Rough Idle HELP!

[02YukDenXL]

I saw a YouTube video with those tests the other day. I'm itching to hookup my new gauge and check things out. I'll definitely be doing this tomorrow. Thanks man!

 

[#1taho]

You should always use O2's and Fuel Trims (which are basically interpretad data from O2's) to diagnose drivability issues. They are a window into the engine.

I have to correct myself. I meant not look at the O2 as in replacing it till the last. Your correct it is a window to help see whats going on with your engine.

 

[ccapehartusarmyINF.(ret)]

my jedi powers are the window to my engine

 

[02YukDenXL]

Initial fuel pressure spike with KOEO was 57psi for a second or two before quickly settling off at 52 psi.

Idle fuel pressure fluctuated between 49-50 psi.

Fuel pressure in drive with foot in brake at 2100 rpm approximately 55-56 psi.

 

[SLCHOE]

Seems to be ok then. I'd move forward and check the cats.

 

[ccapehartusarmyINF.(ret)]

i hate cats they are evil creatures that can steal your soul

 

[02YukDenXL]

I ordered some Aero Kroil on Amazon to help free up the O2 sensors. I'm gonna buy a back pressure gauge to test my cats.

If I had one clogged cat, wouldn't the misfire only happen on one side? What are the odds that both cats are plugged?

 

[ccapehartusarmyINF.(ret)]

i would take this oppertunity remove the cats from the equation completely like i did with my tahoe
and as for passing emissions i just paid up my tabs two years out and id just cross that bridge when i got there as far as when it did infact come time for emissions
and there is several ways to keep yer post cat 02 sensors from throwwing a code

 

[02YukDenXL]

I'm not just going to remove my cats completely. If they're clogged then I'll be replacing them.

 

[#1taho]

I'm not just going to remove my cats completely. If they're clogged then I'll be replacing them.

How are you making out with you diagnoses ? You definitely have a tricky one!

 

[02YukDenXL]

I won't have time to pull the O2's and test the back pressure for a week or so. Too much going on with my professional engineering exam at the end of the week and moving into a new house this weekend. Good thing is the new house has a two car garage [emoji106] It'll be getting some good use.

 

[SLCHOE]

I ordered some Aero Kroil on Amazon to help free up the O2 sensors. I'm gonna buy a back pressure gauge to test my cats.

If I had one clogged cat, wouldn't the misfire only happen on one side? What are the odds that both cats are plugged?

To be honest... Not likely in your case since you have misfires across both banks. I think we've missed something. At this point I would recheck everything I find questionable.

1) Spark. You may have it but is it consistant over a given period of time?

2) Fuel pressure. Rock solid at idle and you power braked it and it was still good?

3) Timing? (you still have the scan tool?) Look at cam / crank co-relation.

4) Compression? You sure compression is good?

5) fuel trims ok. Hmmm... something is not adding up.

 

[02YukDenXL]

At times I've also been suspicious of my computer. Is it possible the computer could be bad and cause a misfire?

 

[klee7013]

Posting just to keep track of your progress

 

[SLCHOE]

At times I've also been suspicious of my computer. Is it possible the computer could be bad and cause a misfire?

a bad ECM could most certainly cause a misfire but that's usally the last place to look.

There has to be something missed.

At this point in my shop I'd start by doing a relative compression test and if needed put each secondary ignition wire on the scope aswell. That would be the tell-all. If you don't have the equipment to do it yourself (not likely unless you have a quality oscilliscope), take it to somebody who does and knows how to use one. If I was close by I'd have you bring it by my shop as this is really frustrating not having first-hand access to it.

 

[02YukDenXL]

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?

 

[about20ninj45]

So i have a suggestion? have you ever tried swapping out your map sensor or checking for broken wires near it?

 

[02YukDenXL]

I replaced the MAP sensor with an OEM ACDelco sensor about 6-8 weeks ago. Connector and wires near the sensor looked intact and in reasonable shape.

 

[about20ninj45]

I replaced the MAP sensor with an OEM ACDelco sensor about 6-8 weeks ago. Connector and wires near the sensor looked intact and in reasonable shape.

Damn,

Next step

Exorcism

 

[YukonCrazy]

I seem to have the same issue. Rough idle with no codes that just started one day.