Looking for some more answers. My 93 4x4 starts and runs fine. It has been cold here lately around -23 C. My problem is that after the engine warms on my truck the check engine light comes on. It may stay on for anywhere from 5-15 minutes and then go out only to come on again 10 minutes later. I pulled the codes several times and get codes 172 and 176 in continious memory. Intake has new gaskets and is torqued properly. Vac has been checked with a gauge and seems to be ok 18-21 hg. Is there anywhere else to look except replacing both O2 sensors. Can't afford to just throw money at the problem without knowing the cause. Truck has the 4.0 engine.

 

the vacuum should be steady, is it jumping between 18 and 21 inches?

 

Its fairly steady at about 18 inches. I live in Calgary at approx 3440 feet above sea level so i believe this translates to about 21 inches. Please correct me if i am wrong. Wondering if a sticking egr valve could cause this. Where is the egr valve located on this engine? I've only had the truck for a couple weeks. Thanks for the help.

 

Welcome to FTE!

You've checked all other sources of air leaks, such as vacuum hoses/connections, the PCV assembly, etc.? (Your '93 does not have an EGR valve).

Which intake gaskets are new? Upper? Sometimes the lower intake gasket and/or bolts have a tendency to loosen up, allowing air in.

Don't forget lean codes can also be caused by lack of fuel. So, how about the fuel pressure, is it within specs? A clogged fuel filter, bad fuel pressure regulator, failing fuel pump etc. should all be on the list of things to consider, as well.

You should clean the MAF sensor: Cleaning Your MAF Sensor.

(See also, Dirty MAF and Lean Codes)

 

Thanks for your help. I replaced all the intake gaskets couple of days ago. I am now going to retorque all bolts today and recheck all vacuum lines. I pulled the codes again last night an got 114,172,173,176,and 177 in continious memory this time. Could the Air Charge temp Sensor cause these codes? Im going to replace it this weekend.

 

I would run the pinpoint test for the IAT before replacing it. The IAT could cause mixture problems, now your getting rich & lean codes.

PRE-DIAGNOSTIC INFORMATION


IAT/ECT Sensors

Engine coolant temperature must be greater than 10°C (50°F) to pass the KOEO Self-Test and greater than 82°C (180°F) to pass the KOER Self-Test. To accomplish this, the engine should be at normal operating temperature.

Ambient temperature should be above 10°C (50°F) to receive acceptable input from the Intake Air Temperature (IAT) sensor.

DA1 CHECK VREF CIRCUIT VOLTAGE AT THROTTLE POSITION SENSOR


Possible Causes:

-- Low engine coolant level.

-- Damaged harness connector.

-- Damaged sensor.

-- Ambient temperature below 10°C (50°F).

l Key off.

l Disconnect TP sensor.

l Key on, engine off.

l Measure voltage between VREF circuit and SIG RTN circuit at the TP sensor vehicle harness connector.

l Is voltage between 4.0 and 6.0 volts?

Yes
RECONNECT TP sensor. GO to «DA2».

No
REPAIR VREF circuit. RETURN to the Test Step in «Section 3», Symptom Charts, which sent you to this Pinpoint Test.

DA2 CHECK RESISTANCE OF TEMPERATURE SENSOR WITH ENGINE OFF


l Key off.

l Disconnect IAT or ECT sensor.

l Measure resistance between sensor signal circuit and SIG RTN circuit at the temperature sensor. Refer to the table in «Section 6», Reference Values for resistance specifications for IAT/ECT sensor.

l Is resistance within specification?

Yes
GO to «DA3».

No
REPLACE sensor. RECONNECT vehicle harness. RETURN to the Test Step in «Section 3», Symptom Charts, which sent you to this Pinpoint Test.

DA3 CHECK RESISTANCE OF TEMPERATURE SENSOR WITH ENGINE RUNNING


NOTE:
Engine may have cooled down. Always warm engine before taking ECT sensor resistance measurements. Check for open thermostat.

l Key off.

l IAT or ECT sensor disconnected.

l Run engine for two minutes at 2000 rpm.

l Measure resistance between sensor signal circuit and SIG RTN circuit at the temperature sensor. Refer to the table in «Section 6», Reference Values.

l Is resistance within specification?

Yes
GO to «DA4».

No
REPLACE sensor. RECONNECT vehicle harness. RETURN to the Test Step in «Section 3», Symptom Charts, which sent you to this Pinpoint Test.

DA4 CHECK RESISTANCE OF SENSOR SIGNAL AND SIG RTN CIRCUITS


l Key off.

l IAT or ECT sensor disconnected.

l Disconnect Powertrain Control Module (PCM). Inspect for damaged or pushed out pins, corrosion, loose wires. Service as necessary.

l Install breakout box. Leave PCM disconnected.

l Measure resistance between sensor signal circuit at the temperature sensor vehicle harness connector and ECT or IAT at the breakout box.

l Measure resistance between SIG RTN circuit at the temperature sensor vehicle harness connector and SIG RTN at the breakout box.

l Is each resistance less than 5.0 ohms?

Yes
GO to «DA5».

No
SERVICE open circuits. REMOVE breakout box. RECONNECT all components. RETURN to the Test Step in «Section 3», Symptom Charts, which sent you to this Pinpoint Test.

DA5 CHECK FOR SENSOR SIGNAL SHORTED TO VREF


l Key off.

l IAT or ECT sensor disconnected.

l Disconnect PCM. Inspect for damaged or pushed out pins, corrosion, loose wires. Service as necessary.

l Install breakout box. Leave PCM disconnected.

l Measure resistance between sensor signal circuit ECT or IAT and VREF at the breakout box.

l Is each resistance greater than 10,000 ohms?

Yes
GO to «DA6».

No
REMOVE breakout box. RECONNECT all components. LOCATE and SERVICE short to VREF. RETURN to the Test Step in «Section 3», Symptom Charts, which sent you to this Pinpoint Test.

DA6 CHECK TEMPERATURE SENSOR SIGNAL CIRCUIT FOR SHORT TO GROUND


l Key off.

l IAT or ECT sensor disconnected.

l Disconnect Powertrain Control Module (PCM). Inspect for damaged or pushed out pins, corrosion, loose wires. Service as necessary.

l Install breakout box. Leave PCM disconnected.

l Measure resistance between ECT or IAT and PWR GND at the breakout box.

l Is each resistance greater than 10,000 ohms?

Yes
RETURN to the Test Step in «Section 3», Symptom Charts, which sent you to this Pinpoint Test.

No
SERVICE short circuit. REMOVE breakout box. RECONNECT all components. RETURN to the Test Step in «Section 3», Symptom Charts, which sent you to this Pinpoint Test.

 

I will check those sensors tomorrow with my multimeter and see if they test ok. just a note while using the truck today i noticed that the CEL came on as soon as the engin warmed up. That is as soon as the temp gauge hit the start of the normal operating range the light came on and would stay on until the engine was shut off. Its been pretty cold here lately so it takes a long time to heat up. I know that the gauge and computer operate off different sensors so I am wondering if this points to my Coolant temp sensor.

 

While testing the resistance on my ECT the lowest resistance I am getting is 3.8 Kohms. This was with Boiling tap water ( 100 C. ). Would this reading be correct for approx 212 F or is the resistance still too high? Should I replace this sensor B4 continuing with the tests?

 

That resistance is too high, it should be more around 2.07 Kohm.

Check out the chart at the end of the following, the values set forth therein are accurate and indicative of the values you should be getting when testing your own Ranger's ECT:

http://fordfuelinjection.com/index.php?p=28

 

Thinking its gotta be the O2 sensors. I replaced the ECT and IAT sensors yesterday and thought I had the CEL problem beat. I did disconnect the battery all night after changing the sensors. Today when I went for a test ride the temp gauge was almost to the half point b4 the CEL came on. I came home and pulled codes and got 172 and 173 for the right O2 sensor and only 176 for the left O2 sensor. I'm guessing that when the engine enters a closed loop relying on O2 input after warming up the O2 sensors must not be switching fast enough. Going to try to pull them and test tomorrow. If any1 else has any idea's feel please share them with me.

 

In addition my IAC is a littly noisy but I have a steady idle. Another question regarding my idle is sometimes at a light after the CEL is on the idle speed is a steady 1150 rmp or so and 10 mins later at idle it's a steady 800 rpms. Both time its a steady idle with barely any movement of the tach needle. I'm guessing here but i'm thinking one is a lean condition and one a rich condition. Do you think this points to the O2 sensors as a culprit.

 

replaced both O2 sensors a couple of days ago. I got 3 sensors from a scrap yard for 10 dollars. Took a couple minutes to install them. the check engine light has not come on again. Truck appears to be running much better and getting better mileage. No more code 137 in the KOER test either. A heads up to any1 interested I pulled all O2 sensors from early 90's ford Taurus.