Hesitation

[michibronc]

Hi All,

I've got a 96 with 108,000 miles and the 5.8 L engine. When I spend a long time on the expressway, I occasionally get a p1131 code which will usually shut itself off after a few cycles. That code is saying lean for bank 1 of the engine which I believe is the passenger side.

Just this past weekend I was on my way to the north country to ride trails. I noticed after a few hours of driving on the highway that the truck was chugging very slightly and if I gave it gas it would hesitate a little but then accelerate fine. I noticed it on the trails also, it doesn't seem to matter if I'm going slow or fast, only that I'm cruising.

My fuel filter is less than a year old. The code may or may not be related to the symptoms. I can change the upstream oxygen sensor for starters, but don't want to do that if I don't really need to. Any advice where to start looking?

 

[miesk5]

yo M!

P1131 - Lack of HO2S-11 Switch, Sensor Indicates Lean A HEGO sensor indicating lean at the end of a test is trying to correct for an over-rich condition. The test fails when the fuel control system no longer detects switching for a calibrated amount of time.

These codes usually do not indicate a problem with the O2 sensor. Rather, the O2 sensor is correcting rich due to an overly lean air/fuel ratio. Check:

Base Engine Idle, EGR, Fuel System and Air Induction System.

Bank 1 refers to the bank of cylinders containing Cylinder #1. that is Passenger Side

Sensor 1 refers to the O2 sensor closest to the exhaust manifold.

Sensor 2 refers the O2 sensor downstream of the catalytic converter.

Damaged HO2S

Short to VPWR in harness or HO2S

Water in harness connector

Open/Shorted HO2S circuit

Corrosion or poor mating terminals and wiring

Fuel System:

Excessive fuel pressure

Leaking/contaminated fuel injectors

Leaking fuel pressure regulator - Test; "...Pull the red vacuum line & check for gasoline...There shouldn't even be the ODOR of gas in it."

Source: by Steve83

Low fuel pressure or running out of fuel

Vapor recovery system

Induction System:

Air leaks after the MAF - check air tubes, Throttle body, sometimes bolts loosen

Vacuum Leaks

Exhaust leaks before or near the HO2S(s)

PCV system - check valve & hose

Improperly seated engine oil dipstick

EGR System:

Leaking gasket

Stuck EGR valve - should have other codes

Leaking diaphragm or EVR

Base Engine:

Oil overfill

Cam timing

Cylinder compression

Damaged PCM - LESS likely

A fuel control HO2S PID switching across 0.45 volt from 0.2 to 0.9 volt indicates a normal switching HO2S.

Wiring Diagram in a 96 5.0 & 5.8 (Fuse shown is **** fuse #5 in engine compartment Power Distribution Box) Source: by miesk5 at Ford Bronco Zone Forums

 

[BroncoJoe19]

Tips for Checking for vacuum leaks.

Some of the sensors and some of the actuators either read the amount of vacuum, or use vacuum to move controls, therefore it is important to the proper functioning of the engine that your vacuum system is fully intact. Otherwise one may get codes falsely indicating that there is a problem with a controller/actuator, or a sensor when in reality it is caused by a lack of vacuum.

Look at your rubber vacuum hoses (they are about 1/4 - 3/8 inches in diameter, if they are dry rotted or cracked, replace them. IF they slip on/off of their connectors too easily, they may have stretched out a little bit, cut the ends off, and put them back on.

Courtesy Miesk5 BroncoZone.com. You may listen for a leak. Sometimes using a cut off piece of garden hose is a good aid to listen with. Sometimes a cardboard tube (like from gift wrapping paper) is helpful. Just remember that whenever you stick your head inside a running engine compartment, that you are not wearing any loose clothing or jewelry that can get caught.

Another suggestion is to use a spray can of carb cleaner and spray around the bottom of the intake manifold, and the base of the throttle body assembly. IF there is a leak, you should hear a change in your engine.

Keep a fire extinguisher handy, or use water instead of carb cleaner (it works, but not as well.) Be aware that if you use water and the wires get wet and it runs worse... your wires may be bad, and the water is allowing them to arc instead of jump the gap of the spark plug.

Another suggestion is: to take a propane torch, turn it on (but don't light it) and move it over the vacuum hoses and connections. The engine RPM's will increase if there is a leak and the propane gets sucked in.

Courtesy of TheOldWizard fordforumsonline.com ... Don't forget to remind folks to check the PCV valve, hose and grommet !

Courtesy Ramnasal ford-forums... Clamp off the hose that runs to the vacuum booster (brake booster) or pull it and plug it. It is possible that the diaphram on the inside of the booster may go bad and cause a vacuum leak.

And one more place that is not always obvious is that the vacuum reserve canister in older vehicles sometimes rots out and leaks, but rarely gets checked. In older vehicles it looks like a metal juice can, in newer vehicles it is made of plastic.