So two things..

Lately when i start my truck i can smell a faint raw fuel smell coming through the vents, so i took the air intake off the TB and opened the throttle plate and what do you know.. i smelled raw fuel. Leak down test soon to come just to make sure but i think i have a MFI upgrade in my near future. (gas mileage hasn't been the greatest lately either)

But now whats really irritating is this: (oh and its not the air bag light)







So when i first got the truck the temp gauge never moved, so i replaced the thermostat (195*) and that did nothing so i replaced temp sensor and then it heated up to the line in between 100 and 210 then drop to about where it is in the pic. so i figured "well ok my gauge has to be off because it gets up to a certain temp then the thermostat opens and the temp drops a little.. all is well" then i saw the thread where a bunch of people had the same issue with their gauge then replaced the thermostat and everything was fine.

So my question is: Which is bad? i mean its possible that the t-stat was put in the wrong box and is actually a colder temp t-stat, and i guess its possible that my gauge is off.

I really hope its my gauge because ive been running my truck like this for almost 2 years and if its never got up to running temp my carbon build up is probably insane. But that would also explain why my gas mileage hasn't ever been the greatest.

Edit: Well tomorrow i will just take it out and put it in some water on the stove and see what temp it opens at. I do vaguely remember when i very first got my truck seeing the temp gauge go up to 210 when i was on my way up a mountain. but after that it went to 0.

 

One thing to try is clean up the connection to the temp sensor and make sure you put some dielectric grease on when you put it back together.

 

Doesnt 97 still have two coolant temp sensors?

Ohm them both.



BTW: when you do the pot'o'water test on the thermostat, remember it's the temp it starts to open that counts esp in cold weather. That's the min temp. I always knock off a few deg cause a little flow cools a lot.
It should open all the way by or before 210

 

As the engine warms up, the fuel mixture gets leaner. If the stat is stuck open, it will cause the engine to run richer, and that might be what's causing the fuel odor.

The easiest and most accurate way to check engine operating temperature is with a scan tool. If the engine doesn't reach proper operating temperature on the scan tool, you need to make sure the indicating system is working correctly.

Here's an easy way to test the indicating system: After setting 8 to 10 hours without being started, ECT, IAT and ambient temperature should idealy be the same, certainly within 2 or 3 degrees of each other. If two are close to each other, the third one is the problem that you need to diagnose.

 

Ok thanks for the info guys. What kind of a scan tool are we talking about here? A specialty one or one that i can rent at a local parts store? Ive read a lot about testing the actual temperature that the engine is getting up to with the scan tool so thats what i was thinking about doing first, to rule out the gauge. Could i also take a heat gun to the coolant pipe that feeds the thermostat? I know that wont tell me the exact temp but it should be close right?

Oh and is there another sensor that tells the PCM what the engine temperature? I vaguely remember reading that the temp sensor by the thermostat is only for the gauge.

But that would also explain why i have already been through one catalytic converter, and why my exhaust tip gets black pretty quick.

Thanks again


Edit: Well... Good news or...?

 

when i say this im only speaking for myself but "i've never had good luck with aftermarket T-stat's from part stores". always buy from the dealer same with rad caps and its only gonna cost a couple bucks more.

i believe pettyfog is right about the 2 temp sensors, one for the gauge which should be a single wire and a 2 wire sensor for the ecm.

 

yeah i think there is as well. The sensor in the bottom left corner of the picture is for the gauge and im not sure where the other one would be.

So the coolant coming in is about 170* when the gauge reads where its at in the pic. Roughly 130-140?

 

An infra red gun is a very quick, and very accurate way of testing. Most DIYer's tool boxes aren't equipped with them due to the cost involved. Decent ones start around $150. Check the instructions that came with the gun to find out the size of the sample area at a given distance away from the target. Keep the sample area as small as possible. Proper operating temperature reading should be ~195F to 205F on the thermostat outlet pipe.

The ECT sensor is next to the thermostat housing. There's a black, and a yellow wire in the connector. IIRC, there's only one temperature sensor used on 1997 4.3L's. The PCM uses Class II communications to send data from the ECT sensor to the instrument cluster temperature gauge.

 

Oh ok that makes sense.

Well i got some worse news... I took it to the shop to have them take a look at the temperature and none of their scan tools would connect to the computer, they told me they have never had this problem before and that got me thinking about my tuned PCM i just put in. So im not sure if this new PCM just wont connect to their scanners or if something is wrong with my PCM.

But either way now that i know there is only one temp sensor then that means i should replace it or the thermostat if im only seeing 170 at that pipe i had in the picture?

 

Yup, 170F is too low, most likely the thermostat is stuck partially open, or it's the wrong temperature stat. May as well flush the heater core while you've got the cooling system drained. Never had a problem with Stant premium radiator caps and thermostats. AC Delco caps, on the other hand, have had known "issues" regulating pressure, for years.

Not sure what to tell ya on the PCM, might have to go back to stock to diagnose problems.