90rocz

BOZS89IROC, you're correct as to "why" they were created, even more b/c of increasing stronger "start up emissions" standards backed by the EPA. Also, if the sensor also fails to maintain that temp it won't function properly either, and will run rich and cause symptoms like he's describing..it'll "load" up and start to bog badly as you open the throttle..
I've seen many O2 failures, and marginal failures, the fuel fumes they emit will burn your eyes out!...

90rocz

A code 15 will set b/c of a low signal voltage that lasts more than 3 seconds, indicating a temp less than -48*F.
Unplug the harness from the sensor and short the yellow & black wires together. It should read 266*F.
If so, a faulty connection or temp sensor failure.
If not,
Ground the yellow wire, it should read 266*F
If not, faulty connection at ECM, or Bad ECM, or open in the yellow wire circuit.
If so, open coolant ground circuit, faulty connection, or faulty ECM.

kbog54

when I short the yellow + black, it should read 266 on my dash guage if there is something wrong? If I dont get a temp, does that mean something?

Sorry if I'm asking dumb questions, I've never had to deal with this before.

So in your opinion, it is the o2 sensor that is causeing the rich condition and the stumbling? Would a bad temp sending unit cause a code 15?

I checked all the wiring for the cts, nothing wrong with it all the way back to the connector at the firewall. I then switched the wires on the cts, and when I cranked it, fuel (i'm assuming) shot straight up out of both throttle bodies. why would this happen?

90rocz

when you short the yellow & black it should read 266, If the wiring and gage is OK...sensor bad.
Yes a bad temp sender can cause a cod 15, but so can a bad Computer, or shorted wire.
Fuel shooting up out from the T/B has nothing to do with the CTS wired backwards, if it's out of "time"(ignition timing) it will do that, or if real lean..

kbog54

Well, I switched the wires around on the cts, and the fuel shot up when I turned it over. I switched the wires back to normal and didnt have the problem. Same result after several tries. I dont think that it has anything to do with my timing, because it worked fine before I changed the coolant and hoses. Isnt there a wire for setting the timing that runs by the heater core? Maybe I disconnected it by accident. Tommorow I will get a different temp sending unit and see if that makes a difference.

How could I verify that my timing is on? I dont have a timing light or anything.

thanks for all your replies

90rocz

I never heard of that, but I've never reversed the wires before..

If it's(tan wire with black stripe) unplugged you'll get a code for EST #42...Check engine soon light.

kbog54

ok, I switched both sensors, and now my dash guage works. and the idle is a lot lower. Now I pull a code 33.

kbog54

The problem with the backfire and misses at 2200 is still there. It revs just fine until that point. Any ideas? Still pulling a code 33

90rocz

Now that makes more sense to what could be going on.
The black wire from the CTS and the black wire from the MAP are joined at some point.
BUt if there is a rough or unstable idle it can set a code 33, b/c it won't pull enough idle vacuum.
If it idles fine, you can do this:
Check the voltage on the "Gray" wire, it should be 5 volts, it's the reference voltage.
Check the codition of the Vacuum hose to the MAP sensor.
If you "back probe" the "Green"(center)wire and the "Black" wire you should get 4.0volts at idle. Or if you have a scan tool, you can check it that way. They are available at most parts store, but it's an investement, especially if you are going to work on your own cars. It will pay for itself quickly!...
Anyways;
If you "did" get 4.0volts, disconnect the MAP sensor, Your probe should read less than 1 volt.
If less than 1 volt, check the ground cicuit by using a test light connected to the black wire and "Positive" on the battery. If the ground is good the light will come on...
If the light comes on, the vacuum hose is leaking or plugged up or the MAP sensor is faulty.
If more than 1 volt, the green wire is shorted to voltage somewhere, or the ECM is bad.

kbog54

What does the map sensor look like and where is it located? sorry about the newbie questions.

90rocz

Ya know what, I for got to ask what car/motor you have??
I probably shoul've asked at the beggining, sorry;
'90-'92 is on the passenger side of the plenum near the rear. '85-'89 uses MAF not MAP...
And TBI cars are usually on a bracket passenger side rear of intake...
Anyways they are rectangular 1.5"x 3" with a 3-wire connector plugged in from the bottom and a vacuum hose beside the plug...

kbog54

Sorry, should have posted that at the top. I have a '83 Z-28 with a 305 CFI(I know, I know, its not the ideal engine), its also an automatic.

I found the Sensor (is it called MAF or MAP?) It has the vacum lines running to the little round thing near the distributor and the front thottle body, right? The connector has a tab on it that is broken off, so I think I will just get a new one. The vacum line looked alitle worse for wear, so when I get around to it, I will get some and replace all of the lines. I didnt have a chance to test the voltage (voltmeter batteries were dead). I am also in the process of replacing the plugs and wires because of how crappy they were.

Also, one last question. When checking codes, if there is more than one code, how does that show up? does it flash 12-the code-12-different code? Or are all the codes between the 12 code. Will there be a longer pause or something?

thanks

kbog54

Would you recomend getting a 3 wire o2 sensor? Should the engine respond when I unplug the o2 sensor? Because right now when I unplug it, the engine keeps idling the same even right at startup.

90rocz

I'd stick with what you have, at least for now, 'til you get it straight.
It will flash code 12 for 3 times to start, then any other codes 3 times each, then another code 12 3 times when done..
I'll have to look at some books, I don't get to work on any CFI cars here. They're as rare as "Hen's Teeth"..

kbog54

Well, when I check the codes, it flashes code 12 once, and then the error code, and then code 12. Should it stop flashing codes after it has shown all of them? Or will it repeat them over and over.

Regarding books about the CFI, I havent been able to find any manuals or literature about it. The parts store guys just look at me like CFI? If you know where I could get a manual or something I'd like to know.

When I was getting the temp sending unit, the original one had a nipple on it, and none of the 5 part stores in town had ever seen or heard of one like it, so I ended up converting to one with a spade connector.

If I would have known how the CFI was with performance when I first bought it, I probably would have looked for a TPI. But now that I have it, its kind of neat.