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98 Chevy 5.7 Misfire

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#31 silveradobobby



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Posted 31 May 2008 - 11:18 PM

I'm surprised no one has brought this up, but what about a bad knock sensor? My dad's older 454 had one, and it would run EXACTLY as you described, though it was on all cylinders, not just one side as his is TBI. One side being rich would indicate that the knock sensor is detecting knock and trying to compensate for it, but it SHOULD throw a code for that. It might not, though.

The knock sensor wont control just one bank like his is doing especaily on a standard disturator system if it was coil on plug setup that might be the case but not his engine, it adjust all cyclinders to adjust ping.

It wont control fuel on one bank with the CPI system it doesn't have a way of control fuel to one bank like that, on a direct port injection system it can.
It might not control SPARK on one bank, but it WOULD control FUEL. It would dump more fuel into one bank and try to run it rich and stop the knock.

That said, it sounds like he found part of the problem.

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#32 gmax1



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Posted 06 June 2008 - 05:07 PM

UPDATE 5: Now have replaced timing chain and two timing gears. The timing gears were set 180 degrees off. Some slop in the chain but mechanic (Dick) said he's seen worse. Dick thought now we've got it! Started but wouldn't run- was popping. Moved distributor 180 degrees and it runs but Dick says it shouldn't with that setting. Dick called a national tech service that that is well respected they said use TDC on cylinder 6 to set timing. Still not running right. Runs pretty good at idle but bogs down as soon as it is put under load i.e. into drive. This is driving us crazy. These mechanics wake up at night thinking about this truck.

#33 gmax1



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Posted 23 June 2008 - 10:24 PM

Final Update and the cure
For those of you who have been following this post and offered much appreciated suggestions her's what finally fixed the problem. Took truck to GM truck dealership ($973 bill). They replaced O2 sensor on right side (passenger side) forward of the catalytic converter. GM tech also said Duralast ignition wires purchased at Auto Zone were not capable of carrying needed spark all the way through to spark plugs. (Junk wires) GM wire set installed. Pricey at $167 a set but they improved misfiring. I had read on the Internet that Vortecs like GM wires best. Another set of OEM plugs at $9.06 each installed.

Also GM tech says that NAPA distributor part #9591003 GM 01 10000940
bar code 8 81882 38744 7 is for a 4.3L and not for the 5.7 in my truck! This is the second new and complete NAPA distributor that was installed with the same part numbers with the same same result. GM tech had to oval out bolt hole a lot for hold down shoe so distributor could be turned to adjust spark. I have spoken to NAPA manager about this situation but haven't heard back whether NAPA is having a problem with this particular distributor or part number correlation for 5.7 engines.

At this point truck is running well and seems to be getting good mpg but I won't know for awhile what the actual mpg is. After all these repairs I can't afford to fill up the tank!!

#34 BlueGorilla



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Posted 24 June 2008 - 12:26 PM

This only backs up my opinion. Put in Factory parts, cause you get what you pay for.
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#35 wreedZ71



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Posted 26 January 2009 - 11:43 PM

Did you get Packard Wires or ACDelco wires from the dealer?

Edited by wreedZ71, 26 January 2009 - 11:46 PM.

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#36 Stumpuller6.2


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Posted 27 January 2009 - 10:24 AM

Its a bitch for diagnosis when you replace the part you trouble shoot only to find after hours of brain sucking thought that the new part is junk, I`ve seen it in the feild before, good for O.T. but hard on the pride and soul....

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#37 TEE



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Posted 27 January 2009 - 10:46 AM

It was a 4.3 dizzy cap?

#38 vortec 5.7 missfire soluti

vortec 5.7 missfire soluti


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Posted 24 January 2011 - 09:32 PM

My 98 K3500 with 161k was throwing a lot of codes. Replaced all 4 O2 sensors. Then Mass air flow sensor, new AC Delco platinum plugs, new Auto Zone plug wires, New NAPA distributor, tried switching NAPA cap and rotor with new GM brand. Mechanic (Jeff- former Honda, Toy, Subaru dealer mechanic) found cracks in intake manifold gasket and replaced with new upgraded Felpro brand. Still running rough. Jeff unable to find cause.

Brought truck to Dick- former GM dealership mechanic. Dick went through all of the diagnostic proceedures Jeff went through. Truck runs okay on start up but within 1-2 minutes starts running rough at idle and gets worse when put into gear. This has been problem from beginning. Number 4 and 8 plugs skipping the worst. All plugs on that side badly sooted up. Other bank of plugs (odd #) looks good. Sometimes misfire carries over to #1 plug. Truck is blowing black smoke and burning excess fuel. Compression in all cylinders is 175 to 185 with one cylinder showing 160.

Dick pulled O2 sensor before catalytic on passanger side and engine quieted right down. Says truck has plugged catalytic so new cat and muffler assembly for that side ordered from GM and installed. Ouch! Slight improvement but still running very rough, no power, misfires on 4 and 8, and spark as before advanced by 22 degrees.

Pulled NAPA distributer with the new GM cap and rotor button and switched it with a used GM distributor and again used the new GM rotor and cap. No significant change. Replaced central port fuel injector unit with one from a junk yard that supposedly came off a running engine. No significant change. Fuel pressure is 54 or 55 psi.

Headed back to junk yard tomorrow to switch used CPFI with another used one they have that is also supposedly off a running engine. If this doesn't work my next step will be to bring truck to GM dealership and have them diagnose it for possibility of installing new GM CPFI as a cure but that's a $500 - $600 fix and currently I have almost $2000 into labor and parts with Dick. Dick thinks the CPFI may be the problem. If it isn't he does't know what to do next as he has tried everything in his bag of tricks and has consulted with other mechanics he knows. We're both frustrated. Nothing anyone has done has resulted in significant improvement.

This thing is beating my wallet hard. Any suggestions would be appreciated.

#39 vortec 5.7 missfire soluti

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Posted 24 January 2011 - 09:37 PM

1998 5.7 vortec missfire solution.

Random missfire is a Knock Sensor !
Please read my story !
I own a 1998 Z/71 5.7 K1500
Started off missfireing on a hill or when i pulled my small trailer.
Service engine soon, dash lite came on, went to a shop pluged up to a hand held unit. it said missfire on 3&5, cleared codes & thought its just tune up time. WRONG !
Driving around the samething {dash lites up service engine soon }
it RANDOM missfires and shakes loosing power. i return to shop we plug up the hand held unit it says random missfire ? so we think its the coil getting weak, replaced the coil same thing random missfire again.
this is over a 2-3 month period i have to drive the truck easy to work and home like driving Miss. Daisy you kinda get the idea.
someone said the intake gasket is Leaking check it , so with the truck at idle i spray starting fluid all around the intake with no changes in RPM.
NEXT Iam about to do a insurance claim, but i love the truck but its driving me and GM mechanics and all others mechanics up the wall at this time iam looking at a whole lot of money spent already and my truck is not fixed, and thinking about standing on a street with a sighn that reads "will work for repaires on my chevy truck "
ok its time to think again , so i'am putting it all together random missfire no power, piston spark knock, so i called O'Reilly
auto parts Dalton Ga. and told jeff my sad story he said to change the Knock sensor
for $32.99 it was worth a try.
part # BWD 98012 FOR MY TRUCK.
PLEASE READ ON !! It fixed the problem its never ran so great , Throttle responce is great!
The knock sensor tells the computer to advance or retard the timing,
it cannot adjust the advance without the knock sensor telling it what to do. The Knock sensor is located on the passenger side of the block easy to get to under the truck on jack stands. but it screws into the water jacket of the block between the freeze plugs you must drain all the antifreeze from the engine before replacing it. The truck runs like a brand new one with 160.000 miles on it 0-100 mph is no problem bring on the HEMI'S ! :smokin: