Car is a 96 Lt4 and is stock. Yes I have searched but haven't came across my specific problem.

Starts fine when cold, runs perfect. The digital temp gauge works fine has all the correct readings BUT if I shut the car off and go to restart right after the gauge reads 50-60 degrees when 30sec ago when the motor was running it was at 193. The sensor is new and it doesn't go in and out if you wiggle it so the connection is good. Also throws a p0118 here and there that is when the car actually lets me connect the scanner to it.
Could it be a bad ground, or a bad pcm?

Thanks in advance.

 

I would test the coil and ICM many part stores do it for free but many do not really know how. So take them for few. Do not forget the thermal grease.

Reread sorry take a closer look at the connector at the water pump. Did you put sealer on it that does not ground well?

 

How would that affect the gauge?
I kinda know why it's hard to start I think it's getting to much/to little fuel since the pcm thinks it's 50 instead of 193 degrees.

 

Sorry my bad and reposted.

Did you tape it?

 

Tape what?
When dealing with anything electric I only use dielectric grease.

 

The water temp sensor when you screwed it in. And you are misinformed putting dielectric grease on everything electric for contact and might be your problem you are killing good contact. But will not be the first and sure will not be the last.

 

Yep put two wraps of Teflon tape on it.

I don't think the connection is the issue since it always reads the correct temperature and never cuts out or anything when wiggled. It only reads wrong when the car is hot and you shut it down and go to restart... but I could be wrong.

What do recommend to seal out any water and prevent terminals from corrosion?

 

Also thought I should add I don't put a huge glob of dielectric grease, I put a extremely thin coating, and only use on terminals that have a chance or corrosion forming... engine bay,under the car,bulb sockets again a tiny thin film just to "coat" the socket or terminal.

Thanks,

 

Ok so you went out of your way to kill the electrical connection what could go wrong. I would start there. If you do not know dielectric grease is like pipe dope it prevents leaking and kills contact.

 

So I'll ask again what do you recommend to prevent corrosion AND promote a good electrical connection?

I'm not an electrician I was always told to use dielectric on anything that will be open to the elements...
Now if you wanted me to grind some carbide tooling to within +/- .0001 or code a program for a 5 axis mill sure no problem.

I just don't understand how this would cause my initial problem, it's not an intermediate connection problem the pcm "digital gauge" is always perfect on initial start up and is perfectly fine until the second you shut down and go to restart it's like the pcm resets and goes back to 50-60 degrees when in reality the motor is 190+

Any help is appreciated

 

It does not hurt the connection in any way and suggest any that thinks so to learn how the terminals conduct and mate with each other.

Rather than type out th reasons read this

http://www.nyelubricants.com/stuff/c..._connector.pdf

 

but dielectric grease is more than a lubricant and if you have a bad connection it will make it much worse do some homework.

 

They make sensor safe dope. It may not be the problem but I would look at it first a double wrap of tape does not sound good to me.

 

Yes the factory puts grease in sockets for this reason but not dielectric. dielectric is like pipe dope it keeps it from leaking out and not conducive.

 

All this discussion about taping and grease is not focusing on the data of the problem and does not seem to be related.

Bad ground for the sensor or bad PCM would cause this problem. With a 50* reading the mixture would go very rich. A high resistance ground for the sensor would make the reading go high. It is a group ground junction that does relate to other engine sensors also.

You need to find out if the PCM is interpreting the wrong reading or if the voltage back to the PCM is wrong. I would back probe the ECT and connect a voltmeter to it. Monitor the voltage when things are right and then shutdown and turn the key back on. If voltage is the same, PCM might be the problem.

Reseating the connector on the PCM and or cleaning it might be a line of action. I think it's connector "C" pin C25 (but I don’t have the book for a 96 only a 94 but believe is the same).
*** Disconnect battery first before doing this and careful of the locks on the connectors. They break easy and are 20 years old.

 

Wow I can't believe it took that long for something RELATED to my problem to be posted THANK YOU.
I'm going to do what you said pc and report back, it may be a day of two since I'm replacing the master/slave cylinder.

If you have any more details on what to check and what I'm actually checking for would be great but im going to check the FSM aswell.

Again thank you for your helpful post

 

I have one more question about electrical connections. Can I use one of those "electrical contact cleaner" sprays it says it's good for switches and other connections and terminals so I'm guessing it won't hurt and should clean the connections?

Thanks

 

That should be OK, see if it says safe for plastics. Most cleaners are OK unlike decades ago where some weren’t. Alcohol can also be used, be sure to dry out any moisture (blow air) since it does not evaporate quickly like some of the contact cleaners. You can use a straight pin to back probe the ECT connections. Then use a alligator clip jumper on the pin, then to your meter.

First find the ground terminal and check the resistance to ground (engine) (probably black wire). Then do the voltage tests on other pin as I suggested (might be yellow wire).

Also it looks like the global ground goes back to the terminal B, pin B6 of the PCM. This ground might also affect the TPS voltage that the PCM uses for throttle position.

Look up the error code in your FSM for the PCM. It should give you a basic circuit description and some parameters.

Go slow and careful not to short anything to ground. Go step by step as this is a starting point. Additional data will give incite to further direction as in a troubleshooting tree.

 

Late to the party but here you go.

 

Just an update:
I checked all the usual things and it all checks out fine.
The sensor is sending the correct resistance when cold and hot, all connections are good but I still have the problem

It runs fine and starts fine when cold everything warms up correctly but when you shut the car off and go to start it again the temp reads ambient temperature when 30 seconds it was correctly reading 190.

So I borrowed a pcm from another lt4 owner and it does the same thing.... also when I went to hook up the scanner it won't connect now..
But when connected to my original pcm (not always only when it wanted to, and the fuel pump runs when you plug the scanner in?) The temperature the scanner would read is -40 but the gauge reads correctly and the gauge never goes past 193 and never fluctuates it just stays at 193 once warm..

Can someone please try to help me out here,the fsm is really no help at this point and I need the check engine light to be off to get an inspection


EDIT: also if I disconnect the sensor the temperature does not change on the dash it's like the pcm and the sensor aren't connected BUT when started the temp slowly climbs so it's reading something just not the correct sensor??

I honestly don't know where to go from here...

Thank you for any and all help