ethanol causing false check engine lights?

2manyrocks · May 18, 2011

2003 Mazda protege (81,000 miles) check engine light is on and the code is reading too lean condition. The shop suggested I might have an air leak at the fuel hose or a vacuum leak. I'm not finding one.

The check engine light on my 2004 Mazda pickup (51,000 miles) came on today showing both the check engine light and a light for an open fuel cap. The fuel cap is tight and I can't find any problems in the hose.

I was told that ethanol fuel has a higher oxygen content. Is it likely that this ethanol gas I'm paying $3.70 a gallon for is causing these check engine lights to go on? It would seem more than coincidence that both vehicles are doing this at the same time.

If I park both fuel injected vehicles and go back to my 1992 Mazda with a carb, what is the ethanol going to do to it?

LD1 · May 18, 2011

Are you just running the regular 87 gas w/10% ethanol or are you trying to run e-85??

If e-85, that is your problem.

If you are only running the 10% stuff, I doubt that is the issue, but I could be wrong.

Running the 10% stuff shouldnt effect the carb in the older vehichle. It mainly has only been know to cause a few issues with smaller engines. Certain rubbers do not tolerate ethanolvery well. And small engines w/diaphram carbs and rubber fuel hoses can cause issues. Plus ethanol absorbs water. So it has a shorter shelf life. And small engines tend to sit a lot. On a daily driver, this is less of an issue.

MyJoBota · May 18, 2011

The protege most likely has a vacuum leak at the intake gasket , common on those.

The B series most likely needs a filter neck. Rusted and creating a evap. leak if you live in the salt belt.

If you cant fix em just blame the fuel:thumbsup:

tcartwri · May 18, 2011

Stuck or plugged egr valve will give a lean code. The ethanol is not the answer.

Diamondpilot · May 18, 2011

Last car I worked on with a lean code was a Lincoln. Found a leak in the hose for the PCV valve and also a leak in the hose going to the brake booster.

Chris

Car Doc · May 18, 2011

Its not the ethanol but I agree with the intake gasket on the Protege being a strong possibillity it should be missing and could be idling real fast also and may have a Po3xx misfire code as well.

Cant say about the truck evap codes can be a nightmare so an easy fix probably isn't in the cards a pro needs to work on that one.

As a rule most all lean codes I see are mass airflow meters either dirty or just bad. my 2c

crazyal · May 19, 2011

In the old days they would tell you to just squirt starting fluid all around the intake as the engine was running. Once it found the vac leak the engine would suck in the starting fluid and it would rev up. Nowadays I don't think they want you spraying flammable liquids on a running engine.

Car Doc · May 19, 2011

Yup something flammable is the best way still!

I use carb spray or flammable brake clean or a smoke machine thats the preferred way now is use smoke.

I have set engines on fire before using carb spray getting close to a coil or a bad plug wire that is interesting....

PILOON · May 19, 2011

crazyal said:
In the old days they would tell you to just squirt starting fluid all around the intake as the engine was running. Once it found the vac leak the engine would suck in the starting fluid and it would rev up. Nowadays I don't think they want you spraying flammable liquids on a running engine.

I have seen using a plumbers's propane rig with the nozzel reduced to spew propane around the vacume lines.
When the vacume line sucks in propane the RPM's rise thus locating the leak.

DEWFPO · May 19, 2011

PILOON said:
I have seen using a plumbers's propane rig with the nozzel reduced to spew propane around the vacume lines.
When the vacume line sucks in propane the RPM's rise thus locating the leak.

I have used this method to detect an intake manifold gasket leak.

DEWFPO

zzvyb6 · May 19, 2011

Well just in case its not an obvious vacuum leak, the most common cause of a check-engine light is loose or leaking fuel cap, spark plugs and the oxygen sensor.

jonyyuma · May 19, 2011

The oxygen sensor is supposed to be the most common culprit on a check-engine light.

55acwd45 · May 19, 2011

We have a 2010 Cobalt that I suspect throws the CEL from poor fuel or ethanol.

Its the system too lean, bank #, sensor #. It only has 13,000 miles. Dealer couldn't find anything wrong with it but suggested a "routine maintenance" cleaning of the fuel system for ONLY $130 or so. Its not a flexfuel car. Lately the light has stayed off on its own. I've check the car over twice and so has the dealer and they have not found any problems. Adjusting the fuel trim would fix the problem.

Light was off for a while and we had some gas in a can for a month or so and my dad put the gas in the car and it turned the CEL on the next day. It was clean gas.

PoorMansCat · May 19, 2011

I have found that there are several stations here that sell NO ETHANOL fuel... I have started using that on my small engines.. All my carburetor issues and increased fuel consumption issues have since ceased.

crazyal · May 19, 2011

I had a Saturn that had the intake gasket start leaking. The CEL was giving an O2 sensor fail but it was also picking up on a #1 cylinder misfire. That made it real easy to find.

LD1 · May 20, 2011

crazyal said:
I had a Saturn that had the intake gasket start leaking. The CEL was giving an O2 sensor fail but it was also picking up on a #1 cylinder misfire. That made it real easy to find.

Now that you mention it, Dads 2002 SL1 did the EXACT same thing. SAME tw codes. O2 lean condition, and #1 misfire. But it was intermitten when the CEL would come on.

I did some googleing and that pointed me in the direction of an intake leak around #1 cylinder. Did the old "spray with carb clean test" and confirmed that yep, there was a leak.

This was last year or so. Replaced the intake and no trouble since:thumbsup:

MyJoBota · May 20, 2011

My suggestion would be to take it to a parts store like autozone and let them read the engine codes, sell you a bunch of parts that wont fix the problem and tell you how easy it is to replace them. After you are frustrated and about out of money take it to repairshop capable of diagnosing and repairing the car properly. That's how we roll in this neck of the woods.:laughing:

PILOON · May 20, 2011

zzvyb6 said:
Well just in case its not an obvious vacuum leak, the most common cause of a check-engine light is loose or leaking fuel cap, spark plugs and the oxygen sensor.

YEP!
Just 2 weeks back my check light went on and had me worried.
I tightened the fuel cap and the light went off.

2manyrocks · May 20, 2011

The truck check engine light is now off after I disconnected the battery. I drove it to town and back and so far no more light.

MyJoBota--I've been down that road with the protege before I posted here.

The good repair shop next to me sold out and the guy that took over wasn't good. He's out of business. So l have to go through these tips and see if I can find the problem with the Protege.

Thanks all.

LD1 · May 21, 2011

2manyrocks said:
The truck check engine light is now off after I disconnected the battery. I drove it to town and back and so far no more light.

Thanks all.

How were you abe to get it started with the battery disconnected:laughing::laughing:

Sorry, couldnt help myself.