Lower eng temp - maybe too much!

[ltmark]

'85 coupe - I have written several threads re: idle problems and engine temp. I solved both, but may have gone too far! Replacing the coolant temp sensor fixed my idle problems, but I was also concerned about the inherent high running temp of vettes. So, I installed a 195 degree aux fan switch and ran that to my primary fan (since the aux fan is quite a bit louder that the main!) and routed the ECM fan wire - (going to ground at about 128 degrees) to the aux fan.

All was well and it ran cooler. BUT, while solving the idle problems, I was forced to learn how all the involved sensors interact to have the ECM control the cold start air/fuel ratios.

The ECM sends 5 volts to the coolant temp sensor thermister, which slowly drops as the egine warms and eventually stops at 1.5 to 2 volts when hot. However, with the 195 degree fan switch, I have discovered that the coolant temp sensor gets down to 2.3 volts and then when the fan comes on (195 degrees) and the engine temp begins to go down, the coolant sensor voltage naturally goes up, which tells the ecm that the engine is still not completely warm. Hence, the fuel/air ratio is still slightly enriched.

Although it runs great at idle and acceleration, it is sill enriched from what it should be, effecting my gas mileage! Reading another web tech article, I found that 15:1 provides the most power, but 13:1 is most economical. I don't race or hot-rod, so I prefer the 13:1!

Bottom line- I'm going to go to a 210 degree fan temp switch and see if that avoids the coolant temp sensor from always reading higher than the 1.5 to 2 volts. If so, I can still reduce the higher running temp, but also not screw up the ECM's control of the proper fuel delivery/ratios.

Hope this helps someone in troubleshooting similar issues!

 

[vetteboy86]

That is very good info to know. I never thought of some of those issures you are explaining. Looks like I better get out the meter and find out whats up. Thanks for the post.


Craig

 

[I_R_DA_ONE]

Ltmark
I talked to my local chevrolet service manager and he said they can recalibrate the ECM to different settings for the cooling temp...I have not tried this yet...I looked into this because my coolent fan comes on at 230* and then goes off a 218* and I was thinking this is just a bit to high
Mike

 

[ltmark]

That's true, but I have an '85 and my understanding is that the ECM's are only re-progammable on the later vettes.

 

[vetteboy86]

You can put a chip in your car that is custom programmed. Eventually I think that is what I will do.


Craig

 

[WhalePirot]

I have an '85 and my understanding is that the ECM's are only re-progammable on the later vettes.

Not true! The chips in all ECM's are programmable, although the methods change. The latest ones can be done real-time, with the car on a dyno, etc. The older ones are more tedious in that the chip must be removed to be customized; reinstalled to check the ECM's response under real running conditions, then repeated as necessary to get perfect.

Also, your '85 can have the fan controlled by the ECM (later '85) or a separate temperature sending unit (early '85, as in '84).

 

[geekinavette]

Even older ECMs can be reprogrammed "real-time", with this:

http://www.speedtronics.net/aboutprominator.asp

My own little invention there. It replaces the EPROM "chip" with Flash-based ROM so you can just plug in a laptop parallel port directly to the ECM and reprogram it!

 

[WhalePirot]

Even older ECMs can be reprogrammed "real-time", with my own little invention.

:L
I was actually thinking about your device when I was typing, but saved the glory for you.


BTW, I am looking for a box the size of the intake.

 

[COOL-86]

Low Engine Temp

I had a problem with my 86 with the temp running to high for me. I changed the the thermostat to 160 and put in a switch on my fan so I could turn the fan on and off any time I needed. That did the trick for me.

 

[tigmaned]

its easier i think to get a custom porm chip to change when he fan comes on. factory setting is around 225. i got mine made to come on at 200.
WP -did you get a code for the coolant temp sensor you changed and it inproved your idle. mine starts great ALL the time and idles good but then seating at a light or some and it just starts idleing like crap??

 

[Black Bart]

'85 coupe

Although it runs great at idle and acceleration, it is sill enriched from what it should be, effecting my gas mileage! Reading another web tech article, I found that 15:1 provides the most power, but 13:1 is most economical. I don't race or hot-rod, so I prefer the 13:1!

Everything that you say makes sense and as other have posted it can be corrected by reprogramming the ecm.

The above quote from your post is backasswards.
13-1 is richer than 15-1 The higher number is always the air and the low number is fuel. 15 parts air and 1 part fuel is leaner than 13 parts air to 1 part fuel.