Terrible gas mileage!!

**My00Z28** · 12-08-2011, 10:03 PM

Originally Posted by Smittro

Right!

Both are indications of a faulty 02 sensor..

Which currently according to the OP are abviously dirrectly effecting AFR's after the engine is warm hense the poor MPG's.

There is nothing stated about a loss of power which would be an indication of a bad knock sensor pulling too much or not enough timing.

Again poor afr's in turn as I already stated can/will cause a knock issue.

If the heater curcuit is bad then the sensor is bad, if it does'nt turn on it can be assumed it also bad.

It does'nt matter whether it's cold or hot a faulty 02 is a faulty 02..

Target MPG's AND AFR's come after closed loop when the engine is @ operating temp, SO, if the only the heater curcuit is bad then MPG's nor AFR's would not be effected once the designated temp was achieved as it could be assumed the sensor is working aside from the heater curcuit..

The odds of an 02 and the knock going bad @ the exact same time are slim @ best.

If it's the knock sensor then I'll eat my hat..

But I am confident once the 02 issue is corrected the knock sensor code once cleared will not return..

ya i was never saying that the o2 sensor wasnt bad i was just saying if its the heater circuit that the car would default till the sensor its self warms up and starts to read again which shouldnt affect the car(just throw a light)... the sensor needs to be replaced anyways....

i know we could debate about this for years but it really doenst matter till he replaces the sensor and sees what happens...

**Smittro** · 12-08-2011, 10:17 PM

Well lets look @ it in this light..

Black smoke is an indication of a rich condition.

Knock is a good indication of a lean condition.

If the 02 sensor in bank 1 where maintaining the proper AFR's above a lean condition then we can assume there would be no knock code.

Since knock generally happens under a load it's safe to say the bank 1 o2 sensor is causing lean combustion under a load in turn causing the knock issue..

This is why I stated it's likely to be the o2 sensor, not to mention it's way passed over due for changing them @ 80-90k iirc..

Further more since the o2 is dirrectly into the exhaust stream it's likely to go bad before the knock sensor which only sees block wall temps..

I understand what you're saying about the heater curcuit and I agree..

However this is pointing to a bad o2 all together. IMHO

**My00Z28** · 12-09-2011, 03:37 AM

idk i just want to see what it is...
i mean we all know the o2 sensor needs to be replaced. but a knock sensor would also cause poor gas mileage.... lol

**Smittro** · 12-09-2011, 06:34 AM

Ya, all bebating aside you're right we'll just have to see how it goes..

**flybird** · 12-09-2011, 10:05 AM

Lol don't debate till I update. I do appreciate both of you, I can promise you I will let yall know what happens after the replacment.

**flybird** · 12-19-2011, 04:33 PM

Okay o2 sensor has been replaced! Mpg has gone from about 9mpg to 15 mpg city. But I still have a knock sensor code..and now all of a sudden a random miss fire code.. Just my luck huh? Codes poppin everywhere. I had these codes checked and diagnosed.

This v6 enigne is from my old 98 firebird tht I wrecked. I swaped this motor and tranny into my new 99 firebird. But I didnt swap the computer. So the mech. said these codes could be from the computer.

**My00Z28** · 12-19-2011, 08:30 PM

shouldnt the 98-99 computers be exactly the same because they are exactly the same engines? so i cant see the computer causing this issue!

**flybird** · 12-19-2011, 08:58 PM

Idk... in 99 the throttel body was changed to electric instead of a cabel and the engine in 1998 was a Series 1. In 99 it changed to a Series 2 Motor.

**Smittro** · 12-19-2011, 09:09 PM

Originally Posted by My00Z28

shouldnt the 98-99 computers be exactly the same because they are exactly the same engines? so i cant see the computer causing this issue!

Nope.. The fly by wire is a totally different PCM.

Originally Posted by flybird

Idk... in 99 the throttel body was changed to electric instead of a cabel and the engine in 1998 was a Series 1. In 99 it changed to a Series 2 Motor.

The series 2 3800 was released to f-body in 96, no f-body ever came with the series-I 3800..

Check the 2/5 coil for spark strength.

**flybird** · 12-19-2011, 09:16 PM

Ok ill check the coil pack 2moro. How many volts do you think it should be when I test it?

**Smittro** · 12-19-2011, 09:31 PM

Originally Posted by flybird

Ok ill check the coil pack 2moro. How many volts do you think it should be when I test it?

When mine died center coil (it's either the 2/5 or 3/5 can't recall) I was only able to find it buy pulling the plug wires while the car was running.

You'll be looking for a weak (yellow) spark @ idle and try switching the to wires @ the same coil.

Both plugs get fired @ the same time so if the misfire moves then one side of the coil is bad.

Coils are about $26 bucks each if that ends up being the case.

You can also try pulling each coil and checking that the ignition module coil pins are clean and not corroded.

Since the coil contacts are internal on the coil itself there's no way to check the voltage @ the coil.

**Smittro** · 12-19-2011, 09:38 PM

The cause of mine was water/rain and windshield washer fluid was able to bypass my hood seal and drip onto my middle coil.

This caused the coil to fry in my case which resulted in an intermittent misfire code..

here's where the leak was on mine..

**flybird** · 12-19-2011, 10:13 PM

I have an extra set of coil packs from my 98 firebird that I parted out when I totalled it. Could I just use those to replce 2/5?

**Smittro** · 12-20-2011, 03:36 AM

Originally Posted by flybird

I have an extra set of coil packs from my 98 firebird that I parted out when I totalled it. Could I just use those to replce 2/5?

Yes. They're exactly the same..

**My00Z28** · 12-20-2011, 04:51 AM

Originally Posted by Smittro

Nope.. The fly by wire is a totally different PCM.

Haha ok so you would have to switch the trottle bodies over which would make it the correct engine for the harness/computer....

The series 2 3800 was released to f-body in 96, no f-body ever came with the series-I 3800..

Check the 2/5 coil for spark strength.

O and pulling wires while its running can hurt be prepared to get shocked

**Smittro** · 12-20-2011, 06:40 AM

Originally Posted by My00Z28

O and pulling wires while its running can hurt be prepared to get shocked

Haha ya you can get a jolt, but I did'nt get juiced just have to keep the fingers away from the end of the boot.

If it has weak spark it may not even be able to jump the gap.

Mine was so weak you almost had to put the boot back over the pin to get it to jump the gap.

**flybird** · 12-20-2011, 08:57 AM

Thanks guys, ill update after I replace coils. Which will prolly be 2moro since I have school.and work today.

**flybird** · 12-20-2011, 10:26 AM

Smittro, is this the yellow posts in the coils you were telling me about?

**flybird** · 12-20-2011, 10:36 AM

I pored water on my windsheild and water pored all over the coils, there is a hole somewhere. Coil posts 2,5,1,4 are all yellow. 3,6 are silver and look fine

**Smittro** · 12-20-2011, 11:05 AM

Originally Posted by flybird

Smittro, is this the yellow posts in the coils you were telling me about?

Not quite but there is definetly something amiss there.

They should be identical.

There are 2 pins under the coil itself that get corroded and can cause all sorts of issues..

The coil is held to the ignition module by 2- 5mm flanged bolts that also serve as coil grounds.

One bolt is in front of the coil between the spark plug wire posts and the other is on the oposite side.

Once the bolts are removed the coil will lift right out and expose the power pins from the ignition module.

Try to clean them up with a small wire brush or a chunk of sand paper prior to installing the other coil.

Just don't He-man them as if they snap off you'll have to replace the module too..

Also check the module bridge plug for corrosion as well, it's a pain but worth the time to ensure good contacts and spark.

Originally Posted by flybird

I pored water on my windsheild and water pored all over the coils, there is a hole somewhere. Coil posts 2,5,1,4 are all yellow. 3,6 are silver and look fine

I am not sure why you have gold and silver pins..

They should all look the same.

Don't forget to use a little dab of anti arc compound when you get to where you're going to snap the wires back on..