95 z28
Posted Today at 10:12 PM by bigbluegmen2008
i have a problem that the fans are not turning on (car is only being cooled by the coolant and thermostat) but when i disconnect the map sensor plug the fans turn on and stay on till i plug it back up. its the v8 lt1 and also the car runs rough for about the first five minutes then is fine what causes these problems please help

 

Factory fans don't turn on until 227 degrees (high speed at 235 degrees). How hot is the motor getting?

 

Here is some information about the cooling system and when and why the fans come on.

Running rough could be a lot of things. When was your last tune-up? What have you looked at or checked? What mods do you have?

 

The fan problem, if they don't turn on at 226/235*F may be related to problems with the coolant temp sensor not telling the PCM the engine is hot. Similarly, if the temp sensor is not telling the PCM the engine is cold, its not going to richen the A/F mixture for cold start, and the engine will run rough until it warms up.

If you can get a scanner on it, observe the coolant temp sensor under cold start and under very high coolant temps. It may not be responding correctly. I's connected, but it may not be covering the full temperature range. My son had a problem with his 96 Saturn. The dealer told him he needed a new engine. I tracked it down to a cracked coolant temp sensor. $18 repair.

Its normal for the PCM to turn the fans on when the coolant temp sensor is disconnected. Since it has no indication what the temp is, it turns on the fans to protect the engine. It does that with many other trouble codes as well.

 

the car had the full tune up as well as a new water pump and a thermostat from what the persn i bought it from said. i drove the car 2 hours when i got it with no problems but obviosly cause constant air flow. i figured the rough idle was the idle position sensor and i changed that with no results the car gets up to about 230 then the thermo opens but no fans come on

 

The stock thermostat is 180*F. It should be fully open by 200*F. If you are somehow able to determine that its not opening until 230*F, its defective and needs to be tested and replaced if necessary.

A "full tune up" would not include replacing the coolant temp sensor. A faulty TPS sensor will generally not cause a rough idle. If its far enough "off", it will set a code.

 

thank you injuneer i will check both thermo and tps

 

I wasn't suggesting that you look at the TPS.... I thought that was what you meant when you said "i figured the rough idle was the idle position sensor". Apparently, you meant idle air control (IAC), or "motor". Its not a position sensor, its a stepper motor that controls the idle air flow. It only affects idle speed, not smoothness.

 

sorry meant the coolant temp sensor, not tps (i changed that as per my mechanic)