Odd ECT problem

[RYC CUKR]

I am having a strange ECT problem with my 88.

Here is a little back ground on the car.

The car ran extremely rough at idle. When I swapped the intake for my Trackheat I found that most of the vacuum caps he had used to block off unused vacuum ports on the underside of the stock intake were had cracked and were leaking so I replaced them all. Helped out immensely. You can now start the car and it will idle while cold. So now the car is running pretty good. It has no functional EGR and no ECT sensor.

When I bought it the guy that had it before me had done some stupid things, in my opinion. The heater core had gone bad and they had bypassed it, by removing the entire metal heater tube and putting a plug in the threaded boss in the lower intake. So it did not have an ECT sensor in it. They also deleted all the EGR vacuum lines. Now I'm in the process of fixing the issues with the car.

When I put my longtubes on the car I got a threaded brass reducing bushing so that I could put a new ECT sensor in and hook it back up. After I put the sensor in I noticed that every now and again the car would stutter and pop through the intake at low RPM. Gradually it got worse. If it was at WOT or above 3000 rpm it ran pretty good below that it was hit or miss. Sometimes it was fine other times it ran like ass.

So I went back and unplugged the ECT sensor and voila the car runs good again. No stuttering or popping. Kinda baffling to me as to why it would run better with the ECT unhooked than with it hooked up. I haven't pulled the codes yet cause I have been to busy to really do anything with the car.

Just wondered if anyone else had ever heard of this or had any ideas as to what would cause that problem.

 

[HISSIN50]

I'd look in the Probst manual or see Jrichker's list for resistance vs temp listings. You can check the sensor to get an idea of its calibration.

When the ECT is disco'd, the EEC tends to run rich. I wonder if this helps mask another issue (e.e., do you think you have any issue with LT's and the O2's?).

Just my random weird thoughts.
Good luck.

 

[superhuaman]

What about your water pump tubes? One should go into the thermostat housing...and the other one should be plumbed into that place where you have the plug. Cuz when you have the heater core tubes in place, that is how the coolant is routed.

 

[jrichker]

Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see http://www.midwayautosupply.com/pc-7208-90-equus-digital-ford-code-reader-3145.aspx – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $35.

Look for codes 21 & 51 . here's the code 21 test table...

Code 21 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor.
Note that that if the outside air temp is below 50 degrees F that the test for the
ECT can be in error.

The ECT sensor has absolutely nothing to do with the temperature gauge. They are
different animals. The ECT sensor is normally located it the RH front of the engine in
the water feed tubes for the heater.

The ACT & ECT have the same thermistor, so the table values are the same

ACT & ECT test data:

Use Pin 46 on the computer for ground for both ECT & ACT to get most accurate
readings.

Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is
a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower
intake manifold, the voltage readings will be lower because of the heat transfer.

Voltages may be measured across the ECT/ACT by probing the connector from
the rear. A pair of safety pins may be helpful in doing this. Use care in doing it
so that you don't damage the wiring or connector.

Here's the table :

68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61

Note that all resistance tests must be done with power off. Measuring resistance
with a circuit powered on will give false readings and possibly damage the meter.

Ohms measures at the computer with the computer disconnected, or at the sensor
with the sensor disconnected.
50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

 

[RYC CUKR]

Thanks for the info guys.

I think that I am going to fix the problems that I know that I have, i.e. get the EGR working again and then I will pull the codes and see what the computer tells me.