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1979 Cadillac Elorado Air/Coolant sensor the same???

Started by nanaimogene, October 11, 2015, 12:30:09 AM

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nanaimogene

Its nice to be back here since I sold my 57 Caddy last year. Now I have 79 Caddy Eldorado Briarritz. I had a dead Air Temperature sensor. I replaced it with a universal
sensor that on the ohm meter reads 2.78 which is correct according to Google mechanics. Now my Shop Manual says the Coolant sensor and the intake air one are the
same ???? The previous owner had installed a new coolant sensor in 2013 from Hewitt Industries. I tested it cold and read 94 and when the car warmed up it read 1.28.
I thought the numbers should go down not up??  There used original sensors available but at $100 each.
Also the Google guys say I should get 5 volts from the computer, I get 10 volts ???         Also which signals the computer to slow the fast idle down...the one in the throttle body or the coolant sensor??      Glad to with you guys again Gene

Scot Minesinger

Electrical resistance increases as the temperature goes up in metals conducting electricity.  Power lines in Alaska can be a smaller wire size (less resistance) then power lines in TX carrying same current.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

TJ Hopland

MTS has new sensors $130.   http://www.500cid.com/#!product/prd1/3490104961/mts-efi-water-%26-temp-sensor

Both are the same sensor.   I'm far from an expert on these systems but if it was easy to substitute a more modern sensor on these people would be doing it.  Those sensors apparently have never been that reliable and at times have been very hard to find.   The 'computer' for these is an analog device so its quite different than any other fuel injection system ever made so I suspect that these sensors don't operate like most and that is why they are not reliable or easy to retrofit.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Gene Beaird

As TJ says, they are not generic, abd they do go bad. You should order three from MTS, two to replace what you have, and a spare for the parts bin.
Gene Beaird,
1968 Calais
1979 Seville
Pearland, Texas
CLC Member No. 29873

bcroe

Quote from: nanaimogeneI have 79 Caddy Eldorado Briarritz. I had a dead Air Temperature sensor.
I replaced it with a universal sensor that on the ohm meter reads 2.78 which is correct according to Google mechanics. Now my Shop Manual says the Coolant sensor and the intake air one are the
same ???? The previous owner had installed a new coolant sensor in 2013 from Hewitt Industries. I
tested it cold and read 94 and when the car warmed up it read 1.28.
I thought the numbers should go down not up??  There used original sensors available but at $100 each.
Also the Google guys say I should get 5 volts from the computer, I get 10 volts ???   Also which signals the computer to slow the fast idle down...the one in the throttle body or the coolant sensor??      Gene 

That sensor unplugged should measure ballpark 1000 ohms cold.  Being close to linear, the analog ECU
could couple them directly into the temp circuits.  The usual log curve are applied by a look up translation
for later EFIs.  The sensors control cold enrichment (no effect when hot), but engine idle is controlled by
the cold idle air valve on top of the throttle body.  Warmed up, if pushing down on that black plastic with
the heater connector causes the engine to slow down, it hasn't closed all the way.  Try cleaning it up
(DON'T break off that tiny microswitch arm).  If that doesn't do it, a shim (something like a dime) under
the brass rod can push it farther shut. 

The 70s EFIs like to burn out the fuel pump circuit through the precious ECU, about 30% of the ones I
see have this.  You can add an external relay to protect the ECU as describes on my PHOTOBUCKET; I
also have a kit for that.  If the car looses power under acceleration with a low gauge, your fuel tank
pump has died. 

I recommend getting the Generals blue & white manual, 76 CADILLAC ELECTRONIC FUEL INJECTION
DIAGNOSIS if you own a 70s EFI Cad, on Eb*y all the time.  And that era always need any original
timing chain set (with plastic teeth) replaced before it falls apart.  Don't tell me how hard that is
esp on a front driver, I have done enough of them to know all about it.  Not sure where you are
measuring those voltages, but the logic in the ECU runs on 9.5V, not 5V.  ECU circuit is on the 7th
or 8th album of my PHOTOBUCKET. 

Check for coolant leaks on that aluminum intake.  If the trans doesn't shift quite right, the accumulator
spring (under the big round cover on left side) is probably broken. 

And yea, I have owned a 79 Eldo for decades and 100s of thousands of miles.  Can tell more of what
is likely to break and how to fix it.  Read about these EFI systems and other stuff on
the first and some later albums of my PHOTOBUCKET.  good luck,

     http://s93.photobucket.com/albums/L71/bcroe/

  click on an Album
  click on a picture to enlarge + description

BRUCE ROE                                  bcroe@juno.com
5719 EAST SKINNER ROAD,
STILLMAN VLY, IL    61084-9215       Phone  815 234-8039

nanaimogene

I agree with you all. The universal newer sensors are not for the analog ECU's. The current coolant temp sensor reads correctly according to the shop manual which says in ohms..........at 60 F  950ohms   at 180 F    1200ohms. This probably why it needs 10 volts to function correctly. I noticed my universal air temp sensor on a warm engine reads
580ohms...car does run fine. However I better buy the correct sensor. Hewitt Industries of LA did sell the air/coolant correct sensors for $64.05 in 2013. I will see what they are charging for them now and let members here know.

nanaimogene

Bruce thank you for good info.  My intake manifold air temperature sensor is on its way to me. Removing the fast idle valve from the throttle body (carefully) and putting a dime under the brass rod as you said ...will that speed up the shut down of the fast idle valve since it takes 3 to 4 min to normal idle.  Also will this trick reduce the high rpm on a cold start.
Im used to carb choke set ups that will kick down when you press the gas pedal. My other Cadillac is 87 Coupe de Ville (with the fake convertible top) and its cold start is around 1000 to 1500 rpm which is fine. My 79 Eldorado is about 2000 to 2500 rpm on a cold start which scares me. You mentioned timing chains and the plastic teeth. A friend worked for Ford for years and said the PCV not being changed was the one of the causes of Fords plastic in the timing chain set up failing.

bcroe

Quote from: nanaimogene on October 14, 2015, 01:54:48 AM
Bruce thank you for good info.  My intake manifold air temperature sensor is on its way to me. Removing the fast idle valve from the throttle body (carefully) and putting a dime under the brass rod as you said ...will that speed up the shut down of the fast idle valve since it takes 3 to 4 min to normal idle.  Also will this trick reduce the high rpm on a cold start.
Im used to carb choke set ups that will kick down when you press the gas pedal. My other Cadillac is 87 Coupe de Ville (with the fake convertible top) and its cold start is around 1000 to 1500 rpm which is fine. My 79 Eldorado is about 2000 to 2500 rpm on a cold start which scares me. You mentioned timing chains and the plastic teeth. A friend worked for Ford for years and said the PCV not being changed was the one of the causes of Fords plastic in the timing chain set up failing.

engine idle is controlled by the cold idle air valve on top of the throttle body.  Warmed up, if
pushing down on that black plastic with the heater connector causes the engine to slow down,
it hasn't closed all the way.  Try cleaning it up (DON'T break off that tiny microswitch arm).  If
that doesn't do it, a shim (something like a dime) under the brass rod can push it farther shut. 

I never actually used a dime, it just pushes the valve a little more closed, hopfully all the
way when hot.  Otherwise the heater may need replacement.  Once the cold idle valve is
working (warm engine does not slow when valve pushed down), there is a mechanical screw
on the throttle body, but its typically OK.  Close it too much and the engine will be stalling
when really well warmed up. 

You can choose when to change the timing chain set, or some day the car will choose the
time for you.  Bruce Roe