lost in the land of confusion

[vinceyspa]

Ok where to begin ? i did a tune up on a 2003 chevy silverado 4.3 L with a/c plugs(autolite) cap and rotor (auto zone ) new belt, air filter new pvc checked for collapsed elbows etc. so flash forward about 2 weeks the truck now shows code p301 then went into p300 , with check engine light came on , engine missing p301 replaced plug thinking bad plug. also replaced wires , original plug was heavy carbon on it after 2 weeks. i took the truck to a mechanic who hooked up his scanner came up with p300 . Very bad idle back fires can not go above 45 mph without back fire ,missing while idling, any ideas should not go from hero to zero that fast . Now i did see that if the belt is having issues that maybe causing the timing to be off

[Bob D]

Welcome vinceyspa

Couple Qs:

Did problem arise immediately after your tuneup?

How many miles on this thing?

What is your level of expertise?

"if the belt is having issues that maybe causing the timing to be off" Nope.

[demonte1997]

Going in the direction that this new issue is mutually exclusive from what you did on prior maintenance...

 

Possibly a bad cat?

[gmtech4]

use OEM cap and rotor and clear codes and road test again

[vinceyspa]

my basic experience is tune up , oil changes, filter replacements, brakes etc. i however am not experienced in total tear downs i leave that to the professionals. the truck has approx 109k miles

the problem didn't start until appprox 2 weeks of istallation of plugs, cap and rotor at that time along with air filter and pvc valve ,.

when problem started took it to oreilleys and used the scan tool which came back p0301 thinking i had a bad plus i replaced the plug rechecked at autozone which came back with a po300 p0172 possible maf possible o2 sensor we were advised to use lucas to clear out injectors. i also checked all rubber vac line especially the 90 degree elbows (know this from experience on my f150 which the elbow had collapased)

 

as of last night took truck to company mechanic (asce master mechanic) (i work for a bus company) he put it on his scan machine did not find that o2 sensor as bad or p0172 was o but not great it was still showing p0300 he double checked the firing order, he suggested a new maf.

 

today after reading all posts on this site i replaced the plugs with ac delco gapped at .040 per gm specs. installed a new fuel filter put the orginal plug wires back on major improvement still a small miss and a back fire or a ( putt putt ) when driving down the road only thing i haven't done is install oem cap and rotor which i think i might have to do .

 

the person who owns the truck will takeit to oreillys tomorrow (sunday) to clear the codes . stay tuned .... thanks for all the in put

 

side note she seems to have a bad oil sensor gauge goes all the way down sometime works don't know if that is any indication of the (putt putt)

[vinceyspa]

one other note the trucks history is unknown , this owner has had it 6 yrs so first tune up for it since she's bought it

[pm26]

I have seen engine misfire code on my Mazda 626 due to a bad injector not firing. You could not tell whether it was ignition related or not just from the code. Does this truck have multiple port injection (individual injectors) or a throttle body type injection system?

[Duelin]

From your post I couldn't tell if you used AC or AutoLite plugs. I never use AutoLite plugs. Also never use autozone cap and rotors. did you replace all the wires? If so did you use good ones or go the cheap way (you get what you pay for). Belt won't affect timing unless you have wrapped around the distributor cap and pulling on that. The 4.3 uses a timing chain. Now Have you done anything to diagnose the problem besides pulling a code and changing a plug? Have you done a compression check? Check the injector? Vac leaks? Also the bushing in the dist. could be worn and causing the shaft to wobble and cause a miss fire.

[99kon]

I went through this with a 5.3 in a 2004 tahoe. Truck ran good when i bought it then it developed a small miss after about a month

then progressed to code P0300

 

Heavy carbon build up on plugs and exhaust tip

had to literally floor it fo it to move and after a big puff of black smoke it would move

 

Had it a at a mechanic friend of mines shop for 2 weeks looking for leaks and diagnosing it after i replaced what is mentioned below. He suggested the ECM but nothing worked.

 

replaced the following

ecm

fuel pump

intake gaskets

plugs

wires

fuel filter 3 times after a lot of crap coming from fuel tank

blew fuel lines out

various fuel system cleaners

injectors

coils

checked cats

throttle body

intake

I had spare engine parts from previous builds that i knew were good

Finally after about a month of messing with bought a used 5.3 for $450 and replaced the motor

been running fine for about a year now.

 

Took heads off and found nothing out of the ordinary

May have been a bent valve or warped head

[MikeNH]

use OEM cap and rotor and clear codes and road test again

 

 

This. Had a friend with a 2000 Blazer who went through all manner of hugely expensive repairs before realizing it was the crap autozone cap/rotor. Their electrical stuff is junk. OE is the only option IMO.

[mawint]

Change the O2 sensor if your getting a code. Mine developed a similar situation before I changed plugs and wires, still ran terrible afterwards. Ended up going to have it read and the freeze frame for one of the O2 sensors showed a negative value, replaced that O2 sensor and all was good. Mine happened to be the upstream one on the passenger side.

 

At O'Reilly's the sensor was around $50.