CODE 41 TO 92 - Fuel Pressure Regulator

[AnthonyR23]

Hi so I was getting error 41, but checked my fuel pressure regulator without vacuum and was getting more like 34 psi. So I increased it to 42psi area. Now I am getting error 92. So I tried to back it off, kinda sensitive 38 39ish. Now it's back to 41. Any tips?

 

[jrichker]

Code 41 or 91 Three digit code 172 or 176 - O2 sensor indicates system lean. Look for a vacuum leak or failing O2 sensor.

Revised 22-Jun-2009 to include 3 digit code and wiring for 94-95 5.0 Mustangs

Code 41 is a RH side sensor,
Code 91 is the LH side sensor.

Code 172 is the RH side sensor
Code 176 is the LH side sensor

The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

Testing the O2 sensors 87-93 5.0 Mustangs
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


Testing the O2 sensors 94-95 5.0 Mustangs
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a red/black wire) and 27 (RH O2 with a gray/lt blue wire). Use pin 32 (gray/red wire) to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

Testing the O2 sensor wiring harness
Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer.

The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

Make sure you have the proper 3 wire O2 sensors. Only the 4 cylinder cars used a 4 wire sensor, which is not compatible with the V8 wiring harness.

Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

If you get only code 41 and have changed the sensor, look for vacuum leaks. This is especially true if you are having idle problems. The small plastic tubing is very brittle after many years of the heating it receives. Replace the tubing and check the PVC and the hoses connected to it.
A secondary problem with only a code 41 is for cars with an intact smog pump and cats. If the tube on the back of the heads clogs up the driver’s side, all the air from the smog pump gets dumped into one side. This excess air upsets the O2 sensor calibration and can set a false code 41. The cure is to remove the crossover tube and thoroughly clean the insides so that there is no carbon blocking the free flow of air to both heads.

 

[AnthonyR23]

Jrichker, when I turned up the fuel pressure a bit code 41 went away and 92 came up, still with pesky 13, but I need to purchase a new iac motor. Used to have both 41 and 91, but got rid of 91. Replaced both 02's, the one on the right replaced again. So with the pressure up a bit I am getting just 92 and 13. So I am going to try to back of the pressure by .5 at a time. Until 92 goes away. Just hope 41 doesn't come back. Any way 13 could trigger either 92 or 41, and anything else I could check? I bought my mass air meter off ebay. Was said to be 70mm calibrated for 30lb injectors which I have. Just took the guys word for it. Hope that isn't an issue. Any other suggestions or reason's why I could be getting 92? Thanks

I've got the passenger kick panel off and am going to check both o2 sensor's at those pins tomorrow morning/today.

 

[strtrcr50]

Try setting the fuel pressure to 39-41 and clearing the computer(unhook battery and hold down brake pedal for 2-3 minutes) The computer adjusted the KAM(Keep Alive Memory) for the low fuel pressure and it will take a while to adjust back the other way. Better to just start at neutral KAM.

 

[AnthonyR23]

okay I'll try that, then I'll take it for a drive to canadian tire to get a new iac motor. If they have one.

 

[AnthonyR23]

Hi, so today first thing I did was reset the fuel psi to 39. Then took the negative battery cable off, and held down the brake for a minute or so. Then reconnected took it for a drive and came back and checked the error codes. Once again got 41 and 13.

So right now just concentrating on the 41. So what I was thinking rather than checking the voltage at the comp, is if I am not getting code 91 then it is probably safe to assume that the drive side 02 is okay. So I jacked the car up and took the good o2 off and switched it to the passenger side to see if I would still trigger code 41. And put another spare o2 on the passenger side. So I have now gone through all 4 o2's.

So took it for a drive and when I got back still got 41 and 13. So this time rather than messing with the fuel pressure, I reset the engine running codes, restarted and rechecked. This time got 92 and 13 again.

So this is where I'm at still 92 and 13. Called Canadian tire and Part Source but both would need to order the iac and its about 120. So I'll be off to the wreckers for that one. Anyways. Regarding 92. Might turn down the fuel pressure by 1 psi or so, reset the engine running codes again. And see what I get tonight.

What a frustration. To lean then too rich. Oh just a thought, I have a new 190lph in tank fuel pump that I haven't got on yet. Still using the stock one. Is there any way the fuel pump could be causing this trouble. Just dreading the job of changing it and the fuel filter.

Thanks, still any suggestions regarding now code 92 would be great!

 

[jrichker]

Are you sure the computer you have is an A9L or A9P?

Has the engine mounted EFI harness been modified in any way?

Are you running a cam with the HO firing order?

Do you have the orange O2 sensor ground wire grounded to the block or intake manifold?

Do you have the secondary power ground in place and it good condition?

 

[AnthonyR23]

It's definitely A9L. Only mod's are the two pins I had to move for the thermactor system, pink/black wire for pin 19 for fuel pump circuit, which may be giving me code 96 engine off, the only engine off code, and the mass air meter meter wires for the mass air conversion. But other than that no mods, I rechecked to make sure pin 19 was wired to the pink/black wire at the computer.

The engine mounted EFI harness has only been modified to move the temp sensor for my temp gauge to the back of the manifold, and modified to move the ect to the back of the manifold aswell. Other than that it is the same EFI harness unmodified.

I am running the powermax 2030 cam.

I have the orange o2 sensor ground wired to the firewall, I sanded down the firewall to make sure I got a good ground and changed the end of the orange wire to put a smaller end on it so it could be screwed into the firewall rather than using the big bolt end.

Secondary power ground in place, not really sure where that is so I'm not sure about that one. Could that have to do with code 96? Thanks

Still getting 13 and 92.

Is there any way I can check the IAC motor when it is off the vehicle, other than cleaning?

Thanks Jricher. Wondering if I should be putting that new 190 pump in. Just seriously dreading dropping the gas tank.

 

[strtrcr50]

I did my fuel pump in the street after getting the car down to 1/8 tank. Piece of cake, don't think twice. I put the 2 passenger side tires on the curb and didn't even have to jack the car up.

 

[AnthonyR23]

So, what I am going to do tomorrow, cause just throwing this out there, and my theory could be totally wrong, but I'm thinking maybe what could be causing the lean to rich codes may not be that I am setting my fuel pressure wrong, checked again today and it was around 39 but seems to fluctuate a bit.

So I'm thinking the pump may not be pumping a consistent amount of fuel, or could be running hard or at high load. So when I had the idle set to 39psi I'm thinking it could be possible that at idle it was getting enough fuel but during the test when the engine rev's up, the pump may not be able to supply or keep up enough pressure but at idle it may have been fine. So I'm thinking that could cause the lean condition code, then when I increased pressure probably too high for idle, I'm think when the engine revs up to check whatever it is checking and because the pressure is turned up to high it could be fine and not reading lean anymore, but when it goes to normal and idle it is running to rich. This theory could be totally wrong and it could be completely different. So just to be sure and because I have the adjustable anyways, first thing tomorrow morning, (still on holidays for this week), I am going to drop the gas tank enough to install the new fuel pump and while I'm at it I will install a new fuel filter.

Then I will reset my base idle (no vacuum to 39psi), and will install the extra IAC motor I finally found (thought I had one)... and hopefully I will never see 41, 91, 12, 92 or 13 ever again.

Will let you guys know how it goes.. Still have one question for jricher.... or anyone who knows....

Where is the secondary power ground... because I replaced my fuel pump relay, checked to make sure pin 19 was installed right from the mass air conversion to the pink/black wire from the relay. And am still getting engine off code 96. So thinking if this secondary power ground isn't grounded right, maybe that could be the problem with code 96? Who knows!

Thanks again guys!!

We'll see how it goes tomorrow!!!! What a headach! I don't mind working on my car, under the hood or wiring, but I don't like working under the car, like on exhaust etc. Just don't enjoy it!

 

[jrichker]

Some help on the grounding questions...

The secondary power ground is between the back of the
intake manifold and the driver's side firewall. It is often missing or
loose. It supplies ground for the alternator, A/C compressor
clutch and other electrical accessories such as the gauges.
Any car that has a 3G or high output current alternator needs
a 4 gauge ground wire running from the block to the chassis
ground where the battery pigtail ground connects.
The 3G has a 130 amp capacity, so you wire the power side
with 4 gauge wire. It stands to reason that the ground side
handles just a much current, so it needs to be 4 gauge too.

The picture shows the common ground point for the battery & extra 3G
alternator ground wire as described above in paragraph 2. A screwdriver
points to the bolt that is the common ground point.
The battery common ground is a 10 gauge pigtail with the computer ground
attached to it.

Picture courtesy timewarped1972