Question about 1999 Chevrolet Tahoe
This is one of those situations that a professional diag would of saved you alot of money. Its possible you just got bad gas and your injectors are partially clogged. An 02 sensor would not give multible misfires. EGR would only misfire at idle if stuck partially open since its suppose to be open cruising. Fuel filter would give you a starvation issue but if the misfires happens at idle then the filter most likley is ok.
Data from a professional data scanner will store the conditions when the misfire occurs. Also for a chevy each cylinder will have a misfire counter and one can see the misfire happening as it happens. If its idling and misfiring and gets better as you rev it up most likely you have clogged injectors or a intake vacuum leak. You can test for a intake leak by spraying the intake area with water(idle will faulter if it draws water in), or use brake cleaner (idle will raise when fluid gets drawn in).
If no leaks are found I would do an injection service or at least add two bottles of techron to a full tank, drve till half a tank then top off again.
Also if the catalytic converter is clogged the backpressure could cause all sorts of misfire issues. Removing the two upfront 02 sensors and driving will indicate the exhaust is clogged or not. We put a pressure sensor in place of the 02 sensor. If the pressure is above 5psi this would indicate some blockage. It should be below 3psi at 2000 rpm. Also if you have K/N filter the oil from it will coat the maf sensor wires in time,, (always). You can remove the sensor and spray the wires with brake cleaner to clean. DO NOT touch them. They can be brittle. Look at the wires for color. They should be shiny silver. If its coated the PCM will not see the air volume or accurately see the air temperature. Without this information the PCM will not add enough fuel which will create a misfire.
Posted on Jul 07, 2010
I had the same problem with my 1998 5.7 and changed everything possible. it ended up being the injector spider...good luck part alone was $600.00 but its fixed
Posted on Jan 31, 2014
Just had the same problem on my 1998 5.7 vortec first it started with just the #6 misfire then multiple misfires. turns out it was a bad fuel injectors. Since i was towing my boat i ignored it for a couple hundred mile till i got to my destination. BAD MOVE!!!! because the injector wasnt working the cylinder was lean and burned my exhaust valve and froze it in the open position. SO fix it right away. not only did i have to replace the fuel injectors i had to replace the head....
Posted on Aug 11, 2010
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Posted on Jan 02, 2017
Most of the time when you run a fuel system cleaner in a engine that has not had a cleaning the sludge will clog the fuel filter. I would check the fuel filter before anything and if that is good, I recommend running a complete test on the vacuum lines sometimes if there is a leak in a vacumn line it will mess with the timing advance and cause the vehicle to behave different at certain RPM ranges
Posted on May 18, 2010
loose vacuum line, check for same, also check the map sensor and the measure the fuel pressure, make sure its at spec
Posted on Jul 29, 2009
hi there, i had the same problem with my 98 astro van, and took it to the shop, the computer pumped out a mass airflow sensor, they replaced it at considerable cost lol, but the van now runs good
Posted on Jul 03, 2010
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