I just replaced my cap & rotor, spark plugs and wires, had a tune up, and for some reason, my mielage actually dropped, I expecred the opposite. I'm gonna replace the fuel filter, pcv valve, and change the oil this weekend, also I plan on checking the tire pressure.

My main question is what else could/should I do to get better gas mielage (while still keeping a thirdgen ) Any free mods? Also, why did the tuneup and everything else drop my mpg? oh, it's a 305 LG4.
Thanks

 

I manage to get about 17 MPG on the highway with my setup. Its all LG4 parts cept the block which is a 400 block. I tuned my carb the best I could. There are adjustment screws on the carb, and there a 3 which directly affect gas mileage. There are 2 on the front of the car, but they are covered and you have to grind the covers off the adjust them, so I wouldnt owrry about them. I only had to adjust ming cus some doofus ground the covers off and messed them all up. There is a screw on the carb top which is very hard to adjust, I had to make a tool by bending a tiny brass tube into an oval to grab the screw head. Anyways, it adjusts the mixture control solenoid up/down. Up is more gas, richer running, worse mileage. Down is less gad, better mileage, less HP and possible bogging. You kinda just have to play with it until you get it right at the point where it doesnt bog, but doesnt run too rich.

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1983 Firebird
TH700R4 Auto
Small Block 400
LG4 ECM, Intake, Carb, Distributor, etc.
Soon to be non-computer.
Clarion Head Unit 45X4
2 Pioneer 400W 12" Subs
Third Gen Performance
"A four cylinder is half an engine."

 

well, I used to get about 24mpg on the highway, it's dropped to maybe 20-21, so it's still good, I just want it back where it was. I might try adjusting the carb, thanks.

anoyone else have any tips?

 

24 is quite a hefty shoe to fill for the LG4... if you were getting 24 and the tune up reduced mileage, they rpobably made it run a little richer... the difference between rich and lean performance would only be noticeable by tenths of a second on a stop watch and maybe that 3 MPG drop you saw... other than that, it is hard to notice. You might also look at any changes you've made recently in driving routes and techniques... M\my LG4 seems to get 22 MPG when I'm traveling at highway speeds for extended periods (70-100 Mi.) and about 16 MPG when I'm speeding around town on the weekends... I was driving a Honda CRX up untill it fell apart a month ago, that thing got 38 MPG, thats all I miss about it though...

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1984 Firebird T/A - Daily driver
305 LG4, T5 - Hurst Short Shifter
Edelbrock 600 CFM Performer Carb
Open Element Air Filter
Gutted Cat... missing stuff I'll need next year
IROC 16x8 Wheels
Goodyear P215/60/R16 87S - S stands for suck
(but I'm a cheap *** and I don't go 112... don't think I do...)
Quote from my sister: "It sounds like a boat"

 

Ever change the PVC Valve, O2 Sensor has been known to hurt mileage in our cars, what about the Fuel Filter. I know the O2 and PVC can affect gas mileage. How is your exhaust setup, your converter clogging?

Could always reduce the weight of the car, fiberglass hood, remove excess stereo stuff, run with lonely ½ a tank, check tire pressure.

 

advance the timing to 8* BTDC base and it will pick up a couple of mpg.

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'89 Red Formula 350- 350 .060 over forged pistons 232* @ .020 cam Performer RPM Holley 750 DP Vortec 1.94 1.50 Accel Coil and dist. Hedman shorty headers Dual Exhaust w/ cutouts 1LE WS6 suspension, wheels, and brakes, 9 Bolt 3.27 Posi Edelbrock LCA's & Track bar subframe connectors 700R4 Harwood snorkel scoop Eclipse Head Unit Delco Bose Speakers 2 12" Pioneer subs w/ 400 watt/chanel amp

 

The most EFFECTIVE way to increase gas mileage is to invoke "Highway Mode/Lean Cruise" in the eprom.

I get 30 US MPGs on the highway with my L98.

 

What was done in the "tune up" that didn't involve the cap & rotor, spark plugs and wires? About the only things left are timing and carb adjustment, neither of which are typically needed with the systems involved. But, if the timing was advanced before and was adjusted back to factory specs, that would drop you back a bit. 8 degrees might be a bit too much, but 4-6 should be fine.

You didn't mention air filter. It should be checked, at least, or replaced. Fuel filter won't affect mileage directly.

A bad O2 sensor will adversely affect mileage, but that wasn't something that changed. Can't hurt to replace it, though.

I typically get 18-20 mpg commuting, and my TCC lockup doesn't work. The only road trip I've taken with the Camaro I averaged 26 round trip, had 2.73 gears at that time.

Synthetic lubes can help improve mileage. Consider that when changing your oil.

------------------
82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

 

Thanks for all your help, I've already got the PCV valve and fuel filter for my oil change sunday ( change the PCV every year, every 18-24 months for the fuel filter), and I'm using Amsoil pure synthetic oil (have since I bought it). I'll look into the O2 sensor as well.

I also use an amsoil air filter (changing the filter oil in the foam piece along with the oil on sunday). It allows for real high flow, as good or better than K&N, plus a dual snorkle intake to boot.

I have a 3" catback with dual exits/no muffler. I'm not sure about the cat though, it might be clogging...hell, I had a chunk fall out of the tail pipe once, might replace that with a high flow cat soon.

Fiberglass hood isn't in the plan for a few years at least, but I don't really have any excess weight above stock, save for a cd changer (and myself ).

What everyone said about the timing and carb adjustment sounds like a distinct possibility, they said I was running a little lean (said the accelerator pump was gettin weak) so they may have asjusted that. Also, I'll check to see if they reset the timing. I meant to tell them to advance it 6°, but I forgot.

I think I also have 2.73 gears (hence the decent gas mielage to begin with).

Anyway, thanks to everyone for their input, I appreciate how helpful you have all been.

Thanks
Rich

 

Since you obviously have spent some major bucks I would replace the CTS for about 10 bucks and recheck all the vacuum lines to carb.

On my LG-4 the temp sensor was out which made the car run rich, kept it from going closed loop and kept the TCC from locking up which sent my MPG to squat. 10 bucks later my MPG doubled.

 

Get the MSD 6AL ignition box....

I was at the Jersey F-Body Association meeting and someone installed the MSD 6AL box onto there L98 GTA and he said that his gas mileage went way up. I want one of those ever since I heard that!

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***The driver formerly known as 89IROCZ***

1989 Chevrolet Camaro IROC-Z
350c.i. TPI, rebuilt 700R4 auto w/shift kit, Dual catalyst Monza PaceSetter Cat-Back (currently no muffler, sounds on webpage) 3.23 Posi rear, Hypertech chip with 160stat, Under-Drive pulleys, AFPR, K&N's, !Air Box w/ Ram Air, moddified MAF, throttle body coolant bypass, Alarm, Keyless entry, remote starter, 92 Z28 AeroWing, Brand New Paint (6/21/01)

Future: ZZ4 TPI w/EGR, T56, 3.42 or 3.73, Spohn SFC, strut tower brace and LCA's

1989 Chevrolet Celebrity Eurosport
2.8 MPFI, no mods
225,000 miles and still ticking!

More info, pictures and sounds (of the IROC) available on my webpage: http://go.to/iroc-z

AOL IMer: GPA 0point0

 

the ign. box isnt going to increase mileage, unless your current ignition is just putting out enough spark to ignite the fuel. They are marketed as some radical thing that does all sorts of things for power and mileage, but they arent. I have one. just have a good ignition and forget the box.

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• 83 Z28-- not a pretty site to look at, 200k miles and im sure it was treated like a rental car every day of its sad life(before i got it).. sold, thank the lord
• 74 Z28-- 383/400, green on black. pretty clean. FOR SALE!!!

 

Yea the ignition wont do squat unless yours is failing. You should change that o2 sensor mentioned above that is probably the only thing that could be causing poor gas milage. Since you eliminated every thing but the cat and the 02 you might as well do the easyest 1st.

LG4, comp 270H, edelbrock 1406, open element accel 14x3, turbo 350, 2:73. solid 22mpg city
SSC

 

Okay, forgive my ignorance, but what's the CTS and what does it do?

 

I had put some crappy autozone wires on my car and lost 2 MPG. I added the MSD and gained it back. I then switched to those $30 accel wires everybody sells and gained .5~21 MPG. Cheap ignition parts, especially wires, will kill the whole deal.

James

 

Coolant Temperature Sensor

 

I get about 20-22 mpg driving in my town (i dont venture out much), and thats even flooring at every stop! Cruise control = god.

------------------
1992 Pontiac Firebird
- 305ci V8 TBI / Automatic Trans / Loaded
- MODS: Edelbrock 14x3 Open Element Air Cleaner, Dual outlet exhaust
1985 Chevy Z28
- 350ci V8 TPI / Automatic Trans / Paid $200 for it
- In the process of restoration!

 

Mine were borg warner nascar select wires (cap & rotor too), should be okay

 

how does the pcv valve affect gas mileage?

 

LOL, fuel injection probably helps a lot too

 

Okay, changed my oil today, fuel filter was a little dirty, replaced that, the PCV valve wasn't functioning right, replaced it too. I'll go ahead and see if this has an effect on gas mielage (should know in a few days) than I'll consider the O2 and CTS if I don't see much of an improvement. If after that I'm still down a few mpg, I'll go ahead and assume that the loss was due to a reset to factory timing and richer tuning of the carb

Thanks again to everyone for their input

 

shoot i get about 18mpg city driving in my car, on the 4th i leave for colorado so i will get my first taste of highway mileage, i dont get enough hear to tell what i get. but i am guessing anywhere from 22-25mpg. thats good for my L98.

 

lol, so I'm stingy, sue me

 

Think about what you said in the first post. You replaced questionable components with theoretically known good components. And your mileage went down. Something is wrong right there. Wrong wires, wrong plugs, wrong gap, wrong cap/coil/rotor?

The CTS is a "peace of mind" issue. The ECM calibrates many functions based on CTS readings. And since it's only a $10.00 part, you really can't go wrong replacing it to be safe.

The 02 sensor is fairly critical regarding gas mileage. Recommended replacement is around 30K miles. While I think that's a little premature some cars NEVER have had them replaced. Again, a relatively low cost part that probably will improve your MPG a bit.

Even so, you're using the same CTS and O2 with the new parts as you were the old and your mileage should not have gone down. I would double check the vacuum lines around where you were working.

Also, I would disagree that a higher voltage coil would not increase mileage. If you guys are not seeing gains something isn't set up right. By increasing your coil voltage you can increase your spark gap. Additionally with a hotter coil you could mod your plug ground electrode like:



...then gap it to .50

Doing so increases your spark face exposure which will:

Increase Horsepower
Decrease Emissions
Increase MPG

...by burning more of your fuel mixture and exhausting less unspent fuel.

 

well, I just tested my mpg tonight, I topped off, drove 30 miles out into the desert and came back and topped off again. And well, I think I just set a record for carbed thirdgens, 32.47mpg on the highway!!!!

all I can say is thanks for all of your help, I never could've dreamed of gettin this good of gas mielage.

I'm gonna try replacing the O2 and CTS and see what gains, if any I can get from that.


oh, and mike in AZ, I think the reason my mpg went down is that the shop I took it to retuned the carb to make it run more rich and probably reset the timing.

[This message has been edited by Blue_Meanie86SC (edited July 25, 2001).]

 

Blue, run at least a full tank thru it then check your mpg. Keep us informed on what you mpg is then. If you still are getting 30+ mpg I'm going to switch to a carb on my new engine.

Steve

 

checking the mileage on 30 miles, thats a good one. Using one tank is better, but the more miles you drive the more accurate it will be. Try 3 or 4 tanks.

------------------
350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, current red metallic paint. Lots of other stuff...
82camaro

 

yeah, I relize the more data availible, the better (more accurate) my results. I just wanted to do a quick test. it was 60mi. round trip, but I'd still like to try it with a road trip, maybe I can get a weekend off and just drive


I'll keep you posted on how accurate it is. right now I'm thinking I might have a fuel leak somewhere cause I can smell gas coming from my car about 10 feet away. possibly a combination of a rich carb and a loose connection on the fuel filter nut, I'll look at it in the morning and see if I can find anything. Anyone have another idea of why I'm smell in dinosaurs?

 

oh, and another thing, this smell wasn't there (as strong) last night when I tested my mpg, just seemed to creep up on me today.

 

k, I think if found it, it was leaking pretty bad at the fuel filter housing, I replaced the o-ring and the leak stopped, looks like that was the problem. of course now I'll have to wait till the next tank for an accurate mpg reading since I lost so much fuel to leakage over the 100 miles I drove yesterday. Oh well, I'm gonna do about 3-4 tanks full and average them to get my mpg. and like I say, a road trip is in order to do a tank with nothing but highway miles on it

 

i get about 21 city and 26highway outta my LG4 86z28 stock as a rock with 130 on the clock.

700r with 2.73s and passes emissions with flying colors.

 

Mike,

Was the hotter coil you mentioned in reference to the MSD 6AL unit? If so, that is not a coil, but a multi-spark discharge unit. You still need a coil, but if you aren't burning all of your fuel with one spark, the idea is that multiple sparks might burn it all the way. It's only multi-spark up to about 2K RPMs. It also supposed to make starting easier.

I did buy one of these for my '70 Challenger but haven't installed it yet, so I don't have any real life experience comments.

I don't see people mentioning the MSD stuff much here, so can I assume the stock system when in good shape is good enough?

 

Hummm... I have an 88 LB9 IROC with the T5 and about 155k on the clock. Gas mileage in town is kind of abysmal, even when I drive conservatively. However, on the highway, when I can get it up to 70 or so and hold it there for a long time, it'll go mid-20's. 70 mph in 5th gear is about 2500 RPM. Not too loud inside the car courtesy of Magnaflow.

It's about time for another tuneup, I think I'll go with Rapidfires, MSD or Accel cap and rotor, and maybe a set of Taylor spiro core wires. New O2 sensor time as well.

Anybody running the MSD coil with the stock (remote coil) distributor? Any problems? I tried an Accel coil once a long time ago and sometimes the car wouldn't start. Went back to the stock coil and it starts every time. Anybody want a free Accel coil? Come get it.

Is the "module" in our distributors (TPI computer engines) use like 7 or 8 pins? Anybody make an aftermarket highpo version? All I see are the 4-pin modules from MSD and Pertronix.

 

Anybody notice yet that this post is 3 years old?