Emissions failure

[deltas69]

Past member..had to re register...that said .my '93 failed the HC test at emissions this week..allowed 220..blew a 252..506K on it, plugs wires, timing belt at 60K..runs fine, no CEL, I suspect an O2 sensor..does it have one or two..I'm in the parts biz and my source says only one upstream..and where is the location ? I'm 67 and not in the best shape to crawl around with steel hip and recovering from heart bypass..have the denso sensor from work...looking for ideas on making the truck pass..all comments appreciated..thanks...

 

[RonD]

Welcome to TRS

Usually there are two separate RPMs where they test HC
Near idle or idle RPMs and above 2,000RPMs
Did you fail both or is there only one and what RPM was it?


Yes, 1994 and earlier Rangers just have upstream O2 sensors, on a 4cyl that would just be the one O2 sensor.

Not a bad part to replace, they do use a chemical reaction, like car batteries do, so they for sure wear out, 125-150k is approx. life span
And failing O2 will reduce MPG a bit as it gets older so new one will pay for itself over the next 100k miles in better MPG

If its only higher HC levels then Cat converter should be OK

Vacuum leaks can cause higher HC levels
Warm up engine and let it idle
Unplug the 2 wire connector on the IAC Valve
RPMs should drop down to 500 or so, or engine may even stall, either is GOOD, it means no vacuum leak
If idle doesn't drop then there is a leak

If you have or can get a vacuum gauge I would test compression, steady 18-21" of vacuum at warm idle means compression is OK.
Lower vacuum can be vacuum leak or low compression, both raise HC levels

Run a can of injector cleaner in the gas tank.

 

[deltas69]

Thanks the techs did have me run the idle up to around 4000 RPM and holD it..the O2 sensor is original as far as I know..so it has 505K on it... The cat was replaced at 141K.. I did notice an unhooked vacum line I think coming off the MAF area..followed it..but haven't found an obvious connection yet..is the O2 sensor location accessible from the top..by removing the air intake etc ?? Could a failing ICM cause this..replaced it about 300K ago. I drive highway speeds 75 mph 200 miles per day..mpg is down from 26 to about 22 at that speed.. thanks again

 

[RonD]

Yes, on the 4cyl engine the O2 sensor should be accessible from the top but bending over is required, lol.

Video here for 1989 Ranger 4cyl, should be the same on 1993: https://www.youtube.com/watch?v=3l3APDUNw3Q

fast forward to 4:30 for location

 

[deltas69]

Thanks bending over is much easier than getting up at my age..lol..getting down is easy..you just FALL...it's getting up that's a booger

 

[deltas69]

Thanks bending over is much easier than getting up at my age..lol..getting down is easy..you just FALL...it's getting up that's a booger

 

[tomw]

I'm a bit older and so is my Ranger. I replaced the O2 sensor last summer, and it was a activity I am glad I finished. It had been installed at the factory in 1984, and did not want to go readily.
I got a O2 sensor specific socket at HF, and used a 1/2" impact wrench to get it to come out. I doubt I could have done it using a breaker bar. Mine was on the underside of the exhaust manifold.
I would suggest getting a 'catalyst safe' carburetor or fuel injection spray cleaner. Remove the throttle body/plate assembly. A 12-pt socket will do, but it takes some wriggling to get behind some of the bits. Anyway, I'd bet the inner surface of your upper(and lower) intake, the curved part, is coated with PCV oil and a good bit of carbon. The carbon coating will/can hold fuel fumes and release them into the intake gas flow when you start the engine. That is enough, apparently, to cause excess HC when tested. My truck would not pass the SMOG test in Calif when it was new and had less than 2k miles on it. It failed again and again, and I had to have it tested by the CARB referee. It still failed. Years on, when tested it either failed, or came very close(in GA), so I douched the intake and let the cleaner sit for an hour or so. Re-assembled and it put out a cloud of smoke. It ran better than it had since new. The intake was covered with black, and was seemingly oily. The throttle plate also needed to be cleaned, and it was. The test was passed.
One other thing to consider is that the oil in the pan may be somewhat contaminated with fuel if you are in a cold climate. Do an oil change before taking the test to insure that the sump is not contributing to the HC count out the tailpipe.
tom

 

[deltas69]

Just a quick followup..on a Lark through a can of Sea Foam in the tank, drove it ten miles, and the next morning went to a different test station..truck passed with no problem...who knows..lol I will install a new O2 sensor soon however..this one is original and has over 500K miles on it..Thanks for all the help...now to post a new issue...