temp sensor and emissions sensor "mod"

Okay, So I am looking for some advice on some sensor locations on my 84 caprice estate chevy 305. the question is about the emissions/vacuum sensor, and the ecm temp sensor. What I am wondering is if anyone has swapped locations on these two sensors. and If there are any ill effects. So if you are wondering what I am talking about the emissions sensor for the air pump is in the intake manifold. The temp sensor is in the thermostat housing AFTER the thermostat. This is the situation I have noticed and from what I have been told over the years "A rich engine is a COLD engine, A lean engine is a HOT engine". So I want to help it heat up by leaning it out sooner this winter by getting heat to the ecm temperature sensor asap. I am currently running a 195f thermostat. So if my logic is correct and what I can tell upon start up the engine is in its cold loop until the thermostat starts to open then the sensor is able to get a signal upon which it flips to the warm loop and leans out the motor allows lock up in the torque converter, AND FINALLY POWERS THE CHOCK TO OPEN! It seems to do this way to late. and takes the car awhile to finally warm up. So I want to put the sensor in the intake stream of coolant before the thermostat, instead of after. So I hope my question is not too confusing. I cant see how in the summer I would have a not problem. as it would just be in the hot loop sooner instead of later.

 

The system normally works quite well as designed, so if your choke is staying on too long, there are a couple of other things it may be. The thermostat may be opening a bit late, so the sensor isn't warmed when it should. The choke thermostat on the carb my be weak with age, in which case swapping it out is a very simple, inexpensive fix, or it could be that the sensor itself is not opening when it should. Trouble is, leaning the mixture prematurely will result in driveability issues, not to mention emissions issues.

 

well just thought i would post a little update on my question, had an 20 degree morning the other morning and while i was out with the car warming up i popped the hood and got out my trusty light tester. while the engine is warming up i connected the tester to the choke lead and watched as the engine heat cycled and paid attention to the frost melting on the windshield. as the car warmed up i could watch the frost melt and i held the upper hose in my hand for heat i could start to feel heat in the hose and then the engine idle came up from the temp sensor getting heat as this happened the the test light lit up so i knew the choke was now getting power to open. as the hot water exited the engine and the cold water came flooding in the thermostat closed and the engine started to bog as if to be getting flooded also the test light turned off telling me that engine has just heat cycled itself. also the windshield stopped defrosting. so i waited and watched as the cycle repeated itself about 3 times before finally stabilizing, so i have purchased some parts, http://www.ebay.com/itm/THERMOSTAT-...pt=Race_Car_Parts&hash=item35c323f708&vxp=mtr,and a new new choke thermostat. going to place the sensor in the spacer under the thermostat. hoping this will help to stabilize that sensors signal sooner. any ideas on the down falls of this and also thinking about connecting the choke to acc. power and removing control from the computer. does the computer need to be connected to the choke or will cause a check engine light if it does can i trick it by maybe putting a resistor on that wire and just grounding it to the fire wall.

 

oh and before anyone asks, i did not disconnect the choke lead while using the test light. i pushed the probe into the connecter from the wire side so as not to disturb the power from feeding the choke thermostat. and mike i know the thermostat is opening late i have a hotter thermostat than the factory application the factory calls for a 180 and i installed a 195. just like that old girl to get warm inside, if you met my girlfriend you would understand..... she is tiiiiiiny. and every little bit of heat helps.

 

That sounds like there is something wrong with your choke heater power feed.
On your 305, the choke heater coil gets power through the oil pressure switch. As soon as the oil pressure reaches a minimum of 4 psi, you should be getting 12V at the choke heater connector.

There should be a light blue wire feeding the choke heater; it should originate at the oil pressure switch, located at the rear of the block, near the distributor.

 

The first thing that I would try is swapping out the 195 degree thermostat, and installing the correct one specified by the manufacturer. You might be causing your own problems by using the higher temperature thermostat. All thermostats look alike, but some have a higher flow rate while they are closed. Good chance that the thermostat that you have substituted, has a very small opening in it for the closed position. In older cars, they had bypass hoses that would circulate the colder water and mix it with the warmer water even though the thermostat was closed. I have to believe that the engineers that designed the engine knew what they were doing to get the engine to temperature as fast as they could.

 

i would also check the choke pulloff . some cars have only 1 others have 2 , there on the left side of the carb when your standing in front of the car . hook a piece of vacuum line to it and make sure it will hold vacuum.

 

jmt that power wire goes to the oil pressure switch and then goes where to get power from what? junk when the thermostat is closed there is 0 circulation past it. the flow relief is the heater core if the heat is on sbc 262-400 does not have any flow bypass on it, olds motors do at the thermostat housing going back into the water pump. chevy has a vacuum controlled shut off valve for the heater core. mxis4me there is only 1 choke pull off, serving double duty as the secondaries buffer valve. the car uses the e4me rochester carb. and like i said i can see the choke lead get and lose power in direct line with the hot"lean" circuit and cold "rich" circuit. i do understand that i am causing the problem by running a hotter thermostat than recommended, but i am a guy that will to eat my cake....

 

here is a wiring diagram of the car engine bay....... if you follow the diagram the choke lead is interrupted by the oil pressure switch, so if the key is on but not running it wont open the choke, the ecm powers that lead at wire c next to wire 13. also the tcc solenoid does not get power until the engine warms up..http://austinthirdgen.org/mkportal/modules/contents/images/Fig15_1984_5_0L_engine_wiring.gif

 

I'm looking at a 1985 Factory Service manual for the 305 in a Pontiac Parisienne, so the details might vary slightly.

It shows the 12V feed from the C/H fuse is a .8 Brown wire to one side of the oil pressure switch. You should have 12V on the Brown wire when the ignition key is in the "run" position.

The other terminal on the oil pressure switch should have a .8 Tan wire and a .8 Light Blue wire (two wires on the terminal connector). The tan wire goes to the bulkhead connector; it feeds the oil/choke indicator light. The blue wire goes to the choke heater.

You should see 12V at the blue wire (at the choke heater connector or at the Tan & Blue wire terminal on the oil pressure switch) as soon as the engine builds 4psi of oil pressure.

Also; your thermostat is the proper one for the 305 (195F).

 

Well jmt i stand corrected on what is supposed to be the correct thermostat. I put in the correct thermostat by accident. I took out a 180. Previous owner did that called him this morning. Said he did that to try to beat the vapor lock problem car has in the summer. I replaced the radiator last year. Was not a problem for me.

 

i just took a look at the wiring diagram you had posted , the 10 amp fuse marked c-h feeds power to the brown wire going into the choke relay , the other brown wire gets a ground from the alternator which causes the pull coil close the switch in the choke relay and send power to the choke via the lt blue wire .hope this will help oh yea i like that spacer ! thats a good find

 

ok folks so just a little up date, I have installed the thermostat spacer. My temp sensor is now installed in the spacer. now when I start the car the engine warms up normally and the sensor gets a signal sooner and seemingly in a more stable fashion. The engine starts, warms, rpm increases normally as it warms, put a tach on it to verify what i am hearing. the engine rpm starts to drop slightly then right about that moment the carb slips into lean mode. rpm climbs again to about 1500 rpm. at that time my test light turns on at the choke feed. but now as the engine heat cycles from hot coolant to cold coolant from the radiator the light does not turn off again. it stays on heating the choke. so my choke still opens slow so i am going to replace the choke thermostat next. so the choke still does not get power until the ecm is in lean mode. i manually pushed the fast idle cam down to slow the idle and even at a low idle the choke lead has power only when in lean mode, no matter the rpm, so i am guessing the oil pressure switch is working correctly. so far to me its getting better.

 

The choke heater circuit is not working correctly.

You should get 12V at the choke heater connector as soon as the oil pressure gets above 4 or 5psi. (basically, as soon as the engine starts, there should be power to the choke heater coil).

The choke heater is fed from the oil pressure switch. Your wiring diagram shows a "choke heater relay" controlling the poser feed to the choke heater. Actually, the oil pressure switch performs the switching function for the choke heater on carbureted engines.

The oil pressure switch is the two-wire switch at the rear of the engine, it is low on the LH (driver's) side of the block, just above the oil filter. There should be 12V at the Brown wire as soon as you turn your ignition key to the "Run" or "Start" position.

Once the engine starts and there is at least 4psi of oil pressure, you should get 12V at the Light Blue (and Tan, if present) wire on the other terminal of the switch connector. If you do not get these results when checking the oil pressure switch, you should replace the switch.

I can't imagine why there is 12V at the choke heater only when the engine reaches operating temperature, unless someone has messed with the wiring.

 

well jmt i am totally with you on the messing with wiring on this car in full... when i went to the auto parts store to buy the temp sensor they kept showing me a single terminal male round stud type switch but the car has a two terminal oval male pin connector. the car was built 11/83 lists as an 84 but the switch matched an 85? the oil pressure switch has 4 wires on a two terminal oil pressure switch. so i am confused when i went to the parts store for that they showed me this huge single terminal sensor for an 84 but for the 85 was a small pressure switch with two terminals on it. the small two terminal switch is what i have. so no argument on anything from me on any of that statement from me at all. anyway so i removed the electric choke thermostat today. what i found was interesting to me at least. the duck bill prong? for lack of a better term that sticks out of the back of the brown plastic was loose on the spring took the housing off and the spring was left behind. so there was carbon on the spring and inside the duck bill where there was obvious arcing from the loose. found other silly things when i took the carb off to replace the choke thermostat. someone had used the cruise control cable to increase the idle speed by over tightening it, dont know why that was done either. now to just wait for some cold temps to adjust the new choke. but the car is running so much better now that the choke opens. the repositioning of the ecm temp sensor does seem to help it warm up faster. from what i have found the sensor has to be about 110 degrees before it closes the circuit. so the engine being at about 110 degrees when it switches to the lean circuit doesn't sound two outta line two me. and so far it works well.