Never-ending CEL story - What now?

In a seemingly never-ending effort to clear the CEl and more importantly to get my 2.5l Duratec V6, ATX Mystique to pass NYS inspection, I've so far initiated the following repairs:

• New MAF sensor (cleaning didn't clear original codes)
• New UIM/LIM gaskets
• New F/I O-rings
• New Gaskets for TBI, EGR, IAC
• New post-cat O2 Sensors (banks 1 and 2)
• New Spark Plugs
• New fuel filter

For historic perspective, initially, I originally had these codes:

• P0141
• P1131
• P1151

I was going to replace the upstream O2 sensors, then I found this Ford TSB
(see attached), which advised that when codes for both banks are triggered it is rarely bad sensors. It advised me to disconnect the MAF sensor and try driving the car. Doing so noticably improved performance, and I had already tried cleaning the MAF sensor, so I purchased a refurb ($77.00). I removed the bank 2 downstream sensor, which was obviously no good. I replaced both downstream O2S (@$48 ea.). After clearing the CEL, It returned again after a little drive. At that point I took the car to a repair shop.

They charged me $150.00 to read the codes, supposedly do a fuel pressure check and a 'smoke' test. They told me the fuel pressure was okay but I had massive vacuum leaks (LIM/UIM gaskets and just about everything else according to them). They quoted me $1000.00 to repair the vacuum leaks, etc. and would not even guarantee that the CEL codes would clear. I paid up for the diagnosis and did the repairs myself with the aid of the excellent 'how-to' provided on this site.

Wow! Huge improvement in the driving and idle smoothness. I'd forgotten just how nice the car ran when it was new. However, after a day of mixed driving the CEL lights up again. This time it's reporting the following codes:

• P1131
• P0171
• P0174

The Autozone dude told me this could be a bad fuel pump(?) and tried to sell me one for $100.00. Unfortunately, I can't afford to keep throwing parts in without definitive diagnosis and it's virtually impossible to find a truly honest repair shop in my area. I'm considering bringing it to the dealer at this point, although I'm not that confident of their competence either. At this point, I've spent hundreds of dollars and a huge amount of time just to pass the NYS inspection so I can re-register my car, even though car seems to run fine! The obvious next step would be to replace the O2 pre-cat sensors and the fuel pump which would run another $300.00 in parts. My problem is what do I have to do at this point to definitively know if this will finally clear the CEL? Any ideas as to how to put this saga to an end would be appreciated.

[FONT=arial,verdana,helvetica,sans-serif]P1131[/FONT][FONT=arial,verdana,helvetica,sans-serif]Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1. [/FONT]

[FONT=arial,verdana,helvetica,sans-serif]P0171[/FONT][FONT=arial,verdana,helvetica,sans-serif]System Too Lean - Bank No. 1. [/FONT]

[FONT=arial,verdana,helvetica,sans-serif]P0174[/FONT][FONT=arial,verdana,helvetica,sans-serif]System Too Lean - Bank No. 2. [/FONT]

sounds like its time for a new upstream O2 sensor on bank #1. if you want to confirm this swap this sensor with the bank #2 sensor. if the sensor is at fault you will get the same code but for bank 2.

seems you have covered everything else already that would cause both banks to display lean codes.


and for good measure

[FONT=arial,verdana,helvetica,sans-serif]P0141[/FONT][FONT=arial,verdana,helvetica,sans-serif]Downstream Heated Oxygen Sensor Heater circuit fault - Bank No. 1. [/FONT]

[FONT=arial,verdana,helvetica,sans-serif]P1131[/FONT][FONT=arial,verdana,helvetica,sans-serif]Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1. [/FONT]
[FONT=arial,verdana,helvetica,sans-serif]P1151[/FONT][FONT=arial,verdana,helvetica,sans-serif]Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2. [/FONT]

you might actually want to replace both upstream sensors since you previously had a code for them.

I found out the hard way also while chasing a CEL that the O2 sensors are "second run" triggered, meaning if you replace one and clear the code and drive it, it'll stay off, but then come back the 2nd time you drive it. My fault was a shorted 12V line to the O2 sensor so it wasn't getting power, even though I could clear the code. A possibility?

These are the AutoZone computer readouts:

P1131:
Definition: Lack of bank 1 O2 transitions - lean
Explanation: ECM detected bank 1 O2 at its lean limit.
Probable cause:

1. misfire on bank 1
2. vacuum leak affecting bank 1 only
3. fuel injector problem bank 1
4. engine mechanical condition

P0174:
Definition: Fuel trim bank 2 condition.
Explanation: ECM detected a rich or lean air/fuel ratio on bank 2
Probable cause:

1. If bank 1 and 2 are set together suspect a fuel pressure condition or MAF sensor fault
2. Oxygen sensor defective
3. Ignition misfire-repair
4. Fuel injector problem
5. Engine mechanical condition

P0171:
Definition: Fuel trim bank 1 condition.
Explanation: ECM detected a rich or lean air/fuel ratio on bank 1
Probable cause:

1. If bank 1 and 2 codes are set together suspect fuel pressure condition or MAF sensor
2. Oxygen sensor defective
3. Ignition misfire condition
4. Fuel injector problem

Am I supposed to interpret from this that if BOTH banks set the code together (P0171, P0174) it's either fuel pressure of MAF sensor? It seems to me that these codes by themselves really don't tell too much, since there are several interpretations. Is my only recourse to keep buying new parts until it goes away?

Scorpion8 said:

I found out the hard way also while chasing a CEL that the O2 sensors are "second run" triggered, meaning if you replace one and clear the code and drive it, it'll stay off, but then come back the 2nd time you drive it. My fault was a shorted 12V line to the O2 sensor so it wasn't getting power, even though I could clear the code. A possibility?

Click to expand...

I guess I could test the voltage on the upstream sensors. I checked the O2 heater fuse and it was okay. If it was shorted wouldn't that blow the fuse? Man, after reading the horror stories about getting to the firewall-located sensor, I'm not looking forward to it. I'm also not looking forward to coughing up $140 dollars for the sensors then seeing that [expletive deleted] CEL light up again.

abyssius said:

I guess I could test the voltage on the upstream sensors. I checked the O2 heater fuse and it was okay. If it was shorted wouldn't that blow the fuse? Man, after reading the horror stories about getting to the firewall-located sensor, I'm not looking forward to it. I'm also not looking forward to coughing up $140 dollars for the sensors then seeing that [expletive deleted] CEL light up again.

Click to expand...

Turned out my O2 sensor was okay, but a coolant hose had melted thru the wiring harness at a hidden spot and cut the connection. There was no metal-contact to short it out. I was assisted in my troubleshooting and prodded to check the 12V supply voltage on the 4-wire lead. Of course this is only an O2-sensor help.... not all the rest of those symptoms.

Continued lean conditions can come from several sources. Vacuum leaks are common between the intake and PCV valve but can occur at other places in the PCV system. Test your crankcase pulldown. Air can enter the EGR system also. Make sure exhaust and EGR connections are tight and there are no holes on the EGR supply tube. The ECT sensor has a direct effect on mixture so test it with an ohmmeter. Fuel pressure should be measured at idle and at load to see if the fuel pump is good with no restrictions.

A decent scan tool is also a good investment.

Rogerm60 said:

Continued lean conditions can come from several sources. Vacuum leaks are common between the intake and PCV valve but can occur at other places in the PCV system. Test your crankcase pulldown. Air can enter the EGR system also. Make sure exhaust and EGR connections are tight and there are no holes on the EGR supply tube. The ECT sensor has a direct effect on mixture so test it with an ohmmeter. Fuel pressure should be measured at idle and at load to see if the fuel pump is good with no restrictions.

A decent scan tool is also a good investment.

Click to expand...

Everything leads to a vacuum leak somewhere. I'm worried that I didn't torque the UIM and LIM bolts enough. The spec said 10 - 12 nm. My torque wrench barely provided any pull at all to reach that extremely low setting. I can see parts of the gaskets and they don't look very compressed. However, there is no 'hissing' sounds and I sprayed carb cleaner at various points of the junction and didn't see or hear anything. I replaced the PCV valve and checked the 'elbow tube". The PCV is tight and I replaced the small hose that connects to the UIM. I'm suspecting the two plastic vacuum hoses that connect to the UIM.

I went to ford to by new inserts/connectors for the vacuum hoses, and the 'parts' guy said those hoses didn't exist on his diagram!!!! I asked him to walk 50 feet to my car so I could show him, but that was too much for him to do. I asked some mechanics that were hanging about waiting for parts, but none would indicate that they knew what I was talking about. I asked them if they ever heard of the duratecc v6 used in many hundreds of thousands of ford cars and got blank stares. Sometimes, it's hard for me to get used to the fact that no one 'gives a hoot' anymore.

Anyway, is there any good DIY troubleshooting tips for vacuum leaks? I had a smoke test done before I did the UIM/LIM gaskets, which cost me $80.00. I'd rather not pay for that again. I guess I'll spring for the O2 sensor (code P1131). I hear that it is such a PITA, that I wouldn't go trough the trouble of removing it without replacing it with a new unit.

It's a shame, because after I did the gasket job, the car idles super smooth and feels great to drive. I had the fuel pump checked at the same I had the smoke test done and the shop said it was fine. However, I think my problem could be fuel related, because the car doesn't show any obvious signs of vacuum leaks. I will check the ECT sensor. I never thought of that. I'll have to buy a fuel pump tester and a code scanner, but I know my wife (the BOSS) won't let me, as we're in budget woes right now. Oh Well....

i had 1131 and 1151 forever and replaed uim lim gaskets injectors maf etc, however i found it as both 02 sensors so if they are old i would replace them anyways and that may trigger it, i hooked up an a.f ratio gauge to my front o2 and after it got warm it would sometimes stop switching for a moment or the entire ride. replaced and problem solved.

http://www.contour.org/ceg-vb/showthread.php?t=46525 - my story may help

BumpPerformancedotcom said:

i had 1131 and 1151 forever and replaed uim lim gaskets injectors maf etc, however i found it as both 02 sensors so if they are old i would replace them anyways and that may trigger it, i hooked up an a.f ratio gauge to my front o2 and after it got warm it would sometimes stop switching for a moment or the entire ride. replaced and problem solved.

http://www.contour.org/ceg-vb/showthread.php?t=46525 - my story may help

Click to expand...

I did replace the bank 1 pre-cat O2 sensor. I don't know why this is listed as a PITA job. It was kind of easy done from the top. It took longer to remove and replace the coil pack. I used a "crowfoot" O2 wrench and a 3/8" drive ratchet and had no problems. It was a tight fit getting my hand down between the engine and firewall. Got a few scratches, lost a little skin, but got it done. Finally my 'skinny' wrists paid off!

When I restarted the car, the engine idle drifted up and down between 1500 and 1000 rpm for a few minutes then settled down (never did that before). I let the engine warm up and then drove the car. It ran great of course. No stuttering, instant rpms. Smooth as silk idle at around 700 rpm. I turned off the engine, left it for an half-hour. Restarted it and of course - INSTANT CEL.

I'm now faced with the fact that I've got to take this car off the road - even though it runs great and I've replaced 3 of the 4 O2 sensors, the LIM and UIM gaskets, PCV, TB gasket, MAF sensor, new spark plugs - if I can't get it to pass the NY smog test.

I'm afraid what I'll find when I check the CEL codes. I've now become a fixture at Autozone. They all hide when they see me coming.

New code reading

New code reading

Update: Went to Autozone after replacing the bank 1 O2 sensor. Apparently cleared up p1131, but now I'm getting:

p1518

+ the old favorites: p0174 and p0171

What is p1518 about?

abyssius said:

Update: Went to Autozone after replacing the bank 1 O2 sensor. Apparently cleared up p1131, but now I'm getting:

p1518

+ the old favorites: p0174 and p0171

What is p1518 about?

Click to expand...

what brand o2's are you using? stay away from Bosch.... trust me.

GT2SVT said:

what brand o2's are you using? stay away from Bosch.... trust me.

Click to expand...

Oops! too late. I bought three sensors, 1 upstream and 2 downstream, all bosch. $63.00, $48.00, $48.00 respectively. However the O2 codes I was getting, p1151, p1131 and p0141 all cleared up.

These are quotes from different posts on the p0171, p0174 combo:

From Tony2005:
"P0171 and P0174 together is indicative of a massive vacuum leak."

Unfortunately, my experience with a "massive" vacuum leak is usually accompanied by a rough idle. This car's idle is very smooth at about 700rpm.

From Tony2005:
One the reasons for P0171 and P0174 could be "Fuel system not supplying enough fuel during high fuel demand conditions."

Today I did notice a few rattles (pings) when I stepped on the gas more than usual, but the acceleration seems normal and it will go to the redline even with automatic shifting if I use the accelerator accordingly.

p1518 - Intake Manifold Runner Control fault - Stuck Open. Why would this show up all of a sudden? I don't have a clue. I'm beginning to think this car is haunted.

abyssius said:

Oops! too late. I bought three sensors, 1 upstream and 2 downstream, all bosch. $63.00, $48.00, $48.00 respectively. However the O2 codes I was getting, p1151, p1131 and p0141 all cleared up.

These are quotes from different posts on the p0171, p0174 combo:

From Tony2005:
"P0171 and P0174 together is indicative of a massive vacuum leak."

Unfortunately, my experience with a "massive" vacuum leak is usually accompanied by a rough idle. This car's idle is very smooth at about 700rpm.

From Tony2005:
One the reasons for P0171 and P0174 could be "Fuel system not supplying enough fuel during high fuel demand conditions."

Today I did notice a few rattles (pings) when I stepped on the gas more than usual, but the acceleration seems normal and it will go to the redline even with automatic shifting if I use the accelerator accordingly.

p1518 - Intake Manifold Runner Control fault - Stuck Open. Why would this show up all of a sudden? I don't have a clue. I'm beginning to think this car is haunted.

Click to expand...

oh well maybe you'll have better luck than me or my friend had. he bought one and installed it, still got the same code, thinking the problem was elsewere he never thought it would be the o2. well he heard about Bosch from me and other people. bought a Denso installed it and no more codes!
ah the IMRC, I've had this problem happen to me 3 times!
1. I cleaned my intakes while i was changing the gaskets. I had solvent and left over gunk in there that stuck them closed. fixed it my manualy working the IMRC.
2. The cable broke
3. The little plastic clips that hold the IMRC together fell out.
check those out, and maybe your problems will be solved

P0171 & P0174

P0171 & P0174

Please take a very close look at the following link. This is the trouble shooting directions from ford. It allows you to look at all the possible causes. Because you have codes on both sides of the engine I would look to items that are common to both sides. Also when you did your gaskets did you replace you fuel pressure regulator? http://www.v8sho.com/SHO/TSB0197HO2SServiceTips.htm This link has helped me many times. If you study then test you should be able to correct the problem with out throwing mud hoping something sticks. Good luck.

Dan the rug man said:

Please take a very close look at the following link. This is the trouble shooting directions from ford. It allows you to look at all the possible causes. Because you have codes on both sides of the engine I would look to items that are common to both sides. Also when you did your gaskets did you replace you fuel pressure regulator? http://www.v8sho.com/SHO/TSB0197HO2SServiceTips.htm This link has helped me many times. If you study then test you should be able to correct the problem with out throwing mud hoping something sticks. Good luck.

Click to expand...

Thank you for your reply, Dan

The link is very educational, and it is leading me to believe that the problem
might be fuel pressure related, rather than a vacuum leak.

Firstly, the IMRC code P1518 turned out to be an easy fix. I found that the cable
was disconnected from where it sits on the spring mechanism. I probably didn't reconnect it properly after doing the manifolds.

I didn't replace the fuel pressure regulator. That was one of the "options" I chose to ignore in the downloaded instructions. In retrospect, obviously this should have been done. As usual, I go for the penny-wise, pound foolish - Oh Well...

Unfortunately, I don't have any fuel pressure diagnostic equipment. I paid a shop $150.00 to test the fuel pump and do a smoke test. They said the fuel pump was okay and I had vacuum leaks "all over the engine" and quoted me $750.00 to do the job, while refusing to guarantee that this would clear the CEL. I'm sure they didn't bother to check the fuel pump under load, as is recommended in your link.

What I do know is the car is definitely running lean because the ceramic of the spark plugs are snow white. The car idles smoothly and runs okay under light gas pedal pressure. However, yesterday, when I stepped on the gas more that I normally do, I felt a slight bucking on acceleration. I'm wondering if this is indicative of a fuel pressure problem. I was thinking of replacing the fuel pump and the 'sock' filter. But that would be "throwing more mud" if it's a bad pressure regulator, or injectors. If I had the money, I'd replace them all.

QUESTIONS:

(a) What does the bulletin mean when it says "freeze frame data"? How do I get this?

(b) Is there a way to isolate the specific fuel pressure problem, other than
simply replacing parts? (freeze frame data, maybe??)

(c) How do I know if my car has the "tabbed" fuel pump or not, without actually removing the pump? The autozone guy asked me this question when I was going to buy a fuel pump (a.k.a. throwing more mud).

Freeze frame

Freeze frame

I believe you would need to go to a shop with the electronic equipment to read the state of the engine. This should give you the data. Question the tech or service writer prior to committing any money. Make sure they can give the snap shot data. As far as the tabbed data on the pump I have no idea. Maybe one of the more knowledgeable members can answer that question. Dan

Update concerning LIM:

Update concerning LIM:

After "never-ending" attempts to find why my car was throwing those P0171,P0174 codes. I surrendered and took it to a repair shop to see what they could do. After a $95.00 smoke test and code scan, The mechanic told me that they found P0171, P0174, P0420, P0430.

They told me p0171, p0174 were due to leaks at the IRMC throttle rod pivots, and that a new LIM was required to fix the problem (since Ford doesn't sell those seals). He quoted me $1700.00 to fix this and also replace the CATS (per P0420, p0430).

I asked him if I could use a "junk-yard" parts to reduce the price and he said, "What if that one leaks too, or the junk-yard CAT is no good? I'll still charge you for installing it..." etc. etc. He also said he would usually charge $2400.00 for this job.

I'm sure he was sincere, but I told him forget it and drove away because I simply couldn't afford the price. Strangely, he called me back later that day and told me a story about how they've used RTV to fix Windstars with the same problem, and they could do this for $400.00. I reluctantly went for it, because I couldn't find any references to this LIM problem. Amazingly, this cleared the p0174, p0171 codes, but I am still stuck with p0420, p0430.

FYI, This is the contents of the Invoice I received:

LABOR:
Scan PCM codes: P0420, P0430, P0171, P0174
Smoke tests found Vacuum leaks:
IRMC leaking and Bad Cats: $95.00

Fix IRMC on Intake with RTV.
This is not a permitted Fix
Customer told will need lower
intake at some point: $400.00

Unfortunately, this has almost completely wiped me out of available cash, and I need to get it inspected so I can get a job. I am wondering if anyone knows if the MIL eliminator circuits referenced on this site will get rid of p0420, p0430 and fool the inspection test so I can get the bloody thing inspected once and for all?

if rtv on the lim rods solves the lean codes that that is great. however i have never once head of anyone saying that there are air leaks at this location, let alone large enough to cause the pcm to throw codes.

now if you truely have the pre-cat codes and no other codes they could be bad but most likely its a false codes. how does it drive? same as it use to? might suggest mil-eliminators if it runs and performs fine.

BrApple said:

if rtv on the lim rods solves the lean codes that that is great. however i have never once head of anyone saying that there are air leaks at this location, let alone large enough to cause the pcm to throw codes.

now if you truely have the pre-cat codes and no other codes they could be bad but most likely its a false codes. how does it drive? same as it use to? might suggest mil-eliminators if it runs and performs fine.

Click to expand...

I'm surprised you've never heard of this. The mechanic told me that this is such a common problem on Windstars, that their intake mainfolds are on "national back-order." I pointed out that the Windstar was a different engine design. He did say he never saw this problem on a Mystique or Taurus before.

The car runs okay. It idles smoothly at 600 rpm. It seems to rev okay under normal acceleration. Replacing the UIM/LIM gaskets and cleaning out the gunk, noticeably improved the driveability. I was beginning to think something was wrong with the fuel delivery, but this was the second shop that said the fuel-pump, etc. was okay.

The only reason why I gave the lim rods diagnosis any credence was because the original repair shop where I got the first smoke test also told me that these were leaking. He even called Ford while I was there and asked if the seals(?) were available. The Ford parts department person couldn't figure out what he was talking about.

I read a post at another forum that said a hole the size of the head of a pin would trigger those p0171, p0174 codes. I figured he was exaggerating and I didn't pay much attention to it. I'm going to go ahead and build the MIL eliminators today to see if this will end my nightmare.

When I bought this car 10 years ago, the salesman told me that I could drive it for 100,000 without a problem, then I should come to him and get a new car. Maybe he knew something after all. I planned to replace this car with a Milan this year, but I lost my job so I need to feed this car for a little while more.