Hello all, I have recently gotten the 0171 code again, the last time it was both of them 0171 and 0174 along with some egr codes. That one turned out to be the vacuum control solenoid that controls the vacuum to the egr valve. Been driving it well over a year now with no more problems. Now the cel has come back on a couple of times with just the 0171 code. Just for kicks I tried purchasing my gas elsewhere that doesn't put ethanol in the gas. It's been fine the last couple of months, no cel. My wife just put gas in from wal-mart the other day, now I have the 0171 code again. I am wondering if this is just a coincidence or something more maybe.

it's a coincidance

it's a coincidance

when you have a mechanical/electrical problem and it disappears by itself, be sure that it will always finish by appearing again.
Is it really? I haul fuel for a living, I load a bunch of it with ethanol and believe me when i say that the mixture is not always 90/10. IMO, these vehicles were not intended to run on an alcohol/gasoline mixture especially when that mixture isn't correct. So, the ECM monitors the air/fuel ratio, how does it monitor the fuel when it isn't designed for alcohol? I have a friend that is having a similar problem with a toyota every now and then after buying fuel for it. These are just some questions that I have, it may be a mechanical issue. But the last time I was getting both codes it was as wiswind says in his tutorial, a vacuum leak. It took some time tracking it down but I finally found it with the egr vacuum control solenoid. The bottom hose barb was broken for the vacuum line that comes from the manifold to the solenoid. So not only was I getting lean codes, I was getting a couple of egr codes. I ordered the new solenoid and installed it and haven't had any lean codes up until recently. If it is a vacuum leak, wouldn't I be getting both codes like I was before?

On second thought, you're right!
12.5 mole of dioxygen need 114g of octane for a stochiometric combustion.
so the ECU takes 114g of the 90%/10% mixture, but it needs in fact 122g, cause ethanol requires less oxygen to burn, so the mixture will be 4% too lean.

It's not too bad. But if, like you said, the gas/ethanol mixture is weak, the air mixture will be even weaker.

Also, the ethanol corrodes engine, rubber and reduces fuel economy. So yes, you need to stop filling with ethanol.

If it is a vacuum leak, wouldn't I be getting both codes like I was before?

Not necessary, each code is for a different bank of the engine. Because you have just 171 code, then the leak might be on the rear bank of the engine.

On second thought, you're right!
12.5 mole of dioxygen need 114g of octane for a stochiometric combustion.
so the ECU takes 114g of the 90%/10% mixture, but it needs in fact 122g, cause ethanol requires less oxygen to burn, so the mixture will be 7% too lean.

It's not too bad. But if, like you said, the gas/ethanol mixture is weak, the air mixture will be even weaker.

Also, the ethanol corrodes engine, rubber and reduces fuel economy. So yes, you need to stop filling with ethanol.



Not necessary, each code is for a different bank of the engine. Because you have just 171 code, then the leak might be on the rear bank of the engine.
Thanks serge, would you by any chance know what the usual suspects are on that bank. I cleared out the code and drove it and it didn't come back on yesterday so who knows. I have been told though that the 95's were different than all the other model years so a vacuum leak on say a 99 could be a whole different beast altogether.

Before doing anything, burn all your gas, then fill up with pure gasoline.
Each cylinder receive a different ammount of fuel, so a cylinder doesn't have exactly the same mixture that the other ones.
Try to see if it solve the problem. If not, then you'll run some inspection/tests.

Oh. My. God... I never thought I'd see stochiometry again. Damn you! :P

LOL. In the forum, you will see it occasionally.

Oh. My. God... I never thought I'd see stochiometry again. Damn you! :P
I'm just glad you guys understand all that stuff, I need someone to explain it all to me:banghead:

Ok, the combustion reaction of the octane with oxygen is:
C8H18 + 12.5 O2 --> 8 CO2 + 9 H2O
the weight of octane (gas) is 114g/mole.

So if MAF sensor detects the mass of air that contain 12.5 moles of O2, it will inject 114g of fuel (1 mole). It doesn't know what contain the fuel.

The reaction of the ethanol is:
C2H5OH + 3 O2 --> 2 CO2 + 3 H2O

114g of gas/alcohol mixture contains 102.6g of octane and 11.4g of ethanol.

the 102.6g octane is (102.6g/(114g/mol)) 0.9 mole of octane. So it uses (0.9*12.5) 11.25 moles of O2.

the 11.4g ethanol is (11.4g/(46g/mol)) 0.248 mole of ethanol. It uses (0.248*3) 0.74 mole of O2.

If you do the sum, you use in total (11.25+0.74) 11.99 mole of O2.

But MAF sensor have detected 12.5 mole! So the mixture is too lean.

You have 0.51 mole of O2 in excess. It means (0.51/11.99) 4% too lean.

I made a mistake the 1st time I calculate it, it's not 7%.

Freakzilla, I hope you'll not suffer too much. ;)

A vaccum leak can show up on just 1 bank.....a variety of factors can cause this.....maybe it is slight enough that 1 side is catching it....the other is close to catching it?.....or as mentioned....the leak is closer to 1 bank.

As far as ethanol.....that is all I use...except for when I am on a trip and fill up with the "real" stuff.

It is not by choice, but my area....like many parts of the USA are mandated by the EPA to sell ONLY ethanol "enhanced" gasoline.
I would have to drive at least 50 miles to get to a station that sells non-ethanol fuel.......100 miles round trip......cancels out any fuel economy gain in a real hurry.

With the Windstar, we are fine with the 10% or so ethanol......when you get 20% or more.....it gets risky.
So STAY AWAY from E-85........(for the windstar...which is a NON-flex fuel vehicle).

The PCM will correctly adjust the air / fuel mixture with the 10% ethanol mix.
As ethanol has less energy (btu) per equal unit of gasoline.....one would expect slightly lower fuel economy with the ethanol blend....but not by any large amount.

YES, the '95 is unique in the intake manifold for the 3.8L motor......as it does NOT have the cross port system with the IMRC.

I have had lean codes and misfire codes caused by dirty fuel injectors......Berryman's B-12 Chemtool takes care of that better than anything else that I have tried (and I have tried a BUNCH).

I do NOT know how the EGR ports are set up on the '95, so I don't know if clogged EGR ports are a factor for the '95.

With winter upon us.....I would change the fuel filter, if it has not been changed in the past year.

I like to eliminate routine maintenance items before moving on into other things.

Don't forget to carefully check the many vaccum lines (including the line to the PCV valve (rear valve cover for 1995-1998) and the breather line that connects to the front valve cover (1995-1998).....can become disconnected...
They switched these in the 1999 model year and up to have the PCV valve in the front valve cover.

A vaccum leak can show up on just 1 bank.....a variety of factors can cause this.....maybe it is slight enough that 1 side is catching it....the other is close to catching it?.....or as mentioned....the leak is closer to 1 bank.

As far as ethanol.....that is all I use...except for when I am on a trip and fill up with the "real" stuff.

It is not by choice, but my area....like many parts of the USA are mandated by the EPA to sell ONLY ethanol "enhanced" gasoline.
I would have to drive at least 50 miles to get to a station that sells non-ethanol fuel.......100 miles round trip......cancels out any fuel economy gain in a real hurry.

With the Windstar, we are fine with the 10% or so ethanol......when you get 20% or more.....it gets risky.
So STAY AWAY from E-85........(for the windstar...which is a NON-flex fuel vehicle).

The PCM will correctly adjust the air / fuel mixture with the 10% ethanol mix.
As ethanol has less energy (btu) per equal unit of gasoline.....one would expect slightly lower fuel economy with the ethanol blend....but not by any large amount.

YES, the '95 is unique in the intake manifold for the 3.8L motor......as it does NOT have the cross port system with the IMRC.

I have had lean codes and misfire codes caused by dirty fuel injectors......Berryman's B-12 Chemtool takes care of that better than anything else that I have tried (and I have tried a BUNCH).

I do NOT know how the EGR ports are set up on the '95, so I don't know if clogged EGR ports are a factor for the '95.

With winter upon us.....I would change the fuel filter, if it has not been changed in the past year.

I like to eliminate routine maintenance items before moving on into other things.

Don't forget to carefully check the many vaccum lines (including the line to the PCV valve (rear valve cover for 1995-1998) and the breather line that connects to the front valve cover (1995-1998).....can become disconnected...
They switched these in the 1999 model year and up to have the PCV valve in the front valve cover.
Thanks wiswind, I cleared the code out last tuesday and have been driving it ever since with no problems. The CEL came back on today, I guess I'll have to go over it again to see it there's something i've missed.