P1151 code?

cowboycowboy91 · Jul 25, 2015

I have been told its a vacuum leak and have search high and low and every nock and cranny and cannot find any vaccum leaks. Furthermore, my 3.0L ff engine spun a rod bearing last week, so I yanked it out and put another 3.0 out of the salvage into it with only 120000 miles give or take...and wouldn't you know it...the same darn code pops back up after clearing computer. So, this leads me to believe its a faulty O2 sensor on bank 2 upstream. I replaced it and cleared computer...same damn code came back a few miles later...I though hmmm, I'll change the inline fuel filter...same code came back. There is only 2 vaccum lines that I found that go off of the motor to an external place on the vehicle...the fuel vap line that goes to fuel tank and the 2 vacuum lines that go to your vacuum resevior for your heater and a/c crap inside the truck...every other vacuum line is on the engine itself and was replaced with the salvage engine...so, what the freaking crap is it? I am at my wits end and am getting frustrated. There is only 3 other external things that I see it could be...the MAF sensor, the intake air temp sensor, or the other 2 O2 sensors...I have suggested the MAF to people and they say NO WAY in hell is it that, its a vacuum leak! I have checked and checked though. I've used starting fluid, soap and water, and propane and CANNOT find a vacuum leak. I am sorry for this book long story, but I just wanted to give as much detail as possible and explanations of what I already did. What is you guys ideas? Also, fuel milage is horrible...like 9 or 10 mpg...

Earl43P · Jul 28, 2015

P1151 Ford - Lack of Upstream Heated Oxygen Sensor Switch Sensor Indicates Lean Bank 2

Read more: http://engine-codes.com/p1151_ford.html#ixzz3hEsY969l
Possible causes
- Faulty Oxygen Sensor
- Fuel pressure high or low
- MAF sensor dirty/defective
- Vacuum leak on engine
- Leaking fuel injector or fuel pressure regulator
- Faulty Powertrain Control Module

Read more: http://engine-codes.com/p1151_ford.html#ixzz3hEsli0IC

Did you check the PCV tubing and the elbow where it goes into the back of the valve cover/head? Those elbows are notorious for cracking.

RonD · Jul 28, 2015

Lean on one bank of a V6 or V8 engine would not be a main vacuum leak, it would show up on both banks.
P1151 also means O2 sensor on Bank2 wiring could be at fault, no switching means computer is not reading O2 sensor changing when computer changes air:fuel ratio.

Lean code means the computer is having to add more fuel to bank 2 than it should to get the O2 sensor's Oxygen level to .45v, .1volt = rich, .9volts = lean, .45v = just the right amount of oxygen in the exhaust
O2 reads oxygen in exhaust, which creates the voltage.
But O2 isn't even changing with P1151.

Computer uses 14:1 air:fuel ratio
It adds that amount of fuel to the air that was measured by the MAF sensor.
If there is not enough fuel added to air then not enough oxygen from the air will be burned up, and O2 will show .6 and up voltage, if too much fuel is added then most of the oxygen will be burned up and O2 will show .3v and lower.
Computer then adjusts the fuel injector open time(pulse width) to add more or less fuel, to get O2 to read .45
If it has to open injector too long or not long enough it will set a code fro that, Lean or Rich code

If MAF sensor was reading wrong then that would effect both banks, same for an upper intake vacuum leak.
Lower intake could leak on just one bank, one cylinder.

A dirty injector could be delivering less fuel on that bank, you might hear pinging if this was the case.

An exhaust manifold leak or any exhaust leak before O2, will suck in air, O2 sensor just sees the oxygen so lean voltage.

A misfire means no oxygen was burned, so lean voltage on O2.

Could even be a computer error, bad bank 2 circuit

But in all these the engine was never running lean, the lean code means computer had to add more fuel than it calculated based on 14:1 and it is telling the driver to check things out.

I would pull out the 3 spark plugs on bank 2(drivers side) and see if they tell you anything, if they are blackish so running rich then O2, O2 wiring or computer is the problem.
If one is different than the others then that cylinder is misfiring or is running lean and the cause of the extra oxygen in exhaust.
Check its fuel injector and coil pack.

cowboycowboy91 · Jul 30, 2015

RonD said:
Lean on one bank of a V6 or V8 engine would not be a main vacuum leak, it would show up on both banks.
P1151 also means O2 sensor on Bank2 wiring could be at fault, no switching means computer is not reading O2 sensor changing when computer changes air:fuel ratio.

Lean code means the computer is having to add more fuel to bank 2 than it should to get the O2 sensor's Oxygen level to .45v, .1volt = rich, .9volts = lean, .45v = just the right amount of oxygen in the exhaust
O2 reads oxygen in exhaust, which creates the voltage.
But O2 isn't even changing with P1151.

Computer uses 14:1 air:fuel ratio
It adds that amount of fuel to the air that was measured by the MAF sensor.
If there is not enough fuel added to air then not enough oxygen from the air will be burned up, and O2 will show .6 and up voltage, if too much fuel is added then most of the oxygen will be burned up and O2 will show .3v and lower.
Computer then adjusts the fuel injector open time(pulse width) to add more or less fuel, to get O2 to read .45
If it has to open injector too long or not long enough it will set a code fro that, Lean or Rich code

If MAF sensor was reading wrong then that would effect both banks, same for an upper intake vacuum leak.
Lower intake could leak on just one bank, one cylinder.

A dirty injector could be delivering less fuel on that bank, you might hear pinging if this was the case.

An exhaust manifold leak or any exhaust leak before O2, will suck in air, O2 sensor just sees the oxygen so lean voltage.

A misfire means no oxygen was burned, so lean voltage on O2.

Could even be a computer error, bad bank 2 circuit

But in all these the engine was never running lean, the lean code means computer had to add more fuel than it calculated based on 14:1 and it is telling the driver to check things out.

I would pull out the 3 spark plugs on bank 2(drivers side) and see if they tell you anything, if they are blackish so running rich then O2, O2 wiring or computer is the problem.
If one is different than the others then that cylinder is misfiring or is running lean and the cause of the extra oxygen in exhaust.
Check its fuel injector and coil pack.

Yeah, it could be alot of those things. I changed in new plugs before I started the new engine ip, but that doesn't mean that they aren't fouled up now or are displaying signs of a bad cylinder...What really gets me is that BOTH engines are showing the exact same code...that is possible that they both had the same problem, but I tend to think its elsewhere besides the engine. Possibly the air induction or exhaust. The cat has been cut open and very sloppy welding job repatching it..why is it cut open? Was it stopped up and some moron decided to cut it open and knock the guts out? Anyways, I appreciate your advise. I'll pull the plugs and also test the coil packs...thanks again.

ratdude747 · Jul 30, 2015

^You sure the guy didn't gut the cat (I.E cut the platnum mesh out and weld it back together to "look" legal? That's what that's screaming to me.

Makes me think that that may be at least part of the issue. Here's a test: use an infrared thermometer (or the like) and measure the input and output temperatures when warmed up. The outlet should be 100 degrees F hotter than the inlet; if not, the cat isn't doing it's job.

sebastian323 · Aug 2, 2021

RonD said:
Lean on one bank of a V6 or V8 engine would not be a main vacuum leak, it would show up on both banks.
P1151 also means O2 sensor on Bank2 wiring could be at fault, no switching means computer is not reading O2 sensor changing when computer changes air:fuel ratio.

I have this same code, and the driver side O2 sensor sems to share wiring with the VSS, which i know for a fact has failed wiring. Im guessing the harness failed somewhere under the car by the side of the transmission ? car is a 1996. Are wiring failures common at that age ?

Also can I swap the O2 sensor from bank 1 with bank 2 and see if the problem migrates to verify the oxygen sensors are good ?

RonD · Aug 2, 2021

Yes, you can swap around O2s, Rangers used the same type of O2 sensors in all positions

20+ year old wiring can fail, especially near heat sources like exhaust

O2 sensor are the only sensors that will wear out, they use a chemical to detect Oxygen and it gets used up, MPG starts to go down as this happens, but no codes until they completely fail

So changing O2s is free in the long run since you will save money on fuel as they start to go lean
100k miles or 12 years is when you should change O2 sensors

P1151 code?

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