Hey everyone,

My check engine light for my 1991 civic dx keep coming on around 5 to 10 minutes whenever Im on the highway. It seems to only come on in 5th gear. City driving doesn't seem to trigger the light. Engine light goes away when I turn the engune off. As far as I'm aware it's stock internal. Any idea where I should start looking?

Thanks.

 

change and bleed your coolant.
Highway driving usually the rpms are higher and air in the coolant will be more noticeable.
Causing false readings from the temp sensor to the ecu.

Or your distributor, fuel pressure should be @ 39 psi I think

 

You can start by looking at what the actual check engine light (CEL) code is.

 

yeah. pull the carpet back at the passenger footwell. count the LED blinks.

download a copy of the factory shop manual. look up the code.


your engine light has nothing to do with being in 5th gear. probably just related to going at high speed.

without the code, anyone guessing like the first reply is simply a guess and worthless. (quite frankly made no sense either.)

 

Good point.... Never thought of finding codes. Thanks everyone.

Edit: checked the code a couple times. It's 1 and 16. So oxygen sensor and fuel injectors. Any suggestion what could have gone wrong with those parts?

 

oxygen sensor is hard because it doesn't mean the o2 sensor is the problem. Just that there is an abnormal reading
It could be anything that relates to the air fuel ratio.

That's why checking the cels is not very useful at all.

To check the fuel injectors, hold a screwdriver on the injector and the plastic handle to your ear. You will hear if it's pulsing.

I advise you check your fuel pressure. It probably is low and is not delivering enough fuel at highway speed.

Could be a failing fuel pump or clogged filter. (The pumps hardly fail in these cars)

In the meantime, some things you should check, that would only cost you a bit of time.


Ground cables
Vacuum leaks
Ignition components
Coolant level


Aside from the light, does it run okay?

 

I disagree about the check engine lights. They are not an end all answer but they point you in the right direction once you make use of the factory service manual troubleshooting guides. Not only will they have specs and procedures they often indicate when different codes are related rather than separate issues.


Run the code 16 troubleshooting guide in the service manual. Im willing to bet you will find what's wrong pretty easily.

 

go through the troubleshooting for sure.

might as well replace the o2 sensor, it will likely solve code 1.

check your timing. replace plugs. do these for regular maintenance because your o2 sensor may have gone bad because it got fouled somehow, like lack of maintenance.

 

Does any o2 sensor works as long as I hook the wire up properly?

 

what do you mean "any"?

you go to the parts store, you tell them your car and model, you get the right part.

 

I think you are missing the purpose of the CEL codes. They only give you a heads up with which sensor is sending problem data to the ECU. Based on the codes, you are supposed to follow the troubleshooting flowcharts to determine the problem part.

Sort of like an oil dipstick - an analog sensor for your oil. If it reads that you are low on oil do you get a new dipstick? Do you change your radiator fluid? No and no - you check for external and internal oil leaks.



OBD2 takes the CEL codes even further and does a lot of the flowchart troubleshooting for you.

 

Alright. I'll have to hunt down a service manual to trouble shoot these problems properly. Thanks everyone for the help.

 

They are not expensive since they are only obd0 one wire sensors. They have Bosch universals you splice in, that are @15.00 and Bosh OEM are 24.00
Really the Denso ones are best. But they are the most expensive.
Like has been mentioned already, maybe something could have fouled the sensor. So for now, go with one of the Bosch. Because you could end up fouling it again.

U rite