To start I had a code on the car for awhile P0420, then it started to run rough like a misfire check the plugs they were at more than twice the gap. I replaced them it took care of the misfire and the code. Two days later the misfire came back very minor mostly when going up hill would have shift in second to stop the chugging. Tested the coil wasn't good so replaced two days and it came back. Wires are only one year old. I touched the coil it was burning hot so I put foil under it fixed for a day. Then I replaced the fuel presure regulator no change. Fed up took it to dealer "compression good, spark good, fuel presure good, we don't know, no codes, could be timing belt or cat" Thanks a lot heres $90. So I dug into the timing belt, wasn't the problem but I replaced anyways because it took forever to get to. Pulled the downstream O2 to alow an opening before Cat no change. Read on the internet all the different causes. Tested TPS good, MAP good, replaced knock, cam, and crank sensors. Cam sensor wire was full of oil looked like leaking from sensor cleaned replaced no change. Disconnected the upper O2 no change. Pulled the injectors, number 4 was clogged cleaned all tested for leaks and open close operation all worked good reinstalled ran a little better but when warm misfire is still there. After replacing crank sensor I was messing with wires while running and the fan came on odd because the upper hose was cold. Then I let it get hot both upper and lower hose was burning hot and no fan. Turned on the A/C no fan. Knowing now that it is overheating I tested the fan it works. Replaced the coolant temp sensor, fan relay, and thermostat. It seemed to run a little better but the fan still would not come on and overheated ran worse. So I unplugged the temp sensor started, hard to keep running but the PCM did tell the fan to come on. So now I'm lost, I'm thinking the PCM is bad. On a side note when I tested the signal wire for the crank sensor while unplugged key on it was getting volts, I thought it's only supose to get volts from the sensor which tells the computer when to fire. Why would there be about 2 volts on that wire if unplugged from sensor?

In short, misfire, runs rich, overheating, PCM not turning on fan, volts from crank signal wire when unplugged. Codes only trip for misfire when pushed real hard. Aside from trading it in what should I do?

 

Replace the coolant temp sensor and thermostat and see what it does.

 

Yesterday I pull the harness out checked most of the important wires all good. Found the oil pressure switch was leaking oil, replaced. I changed the oil and filter. Found a tiny bit of oil on the PCM terminals cleaned the best I could. And put it all back together.

As soon as it starts, I get a low rough idle. Put in gear tries to stall. Add some gas and it loops the engine seems to be missing like in one cyl on and off. Fan came on just as the radiator got hot for about 1 min. Once off never came back on. I know the fan is good and PCM tells it to turn on but something is not telling it to come back on when hot.

Even if replacing the injectors fixs my misfire, that doesn't explan why the fan is not coming back on.

I ordered a PCM off ebay from a trusted seller. I'm hoping it fixes the problem as with talking to someone that had a sim. problem. He ended up replacing the PCM and his car ran like new.

Fingers crossed!

 

Change the coolant temp sensor and see what it does.

 

if you read my first post you would know that I already have.
"Replaced the coolant temp sensor, fan relay, and thermostat. It seemed to run a little better but the fan still would not come on and overheated ran worse."

 

Sorry, missed it in the giant cluster****. Hope the PCM works out.

 

So the PCM did not work, the car would start and stall after 5 seconds, after the 5th try it would not turn over. So I put the old one back in started right up.

Here is what I know, the car is misfiring from running rich and overheating. Took out plugs black from carbon, rich. The overheating is from fan not coming on. I believe something is telling the PCM that it is cold, reason for rich and no fan. The dash gauge never goes above normal. The fan works unplug the coolant temp sensor and full speed but because it is already running rich the PCM dumps more fuel in and stalls the car. The fan also doesn't come on with A/C, unplugged it no change.

Parts replaced for the overheating, Coolant temp sensor, thermostat, fan relay, radiator cap, hose to overflow tank. Wires checked. Pump seems to work fine the inside of car gets the full heat. With the location of the cap it's hard to check for the flow of coolant since it just pours out. I don't think there is an air pocket on the coolant sensor because the head is cooking at that location. None of the fluids are mixing.

I'm not sure what to do next. I tested everything and replaced over $300 in parts.

 

Take the coolant temp sensor back and tell them it was bad. It happens from time to time.

 

so based on the coolant temp sensor idea I looked up a bunch of info. I tested the old sensor since it was easy to get to. I watched videos on it one said at 32F 4400-6600 ohms, 176F 270-380 ohms.

I set my ohms at 20k put it into water with ice got 16, water about 170F dropped to 2.1. Which means the ohms are 16000 and 2100, if correct that means the sensor is way off. Could not find out if this is normal for these cars. But if this was the problem then that explains why the car is running like it's cold.

When I get a chance maybe tonight I'll test the new sensor see if I get same readings. If so back to parts store. I'm also trying to convince my mother to trade it in so I don't have to see it anymore.

 

So I tested the new sensor got the same results returned it got replacement. Tested it before installing same results. Watched some more videos found out that the other video gives the wrong numbers. And all the sensors are correct including the old one.

Now I know the sensor is good and I checked the wires. The gauge on the dash reads normal but I know for sure it's over heating all the hoses get burning hot and the radiator but no fan and keeps running rich. I know it's running rich because the volts on the downstream O2 reads .8 volts with once a min drop to .2 for a second.

What I don't get is if the PCM knows the temp why won't it turn on the fan? What else could cause it to run rich and not turn on the fan?