1999 4.3 misfiring
I'm running out of ideas on a problem with my 99 S10 4.3
The truck will start and idle fine however as soon as you feed a little gas it starts to miss.
Giving it even more gas is either covering up the misfire or it is clearing and seeems to run better.
I've just replaced cap/rotor wires and plugs.
The problem seems to get worse whenever it gets even slightly wet/humid.
I had Cragen hookup a analyzer and it gave a "random misfire" error code.
Does anyone have an idea of where to look?
I would look at replacing your coil, moisture will commonly mess them up if they have a crack in them. If the coil is going out, the more you require from it, the more the engine will miss. It would create the code given. That would be my best educated guess from the information you gave.
Just as a possibility I may also suggest trying a MAF cleanner, it should be about $8 a can. If it improve significantly, then I recommend replacing the MAF. Even though the frequency could be operating within specification, if it does not change as quickly as load on the engine changes, the engine may not be able to fire at the right time.
your problem is a bad throttle position sensor, i had the exact sme problem, changed everything out but that sensor and it finally stopped doin that once i replaced the TPS. same exact conditions, whebn it got humid or after a rain it ran like shit lol
I have this same problem with my 99 s10 4.3. the code reader says miss fire cylinder #2... so I replaced wires, plugs, distributer cap and rotor. after 2 days this problem got worse. again I read the codes and it read the same code, cylinder #2. good old GM I guess
I know this an old thread, but seen alot of questions across these forums while searching for an answer to problem that seems to be irritating all of us 4.3 vortec owners. "The dreaded mystery coldstart misfire." I like many others had the shudder between 1500-1800 rpms until the engine came up to operating temperature. I just found the root of all evil hiding under the EGR valve. Removed EGR to clean and realized there was a blow by in the gasket. Removed gasket and noticed it was on the topside and underside of the gasket. Scraped the remainder off, cleaned the surface, and installed new gasket with original EGR valve. Instant success! I can see why people got rid of the issue when replacing spider injector because they probably removed and reinstalled new gasket when replacing EGR. Less than an $2.00 fix compared to the $300.00 cost of new injectors.(I still need to replace injectors as mine has over 300,000 miles on original but thats another project) Also remedied some annoying valve chatter. Worked for me...hope this information helps others!
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