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Our Truck 4-2012 4/24/2012, P.J.C. ~ REV. 4/25/2012 ~


1998 4.3L, "W" (190 HP) S-10, Blazer , 4x4 (Four Door LS)

18 Gallon fuel Tank

166000 Miles


Parts Installed at 166K;


Spark Plugs

Air Filter

Fuel Filter

PCV Valve

Vacume hoses as posb..

O2 Sensors (Heated 4 wire) Both Up-Stream( Bosh brand)


MAF (un-nessary part, I got talked into)


Intake Manafold Gasket (Lower done only)



Codes Found at 166K; (first PO is Gm, 2nd is what test guy told me)


PO404 EGR Valve Pintle Position / 2nd ~~ EGR out of range


PO420 TWC System Low Efficiency-Bank 1 / 2nd Cat Effecitnty below threshold


PO101 MAF System Performance


PO-xxx HO2S ~~ Bank 1, Sensor 1 (Code removed by test guy)



Work Done at 166K;


Pressure Wash off Motor top and bottom, as needed.


Cleaned sludge from Intake ports in manafold and Cylinder Head ports,

Used o2 safe carb cleaner & Sea-Foam can added to 1/2 tank of fuel,

Found and removed plastic tubeing type assamble plug left in at OE manufacture

(truck ran 166K with this in head from Factory)



when i pulled and marked distribtor for base timming

the drive gear was worn bad, i hear thats sorta normal for a high millage 4.3L

But Can this retard timing so much as to make timing probs?


all above parts had been installed and the driveabilaty probs are still there..

It needed lots of maint. and I do feel only part not needed so far is the MAF i got talked into,,


I also have checked and replaced vacume hoses as a mesure to head off issues


Seems to have low vacume like 15hg

and as i give it throttle it dont look like a converter

but on my vac guadge it at the retarded timing band on gadge fpor what its worth..


I have rechecked all the work i have done and dont want to start to shovle money at this pig, most i had done was maint so far.





Truck runs and starts okay. (Other then what i feel is lack of power)

after a drive of about 50-100 miles ( far from home )

At Full operating temp

it starts to Bog bad and slow down to a stop

loud ping and have to play with pettle to floor and let up as anything to keep it running to get home,, (Labors bad, ping, bucks and surges,)

we saw Serious red hot pipes of manafoulds and it still did not re-set a CEL??

shut it off before it killed more then it has and posb fire.


sorta feels like its running out of fuel and restarting at times

has no funny smoke out of ext?


where to go next? and what I hope to try to do;;


Check and clean EGR


install and leave fuel pressure gadge on it and wait for it to do its thing

its got 60-55PSI KOEO & about 50-55 KOER?

(Pumps less then a year old and is a delphi brand)


Try to beg, browr an Cat presure tester for back pressure,,

or pull o2 sensor/s to see if it gets better

or just try to drop cat and drive it..

(but would seem like that would be hapin all the time, but would be the dog part of this prob)



all this works being done on my stone driveway so sorta

a real bear, with weather here.

Please if you might have some other Ideas for me

post here so i might try to end this nightmare. LOL


Thank-you all in advance



AKA; Sparkz




Up-Date; 4/25/2012



I Pulled the o2 Sensor on Bank #2

and drove truck about 1/4 - 1/2 mile

Brake-Tourqued (Loaded converter and relesed)

it's seemed to have not a ton of diff from when o2 was installed


(think it might could use less restriction but sure not all in cat?

I will try to look deeper into that for sure,,

just cant spend 300 bux for un-nessary parts)


Other tests I could do so far,

Used can of o2 safe Carb. cleaner to look for posb vacume leaks that might lean out motor

checked ign wires yet again for burns and or damage/s

and any white flashed leaks wire to wire and to just about everything around them,

wires are on my "Wish list" but they are like most things 166K old,

but do not have bad spots i can see (Both dry and wet in the dark)


Hooked up the Vacume gaudge and Fuel Pressure



53 - 54 PSI (sm bounce in nettle)

18-1/2 Inches vacume


At a Punch (Snaped throttle and return to Idle),,

62 - 51 PSI smooth rise and return

0 - 24" Inches Vacume


2500 RPM (Sliped a Quarter in TB Stop to hold) lol

52 PSI Solid reading

Vacume solid at 22 Inches Vacume



Motor OFF,,

Fuel Pressure held 60 PSI for over 10 minuits

and was still 50 PSI 30 minuits later




I am waiting for it to cool down right now

so i might reinstall o2 sensor

and have a 2nd look at vacume,, in an atempt to

confirm or rule out converter issues..


and to try to remove and check / clean / test EGR


Please if you might had seen this or know of other things i might or should be looking at, Please advise


Thank-you in advance

for any help / ideas commonts you may give or have



AKA; Sparkz

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Sounds to me like the Catalytic converter. Had this problem with my 4.3 S10. Was OK at startup until it got to normal operating temp and then just became a dog. I had problems getting the thing up to speed. Almost like I was running 2cyl. I would get that checked if you havent...like 100 bucks for a new one.

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