concerning engine lugging and multiple sensor
replacement, and the value of being able to
read spark plug condition.......
(for those who care....read the thread for all
the impotent stuff...too much cut and paste)
2 cents worth......
Original plugs had light brownish coloring....
(a good indicator of additives, was the electrode burn't?~lean
Screams out Fuel Additives have been used,
and likely wrong fuel mixture.
Catalytic Convertors getting hot and possibly
glowing red.....no black smoke out the pipes...
Screams out Lean Burn condition.
O2 sensor reading rich condition.....
(coupled with the above indicators...)
Screams out ECM possibly dumping fuel to
correct a misfire detection or compensate for
a lean condition.
Multiple codes set.......and sensors changed
to correct the problems.....
Screams out....the need for the truck to be
put on an oscillescope and have an end put
to all the guess work...
(multiple codes and sensor failures are extremely unusual)
#5 (what started the thread)
Engine lugs on part throttle, engine surges up
and down like it's trying die out....surging, seems to have good power
under full throttle...
Screams out fuel mixture..OR...ignition trouble..
(weak spark at the plugs)
before you go spending more money.....
hit all the vacume areas and around the
intake with some starting fluid and see if you
can locate some vac leaks........the engine
rpm should increase noticeably on a lean
running engine.......and decrease noticeably
on a rich running engine.
If you "suspect" the EGR diaphram is sucking
air.....stick a long enough vac hose on it, and
suck it down with yer mout....see if it's holding
vacume...no need to buy a vac pump when yer
lungs will do the same thing.
take a look under the hood at night....no lights
around.....see if there's any fireworks going on
up and down the wires and around the primary
ignition system from shorting.
remember......if it's running fairly good at cruise,
during full throttle, or if it runs good only some
of the time....it's still capable of running good...
The ECM and THE SENSORS are capable of
maintaining the fuel ratio and spark...enough to
let the engine run well (which means they're
likely working good),
The catalyst is not likely restricted enough to cause a loss of power
(you would be feeling a power loss all the time),
And....... the overall condition of the engine is within specs,
allowing the thing to be CAPABLE OF RUNNING GOOD even some of the time.
(compression, exhaust flow, timing, fuel flow)
............which would lead me to believe you've got a simple problem
with a simple fix,
and what's simpler than bad ignition components, vacume leaks, and dirty
body.....all of which you can fix yerself.
jest my 2 cents worth,