Start the car cold ,the fans come on in seconds and stay on until the car reaches the correct temp for them to come on, then.....they shut off ,the car starts running like crap and shuts down. Whats weird is if i hold the pedal about a half inch down it will start back up (sometimes)but the fans don't come back on unless I let the car cool down. I just put a 1995 long block in this car ,did the job by the book . changed all the sensors ,knock,temp sensors both of them.Tested the relays everthing I could think of. If any one out there could help ,thanks in advance.

 

Have you scanned if for codes? Many codes cause the fans to come on when you start the engine, particularly the code for the AIR pump.

 

Yes I have a hand held reader from auto zone,and it comes up with three codes .o2 sensor bank2 no activity detected.I did not replace the 02 sesor,should I?,The codes I got are high voltage @the temp sensor and crank shaft position sensor . Replaced all of them . I only replaced the 2 water temp sensors ,one on the head and the one on the radiator. Is there another one on the pump? I can hear the air pump kicking on and off a lot. The weird thing is that the cooling system seems to be working in reverse ,fans on when should be off (motor cold)off when the car comes up to temp.......strange.I put a motor and trans out of a wrecked 95 that ran strong in the 96 ..Did all the work myself and i am very particular about detail . I had to change the tail piece on trans ,timing cover ,and used the 96 body and wiring harness so that it would be stock. Car runs like a champ when its cold ,but as soon as it comes up to temp it starts miss firing when the fans shut down,and stalls out .Let it cool down and it starts right back up.......losing my mind...please help

 

Which numerical code did you get? There are codes for both the pre-cat (P0154) and after-cat (P0160) O2 sensors on Bank 2. the pre-cat sensor is critical to the PCM maintaining the correct A/F ratio. If its that one, look the system over before just buying a new sensor. Maybe its unplugged, maybe the wiring is damaged. If its the after-cat sensor, its only there to make sure the cat is there and working. Replace it, get a SIM or have it programmed out to get rid of the SES light.

The coolant temp sensor in the head is only for the dash gauge, and is not connected to the PCM, so its not possible that caused the code. The coolant temp sensor for the PCM is in the water pump, not in the radiator. What "temp sensor..... on the radiator" did you replace? Possibly you replaced the coolant level sensor?

Again, what was the exact code you got for the CKP sensor? There are codes for circuit malfunction (P0335), and one for incorrect duty cycle (P0336). Both the codes are based on duty cycle, not on voltage. I'm assuming with your attention to detail, when you swapped the timing cover to allow the use of the CKP sensor, that you put the reluctor on the nose of the crank.

Are you sure? It should come on when you start the engine, and run for 3 or 4 minutes. Then its done, and should not run again, except for a diagnostic that runs it for 3 seconds, uop to three times per trip, only if it failed the passive diagnostic, which is the PCM looking for a low O2 sensor reading in open loop.

If your AIR pump is running when the engine is warmed up and the PCM is in closed loop, it's screwing up the O2 sensor readings and will cause the engine to run excessively rich.

As noted, there may be more here than you have uncovered so far. The PCM may not be detecting the AIR pump on startup, because of the problem with the O2 sensor. If that was the case, it would run the fans at startup. After the PCM indicates the engine has warmed up, and the PCM has gone into closed loop (not going to do that if you have a faulty pre-cat O2 sensor) it sounds like its running the closed loop diagnostic to verify the AIR pump is working, and then shutting the fans off when it determines the pump is capable of running. Then there's the code for the coolant temp sensor, and that would definitely cause the fans to run.

When you say "off when the car comes up to temp", that would be normal - the fans aren't supposed to run if the coolant temp is under 226*F, unless the A/C is on.

 

Thanks for the input ,priceless.. I don't think I changed the reluctor from the 95 to the 96 going trough the parts ....im assuming that if i used the 95 reluctor on the 96 that's the reason for the codes po336 po335? Thanks so much for the info!! I also found the plug that goes into the water pump had a smashed pin connector .Fixed the plug end and the cooling problem went away. Awesome!!

 

po154 is the code for the o2 sensor. wires look ok .

 

There was no CKP reluctor on the 95, because there was no CKP sensor on the 95. The CKP wasn't added until 1996, to provide the misfire detection required in OBD-II. The damper hub is also different between the 95 and the 96. The 96 hub is shorter, to make room for the reluctor to fit behind the hub.

 

So if I installed the reluctor from the 96 but used the 95 hub and harmonic balance ,I would need to remove the hub and harmonic balance and install the 96 hub and harmonic balance.Would what ive already done messed anything up in your opinion?Havn't drove the car but a few times around the block wondering if I should remove the timing cover and check. Really dont want to do this ,but if its ness. I will....Did I mention you are the man!!!!Thank You for all the great info!

 

Leaving the CKP sensor off, or not using the reluctor won't "mess anything up", as long as you have the 95 damper hub on there when there is no reluctor. The CKP sensor is only there to detect misfires. Engine runs fine without it. You can live without misfire detection. But if you want it to work, yes you need to use the 96 cover with the hole for the sensor, the 96 hub and the 96 reluctor.

And its not a "harmonic balance", its simply a harmonic damper. There is no balance function.

 

How would I go about deactivating the CKP sensor so that the check eng. light will go off?

 

You need to have the diagnostic programmed out of the PCM. Try Trifecta, one of our supporting vendors, madz28 or pcmforless - all "mail-order" tuners.

 

Thanks bro,you are the man!