Code 15, doesnt rev past 2200rpms

I flushed the radiator and replaced all of the hoses today, and now my Z doestn run right. I just finished installing long tube headers yesterday, and it ran well with open headers, I hooked up the exhaust, and now I get a code 15. The engine idles fine, but as soon as I try to rev it up, once it gets up to like 2000 rpms, it starts dogging and backfiring, and won rev any higher. It seems like my exhaust was a little rich, how can you tell? Also, do you think I need a heated O2 sensor?

thanks

15 is for the Coolant Temperature Sensor. It's located in the driver's head between the #1 and #3 header primaries. More specifically, 15 is for a high voltage on the CTS circuit, so most likely you will need to replace the sensor. That would definately cause a rich condition. As far as the intake backfiring, check your plug wire connections and routing. Where is your O2 sensor located now?

my sensor is just after the header collector. I fired it up with open headers and it idled just fine and reved well. but I moved the 02 sensor back about 4 inches, and now it doesnt run right. Maybe I need a new o2 sensor? its been through alot.

would the coolant sensor explain the engine not reving high? I know all the wires are in the right spot because I already double and triple checked them.

Well, with the LT headers you'll probably need a "heated" O2 sensor, the headers bleed too much heat...And are too efficient for even stock placement. That combined with a bad CTS could do it...:think:
But that does still sound ignition related...Does it miss(studder) the whole time you rev it??

Originally posted by 90rocz
Well, with the LT headers you'll probably need a "heated" O2 sensor, the headers bleed too much heat...And are too efficient for even stock placement. That combined with a bad CTS could do it...:think:
But that does still sound ignition related...Does it miss(studder) the whole time you rev it??

Heated O2 sensors were made because the response of an O2 sensor is affected by temp and until the sensor is warmed up it will not operate. In order to make the sensor active in the shortest possible time, and to stabilize temp related to performance, sensors with an internal heating element were created. But most O2 sensors are only accurate at or near stoichiometry. If the O2 sensor is damaged or not working properly than the sensor is not sending a signal to the computer to adjust the air/fuel ratio and the computer automatically reverts to the "limp home" mode.

unplug the cts and see if that helps it any, then unplug the 02, then unplug both and see if anything changes. doesnt cost anything to try and you may find which sensor is bad. o2's are 40$ canadian dunno about cts. if the cts is big $ replace the o2 and give it try

Originally posted by Marc 85Z28
15 is for the Coolant Temperature Sensor. It's located in the driver's head between the #1 and #3 header primaries. More specifically, 15 is for a high voltage on the CTS circuit, so most likely you will need to replace the sensor. That would definately cause a rich condition. As far as the intake backfiring, check your plug wire connections and routing. Where is your O2 sensor located now?

Actually, the location you describe is the temp sensor for the dash gauge. The coolant temp sensor for the computer is in the front of the intake manifold near where the thermostat is. Check to make sure that is plugged in.

fix the code 15 first , dont start guessing what your problem is when you have an on board diagnostic computer telling you the coolant temp. sensor is malfuntioning , and yes a coolant temp sensor will cause your problem. hard to have the right fuel ratio when the sensor is telling your puter that the engine 280 deg. and the engine is actually 195 deg. it will run like shiznit.


Chad

I have a loose wire that runs to the front of the engine near the top radiator hose, but I cant find anywhere to plug it in. Also, when I got the new cts ($10) it has a spot where something plugs in. My old one doesnt, it just has a round end with a stub on it. Also, when I unplug my o2 sensor, it doesnt make a difference in the way it idles, it idles fine at the normal rpms, and revs just normal up to 2200rpms, but then starts to crackle and miss and backfire if I try to rev any higher. The exhaust also looks like it is running way rich, black soot is on the floor at my turndowns.

I got that code on my 88' Z, definitely a bad sensor (only 6 months old). The sensor between #1 & #3 is the temp gauge sender, and must have a good engine head ground to work properly.

On my 88' TPI there are two sensors on the front of the intake, one has a connector Identical to the fuel injectors (cold start temp switch for ninth injector,) the other is the CTS sender (my wires are yel & blk.)

The CTS uses computer ground (not engine ground) and it's only shared with the MAT (same sensor and connector as CTS underneath plenum,) and TPS sensors.

AutoZone Wells part number is SU109, about $10 warranty is 3 months, so now I know why mine took 6 months to die.

Ok, so all I have to do is ground out the temperature sender for the dash, its not hooked up right now, do you know where the wire that connects to it comes from?

the loose wire runs up behind the alternator, so that must the computer cts. I will check that tonight

Well, I put the new sensor in, and it didnt change anything. Nothing changes if I unplug the o2 sensor or if I change the connection between the old cts and the new one. However, if I unplug either cts, the engine wont run. Still pulling a code 15.

I also hooked the dash temp sender gage back up.

I think I will go back and get a different sensor and try that.

Is there anyway I can test a cts or o2 sensor using a voltmeter?

Any Ideas?

You can test the O2 sensor if you know what to look for. You could get a voltage and if you see it change back and forth, it is probably ok because it will go from rich to lean to rich and so on if it is working properly. When the sensors get old, they get lazy and move slowly. Low voltage is lean and high voltage is rich and it should not be less than 0 and not more than 1 V.

Does anyone have an idea of what my problem might be? I dont know what could have gone that wrong since the car has been sitting in my shop for the last 3 months.

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!...

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.

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?

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..

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

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.

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

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

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.

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

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...

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

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.

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"..:D

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? :confused: 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.

I just found a niple for a vacuum hose on the front throttle body near the MAP. I'll cap it off and see if that changes anything.

I have a Chilton manual "Cheverolet Camaro 1982-92" Part # 8260 that DOES have the CFI info in it..(dual single-injector throttle bodies, offset like a "cross ram")
Reguarding the "nipple" on the temp sender, do you mean for a hose? And where was the location of the one you replaced?

Ok, I have vaccum coming into the MAP sensor, but no vacuum coming out of the second hose. I ordered a new sensor (its 20 years old, why not?). I am now pulling a code 42.

The MAP sensor only should have one hose, not 100% sure about the one on a CFI car tho. The EGR solenoid and the MAP are usually side by side, make sure it's the right one. The solenoid will have one hose going to the EGR valve..
Code 42 is the EST(electronic spark timing)circuit, usually set if you unplugged the single wire connector, a "Tan wire with a black stripe".
If not, clear codes and idle for at least 1 minute.(interrupt battery power for at least 10 seconds)
If the code 42 comes back, check for good ignition module connections, and have the module tested if they look good.
A Prom chip that's not fully seated in the ECM will set a code 42 too.
Check connections and see if it still sets a code 42, there's a long proccess using a meter to check harness grounds and resistance. A scanner will be useless for checking this...

Ok, maybe I checked the wrong sensor. The one that isnt pulling any vacuum is on top of the intake manifold-the vacuum line comes from the front right throttle body, enters a sensor with a 3 wire connector on top of it, and then has a hose going to the top of a round object near the distributor. There is also another larger vacuum hose that runs from the rear tb up to a sensor on the drivers side firewall. Which one is the MAP?

Also, where does the spark timing wire run to? Where is it unplugged?

Your MAP is on the Firewall, the other is the EGR sloenoid(activator)the round device is the EGR valve...
The spark timing wire usually has a short length, purposely left out of the main harness exposing a single connector. Usually near the firewall...Your under hood sticker should tell you in fine print...see "timing adjustment"...

Sorry to bring this post back from the dead, but I solved the problem (for now) I replaced all of the vacuum hoses, and that didnt make much of a difference. While replacing my wires, I noticed that my dist. cap was loose. When I checked it out, I found that the rotor was chewed to bits, and busted off the shaft. :rolleyes: So thanks for the help guys.