Fuel Pump Relay question

[Jan Pinkowish]

Chris Hall wrote:
> Latest on my 85 Coupe GT
> 
> I tried to "jump" the wires to the "NCT" (ECU coolant temp sensor) and
> that didn't work.  I checked the resistance on that sensor, and it
> came up to be 2700 ohms or something like that... which I think I've
> read is pretty close to spec (2500 cold?).
> 
> Last night I tried starting the car again, and it did that thing where
> it starts to combust, but never kicks in all the way.  I know the fuel
> pump -pumps- and I'm guessing it's providing enough pressure because I
> think it's only 4 or so years old...
> 
> Fuel pump relay appears to be working as it should, and I even jumped
> the slots and still no starting.
> 
> Someone please get back to me if that value for the ecu's coolant temp
> sensor is way off...
> 

...and Tony Lum replied
> Sounds like your temp sensor is working.  IME, the sensor reads around
> 100 ohms fully warmed up.  When bad, they're usually open or read like
> 100K ohms cold.  Are you sure you're getting spark? Check the Hall
> sensor on the distributor.  Check the contacts and make sure all the
> wires are fully seated with no corrosion on the contacts.  It would also
> help to pull the connector on the ecu (next to the glove box) and see if
>  those contacts are good and that the signal wires from the sensor are
> also present on the ecu's connector.  Maker sure the idle/WOT switch is
> working.  Your F.I. system is CIS-E, which means that the grey
> differential pressure regulator that's attached to the fuel distributor
> should be receiving some current.  To measure this you have to make up
> an adapter to place a current meter in series with the DPR.  Should
> measure something like 8-10 mA under normal conditions.

Chris,
To expand on Tonys reply:
Your ECU temp sensor should read 5.5k to 6.5k ohms at 68degF.  When the car is fully warm, the sensor reads 300-500 ohms.  As the sensor decreases in resistance, the ECU leans out the fuel mixture.  So, if the sensor is 2700 ohms when the engine is cold, this may cause a bit of a cold start problem.  When the sensor fails, it doesn't change resistance.  If it fails high, the car starts fine, your fuel mixture remains rich and your MPG drops big time.  If it fails low, the engine is hard to start and runs rough until the operating temp comes up.

Get yourself a 10k ohm resistor and attach it to the temp sender leads.  If the car starts and runs smoothly, replace your temp sensor.

If that doesn't work, remember to check your "spare" fuse in the fuse box that controls the fuel pump reply/ECU.

After that, start with the basics described by Tony:
--clean and uncracked dist cap/rotor
--check your plugs for proper color and make sure the ig wire ends aren't cheesey
--check your ignition wires for integrity/arcing(use the water mist in the dark method)
--check for spark on each cylinder

HTH

Jan Pinkowish
'85 4ksq
Bristol, CT