I have been chasing my tail for 2 months on my 4.9 Elderado motor in my Fiero, it is the late model 4.9 that uses the dual O2 sensors. Running really rich and getting horrid gas mileage around 10mpg in town. To drive from Surrey to Van and back cost me $25 in gas. About 2 months ago I installed 2 brand new NTK O2 sensors. I notice on the scan tool that the O2 voltage is at a constant 444mv I talk to a couple of people and no one seems to really have any idea and one person said "that is just the way they are" so I left that alone, after all they were brand new O2 sensors. So I went on trying to find out why the dang thing ran so rich all the time. Car was so rich that it would burn your eyes at idle.

So today I bought 2 Genuine Delco O2 Sensors.( AFS23 ) I installed one and left the NTK in the other bank. I fired up the car and checked the scan tool. Sure as crap, the NTK stays at 444mv while the new GM one was constantly moving from 84mv all the way to 900mv so rapidly that the Dash mounted scanner could not keep up.

So I pulled the other NTK out and installed the 2nd O2 sensor from GM AFS23 and took the car for a drive, instantly the car was better, smoother, ran awesome, pull from idle to 4000 and part throttle was so much smoother. It was like a hole new car. Even the high idle issue I was having seems to have partly cleared up. I am so happy.

I hear so many people with bad gas mileage problems, cars running horribly rich. I can't help but wonder if that NEW O2 sensor is really doing its job.

This is just a huge heads up.

As for me, I am off to go driving around.

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85GT 5spd MSD Everything,4.9 With Nitrous. www.captfiero.com

This may be my problem with the 4.9 in my GT installed by Rockcrawl. He got the o2 sensor from Autozone brand unknown. My gas mileage is about 18 on a good day driving easy and has bad throtle response at a stop. If I blip the peddle it revs up than almost dies (about 2-300 rpms) and has, than returns to the 900. If I am driving along and put it in neutral and coast down the road my idle is at 1500 untilthe wheels stop a second later it drops to the 900.

Earl

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1986 FieroGT now a 4.9

Hmm... Another thing to check! Not sure the brand of the new one I installed from Autozone, but I suppose that is a possibility. I get the same (or better) gas mileage doing in excess of 100mph that I do when I do normal speeds.. My scanner stinks but I've got to figure it out!

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Bob Williams
Multi-colored '86 Mutt, a work in progress! (3800SC running great! Fixed the bent roof, now I need an intercooler! Yeehaa!)

Hey Aqua-Man you better pick up 2 new GM sensors for Sunday. Might be the whole problem.

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quote Originally posted by aqua-man: If I am driving along and put it in neutral and coast down the road my idle is at 1500 untilthe wheels stop a second later it drops to the 900. Earl

As far as I know, this is normal operation for these caddy motors. Mine did the same thing before it started burning more oil than gas. I think it's designed to not jerk the old people forward, to give them a nice smooth decel when they let off the pedal.

Eric

Well just got back from my drive, went out and bought a couple of RC Cars, and then went out for drinks with friends. The drive would have usually taken 10 bucks or more in fuel, I think I barely saw the needle move enough for about 5 bucks. I am very happy.

Before as I would press the gas down about 3/4 throttle it would just come alive and take off, now it is a nice smooth transition as I press harder the car takes off faster. It is like a whole new car.

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85GT 5spd MSD Everything,4.9 With Nitrous. www.captfiero.com

quote Originally posted by aqua-man: This may be my problem with the 4.9 in my GT installed by Rockcrawl. He got the o2 sensor from Autozone brand unknown. My gas mileage is about 18 on a good day driving easy and has bad throtle response at a stop. If I blip the peddle it revs up than almost dies (about 2-300 rpms) and has, than returns to the 900. If I am driving along and put it in neutral and coast down the road my idle is at 1500 untilthe wheels stop a second later it drops to the 900. Earl

This is a known issue to GM, do a search on here for the idle learn proceedure.

quote Originally posted by Mickey_Moose: This is a known issue to GM, do a search on here for the idle learn proceedure.

And one I've seen, and fixed before... but isn't it odd how Capt JUST changed the O2 sensors, and his problem went away right on the spot!

I was there! No other fiddling was involved...

quote got the o2 sensor from Autozone brand unknown

Earl, yours is a Bosch sensor. It only uses one. When you bring the car here on Sunday I want to weld in a second bung and compare the Bosch sensor against my wideband O2. It may not be a bad idea to pick up a new Delco sensor just in case.

It is normal for the RPM to follow the vehicle speed to a certain point. If everything is set up and working properly it will just seem a bit weird and not cause any real problem, but if it's excessive it can push you through a stoplight with an automatic car. The problem could be caused by incorrect adjustment or un-learned ISC motor, a slow ISC motor or defective throttle switch, or incorrect setting of the speed sensor constant in the ECM. The manual swaps are more sensitive to problems with the chip programming because the Fiero VSS has 1/6th the resolution of the Caddy sensor.

Earl, Yours seemed to be working normally, so I never made any adjustments to it. I'll go over it on Sunday. You also said the Speedometer is off by a few MPH, and it may also be affecting the coast-down idle speed. I'll correct that too.

MY Quad 4 is acting dinky with new O2 sensors too. I think it is because the fuel pressure is low when cold because of a bad fuel pressure regulator, bit I have a new Bosch one in there now, and it does the same thing as a cheaper one from the parts store that I work at. IT will start ok, and after a few minutes, it will bog and sometimes die and dick around for a few seconds, then be good until it gets cool again. The bosch o2 does the same thing but waits until you pull out onto the road, then it does that, I can back out of my parking spot drive around the parking lot, but do it as soon as I touch the gas to pull out of the parking lot, if it stalls, I start it up and it works fine, this is the part that makes me think it is the o2 sensor. If I stick the well used original O2 sensor in, it does not do this at all.

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84 Fiero Sport Coupe #1192 :: 86 Fiero Base Coupe Quad 4 :: 84 Chevette CS 4 Door

well im glad to see im not the only one having problems with my car smelling like its running rich , and not great milage.
might have to look into this o2 sensor . and check the isc

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86 and 87 fiero database www.geocities.com/cwandall/fiero.html

I can't find a AC Delco distributor in my area without going to a Caddy dealer. The Caddy dealer wants $65.00 for a AFS-23 Oxy sensor and didn't really want to sell it to me. That was because I couldn't give him a vin # of the car and when I explained it was for a engine swap into a Fiero I really got the you will have to talk to someone else and put on hold for a few minuets. On line I can get it for $40.00 shipped. I just don't see the Genuine AC Delco parts signs up at dealers or service stations any longer. I wonder why that is?

Earl

Hmmm,
nice write up-plus for you.
I am using the o2 sensor that was on the caddy in the u pull it---I am running rockcrawl's chip and it does smell a bit rich but gets about 26-28mpg with the 4t60e and Parks Harness is being used.

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Proud Member of the North Florida Fiero club

4T60E Parks harness/ Rockcrawl chip-- more to come--

My 3.4DOHC will make your eyes burn, but a scantool shows the O2 funcitoning "properly" (high low high low high low ) whether or not its right.....

I had my 4.9 checked out today by the installer (Rockcrawl) and found the Bosch O2 sensor would work but seems not fast enough and sometimes not at all. It showed it was running rich most of the time. I got home and ordered on line a AC Delco AFS23 Oxy sensor and will try that to see if mileage gets better than 18. I will post when it gets installed to see if it helps.

Earl

Well I took my car on a run from Surrey to Abbotsford and back to Surrey thien around guildford and over to the Red Robin and then home. It would usually take at least $25 in fuel to make this run, Total today was less than $10 in fuel. I am VERY VERY happy.

The only draw back to the hole deal is that now that the car is not running PIG rich, the exhaust is now getting hot enough to melt any plastic loom or other meltable stuff. So I have had to stop and re-arrange stuff not once but twice in the past couple of days.

With the good chip in it, the extreme high flow exhuast and a 5spd this car is a real joy to drive now.

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85GT 5spd MSD Everything,4.9 With Nitrous. www.captfiero.com

Finally had some time to take the GT for a long ride after installing the AC Delco o2 sensor. I originally had a Bosch installed new by Rockcrawl when he did the engine. The AC Delco seems to have cured the problem of it running rich. I am doing this by the idle smell test and the rich smell is not there from what I can tell. Tomorrow I will hook up my AutoXray 6000 and the laptop and see with the scanner if it has done the job or not.

Earl

My gas mileage seems to have nearly tripped since changing to the Delco O2 sensors from the NTK branded ones.

I am curious as to what other people are getting for mileage.

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85GT 5spd MSD Everything,4.9 With Nitrous. www.captfiero.com

Been getting in the 20's for an average with mine.

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88 Coupe: Modded 4.9L V8 5 speed
86 GT: Stock 4 speed
86 SE: 3.4 DOHC 4 speed
http://www.geocities.com/fast88fiero

Can't supply an actual mileage number (since I did the conversion for someone else!), but he HAS reported back to me that the car runs MUCH better, and there is no fuel stench while standing at the back anymore.

So - rack up another "win" for the Delco O2!