gallons and that is 23mpg. I dont drive it on the highway so that's all "city" milage. I'm sure I'd probibly be in the 25-28mpg range with mixed driving.

I also had an issue with the trans being fluid starved that I got fixed about 1/2 way through the tank so that number is probibly NOT the same now. I know that when I started having that trans problem my fuel economy went WAY down.

BUT......... having your tires properly inflated makes a big difference, so does changing your oil on normal intervals(found that one out in the saturn). Dont carry a ton of **** in the car, dont hammer on it, and dont brake hard. Those will help.......

If you want to spend some money..... GET A NEW O2 SENSOR! That made a BIG difference in my old 90GT. I went from ~20 mpg mixed to ~27 mpg mixed. New fuel filter, Delco copper plugs, good wires, and a correct functioning coolant system makes a difference too. Plus, remove and clean the EGR/Upper Intake Manifold and all the passages and you should be set.

john266 · Post by **john266** » Sat Nov 08, 2008 10:57 pm

Considering the spark plug situation, I'm gonna toss the copper Autolites and go with AC's. The question is which ones? I work at Advance Auto and the Beretta can take one of three plugs for the '90 model:

AC Rapidfire Part # 6
Standard AC Copper Part # R44LTSM6
Standard AC Nickel Alloy Part # R44LTSM

Which is the best bang for the buck?

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