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Discussion Starter #1
First I want to say just about everything I’ve fixed so far on our new-to-us T-Bird cane from suggestions, and past posts here. This site has been a huge help! I did read a lot of old posts regarding the code I’m having, but nothing seems to have a solution, nor my exact symptoms..

Since day 1 the car has been throwing a P1131 code, which has to do with the system detecting a lean condition on Bank 1 (you can physically smell it when standing beside the passenger side sometimes). The car also idles a bit rough.

Spark plugs, and oil are the first things I did when I got the car running, so I don’t think spark plugs are the idle issue. Car does drive rather fine, showing very little signs of issue aside from the moaning sound that users here suggest is a faulty IAC. I took that out, and cleaned it, nothing changed.

Went vacuum leak hunting.. Found a cluster f*** of a hack job under the bumper (passenger side, below air intake) where two hoses weren’t even hooked up. Reconnected it all, checked for further leaks, no progress. (.... except for a slight gain in MPG’s)

Cleaned the MAF sensor.. Still no progress.

Put in a brand new upstream 02 sensor on Bank 1. Still no progress.

I feel like I’m chasing a needle in the hay stack at this point, and currently do not have money to throw at a mechanic so I’m figuring this out at home the best I can. The rough idle isn’t what I’d call heavy, but certainly noticeable, while the lean/rich smell is evident sometimes coming from the passenger side f the car.

The only other odd thing that has happened was today while on the highway the car stuttered a bit noticeably while cruising at 65, but the RPM gauge didn’t bounce around at all, nor did the speed decrease. Not sure if this is a side effect from whatever is causing the P1131 code.

Any suggestions are greatly appreciated!
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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If you're certain there are no vacuum leaks, running the car with the MAF sensor unplugged will help determine if the MAF sensor is in spec. If the car runs better with the sensor unplugged, it may mean it has an electrical fault and need replacement.

You can also progressively search for vacuum leaks if you disconnect all the vacuum hoses from the manifold (brake booster/HVAC feed, EVR solenoid (red/green), EVAP, and PCV, then plug each of the lines with some capped off spare hose, then reconnect each system one at a time and observe the behavior. You may also want to check the EGR valve to be sure it isn't leaking exhaust into the intake when closed either. The EVAP lines are the most common to leak though, just because of the sheer length of the lines in total.
 

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Discussion Starter #3
The EVAP canister (I believe it was) had been disconnected when I pulled the wheel liner out while following hoses.. I put new hoses in there, but who knows how long the previous owner drove with it like that.
 

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Kudos on your persistence in getting your 96 LX to perform like it should.

An engine running lean will run hotter than spec which causes production of NOx that when mixed with the moisture produces nitric acid and the smell.

My 95 LX gave me a P1131 and it went away after I replaced the upstream and downstream O2 sensors. Although it came back a couple months later after some serious highway driving, cleared it and it hasn't come back and it's been over a year.

Could be an EGR issue... the engine wants more EGR to quench the cylinders and reduce temperature. But why no P04xx codes I don't know. I don't know the configuration of the EGR in a 96 4.6 as compared to the 95 like I have, maybe carbon in the throttle body plenum or EGR passages aren't allowing full impact to the left side of the engine?

Have you checked any scan data? Do the left bank fuel trims correspond to the lean trouble code, i.e., fuel being added to compensate for the system sensing lean?
 

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What year is the T-Bird? Please add it to your sig. 94-95 EGR issues are a lot different than 96-97.

Did you replace the EVAP hoses behind the bumper, or just hook them back together? They become disconnected because they fall apart. They need replaced.

You had to have had a code P1443 before connecting the hoses back. It is possible they are hooked up backwards. Does the gas cap have a strong vacuum when you remove it?

Regarding the spark plugs - what number plug did you put in? A misfiring plug could cause the sputter. Maybe a plug wire isn't pushed all the way on.

You can test the EGR by applying a vacuum to open it at idle with a Mighty-vac. If the sputtering idle gets worse, it's fine. If the sputtering idle doesn't change, then it's bad. They are not supposed to open at idle, and will make the car run rough if they do.

Al
 

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Something I also discovered recently is that the EGR solenoid hoses are top/bottom specific. I had mine swapped around which was giving the EGR full vacuum at idle. Try pulling the vac line off the EGR and blocking the hose with your finger, if the idle smooths out you will want to swap the hoses going in and out of the solenoid.
 

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Discussion Starter #7
Kudos on your persistence in getting your 96 LX to perform like it should.

An engine running lean will run hotter than spec which causes production of NOx that when mixed with the moisture produces nitric acid and the smell.

My 95 LX gave me a P1131 and it went away after I replaced the upstream and downstream O2 sensors. Although it came back a couple months later after some serious highway driving, cleared it and it hasn't come back and it's been over a year.

Could be an EGR issue... the engine wants more EGR to quench the cylinders and reduce temperature. But why no P04xx codes I don't know. I don't know the configuration of the EGR in a 96 4.6 as compared to the 95 like I have, maybe carbon in the throttle body plenum or EGR passages aren't allowing full impact to the left side of the engine?

Have you checked any scan data? Do the left bank fuel trims correspond to the lean trouble code, i.e., fuel being added to compensate for the system sensing lean?
It just throws either a single, or two P1131 codes. No data seems to come with it.

I can try to clean the EGR valve and see if that makes any difference. That or just buy a new one. Car is out with my better half right now as I write this so I’ll post a reply regarding how that goes later today.
 

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Discussion Starter #8
Things we've done so far:

EGR Valve (New): original was gunked up, and sticking. Still rough idling, and P1131 code
IAC Valve (Junkyard): Eliminated moaning noise.
New PCV valve: No difference in anything (edit my better half reported the rough idle seems to be noticeably better)
Various new hoses: Still rough idling, and P1131 code
New Spark plugs: Still no difference

Gonna keep hunting. Not bummed out over it not being sorted out yet because not only am I learning a TON about this engine set up, but as I dig around i'm finding things that do look like they need to be replaced.
 

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I just went through hell tracking down a P1131 and P1130 code issue.

Bank left and right lean.

Car ran perfectly fine. But was throwing a SEL light and codes so no emission test and no tags.

The actual problem was not what you think.

My first Guess was a vacuum leak. And while I found and repaired a few pin holes in the process none where large enough to actually cause a lean condition.

Bought a Smoker and Smoked the entire intake system. Nothing although the EGR showed the tiniest wisp of smoke. Some sources said that was normal. Others said not. Replaced the EGR. No difference.

Right about now the ever popular Misfire detected Cylinder #2 and #4 shows up.

On go new wires. And that’s fixed. A lean condition CAN cause a misfire. But at that point the car is normally running like crap and there’s a obvious vacuum leak. Not the case here. It’s just setting codes and still running fine. Even the misfires was were undetectable to the seat of the pants.

At this point I’ve replaced some dry rotted hose to the PCV on both the valve cover hose. And the runs to the PCV valve. The molded plastic line from the back of the throttle body to purge valve hardline on the passengers fender. Smoked the whole system. Replaced the EGR which had never tripped a code. Cleaned the MAF. Misfire codes gone but the lean codes remain. Cleaned the injectors. Verified fuel pressure. All good.

It’s tripping the lean code because the fuel trims are over 20%. In other words it’s still running fine and likely within emissions. But the computer is having to over correct. Somethings not right.
There’s one other bit of odd behavior.

After tripping the normal P1000 system readiness code everything is checking in but the 02 Sensers and the Heated 02 sensors. They’ve checked in on prior resets and now they are just taking their time. So the 02 sensors are definitely suspect.

But... The Catalyst system IS checking in ready. If there’s a issue with the O2 sensors up and downstream why is it not tripping a O2 sensor fault. There’s no way to check in the Cats without the upper and lower O2s being read by the computer. So they are there and working. Perhaps out of spec but not tripping O2 sensor codes either.

One night I started the car to take it for a short spin and boom. The miss is back. And it’s BAD. And I also get coolant sensor high and intermittent codes. I reset the computer and restart the car. And the miss and sensor codes are gone. Go for a ride and as I turn into the drive the mis comes back.

So that Saturday I replace my plugs with new Motorcraft iridium's and redo all the plug wires. And the misfire is gone. Smooth as silk.

A buddy’s a retired master tech and we check the 02’s and the fuel trim by injecting propane into the intake. 02 sensor voltages are responding and the fuel trims drop slightly. So the O2’s are working but not checking in with the PCM as ready.

And all of a sudden the Misfire #2 and #4 for codes come back and the cars idling rough. New plugs and new wires. I’ve got a spare coil pack and at this point I’ve got the secondary ignition wiring committed to memory so I swap the drivers side coil pack and viola! Misfires gone. It’s a coil pack.

I mention the engine coolant sensor tripping a code for intermittent and circuit voltage low. There’s two actually. One for the gauge and one for the PCM. We’re not sure which so we turn the car off and I pull the plug on the passenger side sensor and it doesn’t trip a code. Put it back and pull the other sensor and get the Engine Coolant Sensor low code. Plug that back in and pull the passenger side and verify it’s not tripping a code and that it’s for the gauge sender.

The codes have been reset and there’s nothing but the lean codes and a swear I smell coolant. And I do. The reservoir overflows. Still no coolant sensor code but the electric fan never came on. And that fan is controlled by the coolant sensor. Let it cool down and reset the codes. Still nothing.

Run to ORiellys for a sensor but it’s not in stock. Nor in running distance. They will have it noon Sunday.

Put in the new coolant sensor and reset the PCM and I’m still only show the lean codes. With one difference.

The Fuel Trims are dropping like rocks. Short term drops. Long term drops. Right into specs. I reset the codes one last time. Restart the car and the fuel trims are still normal.

Take it for a spin and they stay normal. All the subsystems check in quickly and report ready.

My P Codes for Bank Left and Right Lean where due to a faulty coolant sensor. Not a vacuum leak or hoses or a dirty MAF.

In retrospect what was going on was the coolant sensor was in spec enough to run well and not throw a code for well over a month. And the car was never quite going into closed loop mode because of it. The cats checked in but the O2 sensors did not because it wasn’t in closed loop. Since it was in open loop mode it was running in cold start or artificial enrichment. It wasn’t running lean at all. The fuel trims where over 20% because it wasn’t in closed loop mode and running enriched.

Check your fuel trims. Anything over 20% will trip a cylinder bank lean OBD II code because the PCM thinks it’s running lean. Even if it’s not.

I opted for the motorcraft sensor at 30.00 bucks but there are other choices starting at 15.00.

If your P1000 readiness states are slow or erratic checking in or not checking in at all. You might just want to replace what’s likely the single cheapest part or sensor and see what happens.

Very long post. Sorry about that. But if I said throw a coolant sensor at a vacuum leak y’all would laugh. Especially if the lean code was all you had for months and the coolant sensor itself was not tripping any type of code during that time.



Scott
 

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A lean condition CAN cause a misfire.
Actually, in this case t's the other way around. When the car misfires, it reads lean on a wideband o2 gauge. That's what is causing the lean code. You can really see it if you put a car on a two-step (which is programmed misfire) to launch it at the dragstrip - the gauge reads full lean.

Al
 

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Sorry Al, Scott is right - if the car is running lean, it sure can misfire. Same thing happens in aircraft engines and is something pilots are cautioned about (and experience) in training. Lean it out too much and it will run rough, stumble, misfire, and stall. Lean combustion is hotter combustion, and reduces tolerance for spark thereby causing additional intolerance for combustion occurring at the proper time in the stroke. Too lean, too hot, and pre-ignition galore. Depending on how the car misfires, it can also show up as rich due to uncombusted fuel in the exhaust.
 

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I just went through hell tracking down a P1131 and P1130 code issue.

Bank left and right lean.

Car ran perfectly fine. But was throwing a SEL light and codes so no emission test and no tags.

The actual problem was not what you think.

My first Guess was a vacuum leak. And while I found and repaired a few pin holes in the process none where large enough to actually cause a lean condition.

Bought a Smoker and Smoked the entire intake system. Nothing although the EGR showed the tiniest wisp of smoke. Some sources said that was normal. Others said not. Replaced the EGR. No difference.

Right about now the ever popular Misfire detected Cylinder #2 and #4 shows up.

On go new wires. And that’s fixed. A lean condition CAN cause a misfire. But at that point the car is normally running like crap and there’s a obvious vacuum leak. Not the case here. It’s just setting codes and still running fine. Even the misfires was were undetectable to the seat of the pants.

At this point I’ve replaced some dry rotted hose to the PCV on both the valve cover hose. And the runs to the PCV valve. The molded plastic line from the back of the throttle body to purge valve hardline on the passengers fender. Smoked the whole system. Replaced the EGR which had never tripped a code. Cleaned the MAF. Misfire codes gone but the lean codes remain. Cleaned the injectors. Verified fuel pressure. All good.

It’s tripping the lean code because the fuel trims are over 20%. In other words it’s still running fine and likely within emissions. But the computer is having to over correct. Somethings not right.
There’s one other bit of odd behavior.

After tripping the normal P1000 system readiness code everything is checking in but the 02 Sensers and the Heated 02 sensors. They’ve checked in on prior resets and now they are just taking their time. So the 02 sensors are definitely suspect.

But... The Catalyst system IS checking in ready. If there’s a issue with the O2 sensors up and downstream why is it not tripping a O2 sensor fault. There’s no way to check in the Cats without the upper and lower O2s being read by the computer. So they are there and working. Perhaps out of spec but not tripping O2 sensor codes either.

One night I started the car to take it for a short spin and boom. The miss is back. And it’s BAD. And I also get coolant sensor high and intermittent codes. I reset the computer and restart the car. And the miss and sensor codes are gone. Go for a ride and as I turn into the drive the mis comes back.

So that Saturday I replace my plugs with new Motorcraft iridium's and redo all the plug wires. And the misfire is gone. Smooth as silk.

A buddy’s a retired master tech and we check the 02’s and the fuel trim by injecting propane into the intake. 02 sensor voltages are responding and the fuel trims drop slightly. So the O2’s are working but not checking in with the PCM as ready.

And all of a sudden the Misfire #2 and #4 for codes come back and the cars idling rough. New plugs and new wires. I’ve got a spare coil pack and at this point I’ve got the secondary ignition wiring committed to memory so I swap the drivers side coil pack and viola! Misfires gone. It’s a coil pack.

I mention the engine coolant sensor tripping a code for intermittent and circuit voltage low. There’s two actually. One for the gauge and one for the PCM. We’re not sure which so we turn the car off and I pull the plug on the passenger side sensor and it doesn’t trip a code. Put it back and pull the other sensor and get the Engine Coolant Sensor low code. Plug that back in and pull the passenger side and verify it’s not tripping a code and that it’s for the gauge sender.

The codes have been reset and there’s nothing but the lean codes and a swear I smell coolant. And I do. The reservoir overflows. Still no coolant sensor code but the electric fan never came on. And that fan is controlled by the coolant sensor. Let it cool down and reset the codes. Still nothing.

Run to ORiellys for a sensor but it’s not in stock. Nor in running distance. They will have it noon Sunday.

Put in the new coolant sensor and reset the PCM and I’m still only show the lean codes. With one difference.

The Fuel Trims are dropping like rocks. Short term drops. Long term drops. Right into specs. I reset the codes one last time. Restart the car and the fuel trims are still normal.

Take it for a spin and they stay normal. All the subsystems check in quickly and report ready.

My P Codes for Bank Left and Right Lean where due to a faulty coolant sensor. Not a vacuum leak or hoses or a dirty MAF.

In retrospect what was going on was the coolant sensor was in spec enough to run well and not throw a code for well over a month. And the car was never quite going into closed loop mode because of it. The cats checked in but the O2 sensors did not because it wasn’t in closed loop. Since it was in open loop mode it was running in cold start or artificial enrichment. It wasn’t running lean at all. The fuel trims where over 20% because it wasn’t in closed loop mode and running enriched.

Check your fuel trims. Anything over 20% will trip a cylinder bank lean OBD II code because the PCM thinks it’s running lean. Even if it’s not.

I opted for the motorcraft sensor at 30.00 bucks but there are other choices starting at 15.00.

If your P1000 readiness states are slow or erratic checking in or not checking in at all. You might just want to replace what’s likely the single cheapest part or sensor and see what happens.

Very long post. Sorry about that. But if I said throw a coolant sensor at a vacuum leak y’all would laugh. Especially if the lean code was all you had for months and the coolant sensor itself was not tripping any type of code during that time.



Scott
Actually, in this case t's the other way around. When the car misfires, it reads lean on a wideband o2 gauge. That's what is causing the lean code. You can really see it if you put a car on a two-step (which is programmed misfire) to launch it at the dragstrip - the gauge reads full lean.

Al
Some back ground.

The lean code showed up well over a year ago and was the sole code(s)for a number of months before the car was stored. It had newer plug wires at that time I should add. No misfire codes at all. And I drive it most of the summer and part of the winter with just the P1130 and P1131.

The cars had a few vacuum leaks over the years due to mice and and a minor harness repair for the same reason.

The bad module and Miss condition showed up very late in the diagnostic stages and where completely unrelated to the lean codes in this case. The bad module was entirely coincidental.

Having owned 3 1997 30th Anniversaries with the same driveline and each having got new plug wires at least once and a module or two across a accumulated total of 250-300K I’m fairly well versed in Misfire codes. To well versed. My experience indicates that your lucky to get 24-36 months out of a set of Motorcraft wires. The Misfire detection system works very well and will pick up misfires before you feel them.

In this case pretty much everything had been ruled out and I was getting ready to get the car off the ground to meter each 02 individually. They are original as where the plugs. The plugs had 60K and we all know that under most conditions they will make it to 100K easily.

Given the amount of time that only the P113x codes had been in place and the fact that there had been no prior misfire codes I’m simply ruling that out. The wires and plugs where done because they where the low hanging fruit and the replacements had been on there for more than 2 years and in my prior experience that was a good enough time to replace them.

So while I’m not going to argue that a Misfire can’t cause a lean code in this particular case that was not the cause. And the car had sufficient run time with out Misfire codes before the module got flakey to pretty much rule that out.

And of course a major lean condition will cause a Misfire on any vehicle carbed or EFI. But a major leak of that nature does not go undiagnosed for long and normally there will noticeable drivability issues and overheating.

Not the case here. Everything was normal but the fuel trims were out of range. And several subsystems where slow to check in or not checking in at all.

Every bit of work done did nothing to reduce the fuel trims.

The effect of the new coolant sensor was immediate and obvious. I was looking at the fuel trims when I started the car and was frankly surprised to see them immediately drop and stay in the normal range. And suddenly all the readiness sensors checked in.

I put well over 400 miles in trying to get sensors to check in over that month.

The thing is most people are not going to immediately suspect a coolant sensor causing a lean code. Especially if there’s been no history of prior coolant sensor codes. Right up till the very end the coolant sensor was reporting engine temperature in Dash Command correctly.

It’s one of the cheapest sensors on the engine. I’m only suggesting that if the lean code is persistent and normal troubleshooting steps aren’t finding the root cause. And especially if the sub systems are slow in showing readiness or not showing readiness at all.
Maybe tossing a 15.00 part at the problem or subbing a known working sensor at the problem might help.
 

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Didn’t mean to quote half the forum in my reply. I didn’t mean to quote anything at all.

New Forums gonna take some getting used too.
 

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Scott is right - if the car is running lean, it sure can misfire.
I'm sure it will.

What I said was a misfire would show up as a lean spike on an air/fuel ratio gauge - I've seen it many times. I thought maybe that was why he was getting the code for running lean.

EDIT: I thought he had said the problem was a bad coil pack. Now I see it was a coolant temp sensor. It was a lot of reading, lol!

Al
 

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Discussion Starter #16
Still getting a lean issue, and the same P1131 code...

So far we've replaced:
  • Bank 1 O2 sensor upstream (exactly the reason P1131 is supposed to be for)
  • vacuum hoses
  • EGR valve
  • IAC valve
  • PCV (and grommet)
  • hooked up the EVAP canister, and hoses that the previous owner disconnected for whatever reason
  • tested EVAP box... No issues
We did bring it to a mechanic who we know personally.. He hooked it up to a really expensive scanner that picked up the same P1131, but also said the Bank 2 CAT was bad which didn't make any sense because all the issues are on Bank 1, nor is it throwing any codes for the Bank 2 sensors. He suggested maybe the PCM is bad, and throwing codes for things that aren't even broken. Car runs, and drives great with the exception of some mild rough idle, and the stinky lean smell that comes, and goes.
 

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I'm not getting what you mean by "lean smell". Is it a rotten egg smell?

Al
 

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How are you getting "lean" out of a gas smell. Raw gas?

Or maybe you have the same thing I do: a gasoline smell from the outside the passenger side after running the car. I am going to fill the tank tomorrow to see if it is in fact coming from the gas filler neck.

Because of the location of the gas tank under the seat, there are several rubber hoses to deal with, and apparently they wear out.

Al
 

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See post #9 above.

There are 8 pieces of hose in that line.
 
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