O2 sensors and too old for OBD-I or OBD-II


Hi all,

I asked this in a previous discussion but my post was buried in the wrong spot thanks to the new format, so here it is again…

How can you test an 85 Olds Cutlass Supreme (305 V8, RWD) to see if the O2 sensors need replacing? No OBDI/II on those right?

Do older, pre-OBD cars still store problem codes anywhere? If yes, how can you get at them?




I suggest you purchase a service manual, such as Haynes, for your car. It will tell you how to test components and do all kinds of maintenance/repair. These manuals are not very expensive, and they are worth their cost the first time you use them.


Does your car have an SES (service engine soon) light? I’m pretty sure it does. I once owned an '84 Buick and it had such a light. If so you can check the codes yourself. Look under the dash, driver’s side, for the diagnostic connector. It looks like a plug that’s missing its other half. If you have this stuff, check back here for further instructions.


Look underneath the dash on the drivers side. If your car has the C-4 system there should be a black/white wire hanging (memory here is fuzzy). Run a jumper wire to ground and turn the key ON.

If it’s the CCC system there should be a rectangular plug with a parallel row of connections. Jumper, with a paper clip if need be, the 2 connections on the upper right.

In either case, when the key is turned on the Engine Light should flash once, followed by twice more. After a pause, if it does this again repeatedly this means everything is fine; allegedly.
If anything other than 12 pops up (flash, pause, flash/flash) count the flashes and go from there.

You can test the voltage output of an O2 sensor but this should be done with a digital VOM only; never an analog meter nor should you perform a resistance check through the O2 sensor.

Hope some of that helps anyway. :slight_smile:


If it has a feedback carburettor, just be thankful it runs at all. If it has TBI, drive on until you are forced by the emissions test man to replace the sensors and cats too…


Verrrry interesting! I will take a look tomorrow and try this out. Thanks!


Not sure which it is…is there an easy way to find out?

Luckily for me, in Ontario, Canada, once a car is 20 years old or older, it no longer is required to pass the emissions testing…so no worries there, I’m just trying to get as much MPG as I can out of the old girl.


Try this link. It has a listing of components and locations.

If you’re having a gas mileage problem, it’s more than likely not an O2 sensor.
If the EGR system is working properly you could probably get away with advancing the ignition timing a couple of degrees. This would help performance and mileage.

Does the car have a particular problem or are you just trying to squeeze the maximum out of it?


Well, I’ve only tracked the mileage once when I first bought the car (about a year ago) and my number was 16 MPG. Which I guess isn’t too far off the mark for this car…? So I’d say I’m just trying to squeeze the maximum out of it.

I still have a problem, especially in cold weather, where I have to be reallll careful with how much I push on the gas pedal when the car is first started. At startup, it idles like it might stall, then I get out on the street from my driveway and if I was to try to give it a lot of gas then, it’ll stall out. Have to be real gentle with the gas pedal from a stopped position or low speed until it’s been running for 5-7 minutes, then it’s fine, I can hit the gas and it responds normally. BUT, even at the beginning, it feels fine once I’m over 10 MPH or so (i.e. no hesitating, missing, or stumbling). Until I reach a stop sign/red light, etc. of course, within that first 5-7 minutes… I know I’m not explaining this very well…

I’m hoping to do the spark plugs, fuel filter, and PCV valve soon (air filter was done last year, and it’s a K&N…just for fun). Will that help? Or is there something else an inexperienced car guy like me can check/replace?


So this is a warmup problem. And you still haven’t told us whether your car is carburetted or TBI fuel-injected. Lemme take a guess here. You have a carburettor. There should be a short, fat air hose running up from a shield on the exhaust manifold to the air intake sitting atop the carb. This helps the carb to warm up quickly. If you are supposed to have such a hose and it is missing, you will have a slower warmup. I’m just taking a stab. Check under the hood and let us know.

Follow through on the previous advice about the diagnostic connector. It is probably irrelevant at this time but could be very useful later.


Sorry, it is carburetted…and does have that hose, if I’m thinking of the right one…it’s a short metal pipe on mine, and plugs into the air intake housing. Looks to be connected properly.
Will try that diagnostic now…

How long should one let a carb’d engine warm up? Is 30 seconds enough?


make sure the bottom of the air intake hose (pipe) isn’t rotted out, or rusted out. that looks fine, but if there is a hol;e in it, it is letting cold air in.


Well, no luck on the diagnostics…I think I found the connector though, a small black plastic 12 pin connector underneath the dash on the driver’s side…I jumpered the top and bottom pins on the far right of the connector, turned the key to ON, but no flashing lights, just the usual CHARGE “dummy” light. Should I have tried the top two pins?

On a side note, I noticed that 4 of the spark plug wires were off their brackets and touching each other…I put them back on the bracket but they still touch a bit, is this a big deal?
On a positive note, oil level is good :slight_smile: I can’t believe how clean the oil in this engine stays…it’s still a nice light brown after about 2500 miles from the last oil change…the engine supposedly has about 135k miles on it.


The air intake pipe looks good, no rust, has some grease on it…

The car seems to get to operating temp at a decent rate, water temp guage shows 190 in about 5-7 minutes usually…which, coincidentally, is when the low speed/stopped stalling problem goes away…
oil pressure is usually around 35-40 psi, down to 20 at idle after running for a while…ammeter shows maybe +5 without any lights, etc on. goes up to 30, 35 with headlights, brake lights on.


You change it every 40,000 miles. If your car runs at steady speeds without losing power and surging forward when the TPS takes over, there is a good chance that the oxygen sensor is alright.


If the 16 MPG is highway mileage then that’s a bit low. It should do 20 or better easily if everything is right.

Regarding the cold start and running problem this sounds like a faulty choke pull-off diaphragm. It’s the little vacuum pod on the passenger side of the carburetor and it is designed to break the choke flap open about an 1/8" when the vehicle first starts. This prevents overchoking and if the pod is bad (common problem) the engine will run ragged, stumble, or even die.

As I mentioned, you might advance the timing a couple of degrees. This always helps on these models and it’s also a good time to check the vacuum advance on the distributor. Hope that helps.


Read it again, he said the two pins on the UPPER RIGHT. Thats the last two pins on the right on the top row, NOT the upper and lower pins on the right…


The 16MPG is mixed city/highway driving…

I do stomp on the gas pedal a couple times before starting the car cold…would that make a difference? I was told that’s how to start a carb’d vehicle. Doesn’t that open the choke flap to the fully open position?

I will see if I can find someone with a timing light and some know-how…not too comfortable doing that on my own. Thanks for all the suggestions!


Partially correct. On a carbureted engine that is cold you should depress the accelerator pedal once. This allows the choke heater spring to close the choke flap, which then provides the enrichment to start.
If the engine starts right up but idles rough, stumbles, etc. then the problem is the choke pull off diaphragm.

The choke needs to be mostly closed when the engine is cold and the pull-off diaphragm is designed to prevent “overchoking” by opening the flap a small amount. They’re easily tested and replaced if necessary.

16 MPG combined is not that bad for a carbed, heavy vehicle but of course that can always be improved upon.


Thanks OK. If I remove the air cleaner, is this choke pull off diaphragm easy to locate? Can I test it/replace it? Will the kid at my local parts store know what I’m talking about when buying the part? :slight_smile:

One other question…I noticed the rear rails are super rusty…I have nothing to compare it to but it looks bad. Is there any way to repair or make these last longer? I’d like to keep this car for another 2-3 years and have put some money into it. (still looks classic, no 20" wheels…haha)