SN95 5.0 running hot


IZZy

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Sooo I figured I’d make a dedicated thread to try to solve the issue, after getting the motor back in the car and getting it running I noticed the car seems to run on the hot side without actually overheating, I also noticed the electric fan not coming on when the dummy gauge gets up there towards the hot side, I went ahead and disconnected the ECT while the car was running and that made the fans kick on but that’s just a fail safe mode.

my technique for filling the coolant was questionable at best😂 since I didn’t use vacuum so is it possible there is still air pockets?

My main concern is why the fans didn’t work when the car was getting hot, I am trying to find a way to measure actual coolant temp but this thing being OBD1 isn’t helping🙄

is there grounds to suspect the ECT being bad? Is it worth breaking into the CCRM to test the relays? From doing a google search this seems like a common problem for the 94-95 SN’s

Open for suggestions and was hoping Nate Nate could chime in thanks!
 

Mr_Roboto

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If you have the manual or Chiltons etc I'd say there's a decent chance you could figure out which pins control the fans in the ECU.


This video's got the diagram stuff in it that would be useful. I'd just pop the CCRM off and see if you can run a wire between the power and fan pins and see if they kick on. After that I'd get it up to temp/turn the AC on and see if you get power out to the fans.
 

Nate

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IZZy step one is check the resistance of the ecm ect and compare it to the temp vs resistance chart

of course I brought home the 94 electric book for Dale last weekend and left it at the home shop-I’ll add a more in-depth look later
 
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IZZy

IZZy

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If you have the manual or Chiltons etc I'd say there's a decent chance you could figure out which pins control the fans in the ECU.


This video's got the diagram stuff in it that would be useful. I'd just pop the CCRM off and see if you can run a wire between the power and fan pins and see if they kick on. After that I'd get it up to temp/turn the AC on and see if you get power out to the fans.
Came across that vid and that made me want to dig into the CCRM, just haven’t done enough electrical work to know what I’m doing lol
I’ll note that the A/C is out of the car so that option to turn it on to test is out of the question
 
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IZZy

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IZZy step one is check the resistance of the ecm ect and compare it to the temp vs resistance chart

of course I brought home the 94 electric book for Dale last weekend and left it at the home shop-I’ll add a more in-depth look later
Okay I’m a total novice when it comes to electrical work so bare with me lol, test resistance at the sensor with the key on I’m assuming? look forward to that info thanks!
 

Mr_Roboto

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Should be pretty simple. Get 2 pieces of wire. Put a wire between 3&4 which are both hot wires. Put a wire between pins 1&2. Connect those wires together. That will turn on the low speed. Remove the wire from 1&2 and connect to 6&7. That should turn on the high. If it does then you've got a suspect CCRM or a suspect ECU. If it doesn't you need to use a test light to determine power is getting to pins 3&4 on the CCRM connector and check fuses/breakers/fusible links otherwise. After that you'd want to check the fan its self or if you find blown fuses/fusible links.

If you have a suspect CCRM or ECU then you need to determine if it's the box or the CCRM. Not seeing the pins on the connector that actuate the relay but that's what you'd need to determine. In many cases the relay will have +12V applied to one side and then the ECU will pull the other side to ground to complete the circuit. Basically when you think the fan is running you'd want to check and see that you have a ~12V difference across the relay. If you do then check and see if there's power at the fan connectors. If not it's a bad CCRM.

In terms of the coolant temp sensor do these use a separate thermal switch for the fan? If not and it's the one that goes into the ECU you'd probably know if it was bad. The ECU reading cold should dump a significant amount of extra gas into an EFI system when it's broken cold.
 

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Okay I’m a total novice when it comes to electrical work so bare with me lol, test resistance at the sensor with the key on I’m assuming? look forward to that info thanks!
Izzy resistance is always checked with the key off/no power
What I’m saying is disconnect the ect and check the resistance of the sensor itself
 

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I can snag you some trouble shooting and wiring diagrams off AllData later but the internet seems to have you covered!
 
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Izzy resistance is always checked with the key off/no power
What I’m saying is disconnect the ect and check the resistance of the sensor itself
Duh, told you I didn’t know what I’m doing😂
So one wire in each prong? Or does that have multiple ones?
 

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There should be 2 pins in the sensor that hooks into the ECU. Be warned there's a second sensor that should just run the gauge exclusively. Here's a chart you should be in the ball park at any of these given coolant temperature levels.

 
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All right cool I’ll check resistance and report back
 

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Waiting for your resistance report:

here’s how your fans work in simple terms:

the coolant temp sensor tells the computer where it’s at. If it passes a certain temp the pcm will ground either the low speed or high speed relay on the control side and yay: fans!
So what we know: the fan works- you unplugged the ect so the pcm saw -40 and turned on the high speed fan. So with that info we can determine the following

the 60 amp fan fuse is good
The high speed relay is good
The fan motor itself is good
There’s no problems on ground circuit 57 or G103

so it’s running a little warm on the idiot light. Now it’s time for the resistance check on the ect and comparing it to ambient temp

at this point we’re looking for operation of the low speed fan but we need more info before jumping into that so some quick checks next time you have it running

coolant level check. Air pockets will make it run warm
coolant leaks
hose temps as it reaches operating temp (upper and lower)

external heat gun vs thermostat operating temp

start simple and basic. Well walk you through more electrical testing as the time comes

CE3C2B34-A42D-429B-8CA3-7212546FF44C.jpeg
 

Mr_Roboto

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Also, any chances your timing got altered or your fueling's lean? Either can cause heating issues.
 
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Waiting for your resistance report:

here’s how your fans work in simple terms:

the coolant temp sensor tells the computer where it’s at. If it passes a certain temp the pcm will ground either the low speed or high speed relay on the control side and yay: fans!
So what we know: the fan works- you unplugged the ect so the pcm saw -40 and turned on the high speed fan. So with that info we can determine the following

the 60 amp fan fuse is good
The high speed relay is good
The fan motor itself is good
There’s no problems on ground circuit 57 or G103

so it’s running a little warm on the idiot light. Now it’s time for the resistance check on the ect and comparing it to ambient temp

at this point we’re looking for operation of the low speed fan but we need more info before jumping into that so some quick checks next time you have it running

coolant level check. Air pockets will make it run warm
coolant leaks
hose temps as it reaches operating temp (upper and lower)

external heat gun vs thermostat operating temp

start simple and basic. Well walk you through more electrical testing as the time comes

View attachment 59253
I will be doing this tomorrow since I was at work today until pretty late, makes sense what you laid out, I might have air pockets still since all I did to get coolant in the motor was run it at 2k rpm with the radiator cap off until it started puking coolant and did a couple of heat cycles, I have no visible leaks but I’ll double check
 
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IZZy

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Also, any chances your timing got altered or your fueling's lean? Either can cause heating issues.
I set timing with the spout off at 12 degrees, as far as fueling everything stock, perhaps like a bad injector?
 
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As I was idling the car to get it up to temp out of now where it starts smoking blue smoke out the tail pipes and also smoke coming out of the drivers side header/valve cover area... ugh, the wide band went to 10 which is the lowest setting so I’m assuming the car suddenly is running rich as hell out of nowhere, any guesses here? I did replace the oxygen sensor on the side that is showing good combustion, the other oxygen sensor I can only assume was working fine.

I did measure resistance at the ECT before starting the car and it was 36.4, and once the car was warm the temperature on the upper hose was around 160 and lower hose was around 120
 
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Pulled the plugs and passenger side bank all look fairly decent, drivers side where the smoke was coming from not so much, cylinder #5 was kinda soaked in fuel and then the next cylinder (#6) looked to have the most black residue on it, and the rest on that side not as clean as the passenger side but better
 

Mr_Roboto

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Start checking ignition components and maybe swap injectors around. Sounds like something's roached. Also does your FPR go to the intake in that area? If so I'd check that it may be leaking fuel into the intake and those cylinders.
 
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Start checking ignition components and maybe swap injectors around. Sounds like something's roached. Also does your FPR go to the intake in that area? If so I'd check that it may be leaking fuel into the intake and those cylinders.
I’m starting to think one injector could be malfunctioning more specifically #5, the FPR is actually mounted to the rail on the bank where combustion looks decent
 

Mr_Roboto

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I’m starting to think one injector could be malfunctioning more specifically #5, the FPR is actually mounted to the rail on the bank where combustion looks decent
Cool so yeah you don't have to worry about the vacuum line from the reg going into the area where it's leaking then.
 
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Bump, Nate Nate any thoughts on the resistance result?
 

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Resistance on the ect is good. 36 shows an ambient of 70 something. Temp on the hoses is good too I assume u have a 160 in there- that could be the cause of your rich condition as well. Back in the day people would run 160’s to keep it in open loop/get more fuel. I know that was a fox thing but I’m fuzzy if that was a 94/95 4TMO ecm thing as well.
How’s the coolant situation/fan/overall temps now?

just a quick overview of some basic checks to eliminate some variables on the other issues you have going on:

koeo tps voltage .92-.98
Base fuel pressure(assuming u have a adj FPR)
34-38
Base timing: 10-12 btdc
Vacuum line double check
Ground double check esp injector harness to engine/cylinder head to chassis
 
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Resistance on the ect is good. 36 shows an ambient of 70 something. Temp on the hoses is good too I assume u have a 160 in there- that could be the cause of your rich condition as well. Back in the day people would run 160’s to keep it in open loop/get more fuel. I know that was a fox thing but I’m fuzzy if that was a 94/95 4TMO ecm thing as well.
How’s the coolant situation/fan/overall temps now?

just a quick overview of some basic checks to eliminate some variables on the other issues you have going on:

koeo tps voltage .92-.98
Base fuel pressure(assuming u have a adj FPR)
34-38
Base timing: 10-12 btdc
Vacuum line double check
Ground double check esp injector harness to engine/cylinder head to chassis
I shut off the car because of the rich condition so I’m not sure if it got to full temp but I don’t think I have a 160 thermostat, I bought a factory replacement from the part store I’m assuming its the 180.

I’ll check voltage at the tps, don’t have an adjustable FPR so I’d probably have to put a gauge at the rail, timing is good set it at 12, I know I replaced the motor mount to chasis ground but did not have a ground from the back of the head to the firewall or chasis, can I just run one from the head to any place on the firewall? Would that be the injector harness ground you are talking about?

thanks!
 

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