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Discussion Starter #1
Hey everyone. Got a issue that has me wondering if this is the problem all along or not. I have a 94 Roadmaster with the LT1 and I have replaced the coolant temp sensor and the coolant temp sensor for the gauge. I have also replaced the thermostat as well. My issue is that my gauge sits at the first quarter mark and I have gone through to the climate control diagnostics and entered it to 24 and it is saying 90 and stays right at 90. I have also gone to I believe it is 6 or 8 and it reads 173. My issue is that both fans are running and yes the ac is off but the fans stay running and don't shut off unless you turn the car off. Is it possible that the new sensor is bad or could possibly be that the 26 year old connector finally died and now the fans will stay on because of this? The other issue I'm having is that it is a gas hog right now and has a slight hesitation at idle and definitely doesn't like a load on it when driving. I thought maybe it was because of when I did the head swap to camaro heads, the three grounds weren't grounded good on the head. I went ahead and cleaned off the grounds and the engine block and installed it there. Didn't improve the issue but I will admit that my under hood light is a lot brighter now(yes I did the big 3 upgrade from innovative wiring). If it is the connector, anyone have info in testing it. No scan yet because I ordered one today from 1320 electronics. It does have a new optispark distributor that I took apart and removed the optical sensor and put in my mitsu sensor in and used the Accel cap and rotor with msd wires and autolite plats and upgraded to the 96 coil and icm. It's a project car and I am slowly getting everything for it so it can be ready for the cam swap. Thank you
 

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Following is an experienced GUESS:
Just because you replaced the H2Opump coolant temp sensor, does not mean that the wiring behind the H2Opump coolant temp sensor isn't so thin brittle and old, that you need to do more to get the H2Opump coolant temp sensor to actually work properly.
Can't be sure from a distance but it sounds like the wiring that connects to the H2Opump coolant temp sensor is at least intermittently acting as if it's sometimes bad.

On 3 different LT1s I've had to not only replace the H2Opump coolant temp sensor, I've also had to replace / upgrade the wires that connected to that sensor before the repair was effective.
 
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Discussion Starter #3
I was thinking that but figure I would ask the masses to see. It has been a process as of late with either replacing the sensors or the connector or both and I am at a point of just saying screw it, if either don't work replace both sensor and connector to be safe. Thank you
 

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Discussion Starter #4
By any chance, does anyone know when the fans are supposed to come on besides mine coming on when I start the car after it sat all night?
 

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When the key is on, if the pcm decides there's something wrong with the H2Opump's coolant temp sensor, the pcm will turn on both fans.

For so long as the H2Opump coolant temp sensor works as expected, GM's OEM fan-on thresholds are
225°C primary & 232°C secondary.
 

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Discussion Starter #6
Ok. Just installed the new connector and fans weren't on then they both came on with the ac off and it reading 90 again. I'm thinking I might have a bad new sensor
 

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Could the cooling fan controller be malfunctioning or perhaps an associated wiring issue? Maybe something related to the A/C compressor?
 

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Discussion Starter #8
Idk but I put a scanner on it finally and it seems like everything is working. It even goes to close loop very quickly.
 

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Discussion Starter #10
That's what I'm thinking. It was just strange to me that you start the car and both fans come on and the car was already in closed loop. I'm use to the OBD2 vehicles that would not go into closed loop until after it warms up and the fan would come on when the thermostat opens. It just seemed weird to me but after getting a scanner on there and seeing what the computer see's, yeah, it's working. But what I did find is that I have a couple plug wires that are hitting the headers (cia tri-y 2) and I have boot protectors on it but it pretty much burn the protectors and just putting a lot of heat on the boot and causing the issues I'm having which I have to wait until I can get the otvc wires for it
 

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It even goes to close loop very quickly.
It was just strange to me that you start the car and both fans come on and the car was already in closed loop
Not sure what you mean. A "cold start " is one at surrounding air temperature. If this is 70-90F closed loop will happen quickly.

The radiator fans are controlled by the PCM and coolant temperature and A/C freon pressure are the main factors. Most of the time selecting A/C will start the fans but there can be exceptions.

A "Hot start" is usually one occurring after the engine has been to closed loop. Coolant will be hot enough to force closed loop very quickly.

With a scanner the best way is to compare surrounding air temperature with coolant and intake air temperature (IAT) when the car has not been run for several hours(over night). The three temperatures should be close.

I'm use to the OBD2 vehicles that would not go into closed loop until after it warms up and the fan would come on when the thermostat opens.
Not sure what you are driving. When I was dealing with ford, dodge, and chevy trucks inside warm buildings they would all run their fans at key on. If started they would then check their temperature sensors and quickly shut off the fans until setpoint temperature then run the fans as needed. My 96 CV does the same thing.
 

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Discussion Starter #12
No, I have run into a few cars that didn't run the fan when you start the car. Yes I'm talking cold start because when I worked in a shop, I would sit in the car with the scanner and wait for the computer to go closed loop. As for my car, I let it sit overnight and go hook up the scanner the next day and I start the car, it's already in close loop which I'm like wow, it hasn't ran all day but I start it the next day and it is already in close loop.
 

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Discussion Starter #13
I definitely understand if you got the ac on that yeah, the fans come on. In my case, the primary and secondary fans come on when you start the car and stay on. They don't shut off until you turn off the car or you do key on engine off
 

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If you can do this do it:
With a scanner the best way is to compare surrounding air temperature with coolant and intake air temperature (IAT) when the car has not been run for several hours(over night). The three temperatures should be close.
I took a quick look at a couple of stock bin files and found two constants:
min cool temp for closed loop 35C (90F)
min cool temp for closed loop Cold MAT 60C(140F)
I rounded the numbers a little. From this I get a cold start(manifold cold) closed loop of 140F and a hot start(IAT MAT hot) of 90F.
So I would say under most conditions the car should start open loop with over night cool off.

So what does the PCM say the cold start temps are? What are they after a drive?
 

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Discussion Starter #16
Figures, because it is colder out today compared to yesterday when it was in the 80s, it is in open loop. Today the temperature is in the 60s.
 

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Discussion Starter #17
But yeah, yesterday it was close loop on startup. And again today both fans came on when I start the car and stayed on. I'm starting to think that this is normal
 

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Both fans running as soon as you start the car is not normal. They are designed to cycle on and off based on temperature and AC pressures. If they are running full-time, in my opinion, that will kill the fan motors in short order if there is a malfunction. And will also heat up the wiring harness.

The first fan is designed to turn on and run with the AC or if engine temp gets too high. The second fan will only turn on if temp or AC pressure continues to increase. When they are both running, the car is usually very hot or the AC is working really hard. Otherwise you should only see one fan running with the AC on. With AC off, neither fan will run until the engine temp goes up far enough. And then it should cycle to maintain the proper temp.

In my experience, there are only two things that will run both fans immediately upon startup. A PCM fault (many CEL codes will run both fans) or high AC head pressure. I'd have to refresh my memory in the FSM... but both of these conditions immediately come to mind. Of course temp readings at the sensor in the water pump may do that too if it reads too hot, and you need to capture that data to be sure.

Now if the car has been reprogrammed and they lowered the fan temps to something silly like 160 degrees, or a wrong hysteresis was used, that may run them too. But a cold car? Nope. I'd be diagnosing that further. I'd look to see if someone tampered with the wiring.

What are your PCM coolant temp readings when the this is taking place? It gets those readings from the sensor in the water pump (as others have mentioned).

Eliminate the AC head pressure concern by unplugging both AC sensors, on the high and low side and see if fans still run constantly. This will also eliminate the possibility that the AC is stuck on.

If it were me, I'd wire up LEDs to monitor the fans from inside the car while driving. With normal temperature cycling, the fans will be commanded off above a certain speed, always. This is because running fans can interfere with air flow above 40MPH. With high AC pressure, they will not shut off above speed.
 

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Discussion Starter #19
This is factory pcm tune but since you mention cel light, what codes could cause this to happen? I will say that I have a code for the egr and the a.i.r. pump because they are both removed. If either of these will cause the issue with the fans then I will have to save up for a tune
 

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AIR pump delete should not turn on the fans. I've deleted (or helped delete) the AIR pump on many B-Bodies over the years without a code ever being set. Albeit '96 is different. How did you delete it? You should not remove the relay. If the relay is missing, put it back. And reset the codes (battery pull for 5 minutes if you don't have a tool). That should clear the code.

The EGR on the other hand is a different story. I am pretty sure EGR will run the fans when that code is set. If you still have the old solenoid, plug it in, even if it doesn't do anything. This may be a temporary fix as the PCM does cycle the EGR and tests the function based on sensor feedback. If it does not detect that EGR opened when commanded, it will also set the CEL. Deleting EGR without a reprogram is not recommended. I'm guessing this is your problem.

FWIW, any ignition (ie: optispark resolution), evap, o2 sensor, MAF sensor, IAT sensor codes that set CEL will run both fans. The fans basically run any time the CEL is on. The FSM documents this differently, but I have never seen a CEL (with light on) that did not run the fans. There are a few "hidden" codes that do not set the CEL and do not run the fans. A shorted PCM-driven relay to ground, for example (caused by an override switch that I installed) will set a code but not turn on CEL.
 
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