84 Caprice Intermittent Check Engine Light

[bobss396]

I have a new one this week. My '84 Caprice has a 305 and 160k miles on the clock. It runs well, just passed the annual emissions check with no problems.

Starting a few days ago, the check engine light comes on once in a while. It lasts for as little as a .25 mile to 1.5 miles, then poof its out. The computer is 50k miles old, I had my rotted AIR plumbing replaced as well a while back, the PCV valve is new.

Could it be as simple as the oxygen sensor, which is inexpensive and easy to replace.

Thanks, Bob

[silicon212]

Originally Posted by bobss396

I have a new one this week. My '84 Caprice has a 305 and 160k miles on the clock. It runs well, just passed the annual emissions check with no problems.

Starting a few days ago, the check engine light comes on once in a while. It lasts for as little as a .25 mile to 1.5 miles, then poof its out. The computer is 50k miles old, I had my rotted AIR plumbing replaced as well a while back, the PCV valve is new.

Could it be as simple as the oxygen sensor, which is inexpensive and easy to replace.

Thanks, Bob

It probably is sensor-related, but you're going to laugh here - it could be something as simple as a plugged air filter! I'm going to guess that's what it is - do your trouble code check and if it's a code 45, replace that filter.

PS - to ALL who might see this - don't just go and replace your EGO sensor because your computer is displaying a code because of it. 9 times out of 10, that code is because the engine REALLY IS running too lean or too rich. The air filter comment above is a common cause of a 45 (too rich) and is MUCH cheaper than replacing a $20 sensor and then finding you still have the same problem. Replacing the sensor in most cases is like taking Tylenol for a kidney stone - it might make you 'feel' better about doing it, but it won't do dick for the pain!

[bobss396]

Thanks for the quick reply. Looks like I have to do the code thing, something I've never done before. I know I have to make up a 12 gage wire jumper, I saw someone do it once but didn't take notes. Any help is appreciated, I'm sure most of you have done it.

I'll take a peek at the air filter when I leave work, also will make sure my gas cap is tight. Also, what is an EGO sensor?

Thanks, Bob

[silicon212]

EGO = Exhaust gas oxygen

You don't need a 12-gauge wire, a paper clip works fine. Connect together terminals A and B on the ALDL connector, put the key in Run but don't start the engine.

[capriceowns]

You can use a paper clip to jump it to, thats what I did for my 87.

For GM domestic vehicles made before 1995, the diagnostic connector is located under the dash panel by the driver side. To get the check engine codes to flash in your dash panel, use a jumper wire or a paper clip and connect terminals A and B of the diagnostic connector. Turn your ignition key on with engine off and the codes should start to blink. All codes should start with code 12 which is one long flash followed by 2 short flashes. This code 12 means the diagnostic system is normal and will repeat itself continuously if there are no trouble codes. Otherwise, code 12 will flash 3 times before flashing the fault codes. <--- instructions

[Blue Bowtie]

In case you're more visual, this might make it a little less confusing:


With the engine and ignition turned off, locate the ALDL connector under the dash, just to the right of the steering wheel in the driver's foot well area on some models, and on the left on others, depending on the make and year. There may be a small rectangular cover over the access hole in the lower dash trim.



Insert a jumper tool or paper clip formed into a “U” shape into the 'A' and 'B' terminals on the ALDL connector:



WITHOUT STARTING the engine, turn the ignition to the "RUN" position. Watch the Malfunction Indicator Lamp (MIL) - it will begin to flash. This is also commonly called the “Check Engine”, “CEL”, "Service Engine Soon" or "SES" lamp. The first code will flash three times, and will usually be a code '12'. This is encoded by one flash of the lamp, a brief pause, then two successive flashes of the lamp. Each code will repeat three times, so you should see a "Code 12" flash three times. Any other error codes will follow in numerical order, and each code should flash three times. After all codes have been displayed three times, the "Code 12" will again flash three times, then all other codes will follow as described earlier. This cycle will continue until the jumper is removed or the ignition is turned off.

After you have made a note of all error codes, turn off the ignition and remove the jumper immediately. If you forget to remove the jumper and attempt to start the engine with it in place, you could damage the ECM. For this reason you should remove it immediately.

Once you have a note of all error codes, check this file for the decoding:

GM Error Codes.pdf.

You'll need Adobe Acrobat Reader to open/print the file.

[capriceowns]

Blue bowtie do you take all these pics your self? you always seem to have the right pic or diagram for everything. lol

Good work though.

[Blue Bowtie]

I find it's sometimes easier than the "thousand words" or more it would take to properly explain things. After a while, you'll start to notice some similarities in the photos and diagrams.

I'm fairly new here, but I've been doing this since about the time Al Gore "invented" the internet. I got my first digital camera (Kodak DC215) in 1999 just for this purpose, and have worn it out since.

[bobss396]

Thanks for all the information, I have to do it this weekend if the weather is decent.

I changed my air filter, crankcase breather, the PCV valve is recent. It seems to happen only when I'm driving around 55-65 and have gone maybe 3-4 miles. It will stay on for a 1/2 mile to a few miles and blink off, or it will go out once I get below 45 or so. Other than that, the car runs just fine.

Bob

[bobss396]

I suppose that the EGO sensor is the same thing as the Oxygen Sensor that is in my driver side exhaust tube below the exhaust manifold? With some luck that will be the culprit, really easy to get to, there must be some catch though.

Bob

[silicon212]

Originally Posted by bobss396

I suppose that the EGO sensor is the same thing as the Oxygen Sensor that is in my driver side exhaust tube below the exhaust manifold? With some luck that will be the culprit, really easy to get to, there must be some catch though.

Bob

Yes, EGO and O2 are the same thing. Anyways, don't replace it yet. When was the last time the carburetor was serviced?

[bobss396]

Thanks for the clarification on the sensor name. Napa has them for $22.49 if I need one.

I had the electronic choke replaced on it a few years ago, I'm religious about fuel filter changes, aside from that I haven't touched it. I have a local carb shop that has does a great Qjet rebuild if I need it done. It was inspected a couple of months back and all the emissions mumbo jumbo was well within limits.

Bob

[GreyGoose006]

Originally Posted by bobss396

It seems to happen only when I'm driving around 55-65 and have gone maybe 3-4 miles. It will stay on for a 1/2 mile to a few miles and blink off, or it will go out once I get below 45 or so. Other than that, the car runs just fine.

This is exactly what mine did.

what i found is that ineeded to clean the O2 sensor.
i pulled it out and it was a big ball of carbon.
just wiped it off and put it back in.

i think that nothing was even getting to she sensor except when the exhaust velocity was high enough to oush through all that carbon buildup.

[bobss396]

Thanks Greygoose, I like potential cures that cost nothing. With some luck it'll come out without a fight.

Bob

[Blue Bowtie]

So, what code(s) did you find?