HEGO Sensor
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5th Wheeling
Joined: Mar 2024
Posts: 37
Likes: 7
HEGO Sensor
I recently changed all vacuum lines, EGR valve and solenoid, and PCV valve. Then about a week later the distributor rotor broke and the distributor itself was rusty so I replaced the whole thing and adjusted timing. It’s been running way better than it has in a long time. I checked the codes for no real reason (CEL was NOT on) and got code 42-HEGO sensor voltage high/system rich. I really wouldn’t consider it running rich but I saw that a common cause for this code is a faulty fuel pressure regulator. Since I did have vacuum leaks and just replaced all lines I figured it was possible this was faulty so I replaced it and put in some purple power fuel injector cleaner. Code is still there. Anybody know how I would go about testing to see if my sensor is faulty or have a pinpoint test? It is the only code. Also I tried to do a cylinder balance test and the engine died after 2-3 minutes and was still stuck on code 42 without giving a cylinder code-any thoughts? Thanks!
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
What year truck and engine does it have?
The cyl balance test isn't possible on SD EFI trucks.. it requires SEFI MAF control.
What is fuel milage like with your truck?
With that code the O2 sensor could be bad or there could be a wiring problem between the sensor and PCM, or the engine could actually be running rich which could be a result of a number of things. Have the plugs been changed recently? If not they may provide a clue towards what is wrong if for example one of them is dark and wet while the others are normal light tan color or even white, that would indicate a leaking injector.
The cyl balance test isn't possible on SD EFI trucks.. it requires SEFI MAF control.
What is fuel milage like with your truck?
With that code the O2 sensor could be bad or there could be a wiring problem between the sensor and PCM, or the engine could actually be running rich which could be a result of a number of things. Have the plugs been changed recently? If not they may provide a clue towards what is wrong if for example one of them is dark and wet while the others are normal light tan color or even white, that would indicate a leaking injector.
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5th Wheeling
Joined: Mar 2024
Posts: 37
Likes: 7
its a 1993 F150 XLT 5.0
Yeah I have a MAP not a MAF. I didnt know that about the balance test, it doesnt say anything in the book about it. I wonder why it dies like that though, its done it several times and always around 2-3 minutes in.
Other than noticing an improvement in mileage since I've done all this stuff, I haven't paid much attention to it. Previously it was around 12-14mpg.
I replaced plugs and wires maybe 2ish years ago, I'll have to check them.
Yeah thats KOER, KOEO gives no codes including memory.
Thanks for the replies!
Yeah I have a MAP not a MAF. I didnt know that about the balance test, it doesnt say anything in the book about it. I wonder why it dies like that though, its done it several times and always around 2-3 minutes in.
Other than noticing an improvement in mileage since I've done all this stuff, I haven't paid much attention to it. Previously it was around 12-14mpg.
I replaced plugs and wires maybe 2ish years ago, I'll have to check them.
Yeah thats KOER, KOEO gives no codes including memory.
Thanks for the replies!
Hotshot
Joined: Jul 2020
Posts: 10,270
Likes: 2,565
From: Near Salt Lake City
Backprobe the sensor or use a NGS to read the HEGO sensor output (watch it switch) or see if it is slammed rich
Meaning, see if the system is actually running rich or if it's just a sensor issue
The pinpoint tests for code 42 get hairy quick
I can post some of them, if you want, to get you started
Have fun
Meaning, see if the system is actually running rich or if it's just a sensor issue
The pinpoint tests for code 42 get hairy quick
I can post some of them, if you want, to get you started
Have fun
Thread Starter
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5th Wheeling
Joined: Mar 2024
Posts: 37
Likes: 7
Backprobe the sensor or use a NGS to read the HEGO sensor output (watch it switch) or see if it is slammed rich
Meaning, see if the system is actually running rich or if it's just a sensor issue
The pinpoint tests for code 42 get hairy quick
I can post some of them, if you want, to get you started
Have fun
Meaning, see if the system is actually running rich or if it's just a sensor issue
The pinpoint tests for code 42 get hairy quick
I can post some of them, if you want, to get you started
Have fun
If you wouldn't mind, that would be great! Thank you!
Hotshot
Joined: Jul 2020
Posts: 10,270
Likes: 2,565
From: Near Salt Lake City
Read through these
You might not be able to do any of the ones that require the breakout box easily
We all learned to back probe the connectors
Ford hates that as it can damage the pins etc. but it works
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5th Wheeling
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FTE Legend
Joined: Jun 2006
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From: Ottawa, Ontario
A couple notes...
- The O2 sensor cannot be probed directly with a multimeter this reqires an oscilloscope or some other type of computer scanning tool.
- The injector wiring shown in the second pic isn't correct for this truck.
- This truck only has 1 O2 sensor.
- The O2 sensor cannot be probed directly with a multimeter this reqires an oscilloscope or some other type of computer scanning tool.
- The injector wiring shown in the second pic isn't correct for this truck.
- This truck only has 1 O2 sensor.
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