The coninuous cooling/misfire/other issues saga
 

Alright guys this thing is driving me crazy, its symptom after sympton and it seems like everytime i replace something the situation gets worse. So heres the deal, its a 94 fullsize blazer, has a 350 with throttle body injection. A few weeks ago the water pump when, so I replaced that and while I was there, the thermostat. Got that done took it for test drive the next day. During the drive seems fine, then it decides to get hot but never quite overheating. Take it home, top off the coolant it was a little low. Take it for a test drive... check engine light comes on and starts misfireing. The code is 15 which is coolant temp sensor. jumping ahead, its now been a few weeks, replacing both temp sensors, spark plugs, wires, cap and rotor were already pretty new but did check them. Took it for a test today, went about a mile and it got hot (check engine light remains on for temp sensor even after resetting computer). Took it home shut it off, turned it back on an went to press the gas, stalls now it dont start. Just turns and turns. What am i missing guys? Ready to just junk it.

Did you change the coolant temp sensor when you changed the waterpump and thermostat? Or did you unplug it and forget to plug it back in? If it is unplugged, the computer adds too much fuel, and that could be causing the no start. When you do get it started, bleed the air from the system if it hasnt already been done. Good luck!

I replaced it after the water pump, everything is pluged in.

Did thre give you the right temp thermostat? Could account for excess heat.

Almost positive its the right one. I honestly think my problem is electrical.

I think you're right, I think it is electrical becuase I'm having a similar problem with my coolant gauge saying my coolant is too hot. What really caught me about your post is that yous said it gets hot but "doesn't over heat".

Same thing is happening to me, my temp gauge will go to about 230. Just enough to really freak me out, then slowly it will come down below 210. I just put a 180 t-stat in yesterday. I have essentially a brand new cooling system, new radiator pump etc. I thought I fixed it until yesterday driving home...same thing, coolant temp gauge goes way up (But never to overheating) but almost like the thermostat isn't opening.

Where my story differs from yours, I'm not getting any engine codes, but I'm having other electrical issues that are all pointing towards a bad ground connection. The temp gauge is grounded inside the dashboard, my other electrical gremilns are also all things that are grounded inside the dash

-high beam indicator lamp is intermittent
-Voltage gauge drops randomly
-and just recently turning on my head lights killed my truck (read post above yours)
-turning on my dome light caused CEL to come on and engine to start to stumble

here is the connection to why it would kill the engine. The ECM is also grounded under the dash. If you have weak ground it can handle some basic stuff, but as you turn on additional load, suddently voltage drops and ECM doesn' thave enough to run properly and it just stops everything. Or causes the CEL to illuminate.

I'm going to start adding additional ground wires all over form the battery to the fenders and a nice solid one to the firewall, then another directly to the interior dash. You might want to do this too. Just add some nice thick ground wires from engine to firewall.

It would be a cheap thing to try, make sure all your grounds are good, to your engine block and to the firewall dash area. See if this helps. Only cost of some wire and an hour or two labor.

Another thought after re-reading your post. The coolant temp sensor, if it is bad will cause fuel air mixture to be WAY WAY to rich (becuase it thinks the engine is cold and is acting like a choke).

Your truck will start o.k. with the rich mixture and run o.k. until it warms up (but your spark plugs will be black) then it will idle kind of rough (like a misfire) but you can drive it as long as you don't shut it off. But when you shut it off it will be too rich to start becuase now the engine is warm and it is flooding with all that gas (this happened to me) and it will just turn over, sound like it is about to catch, but never will. (and it will smell like gas). In my case a new coolant temp sensor fixed it, but sounds like you've already done that.

Either you coolent temp sensor is still bad, or again as I said before maybe a bad ground is casing the coolant temp sensor to read incorrectly?

Just some more to think about. By the way mine is also TBI 350.

Have either of you verified actual engine temperature? Thermometer or laser type?

No I haven't had a chance to verify the engine temp. The high-temperature event happens so quick that by the time I pulled over and opened the hood it would already have cooled back down.

I assume my gauge is working correctly becuase when I had the 195 t-stat in, other than when the weird reading was occurring the gauge was normally at 200. And when I in stalled the 180 t-stat same thing the gauge stayed close to 180 the whole time.