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Chris (aka- Moose)
Chris (aka- Moose), Technician
Category: Ford
Satisfied Customers: 45554
Experience:  16 years experience
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I have a 99 F250 5.4 Super Duty. OBD is reading -40 degrees.

Customer Question

Hi Chris. I have a 99 F250 5.4 Super Duty. OBD is reading -40 degrees. Engine hesitates while driving. No misfires.
Submitted: 1 year ago.
Category: Ford
Expert:  Chris (aka- Moose) replied 1 year ago.

Has anyone installed one of those resistors on the vehicle to confuse the IAT reading to the PCM?

Customer: replied 1 year ago.
Not that I know of... Third owner of the truck. Thought it was initially fuel injectors or coils.. Or fuel pump.. But the mechanic I've been taking it to insists on it having something to do with the computer system
Customer: replied 1 year ago.
Whether it's a faulty or a corroded wire.. Confirmed the reading today that it was reading - 40. He said once he plugged a sensor back in it should read 1000 degrees????
Customer: replied 1 year ago.
Other opinions included a bad catalytic converter.
Expert:  Chris (aka- Moose) replied 1 year ago.

Are you getting any trouble codes? The cold IAT reading can effect the air fuel ratio and cause running issues. So we need to address the known issues prior to testing other things. Have you done any testing on the IAT in the MAF sensor or its wiring?

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Customer: replied 1 year ago.
I do plan on rating you at a later time. I do appreciate your help! To my knowledgethe truck wasn't throwing any other codes. And there has been no testing to the IAT.
Customer: replied 1 year ago.
Not yet anyways.. The truck does seem to be "dumping" a lot of fuel while driving.
Expert:  Chris (aka- Moose) replied 1 year ago.

Lets do those IAT tests first. See the steps below. I told you wrong on the IAT and MAF integrated, that si not until the next year model. The IAT is a stand alone sensor in the air intake tube to the throttle body.

Unplug the IAT connector and jump the Gray (GY) wire to the Gray/Red (GY/RD) wire and watch the IAT voltage reading on the scanner. If it goes to under 0.1 volts, replace the IAT. If the reading does not change, verify the GY and GY/RD wires are good from the connector back to the Powertrain Control Module (PCM). If all is OK, replace PCM.

Customer: replied 1 year ago.
Thank you Moose. Am I able to ask you questions tomorrow as well?
Customer: replied 1 year ago.
I should mention over the past few weeks there have been moments where the truck drove great but never lasted more than two days. I commute to work about 50 miles total every day.
Expert:  Chris (aka- Moose) replied 1 year ago.

We have 7 days to try and get posts rated. After its rated the post is open forever.

Once we get the IAT reading right we can look into other residual issues remaining.

Expert:  Chris (aka- Moose) replied 1 year ago.

I am sorry you were not pleased with my help. I am still available if you would like to try again. I want you pleased with me.