"Big Picture" approach to looking at diagnostic codes?

I own a 97 Ford Explorer which is producing the following codes:
P0153 - O2 Circuit Slow Response (Bank2, Sensor1)
P0401- EGR Flow Insufficient Detected
P1151- Lack of HO2S21 Switches - Sensor Inicates Lean
P0304 - Cylinder 4 Misfire Detected
P0171 - System Too Lean (Bank 1)
P0174 - System Too Lean (Bank 2)

I realize these codes are showing me symptoms.
http://www.obd-codes.com/trouble_codes/ would help if there was a
single code presented

What do I have to know to back away from the individual symptoms and
diagnosis the root cause(s)? - Mike

You forgot to mention mileage, engine type and any drivability concerns -
all useful information to diagnose the problem(s).
It's unlikely that all these codes appeared at once -- have you been driving
with the CEL on for quite some time?

Hopefully one of the pros who frequent this group will soon chime in. In the
meantime, if you want my 2 cents:
a) The misfire on cylinder 4 is very likely related to the codes on the
relevant bank. Can't tell whether 1 or 2 -- we don't know if it's a V6 or a
V8. I would start with fixing it. Take a good look at the plug in that
cylinder and compare it to the others -- there will be good clues there. A
faulty injector, a stuck valve, etc is possible, but ignition would be my
primary suspect. If the spark plug wires have not been replaced over the
last 30 thousand miles, I would do that, even as a precaution - they don't
last much longer than that. With any luck, that may cure the other bank's
problems as well.
b) The most common code for that EGR-related code is a defective DPFE
sensor. It's fairly easy to test, but if you don't have the tools or the
knowledge, the part is cheap and easy to replace. I believe that there was
an 'extended warranty' issued due to its premature failures, so you may get
this done for free.

"Michael Horowitz" > wrote in message
news
>I own a 97 Ford Explorer which is producing the following codes:
> P0153 - O2 Circuit Slow Response (Bank2, Sensor1)
> P0401- EGR Flow Insufficient Detected
> P1151- Lack of HO2S21 Switches - Sensor Inicates Lean
> P0304 - Cylinder 4 Misfire Detected
> P0171 - System Too Lean (Bank 1)
> P0174 - System Too Lean (Bank 2)
>...
> What do I have to know to back away from the individual symptoms and
> diagnosis the root cause(s)? - Mike

It is important to differentiate between codes that are "causal" and codes
that are "symptomatic".... Putting it as easy as I can, many concerns can
generate multiple codes.... a misfire can generate lean codes since misfires
will increase the amount of unreacted oxygen in the exhaust. A lean system
can generate misfires along with misfire codes. And on and on it can go....

Now, I am having to assume that these codes are continuous memory codes but
I can't assume anything about the capabilities of your code reader. In the
shop, I would have performed the KOEO On Demand test to retrieve the DTCs.
If any of these codes had been returned as an On Demand or "hard" fault, we
would address these before moving on.... If none of these codes appeared as
"hard" faults and were only present in continuous memory, we would run the
KOER test - there are many actuators and sensors that the PCM cannot test
without having the engine run.... KOEO continuous memory codes have the
possibility of being hard codes during the KOER test.... Again, hard codes
are addressed first.

If our scan tool doesn't offer us the ability to perform these two tests,
the only option left is to note the existing codes and then clear continuous
memory... drive the vehicle and see what returns first.

Since your post is totally bereft of any essential information, I can't
offer any more advice than this.

On Sat, 02 Jun 2007 21:57:43 GMT, "Jim Warman"
> wrote:

>
>Since your post is totally bereft of any essential information, I can't
>offer any more advice than this.
>
Jim - I was concentrating on the concept, not expecting a diagnosis;
however if you wanna take a swing at it: 200,000 miles on a 6-cyl,
4.0L engine - MIke

Happy - 200,000 miles on a 6-cyl, 4.0L engine; runs rough at idle and
I can feel it stumble sometime when I accellerate from a stop - Mike

On Sat, 2 Jun 2007 13:17:18 -0700, "Happy Traveler"
> wrote:

>You forgot to mention mileage, engine type and any drivability concerns -
>all useful information to diagnose the problem(s).
>It's unlikely that all these codes appeared at once -- have you been driving
>with the CEL on for quite some time?
>
>Hopefully one of the pros who frequent this group will soon chime in. In the
>meantime, if you want my 2 cents:
>a) The misfire on cylinder 4 is very likely related to the codes on the
>relevant bank. Can't tell whether 1 or 2 -- we don't know if it's a V6 or a
>V8. I would start with fixing it. Take a good look at the plug in that
>cylinder and compare it to the others -- there will be good clues there. A
>faulty injector, a stuck valve, etc is possible, but ignition would be my
>primary suspect. If the spark plug wires have not been replaced over the
>last 30 thousand miles, I would do that, even as a precaution - they don't
>last much longer than that. With any luck, that may cure the other bank's
>problems as well.
>b) The most common code for that EGR-related code is a defective DPFE
>sensor. It's fairly easy to test, but if you don't have the tools or the
>knowledge, the part is cheap and easy to replace. I believe that there was
>an 'extended warranty' issued due to its premature failures, so you may get
>this done for free.
>
>"Michael Horowitz" > wrote in message
>news
>>I own a 97 Ford Explorer which is producing the following codes:
>> P0153 - O2 Circuit Slow Response (Bank2, Sensor1)
>> P0401- EGR Flow Insufficient Detected
>> P1151- Lack of HO2S21 Switches - Sensor Inicates Lean
>> P0304 - Cylinder 4 Misfire Detected
>> P0171 - System Too Lean (Bank 1)
>> P0174 - System Too Lean (Bank 2)
>>...
>> What do I have to know to back away from the individual symptoms and
>> diagnosis the root cause(s)? - Mike
>

Oh, and plugs and wires replace within last 5,000 mi. - Mike

Oddly enough, you are still keeping some important information secret - like
whether it's the pushrod or the overhead cam 4.0L. The latter had its share
of problems, including, if memory serves, a notorious intake manifold vacuum
leak. At 200K, those have probably been repaired a long time ago, but who
knows -- you told us nothing about this vehicle's history.

Jim Warman is the uncontested expert on this group and an overall great guy.
Heed his advice about running on-demand diagnostics and servicing those,
starting with the first code that shows up. Hopefully you have the Power
Train Controls/ Emissions Diagnostics Manual - follow the charts there.

"Michael Horowitz" > wrote in message
news
> Happy - 200,000 miles on a 6-cyl, 4.0L engine; runs rough at idle and
> I can feel it stumble sometime when I accellerate from a stop - Mike

I'm gonna hang my ass way out in the breeze and opine that you will find
there is probably a DPFE in your future.... In the late 90s Ford had (IIRC)
three different flavours of intake manifolds on the OHC engines.... I'm not
sure if any of these featured ported EGR flow - this is something to
consider in regards to the cylinder #4 misfire.

Which ever way, smart money is on repairing any conditions that can be
proven and then re-evaluating.


"Michael Horowitz" > wrote in message
...
> On Sat, 02 Jun 2007 21:57:43 GMT, "Jim Warman"
> > wrote:
>
>>
>>Since your post is totally bereft of any essential information, I can't
>>offer any more advice than this.
>>
> Jim - I was concentrating on the concept, not expecting a diagnosis;
> however if you wanna take a swing at it: 200,000 miles on a 6-cyl,
> 4.0L engine - MIke
>

No secret - I'm new to diagnosis and don't know what's relavant - this
engine has a single overhead cam; History: worked fine until 125,000,
then began to have problems. wiring harness and plugs replaced, MAP
sensor cleaned, transfer case replaced, tranny replaced, now the front
differential is causing problems. - Mike

On Sat, 2 Jun 2007 17:13:08 -0700, "Happy Traveler"
> wrote:

>Oddly enough, you are still keeping some important information secret - like
>whether it's the pushrod or the overhead cam 4.0L. The latter had its share
>of problems, including, if memory serves, a notorious intake manifold vacuum
>leak. At 200K, those have probably been repaired a long time ago, but who
>knows -- you told us nothing about this vehicle's history.
>
>Jim Warman is the uncontested expert on this group and an overall great guy.
>Heed his advice about running on-demand diagnostics and servicing those,
>starting with the first code that shows up. Hopefully you have the Power
>Train Controls/ Emissions Diagnostics Manual - follow the charts there.
>
>"Michael Horowitz" > wrote in message
>news
>> Happy - 200,000 miles on a 6-cyl, 4.0L engine; runs rough at idle and
>> I can feel it stumble sometime when I accellerate from a stop - Mike
>

Michael, this group has amateurs who play with cars in their spare time when
they are not amusing themselves with something else (like me), and very few
high caliber, experienced pros (like Jim Warman). We all deeply appreciate
the latter group contributing their time here for free, when they could be
making oodles of money for themselves or for their employers instead. To
help them help you quickly and efficiently, put yourself in their place.
They can't see or hear your vehicle and don't know its history, so you have
to provide it here. When you have a problem with an engine, you have to say
what engine it is, how it has been maintained, how many miles; and provide
the best description of the problem and what have you done so far to resolve
it, not just a snippet of what your code reader extricated out of the
computer's memory. Makes sense, doesn't it?

My Expy has the 5.0L engine, so I can't contribute anything from my
experience about your 4.0L SOHC. In its early days your engine had a whole
bunch of problems like faulty intake manifold and timing components. If
those have not been taken care of, it's probably a good idea to google the
archives of this group for symptoms and solutions to those. Otherwise there
are no miracles: systematic troubleshooting will get you to the root cause,
and the Power Train Controls/Emissions Diagnostics Manual will provide that
in great detail. With an engine that has already served 200K, I would not
ignore what that manual calls "Base Engine" - mechanical issues related to
the engine itself. Get a good look at the plugs, comparing the one in the
misfiring cylinder to the others. If you don't know how to 'read' plugs,
learn that - the information is available everywhere. A leakdown test is
ideal, but a simple compression test will also point you to a major problem
in that cylinder, like a stuck valve or piston rings that are not sealing.

The code for insufficient EGR flow seems to be an easy target. If that's
consistent, repairing it may address some of the other issues. The most
common cause is a faulty DPFE sensor, but it could be a clogged hose, bad
solenoid, etc, etc. The same manual will guide you through the systematic
diagnostics if you are not a gambler.

Some will question the wisdom of all the time and expense of doing this on
your own -- or even of doing this at all, instead of dumping the 10-year old
vehicle and buying something newer. I don't have a good answer. Except
perhaps that my 22-year old, throttle-body injected LTD still passes
emissions with flying colors (anybody knows a source of replacement window
sweeps?).


"Michael Horowitz" > wrote in message
...
> No secret - I'm new to diagnosis and don't know what's relavant - this
> engine has a single overhead cam; History: worked fine until 125,000,
> then began to have problems. wiring harness and plugs replaced, MAP
> sensor cleaned, transfer case replaced, tranny replaced, now the front
> differential is causing problems. - Mike