Rough Idle HELP!

[02YukDenXL]

How long have you had the issue? Have you done any work to it? Brought it to a mechanic? Etc?

 

[SLCHOE]

So I've been riding out this misfire lately. I haven't had time to work on the truck (We just moved and have 3 kids so its been a bit crazy).

Brought the truck in for an oil change to a newer mechanic. I've been going to him for about 6 months now. I ditched my old mechanic after he jerked me around over a power steering pump fiasco. Asked him to look at the misfire again.

He found three broken bolts on each exhaust manifold. He thinks this is potentially causing the misfire. Thoughts?

Based on your good upstream O2 voltages and your very weak downsteam voltages, I'm not surprised at all. The good news is you had an exhaust leak pre-downstream O2's which leaned out those sensors.... which is a sign of bad cats. Can you get an up-to-date video of your scan tool showing LTFT (1 and 2), STFT (1 and 2), H02S b1s1, b1s2, b2s1 and b2s2 after the engine is up to operating temp (ECT over 190F)?

My thinking is if you still have lean LTFT's you may just have dirty (partially clogged) injector nozzles (pintles). You may need to try a fuel system cleaning with something like a terraclean system.

 

[about20ninj45]

Based on your good upstream O2 voltages and your very weak downsteam voltages, I'm not surprised at all. The good news is you had an exhaust leak pre-downstream O2's which leaned out those sensors.... which is a sign of bad cats. Can you get an up-to-date video of your scan tool showing LTFT (1 and 2), STFT (1 and 2), H02S b1s1, b1s2, b2s1 and b2s2 after the engine is up to operating temp (ECT over 190F)?

My thinking is if you still have lean LTFT's you may just have dirty (partially clogged) injector nozzles (pintles). You may need to try a fuel system cleaning with something like a terraclean system.

Found this on the web...

look at the Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) values. Normal range is plus or minus 8. If the numbers are +10 or higher for STFT and LTFT, the engine is running LEAN. If you rev the engine to 1500 to 2000 rpm and hold it for a minute or so, and the STFT value drops back down to a more normal reading, it confirms the engine has a vacuum leak at idle. If the STFT value does not change much, the lean fuel condition is more likely a fuel delivery problem (weak fuel pump, restricted fuel filter, dirty fuel injectors or a leaky fuel pressure regulator) than a vacuum leak.

Pretty much sound like everything you tried

 

[SLCHOE]

Whqt I would do to your truck is a cylinder balance test. This requires hooking up a fuel pressure gauge to the schrader valve on the fuel rail. Then you need an OEM level scan tool to engage the test. The test primes the fuel system and then pulses each injector for a few seconds. The fuel pressure gauge you hooked up to the rail will show a gradual drop as it pulses the injector. It then stops pulsing the injector and you note the fuel pressure that is left on the gauge for each cylinder. This test will show a plugged injector, internally shorted injector or even a stuck open injector (stuck open is not applicable to your case). I'm going to use random numbers here but lets say the test primes the fuel rail to 65 PSI then fires the injector and the pressure reading after pulsing it is 35 psi. Going through each injector you can find out which injector is malfunctioning. If the next injector ends up at 45 psi after pulsing, it therefore has not flowed as much fuel hence a restriction of some kind.

The issue here is I'm 99% sure that your Actron will do this test.

 

[SLCHOE]

Found this on the web...

look at the Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) values. Normal range is plus or minus 8. If the numbers are +10 or higher for STFT and LTFT, the engine is running LEAN. If you rev the engine to 1500 to 2000 rpm and hold it for a minute or so, and the STFT value drops back down to a more normal reading, it confirms the engine has a vacuum leak at idle. If the STFT value does not change much, the lean fuel condition is more likely a fuel delivery problem (weak fuel pump, restricted fuel filter, dirty fuel injectors or a leaky fuel pressure regulator) than a vacuum leak.

Pretty much sound like everything you tried

That is fuel trim diag 101 and it is spot on. I'm curious to see what the LTFT's read at 2500 RPM and held there for a few seconds.

 

[about20ninj45]

That is fuel trim diag 101 and it is spot on. I'm curious to see what the LTFT's read at 2500 RPM and held there for a few seconds.

Same here... The only time I've ever had an engine run like shit is after I forgot to lash the valves

 

[oldchev]

SLCHOE, ... this 50 minutes of classroom instruction/refresher is top notch. I'm pretty fair at home garage diagnostics but this refresher really brought about a clearer understanding. I have the P0171/P0174 code and will reexamine the STFT/LTFT and other data on the Innova scan tool. Nothing scares me, just want to go after the real problem and let Auto Zone close early.

 

[Brains646]

has a fix been found yet?

 

[VikingTrad3r]

id like to know too!!!