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 ******* 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...
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

 

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.