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2004 Deville base
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13 Posts
Discussion Starter #1
Thanks guys. I appreciate the fast response. And, since there are no vacuum switches in the ac system, I can put the dash board back together.
Now back to the main problem. Nice to know I won't be sidetracked by looking inside the passenger cabin.
As stated previously, I've already replaced the PLENUM COUPLER and the intake manifold gaskets. BTW, the ones from Rockauto were useless...would not even fit into the grooves on the bottom side of the intake manifold. Got better ones at NAPA for a few more $. I've also replaced the rubber 90 elbow connectors and the straight connectors on both the clean and dirty air lines. But, something you just wrote makes me wonder... you called the line from the front valve cover to the throttle body a "clean air line, (not a vacuum hose)". Maybe (for the first time in my life) I made a mistake...I hooked my smoker to that "clean air line", not the one going to the rear valve cover. So maybe I missed possible leaking locations? However, I also tested by spraying with carb cleaner and did not hear any changes in idle speed...no matter where I sprayed.

I can redo the smoke test...which line do you recommend?
Thanks again!
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,595 Posts
Did you replace the rubber connector in the "tunnel" of the intake manifold, front (passenger) end ? Common crack point.

Also, check the intake ducting at and after the MAF - any air leaks at the clamps or breaks in the duct will also set mixture codes.

Click to enlarge, use the < > to scroll, click the little grid lower right for a full picture.


Intake silicone seals2.JPG Intake-PCV end.JPG Intake-plenum end.JPG Intake-plenum.JPG MAF front quarter.jpg
 

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2004 Deville base
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13 Posts
Discussion Starter #3
Hello again. And, thanks again for your timely response. Since my problem is fixing these error codes, I thought I'd start a new thread rather than continuing under the previous one which addressed an ac issue.
I received your comments and, yes, I replaced the elbow at the right side end of the intake manifold connecting the dirty air vacuum hose to the rear valve cover. Following my last post, I did another smoke test, this time connecting my smoker to the power brake vacuum hose. I did this because the first time I used the clean air hose from the throttle body as a connection point and you mentioned this is not a vacuum hose.
Unfortunately, the results came back the same. No detectable leak. In fact, the system came under pressure, until I removed the oil fill cap. Then all the smoke came rushing out in a rather dramatic fashion. And the rubber intake duct leading to the throttle body (from the intake air filter box) returned to it's normal size. At this point, I'm pretty confident there is no detectable leak in vacuum system.
So, what's next?
1. I'm gonna try the diagnostic system built into the car to see if that gives me any additional information. I've been using my OBDII reader which displays error codes and allows me to erase them without disconnecting the battery.
2. Since there are numerous other error codes for the O2 sensors and those have not come up, I'm guessing the problem lies elsewhere.Besides, the exhaust system was replaced at 112,883 miles. Car now has 151k+ miles. That work was done by the dealer so not sure if the sensors were replaced at that time.
3. I'm gonna spray the MAF electrical connector with WD40 in case all this is caused by a poor electrical connection.
4. Gonna closely inspect the portion of the air intake duct which contains the air flow sensor. The duct is 2 pieces, held together by hose clamps. Only the second half of the duct was included in the smoke test because I didn't want to fowl the air flow sensor with smoke.

Any other suggestions would be greatly appreciated.
Thank You!
 

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Super Moderator
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The codes in your title (P0171 & P0174) usually point to a rip in the intake plenum duct , the rubber coupler between the TB and the manifold. The rip is usually at the 6:00 position so it is hard to spot. Press on the duct near the bottom while the engine is at idle. If you hear an RPM increase, you've found it.

573614
 

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2004 Deville base
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13 Posts
Discussion Starter #5
Hi. Thanks for your suggestion but I replaced this rubber coupler last March, along with the manifold gaskets and the rubber connectors for the clean and dirty PCV lines (front and rear valve covers). And, I redid the smoke test day before yesterday and found no detectable leak. Crankcase and air intake held positive pressure until I removed the oil fill cap. To do the test, I disconnected the vacuum hose from the brake vacuum assist unit and used that hose to connect to my rather simple smoke machine. Based on this result, I gotta believe the following parts have no leaks:
crankcase and crankcase gaskets
intake manifold and gaskets
rubber coupler between intake manifold and throttle body
throttle body
dirty air hose and rubber boots between intake manifold and rear valve cover
clean air hose and rubber boots between throttle body and front valve cover
valve covers and valve cover gaskets
hose from throttle body to vacuum assist power brake unit (did not test brake unit itself).
intake air plenum between throttle body and collar holding the air flow sensor (did not smoke/ pressure test that collar but visually inspected it with negative result)
small hose from throttle body to fuel rail pressure regulator

Yesterday I used the on board diagnostic system to see if my hand held scanner had missed any trouble codes . Several history "B" codes (B1004, B0429, & B1327) and one current "U" code (U1000) showed up. After looking up their definitions, I don't believe any of them would trigger the check engine light. I then cleared all the codes.

At this point, the car is back together and the check engine light is off. I plan to test drive the car today to see if the lean fuel indication has "magically" gone away.

Any further suggestions would be greatly appreciated.
Thank you
 

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2004 Deville
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578 Posts
Have you checked the 3/8th rubber elbow inside the passenger side of the intake manifold behind the steering pump ? it's easy to overlook and will throw those codes if split.
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,595 Posts
Good afternoon - your previous vacuum posts from the blend door thread have been moved here for clarity.
 

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2004 Deville base
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13 Posts
Discussion Starter #8
Have you checked the 3/8th rubber elbow inside the passenger side of the intake manifold behind the steering pump ? it's easy to overlook and will throw those codes if split.
Have you checked the 3/8th rubber elbow inside the passenger side of the intake manifold behind the steering pump ? it's easy to overlook and will throw those codes if split.
Yes, That coupling was replaced along with the others. And, it is hard to get at. I replaced it when I had the intake manifold out.
Thanks anyway...
 

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2004 Deville base
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13 Posts
Discussion Starter #9
Good afternoon - your previous vacuum posts from the blend door thread have been moved here for clarity.

Thank you. Not sure I know how to do that...
Up date from this morning:
During my test drive (@ 20 miles with 2 stops) the car ran perfect. Getting 19.2 mpg in city driving conditions. No loping, rough idle,hesitation,etc. But...at around mile 19, the dreaded check engine light came back on!
Ran the on board diagnostic system. Aside from 7 historic records, the system recorded the following current trouble codes:
B0429 Temperature control #3 rear circuit range/performance
U1000 Class 2 communication malfunction
I also checked with my hand held scanner. It showed:
P0174 Current
P0174 Pending
Funny, the on board didn't pick up the P0174... and P0171 magically dissappeared!
I think the U1000 is because we don't use onstar or the on board telephone connection. Kinda old school...
What's the B0429 all about? Would that code trigger the Check engine light?
Again, thanks for your help.
 

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2004 Deville
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578 Posts
B0429 is the temperature blend door actuator, one of the motors inside it has failed, it is behind the glove box on the left ( you need to remove the glovebox to see it ) 5 minutes to change once the glovebox is out.
"P" stands for PCM or powertrain control module, as stated only p codes will turn on the engine light. It is a good idea to check codes every so often, there are many codes that will not turn on a light.
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,595 Posts
Thank you. Not sure I know how to do that...

What's the B0429 all about? Would that code trigger the Check engine light
You can't move stuff - Moderators can.,

B 0429 C says the rear seat console air supply door or actuator is faulty. No, No SES or P codes associated.
 

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2004 Deville base
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13 Posts
Discussion Starter #13
B0429 is the temperature blend door actuator, one of the motors inside it has failed, it is behind the glove box on the left ( you need to remove the glovebox to see it ) 5 minutes to change once the glovebox is out.
"P" stands for PCM or powertrain control module, as stated only p codes will turn on the engine light. It is a good idea to check codes every so often, there are many codes that will not turn on a light.
Thank you! Guess I'll save that one for after the P0174 mystery is solved. I replaced the left hand blend door actuator awhile ago. Was no fun but I understand the right side is easier to get to...Is the right hand actuator the same part number as the left side?

Has anyone had the P0174 issue fixed by anything other than a vacuum leak?
Thanks
 

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2004 Deville
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578 Posts
I've had the 0174 code in my car 3 times over the years that I've owned it, and each time it was caused by something already mentioned in this thread.
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,595 Posts
Post #12 for the B 0429 code.

P 0174 - click the below link and scroll down to B then P codes.


P 0174 (C or H) - Fuel trim system lean bank 2 - C = Current, H = History.

Bank 2 is the left (front) bank, cylinders 2-4-6-8. Vacuum leak, sticky injector, off-calibration O2 sensor (B2S1 is in the left bank exhaust manifold collector).

Front O2 sensor B2 S1.gif
 

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2004 Deville base
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13 Posts
Discussion Starter #16
I've had the 0174 code in my car 3 times over the years that I've owned it, and each time it was caused by something already mentioned in this thread.
Thank you. Unless I've screwed up and missed something, I think all the previously mentioned stuff is not leaking. The strongest evidence I have of this theory is: 1. no visible smoke from any part of the engine during smoke test; 2. Pressure built up in crankcase/vacuum system until I removed the oil fill cap. Then the smoke came rushing out and the intake air duct relaxed back to normal size.
One thing seems weird: I applied smoke and slight pressure to the vacuum system through the hose I disconnected from the power brake unit. The dirty air and clean air hoses connect to the valve covers. Don't thev have a check valve to prevent back pressure into the crankcase? If so, how did the smoke/pressure get into the valve cover and out the oil fill cap? Could that path be up through an open intake valve and past a worn out valve stem seal? But, no evidence of oil leak or dirty/fouled plug...
Sorry for being obtuse, but this is driving me nuts. Mechanically, engines are pretty simple to understand. I'm much better at older stuff (pre-computer). The tests and parts replacements I've done so far seem to rule out a mechanical/physical failure.
I'll keep trying...
 

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2004 Deville base
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13 Posts
Discussion Starter #17
Post #12 for the B 0429 code.

P 0174 - click the below link and scroll down to B then P codes.


P 0174 (C or H) - Fuel trim system lean bank 2 - C = Current, H = History.

Bank 2 is the left (front) bank, cylinders 2-4-6-8. Vacuum leak, sticky injector, off-calibration O2 sensor (B2S1 is in the left bank exhaust manifold collector).

View attachment 573650
Thank you. All the injectors are "clicking" and the car runs and idles smoothly. That makes me think a sticky injector is not the first place to look.
An O2 sensor "out of calibration", if that can trigger a P0174, sounds promising. As mentioned previously, the exhaust system was replaced around 40,000 miles ago, That included the catalytic converters and possibly the sensors after the converters. This work was done by the dealer so I'm not sure exactly what parts were replaced.
From what I've read, the front one is hard to get at and requires a special socket. Should be fun...
 

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Don't thev have a check valve to prevent back pressure into the crankcase?
No, you are thinking of the old rattle type PCV valve. There is no "valve", it's simply a metered orifice.

From what I've read, the front one is hard to get at and requires a special socket. Should be fun...
I believe they all require a special O2 sensor socket. It's basically a slotted deep well socket.
573668


Or an offset type for where a deep well will not fit.
573669
 

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-Administrator- 2002.5 F55 STS 2014 FWD Explorer
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66,595 Posts
The oil fill cap is on the clean air side (atmospheric) of the PCV system. The rattle valve or orifice is the dirty side. Regardless, a smoke test pressurizes the entire inside of the engine - remember that the cam covers have wide open drains to the oil pan, so the PCV dirty air line is equalized between the crankcase and the cam cover - it's restricted only into the intake manifold full vacuum line.

The old rattle valve slammed shut in the event of an intake manifold backfire - and the Northstar has an intake manifold overpressure valve built-in.

2002 vacuum.gif
 

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2004 Deville base
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13 Posts
Discussion Starter #20
No, you are thinking of the old rattle type PCV valve. There is no "valve", it's simply a metered orifice.


I believe they all require a special O2 sensor socket. It's basically a slotted deep well socket.
View attachment 573668

Or an offset type for where a deep well will not fit.
View attachment 573669
Thank you. Found it. I can get an open end wrench on it but it won't budge. Sprayed with penetrating oil. I'll try again this afternoon...
 
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