Check Engine Light

[Rost]

Hello..I own a 1997 Ford truck...therefore my "check engine" light comes on regularly. I usually just unhook the battery for 5 mins then hook it back up and I am set for another 10k miles before it comes on again.

Is there any reason behind this? Obviously, if there was something seriously wrong, the light would come on immediately after I hooked it back up again. I also noticed that each time it comes on, it is in wet, humid conditions. The light is yellow, which I understand is not as serious as the red "check engine".

Should I be concerned?

[Rost]

Also, is there anything I can check (and possibly fix) myself before I finally decide to have them hook it up to the computer?

[IFallsRon]

I had a beater Olds that the check light would go on in rainy conditions but it would go away when the car dried out.

You can buy a code checker for under $20. They typically come with diagnostic information.

Also, some parts stores, like Autozone, will run the checker for free.

Typically, the light is associated to emissions. You may need to replace the O2 senser.

[ChuckN]

Likely an evac code will pop up. You can try this. Check or replace the gas cap. The rubber seal on my gas cap ('97 F150) "rolled over" if you want to call it. There was a leak in the fuel system that the computer detected.

This issue prompted an evac error code. One shop went thru the truck and inspected various vacuum lines and parts in the fuel system, around the fuel tank, and found nothing. No charges to me when the codes continued to pop up and I learned to ignore it and do the battery disconnect thing too.

It took another mechanic 2 years later to simply ask if I've checked the gas cap. Sure enough, we looked at it and the seal rolled. Simply rolled the seal over into it's proper place and problem fixed.

[MattWtech]

evap* not evac.

most ECU's adjust to the slightest of faults, my pa had a 2002 chev with a missfire on cylinder 1 due to lack of fuel, so the computer gave it more fuel, little did the computer know the injector was going bad ebcause it had a restriction. so after a long period of time, it was shooting like 120psi of fuel into that one injector. one day it needed work so i disconnected the battery, and that reset the computer, but the computer didnt know whhat thehell was going on with that injector, so it tripped a check engine light and it missed on that cylinder and couldnt relearn..long story short bought new injectors because the computer kept relearning faults. i dont think this would happen to your truck because its a bit older., just wanted to tell a cool story, but its possible because believe it or not, cars are smart anyway just get it checked out...shouldnt cost much for somone to hook up a brik or a tech2 and read the code.

[Jeremy airjer W]

The check egine light doesn't change colors. If its yellow its yellow if its red its red. It will however flash if there is a serious enough problem that could cause damage to the catalytic converter.

Without knowing what the code is there is not a whole lot we can do to help you. Give your local autoparts store a call to see if the will scan the computer for free. Some will do this. Don't buy anything from them until you consult with us first!!!

A quick note. The computer will change the pulse width (the amount of time an injector is kept open) not fuel pressure on the chevy. Although the fuel pump is more than capable of putting out more than 120psi it is regulated at around 60psi.

[MattWtech]

not if your pressure regulators plugged the injector had varnish in the seat, and coulndet get the fuel all the way out, thats why the pressure rose so high..that along with " if your chev pressure regulator didnt go out once, somone elses did twice"

[federline]

>>Should I be concerned?

Here's a low tech answer: No.

Why? You answered the question yourself - It takes 10K before it happens again. If you had a chronic problem, it would light back up soon after resetting it, as you know.

My Chevy behaves the same way. Multiple mechanics that aren't just out to make a buck have told me that "if nothing changes in the performance of the vehicle around the time when the light comes one, reset it. If it comes back on right away, then I'll look at it."

[Jeremy airjer W]

Sorry dude, thats impossible! Fuel pressure is regulated before it gets to the injectors. For the most part it doesn't deviate a whole lot from 60-65psi. The only way it could get higher than than is if the return line is blocked. All eight of your injectors could have been completely blocked, the pressure would not change from 60 - 65psi.

[Jeremy airjer W]

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>>Should I be concerned?

Here's a low tech answer: No.

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Yes you should be concerned! At the very least you should know what the vehicle is trying to tell you. What if its a code for lean both banks. I would suspect a fairly significant vacumm leak wich could cause a cylinder to run excessively lean which translates into really hot wich could do some real damage. All this and you may not even "feel" that anything has changed.

If it turns out to be a $10 gas cap good deal. If it turns out that you scored a cylinder or burnt a valve all because you ignored the check engine light which would have led you to replacing the $10 worth of intake gaskets your going to kick yourself.

An engine light may seem innocent enough but can turn into a big barrel of kitty cats if ignored!!

[MattWtech]

pressure regulators, these vortecs, are on the return side.. fuel pressure regulator- a device designed to limit the amount of pressure build up in a fuel delivery system..his was clogged. vacuum from the intake is supplis through an opening in the regulator cover to the regulator diaphram, the regulator spring pushes down on the diaphram , and fuel pressure from the pump pushes the diaphram upwards and opens the valve, which allows fuel to flow through this valve and RETURN to the fuel tank..

want nevermind sorry dude we are thinkin completly different things, on some returnLESS systems the regulators before the injectors, and on a return system its after, on the return side.

ok good discussion, peace

[Jeremy airjer W]

Alright matt I see what your sayin however I've never seen a chevy with this problem (probably because they leak long before they would stop working ). However I have seen plenty of F-150's and tempos with a 150PSI of fuel pressure and running like a three legged dog. A new regulator and your back in business!!

[MattWtech]

haha sorry for being frustrating, i know what your talkin bout with those ol tempo's, ill try not to be so argumentative, either that or i gotta find somthing to do instead of go on FM FORUM AT WORK!

[Jeremy airjer W]

Alright, lets stay on the subject now!!

(work is the best place to surf FM!)

[ChuckN]

Evap...stand corrected..

Talking about this check engine light stuff, airjer, '96 Mazda 626 2.0L I have a check engine light pop on and when we run the code, it's an evap code, and not clear what the problem is. Any ideas?

It runs ok, but recently there has been hesitation with the engine when I throttle it up from idle, or when stop-n-go while driving.

[Jeremy airjer W]

Whats the code?

I believe there is a MAF sensor in the air snorkel right after the air filter box. There are usually four tamper proof torx screws holding it in. Remove it carefully!! You may see a build up of debris on the little sensors. If so clean off with carb spray and reinstall. These are pretty common and the symptom you described is what this causes. I just had one burn me a couple of months ago. I spent a lot of time checking a lot of different stuff before the light bulb turned on.

I hope that gets you taken care of!

[ChuckN]

I don't recall the exact code, just an evap error. Something I should look for on the diagnostics?

When we clear the code it lasts about 400-500 miles before the engine light comes back on. I have even had the light turn itself off periodically, but not recently.

Thanks, I will try that.

[Capt. Don*]

I love these questions. Is it something to concern yourself about? "Its just for emissions" and so on. These systems are far more complex then you might realize and the light is on for a reason. Only once you know the root cause of the problem can a decision on whether or not to fix it be made. Ignore it, it causes bigger problems down the road and then its the manufactures fault for building a piece of junk that ends up with low scores in the truck advice responses. There are a few of us on here from time to time that understand this stuff, and well enough to make a living doing it day in and day out, we typically agree on the answers or the diagnostic routines needed when these questions arise. I understand that people want to help and share experiences, but think about the advice your giving. Are you really qualified to give an answer that may cause money to be spent needlessly replacing good parts, or worse causing more damage. I know that no one would intentionally steer someone down the wrong path and you really want to help, but put yourself in the questioners place, would you want a real answer from someone with knowledge in the field, or hope for the best guesses and opinions. Please don't take offense to this, just think about it.

[federline]

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>>Should I be concerned?

Here's a low tech answer: No.

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Yes you should be concerned!

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Really? 10,000 miles for most people is 8 months between lights! If this happened 5 times over 50,000 miles, and nothing else ever changed in the way it runs and drives, and it always stays off for months and months after a reset... I wouldn't get too worked up about it.

It is a person more admirable than me that has the time and money to hunt every first light trigger down. I just don't think it is cost conscious or cause for alarm in this case. My informal response was given in the context of a 10 year old truck, very sporadic light, and no other complaint of performance.

[snapjigger]

2000 Explorer, just had it checked, code was lean left bank turned out to be my intake gaskets so it probably pays to get it checked out.

[Jeremy airjer W]

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2000 Explorer, just had it checked, code was lean left bank turned out to be my intake gaskets so it probably pays to get it checked out.

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Probably a 4.0 SOHC. Super common problem. Started seeing these real frequently a couple of winters ago. They will eventually get bad enough to trigger codes for both banks lean and will start running really bad at cold startup.

[Justfishing]

The check engine light monitors emissions control. It could be something as simple as a gas cap as someone else said. I have had bad gas do trip mine. The thing to do is either buy a code reader or go to an auto parts store that will read them. It may be something simple you can do or maybe you need to take it in.