I am currently running at about 18mph/24highway in my 88GT V6
I have read with the 3 SPD auto I should be around 32mph at 55 don't know if that is high way millage or not.
with 124k miles on the car other then the ecm temp switch what other sensors should i be looking at to replace before i start messing with the fuel/air mix manually?

As it stands it runs good idles low in summer high in winter i was down to 14 mph this last winter. i drive 18 miles one way to work so i go thru 10 gallons a week don't have the money for a swap. no engine check light but when it runs long enough to turn on the fan if i shut it off then start it within 5 min it will stall 75% of the time when I put it in drive if i dont give it a bit of gas the first 30 seconds.

[This message has been edited by hawkebat (edited 06-27-2011).]

Mess with fuel/air mix manually? I think that's a bad idea, but I am not sure what you mean. If your temp sensor is faulty or thermostat is too low the computer will compensate with more fuel.....and if you have a slight vacuum leak it may do the same. check vacuum tubes around the throttle body and MAP sensor. You should get 30 mpg highway at least.

Could be the O2 sensor also.

Check your engine/frame ground also

The fuel/air mixture is controlled by the engines computer (ECM). You cannot adjust it like a carb with jets. You can do silly things like add a resistor to the IAT sensor to fool the engine into thinking the intake air is far warmer than it actually is. This is asking for trouble IMHO.

18/24 for a V6 with the old 3 speed auto? That sounds pretty good to me. 16/22 was advertised by GM.
http://www.fueleconomy.gov/feg/noframes/4152.shtml

I average 19mpg in my GT. From the research I've done that's about the best it gets with the 3-speed auto transmission. Upgrading to a 4-speed (4T60 or 4T60E) is supposed to improve mileage quite a bit.

I'm just going to replace the whole motor with a 4.9/4T60E combination and I expect to get around 25mpg or so (but I won't know for sure until I actually do the swap). If it's better than I currently get, I'll call it a win...

Thanks!!!

Josh

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1988 GT

--Soon to be more new and improved with Rodney's inner/outer tie rods, steering rack bushing, and most importantly, a 4.9 V8...

Sounds like a leaky injector to me (hot restart stalling out unless you give gas).

$0.02.

Mike

Check your EGR hose. They seem to always have a hole in them.
I saw a DIY on how to use a Natuarl Gas pipe from Home Depot to replace your stock broken hose, Seems pretty simple although I can't find the DIY now.

Basically you cut the ends off the original hose and soldier them to the new NG pipe with Silver Soldier and a MAP gas torch.
It's what I plan to do when i get around to replacing mine.

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86 Fiero 2M4 Silver, and 86 GT

My problem like that was a bad O2 sensor, saying it was lean, so ECM kept dumping more gas in.

There might not be much wrong with your mileage. My 86GT auto was getting 18-20 initially, improved to 20-22 w/ oxygen sensor, and most recently measured 24.7 after a couple other fixes/changes, but I need to corroborate that.
My goal has been to reach 25mpg on a route which is mostly cruising, not much traffic. I wouldn't expect to get much beyond that without a transmission swap.

The oxygen sensor affects mileage and it's cheap, so it's worth replacing if it's old. I think it cost $25 including shipping from RockAuto. The Denso is reportedly the same OEM as ACDelco, so that's what I bought. Some people have problems with Bosch.
After installing the new sensor, I even got a rich exhaust error code on the first drive. Apparently the ECM had learned to run rich based on lies from the old sensor.

I also had a bad MAT sensor, which didn't set a code but it was reading high temperature. I'm not sure how common that problem is, but mine was just dirty. After cleaning it, the readings became accurate so didn't need to replace it.
A bad coolant temperature sensor would certainly be a problem. This is the sensor on the psg side of the head, not the same as the gauge sender.

You can test both the MAT and coolant temp sensors with a multimeter, or WinALDL if you have that.
40F = 7500ohms
70F = 3400ohms
100F = 1800ohms

Note: the wiring to my MAT sensor had some test points installed. I don't know if that's factory or somebody's mod. But it's not useful, you have to check the resistance at the disconnected sensor. If you check it at the wiring, the resistance is different. This is apparently normal for the circuit because WinALDL still reports an accurate temperature.

Well i have been fighting a crack on my egr tube 100$ to replace but i will think about that when i replace the egr still fighting the suspension and brake problems in the rear right now had the rotor brakes and hubs replaced in the back and the mechanics turned the cylinders on the calipers "I think they did it on purpose" so one of them locked up now i have to work them free again. argh! anyway with needing inspection and new bushings and e-brake cables for the arms in the back don't have the funds to get the new egr so epoxy works well for a month or so. i have the engine fan and temp gauge switches will get a new O2 sensor this week so I can at least change those out.

ya you have to reset your ECM battery disconnected to reset it
Will get the fuel pressure check once i fix those sensors if it doesn't correct itself.
okay the 32mph was for the duke didn't see that before. NY uses 10% alcohol in their fuel too so that is no help may explain the 14mph i got in the winter

Well off to free up those calipers fun fun :-(

A cracked EGR tube and a little drag on the brakes, and BINGO......bad mileage. The winter problem probably has to do with operating temperature, and is pretty hard to avoid. The ECM is set up to send extra gas to a cool motor, so the quicker it gets to 195* the better.

[This message has been edited by Gall757 (edited 06-26-2011).]

quote Originally posted by Gall757: A cracked EGR tube and a little drag on the brakes, and BINGO......bad mileage. The winter problem probably has to do with operating temperature, and is pretty hard to avoid. The ECM is set up to send extra gas to a cool motor, so the quicker it gets to 195* the better.

well i just replaced the rear brakes before they were not working at all. so I dont count that in the equations. I will go with the O2 sensor and temp sensor for now then i will say how that went.

[This message has been edited by hawkebat (edited 06-26-2011).]

well I found out 2 things

1 stop going to a mechanic and do it myself
2 that the rear brake pads and most likely the front as well are directional and they did not know this
and that is why the rear caliper was locking up.