Can others with a 2.8 & T125C Auto weigh in on what MPG's they are getting. My 86 GT 2.8/auto MPG is terrible.................consistently giving 13 -14 mpg and just can't seem to get it any better. Driving it easy and being attentive to improving fuel economy with good driving habits doesn't really make any difference.

Things that I have done: new cap/rotor/wires/plugs, new MAP sensor, new IAC, new coolant temp sensor, new air charge sensor, new O2 sensor, new 195°F thermostat, new fuel and air filters. Timing has been set @ 10° BTDC (correctly !), new ground strap ran to insure we have adequate grounding, no apparent vacuum leaks, have searched diligently using T.B. cleaner while running and nothing has been found. The car runs and idles great!......nothing that would indicate any obvious issues that would negatively impact fuel mileage. Would think the car would be giving better than 13 mpg. Any thoughts/ideas/input on this one? Searching the forum here and other research have others reporting noticeably better fuel mileage than what I am getting. Any thoughts/ideas/input? ......or do I just need to accept that I have a car that will not do any better than 13-14mpg?

Oh yea..........forgot to add. new EGR valve has also been installed...........this addressed the erratic idle and hesitation on acceleration that was present when I first purchased the car in August 2010.

air pressure in tires at 30psi ? are the Brakes " Dragging" ? new Air cleaner ? What do the spark plugs "look like "?? is the torque converter "locking up " properly ?

Tire pressure good. Brakes all redone and OK, no dragging, new air filter installed and yes TCC is locking up as it should.

Spirited driving around 20mpg. Careful driving around 22-24mpg. Downhill both ways with the radiator quite plugged and engine running close to 220 I got close to 30mpg. Engine running hot help the mpg quite a bit. I don't know if it hurt the engine at all but right after that I changed the radiator and it was back to ~22mpg.

Charlie

??

Leaky injectors, leaky gas line, leaking cold start injector. My 88 GT with a 3.4, th440 auto does 29 mpg. When it had a 3.1 and t125 it did 27 mpg and that engine ran crappy.

Using 93 octane and currently getting about 15mpg on my '87 GT 5spd getrag with spirited driving.

My '86 GT /auto gets crappy mileage as well. I have been told one contributing factor is the slight exhaust leak on the front bank between the exhaust manifold and the head. (Sucks in air and fools the O2 sensor.)

Recently my thermostat bent (long story) and my mileage went down to 13.5 MPG. The best I've ever got has been around 22 MPG. It's usually around 18 MPG, which really sucks considering this is NOT a high performance engine.

One thing I did which helped a lot was to advance the ignition timing as far as I could without it pinging under load (with regular gas). This worked out to be about 14 BTDC. I just need to remember to retard it back to 10 BTDC before taking through the smog test as the emission levels are slightly higher (and I don't run a cat).

I too have exactly the same problem with Gas milage, 10-12 per gallon at best guess. I have discussed this with a mechanic who has worked with several Fiero's and he is going to check it out for me when I can get my 88GT to him. Everything seems fine with the car but the milage. Please keep this thread alive so we all may benifit from the collective knowledge of everyone.

quote Originally posted by cptsnoopy: Spirited driving around 20mpg. Careful driving around 22-24mpg. Downhill both ways with the radiator quite plugged and engine running close to 220 I got close to 30mpg. Engine running hot help the mpg quite a bit. I don't know if it hurt the engine at all but right after that I changed the radiator and it was back to ~22mpg. Charlie

Ditto. I'm hoping my 3800 swap will show an improvement.

my '86 gt use to get 25mpg, but with a blocked off egr tube it gets 20ish mpg. i got no idea for you. how many mile are on the engine? and with mine, sometimes the oil effects the mileage some so.

I have an 86 GT with the 2.8/4-speed Muncie, not sure of gearing but it runs about 3,000 RPM at 60 mph. I get about 22-23 mpg in town, about 28-29 highway.

I think anything below 20 mpg average indicates a problem, even with the automatic. The car is rated at 16/22 with the new EPA rating system. I had a 1989 Beretta with the 2.8 V6 and TH125C and it got about 20 mpg.

Other than making sure all systems are working and timing is correct, maybe synthetic ATF would help? It would not be a huge improvement. I would feel your wheel hubs after you drive and make sure they aren't hot. The Fiero is heavy but not THAT heavy, it should not get worse fuel economy than a Suburban.

My '88 Formula 2.8L V6 with the T125 auto gets fairly poor gas mileage as well, but it's rolling around with a leaking exhaust and leaking injectors. I do baby it when driving though - never above 65 mph on the interstate and no revs above 2500 or so on acceleration. I would say it's in the ballpark of 17 mpg city and maybe on a good day 25 mpg highway.

quote Originally posted by masospaghetti: I have an 86 GT with the 2.8/4-speed Muncie, not sure of gearing but it runs about 3,000 RPM at 60 mph. I get about 22-23 mpg in town, about 28-29 highway. I think anything below 20 mpg average indicates a problem, even with the automatic. The car is rated at 16/22 with the new EPA rating system. I had a 1989 Beretta with the 2.8 V6 and TH125C and it got about 20 mpg. Other than making sure all systems are working and timing is correct, maybe synthetic ATF would help? It would not be a huge improvement. I would feel your wheel hubs after you drive and make sure they aren't hot. The Fiero is heavy but not THAT heavy, it should not get worse fuel economy than a Suburban.

My same setup was at 70 mph @ 2750 rpm. You need to shift into high !

quote Originally posted by damccord: Can others with a 2.8 & T125C Auto weigh in on what MPG's they are getting. My 86 GT 2.8/auto MPG is terrible.................consistently giving 13 -14 mpg and just can't seem to get it any better. Driving it easy and being attentive to improving fuel economy with good driving habits doesn't really make any difference. Things that I have done: new cap/rotor/wires/plugs, new MAP sensor, new IAC, new coolant temp sensor, new air charge sensor, new O2 sensor, new 195°F thermostat, new fuel and air filters. Timing has been set @ 10° BTDC (correctly !), new ground strap ran to insure we have adequate grounding, no apparent vacuum leaks, have searched diligently using T.B. cleaner while running and nothing has been found. The car runs and idles great!......nothing that would indicate any obvious issues that would negatively impact fuel mileage. Would think the car would be giving better than 13 mpg. Any thoughts/ideas/input on this one? Searching the forum here and other research have others reporting noticeably better fuel mileage than what I am getting. Any thoughts/ideas/input? ......or do I just need to accept that I have a car that will not do any better than 13-14mpg?

Back in my car's hay-day, I got:

~17mpg city
~25mpg highway

I have a 1987 Fiero SE / V6 w/ 125Th

That was with 195/70/14s, and the car being in perfect tune.

------------------
Todd,
2008 Jeep Patriot Limited 4x2
2002 Ford Explorer Sport 2dr 4x2
2002 Ford Crown Victoria LX
1987 Pontiac Fiero SE / V6
1973 Volkswagen Type-2 Transporter

My experience was prior to this ethanol junk gas, but my 85 SE V6 Auto with A/C would get 22-23 around town and up to 32 on the road depending on how fast I drove it. Now I only get 27 combined with a Duke automatic

Ethanol only makes up 15% max of gasoline so theres no way it reduced your fuel economy that much, especially since it serves as an octane booster in place of a different chemical.

quote Originally posted by masospaghetti: Ethanol only makes up 15% max of gasoline so theres no way it reduced your fuel economy that much, especially since it serves as an octane booster in place of a different chemical.

that is unless ofcourse he is filling up at a station that is putting water in the gas. Had one here that was and they got caught, shutdown and its been almost 4 months since then and the store is still full of product. rows of Cigarettes, cadies, and drinks all gone bad.

All thanks for weighing in. Gives me a better idea on what others are getting. To answer some questions posed in previous threads. My car is a 77K mile two owner car. Did sit for a while prior to my purchase in August 2010. But it is a nice clean car. Nothing crazy with wheels/brakes hanging up, all appears to be OK. As far as exhaust goes.............maybe there is some restriction in the CAT. Converter? Any experience out there with this being an issue. Doesn't appear to be as the car runs great, CAT does not get excessively hot or glow. What about removing it entirely,,,,,,any experience on how this might impact fuel economy and the way the car runs. Here in Ohio, the car no longer requires E check as of 2011......it's officially 25! The idea of leaking injectors.........maybe? With the car sitting for sometime, maybe seals are dried out and things are leaking down? If so, wouldn't it be obvious in how the thing runs and it would be loading up / running rich?

Here's a thread I had started awhile back. It's very closely related to this one, and I thought you might be interested. https://www.fiero.nl/forum/Forum2/HTML/112611.html

I just posted question ("starting problems" right after your post) about what I think might be fuel problems...with my engine starting properly after installing a new fuel pump, and fuel pressure regulator. I've typically gotten 23-24 mpg, driving somewhat aggressively (with my getrag 5-spd and stage 3 clutch), but since installing my new fuel pump and pressure regulator, my mileage dropped to around 18 mpg. I've got to figure that out now..? I've got all the same up-grades as you, except I'm running a 180 deg. stat in the summer, which seems to help how it runs, but hasn't really affected my mileage much. I've switched back to my 195 for the winter. I think my new fuel pump might be defective, but don't know if that has anything to do with mileage..? Hope you get your mileage problem figured out. I'll watch your string and see if, what, and when you do.

If i am driving in "economy" mode i can get 300miles out of a tank at about 26-28

I just posted question ("starting problems" right after your post) about what I think might be fuel problems...with my engine starting properly after installing a new fuel pump, and fuel pressure regulator. I've typically gotten 23-24 mpg around town, driving somewhat aggressively (with my getrag 5-spd and stage 3 clutch), but since installing my new fuel pump and pressure regulator, my mileage dropped to around 18 mpg. I've got to figure that out now..? I've got all the similar up-grades as you, except I'm running a 180 deg. stat in the summer, which seems to help how it runs, but hasn't really affected my mileage much. I switched back to my 195 for the winter. I think my new fuel pump might be defective, but don't know if that has anything to do with mileage..? Hope you get your mileage problem figured out. I'll watch your string and see if, what, and when you do.

My son got 23-25 around town in his '85 GT with a Isuzu 5-speed. He used to have the stock Muncie 4-speed, and got pretty much the same with it. We both run K&N air filters which helped a couple miles pg. We both have new Cardone distributors, NGK platinum plugs with 8mm wires. Running Royal Purple oil & K&N filter really helps allot too (expensive but worth it). Before he wrecked his car (fell asleep) he had over 210K miles on it, and it used a little oil. We changed the oil to 15-40 Royal Purple (I use 10-30 with 110K miles on mine) just before driving over 300 miles round-trip to a Fiero show. The car ran smoother and stronger than ever, and we were amazed to find out that he had not used any oil driving at 80mph most of the time. It did use a little oil around-town after he got back, but less than before, and his mileage went up. 25 around town and 33 on the highway. Royal Purple is magic to an engine, by our experience. bye-the-way, he got third place in daily driver..lol !

my gt had the cat convert. removed by prev-owner. so i don't know what it does other than reduce emissions, best guess thou.

quote Originally posted by masospaghetti: Ethanol only makes up 15% max of gasoline so theres no way it reduced your fuel economy that much, especially since it serves as an octane booster in place of a different chemical.

Octane ratings are a measure of fuel compressibility before spontaneous ignition, not a measure of potential energy of the fuel. E85 (mostly ethanol) has a higher octane rating than premium gas, but has around 25% (depending on who you quote) less potential energy at combustion and delivers poorer fuel economy. Replacing a fraction of the gasoline with less powerful ethanol has the potential to decrease the power the resulting fuel delivers. The percent mix you see listed on the pump is a maximum. The refiner uses a variety of decision points to calibrate the mix such as cost and environmental regs so its unlikely you'll ever be able to determine the impact.

quote Originally posted by retroman: Using 93 octane and currently getting about 15mpg on my '87 GT 5spd getrag with spirited driving.

Switch back to 87. Running 93 all the time does nothing for you, but waste your money. Unless you raised the compression up to about 10.5:1, by cutting the heads way down or something, you're not getting anything out of it. And if you cut the heads down that much, you're very likely to have valve-piston clearance issues. My 87 GT gets 18 around town, very spirited driving and not using 5th gear much, on 87.

quote Originally posted by dobey: Switch back to 87. Running 93 all the time does nothing for you, but waste your money. Unless you raised the compression up to about 10.5:1, by cutting the heads way down or something, you're not getting anything out of it. And if you cut the heads down that much, you're very likely to have valve-piston clearance issues. My 87 GT gets 18 around town, very spirited driving and not using 5th gear much, on 87.

That's a definate fact, my 2.8 not only had a drop in fuel economy running premium on the stock motor, it also ran hotter. I made that mistake one time.

86GT with 3.4 PR and 5 speed Getrag - 27mpg

86GT 2.8L 15city 17-19 Highway

4 Speed sucks for mpg

quote Originally posted by kalel14: Octane ratings are a measure of fuel compressibility before spontaneous ignition, not a measure of potential energy of the fuel. E85 (mostly ethanol) has a higher octane rating than premium gas, but has around 25% (depending on who you quote) less potential energy at combustion and delivers poorer fuel economy. Replacing a fraction of the gasoline with less powerful ethanol has the potential to decrease the power the resulting fuel delivers. The percent mix you see listed on the pump is a maximum. The refiner uses a variety of decision points to calibrate the mix such as cost and environmental regs so its unlikely you'll ever be able to determine the impact.

Right, my point was that some people claim 40-50% reductions in fuel economy from blended gas, but the MAXIMUM amount of lost chemical energy would be 15% * 25% = 3.75%. In reality, its less than that, because the ethanol is displacing other chemicals that serve only to boost octane (MTBE - I think?)

OK, I just filled the car up and checked the mileage..................10.7 (83.5 miles / 7.8 gallons) !.....REALLY. This is starting to get old and frustrating If you read my original posts in the thread I've done all the things that you would associate with poor fuel mileage. Plugs, wires, cap, rotor, check for vacuum leaks, IAC, O2 Sensor, EGR Valve, Ignition timing, The car runs absolutely fine. I'm out of ideas here........only thing I've got left is Catalytic Converter being plugged/restricted, but would expect that I would have some indications in how the car runs and would be significantly down on power.........am I right in my thought process here? Guess I'll try and advance the timing as far as possible without getting detonation, run some fuel system/injector cleaner with a couple tanks of fuel..............maybe injectors are dirty/varnished and not cimpletely shutting of, resulting in leaking down excessive fuel. Would think that there would be some indication of this in the car running noticeably rich or loading up.....or would the ECM be able to adjust around this and mask it? Another thought that came to mind..................did someone prior to me buying the car put a chip in it and would that deliver the horrible mileage I'm getting? Anyone with experience with running chips able to weigh in? Guess I need to pull the console and check the prom that is installed in the ECM.

At my wit's end with chasing this. Any advice,input, help would be welcomed and appreciated!

Try seafoaming it?

Bad tune won't help matters...

I'd check the fuel pressure.
The base timing is set, but is it advancing with throttle application.
The torque converter is locking up but does the rpm seem appropriate for the speed. A locking torque converter means the converter is not likely slipping, but the clutch pack still can, usually third.
Is the T.V. cable for the trans adjusted properly.
Check your transmission fluid to make sure nothings coming apart.

If the engines running great I'd suspect the trans, or the fuel.
If you don't find anything there, compression and O2 sensor.
Exhaust leak.

Last resort, timing chain.

quote Originally posted by dobey: Switch back to 87. Running 93 all the time does nothing for you, but waste your money. Unless you raised the compression up to about 10.5:1, by cutting the heads way down or something, you're not getting anything out of it. And if you cut the heads down that much, you're very likely to have valve-piston clearance issues. My 87 GT gets 18 around town, very spirited driving and not using 5th gear much, on 87.

I will definitely think about doing that. I also need to replace the air filter and get a good tune up. The valves and lifters look like they have some carbon buildup on them. That could be part of my crappy results as well.

quote Originally posted by damccord: OK, I just filled the car up and checked the mileage..................10.7 (83.5 miles / 7.8 gallons) !.....REALLY. This is starting to get old and frustrating If you read my original posts in the thread I've done all the things that you would associate with poor fuel mileage. Plugs, wires, cap, rotor, check for vacuum leaks, IAC, O2 Sensor, EGR Valve, Ignition timing, The car runs absolutely fine. I'm out of ideas here........only thing I've got left is Catalytic Converter being plugged/restricted, but would expect that I would have some indications in how the car runs and would be significantly down on power.........am I right in my thought process here? Guess I'll try and advance the timing as far as possible without getting detonation, run some fuel system/injector cleaner with a couple tanks of fuel..............maybe injectors are dirty/varnished and not cimpletely shutting of, resulting in leaking down excessive fuel. Would think that there would be some indication of this in the car running noticeably rich or loading up.....or would the ECM be able to adjust around this and mask it? Another thought that came to mind..................did someone prior to me buying the car put a chip in it and would that deliver the horrible mileage I'm getting? Anyone with experience with running chips able to weigh in? Guess I need to pull the console and check the prom that is installed in the ECM. At my wit's end with chasing this. Any advice,input, help would be welcomed and appreciated!

Is there anyone around that you can compare cars with? Like if you were around here I would have you drive mine and I could drive yours and we could compare notes and see if they are driving a like or not. We could then put a scanner on both and see what the readings are... Don't know what else to say... Good Luck?

Charlie

Ok, so help me out with the fuel pressure.........Can check it by putting a gauge on the fuel rail, correct....and what should the psi readings be? Following this theory, would low pressure caused by a weak fuel pump or fuel pressure regulator being low cause the poor mileage? Or am I looking for the fuel pressure regulator being too high and feeding more fuel than should be through the injectors?

10.7 mpg? You sure you aren't leaking fuel, or your odometer is correct?

fuel pressure should be ~40 psi measured at the shrader valve, on the fuel rail. Low pressure would cause a lean condition, not sure how this would affect fuel economy if it were only slightly lean, might actually improve economy at the cost of drivability. How is your air filter, and thermostat?

It's a possibility, but I'm pretty confident that fuel pressure high enough to waste fuel would set a code from running too rich. That's pretty lousy gas mileage for any Fiero. I suggested checking fuel pressure because there was work done in that area if I recall correctly. As for the possibility of leaking fuel, I'm almost certain you'd smell it at some point. If there's a bad connection at the module it's possible you may not be getting the spark advance you should be even that would cause some driveability issues if there were no advance from 10 degrees at all. The car sat for a while, I suspect the transmission. Poor fuel economy and a sound running engine doesn't add up. Check the rpm against the speed. How did you go about confirming TCC lock up?