Volt Meter connected between white/lt blue & yellow/red, reading volts at IAC solenoid. Cold Engine with wiring harness connector attached to IAC solenoid and turning key ON, (Engine NOT running), voltage jumps to 9.75v "BUT" stays there only 2.5 seconds, then drops to zero.

With harness NOT attached to IAC solenoid and turning key ON, voltage jumps to 10.5v "BUT" stays there only 2.5 seconds, then drops to zero.

I get a 5v steady reading on the orange/white whether they're connected or not. No change in the voltage reading. I checked at each indivdual sensor.
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Between this forum, the Haynes manual, and searching the Internet, I found this info about the Throttle Postioning Sensor:

1 - Have the TPS disconnected. Take the volt meter and connect the black lead to the ground terminal on the battery. Connect the red lead to the orange/white prong. The meter should read five volts on the orange/white reference wire for the TPS and if so, you are getting proper reference voltage to the TPS. Therefore you have just eliminated a faulty power feed to ECM..... (I do read 5v on the orange/white wire)

2 - If it reads anything below five volts then you are on the dark green/light green signal wire..... (I read zero volts on this wire)

3 - If it reads nothing on the volt meter, you are on the black/white negative wire.... (I do of course read zero volts on this wire)

4 - Reconnect the Throttle Position Sensor. Put the red lead of the volt meter to the dark green/light green signal wire in the back of the connector (probing). Put the black lead of the volt meter in the black/white negative center wire of the connector, Turn the butterfly shaft gradually and as you turn it you should get a gradual count upwards to five volts. If the volts fluctuate backwards or forwards then you know you have a faulty throttle position sensor.

On step #4, as I move the throttle butterflys from a dead idle position to full throttle, the volt meter increases only to one (1) volt, not 5 volts. On step #2, that sort of suggests that a voltage reading of some kind should be present... but none exists.

TPS bad?

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I went thru the code readings at least a dozen times to make sure I got them right, as follows:

63 - 63 - 1 -51 - 61 - 63 - 33 - 51 - 61 - 63 - 33

NOTE: There was an approximate 7 second delay between the 2nd #63 and #1

1 = ? (Not in book, still looking)
33 = ? (Not in book, still looking)
51 = ECT sensor below minimum, possible short.
61 = ECT sensor below minimum, possible short.
63 = TP sensor below minimum, possible short.

 

Joe,
I wouldn't concern myself with the 33 code at this time. I would look closely at the wires and plug for the coolant temp sensor something is going on there. That has to be fixed first. Were you able to watch the voltage reading on that 5 volt reference wire as you disconnected and reconnected each of the three sensors I suggested? Did any one of them pull the 5 volts down when reconnected?

The 1 flash you received may have only been a pause transferring from hard codes to continuous codes disregard it.
There is a good possibility once you get the coolant sensor system straightened out all the other problems will disappear.
Suggest changing the coolant temp sensor.

 

Hanky... In my very first post about this problem, one of the statements I made was:

"I noticed a sensor at the front portion of the intake manifold or block that was falling apart. The wiring led to the bottom of the throttle body (Throttle Positioning Sensor?). I installed a new sensor but it made no improvement."
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This was in error... there was just 2 wires on that component and upon looking closer, they DID NOT lead to the TPS.

In checking my receipts, I find that this component is listed as the "Sensor Coolant Temp". (sigh)
However, code 51 & 61 point to it... confusing.
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Those 3 sensors.... I will double check tomorrow, making sure that all three are disconnected, testing one at a time for a voltage drop.

Does it make any difference which orange/white wire I leave the volt meter attached to... or should I move the meter red lead directly to the orange/white wire of the sensor I'm testing?

 

That 5 volt supply comes from the computer and is common to all of the sensors I mentioned. You can check it either way whichever is most easy for you.

 

I'll do that today and report back just as soon as it warms up a little. 55 degees this morning.

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Also the new ETC sensor that I had replaced previously, and what you have been leaning towards as a suspected component... I should mention the condition I came to find the original one in.

It sits in the center front of the intake manifold or block, horizontally facing forward. After removing the two hoses between the air filter and carb body, I just happened to spot it while looking for something else.

It looked like something had spilled on it at one time that was corrosive. The connecting plug portion of it had been eaten away, crystallized, heat destroyed, something, leaving the two prongs of the sensor sticking out into thin air with nothing attached to it.

The electric plug, just laying there on the block in front of the sensor, was still firmly attached to the engine wiring harness and contained a good portion of what was normally the sensor part.

The wiring harness electric plug itself looked usable but in hindsight (last night) I got to wondering if the inner workings of that plug may be shorted out, insulated via corrosion, or the inner connection broken somehow.

(Bill... This may fall in line with your broken wire suggestion... similar scenario)

I will be installing a new pigtail plug assembly (firm splice, solder, heat shrink) to eliminate that uncertainly... BUT... I'll wait to do so until after I've checked those three sensors as instructed.

 

Joe,
here are a few more checks you can do,
Per your reply re TPS, you had 5 volts at the TPS with it connected and disconnected. Also with the readings you received per your step4 , it would suggest that the TPS is defective.
On another note, because many people return parts and get credit , we don't know what they did with those parts and in the case of the Idle By Pass Solenoid there is a diode in there and if anything was connected incorrectly and the part returned you would not know it was defective so I will give you the procedure to correctly test that solenoid.
Test leads must be connected as follows:
Red lead gets connected to the terminal that brings power to the solenoid and the black lead to the other terminal. The reading should be 7.0 -13.0 ohms. If not , replace it , it is defective.
One more check you can do is, measure the resistance from either terminal and the outside housing. The reading should be very hi or open, anything else means the windings are shorted to the housing and the solenoid is defective.
You are gonna get so good with these systems we are going to be asking you for advice!!

 

Wires on my 1988 F150 302 engine IAC are: RED and GRAY/WHITE. There are two RED wires leading from the engine wiring harness BUT one RED wire splices into the GRAY/WHITE wire resulting in two (2) wires attached to the IAC connector... one (1) RED and one (1) GRAY/WHITE.

IAC Test:

The ohm reading between the two terminals is: 9 ohms. NOTE that the ohm reading exists in both directions (reversing meter leads)

The voltage "between" the two terminals when disconnected is: 10.5v BUT after 2.5 seconds drops to 2.5v.

The voltage "between" the two terminals when connected is: 9.75v BUT after 2.5 seconds drops to 2.5v.

The voltage between BOTH the RED terminal and the GRAY/WHITE terminal and GROUND when connected is: 11.75v approximately.... when disconnected, same voltage is to RED only.
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Three Sensor Test:

All sensor electrical plugs disconnected.

RED lead of meter probed into common orange/white voltage lead.

Volt meter read a steady and constant 5v when sensor electrical plugs were connected, then disconnected. Voltage held steady at 5v even if just one sensor was connected or all connected.
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TPS Test:

Normal 5v present at orange/white wire.

Only 2/10v between TP signal and RETURN signal terminal.

Observing meter and advancing throttle to full throttle resulted in no voltage difference. (Should have advanced to around 5v)

 

I think I know what you are thinking and agree !! Replace that TPS.

 

Yes, that's what I'm thinking... not looking forward to it though.

From the explanation in the Hayne's book, after installing it, there's an adjustment to make (turning it one way or the other) before reinstalling the throttle body. Hope I"m up to it.

Still need to install the new pigtail/electrical connector to the ECT wiring harness too. Hopefully all goes well and I'll get back soon.

EDIT: 10/28/14... Installed the new connector and pigtail to the wiring harness for the ECT sensor. Staggered, firm mechanical clamp, soldered, heat shrink. Did not run engine at this time.

EDIT: 10/31/14... TPS still not installed yet. Used truck today as is... I noticed that with the new ECT sensor installed, the CEL does go off when the rpm is increased with the throttle pedal. Double checked the TPS... no question that it's faulty. New one will be purchased shortly.

 

Hello! My brother purchase a Ford 150.He had a problem with the truck check engine light coming on and the truck shutting off. What could br the problem? Can anyone help me?