Chasing a rough idle?

[2009TahoeLT]

@2009TahoeLT
I had misfiring/rough idling caused by counterfeit spark plugs.
Here's the thread I did : https://www.tahoeyukonforum.com/thr...iring-at-idle-counterfeit-spark-plugs.146952/

I had thought about that but I bought them from rockauto. Not that they might not have counterfeit stuff come through but I’ve been very happy with parts through them lol

 

[2009TahoeLT]

Replaced the bank 2 upstream o2 today. No change. Cats are not clogged. Still misfiring on every cylinder over 1100 rpm and a rough idle. Did another smoke test, only thing I found leaking was the dipstick tube lol. Any other ideas??

 

[Fless]

The fuel trims are taking away quite a bit of fuel, trying to control the oxygen levels in the exhaust -- something seems to be causing too much fuel delivery. Do we know the fuel rail fuel pressure?

 

[Doubeleive]

connect a fuel pressure gauge and prop it up under the hood hinge so you can see it and see what it shows under a load (driving around)
should read about 44psi (running) 50~65 key on, engine off (cold). heat soak will/may make it rise if the engine is hot (key-on engine-off)

 

[2009TahoeLT]

Sorry it’s been super busy. I ordered a fuel pressure gauge kit. Should be here within a few days, I’ll update from there. Also getting an issue when I brake. It sputters bad when coming to a slow brake. Drops to about 400ish rpm. I had to replace 2 slide pins and boots on the driver front caliper bracket. Some reason the check engine light shut itself off after doing that lol. I’ll get those fuel readings and go from there. Also one of my buddies mentioned the vlom being an issue possibly. Anyone have any insight on that possibility??

 

[2009TahoeLT]

connect a fuel pressure gauge and prop it up under the hood hinge so you can see it and see what it shows under a load (driving around)
should read about 44psi (running) 50~65 key on, engine off (cold). heat soak will/may make it rise if the engine is hot (key-on engine-off)

So about 54 key on engine off, 42 under load.

 

[Doubeleive]

So about 54 key on engine off, 42 under load.

that's bare minimum but passing, does that launch scanner have a misfire counter/graph option?

 

[2009TahoeLT]

that's bare minimum but passing, does that launch scanner have a misfire counter/graph option?

It does.

 

[Doubeleive]

It does.

I would check that and see what it shows with a cold start & idle, rough idle should equate to other symptoms that the scanner should show in that data field
similar to my video here (k2 but data information will be the same) in my case it was bad injectors, misfires like this will not throw a code until it hits a certain count.
so under the threshold it just runs like doodoo

 

[2009TahoeLT]

Yeah idle is choppy but not terrible. It doesn’t pickup any misfires at idle. But between about 1000-1800 rpm it will pickup misfires on all cylinders. It is also throwing a p0171,p0175, p0300 and a large evap code. So bank 1 lean code and bank 2 rich… I can test it later in the morning tomorrow and post the results here.

I would check that and see what it shows with a cold start & idle, rough idle should equate to other symptoms that the scanner should show in that data field
similar to my video here (k2 but data information will be the same) in my case it was bad injectors, misfires like this will not throw a code until it hits a certain count.
so under the threshold it just runs like doodoo

 

[2009TahoeLT]

Zeros are at idle.. pictures with misfires are at 1200 rpm.

 

[Doubeleive]

Zeros are at idle.. pictures with misfires are at 1200 rpm.

with 250k on it I would say the next step is a backpressure test, if a cat is clogged this would possibly explain the issue if everything else is good,
you can get a kit or make one from harbor freight
you stick the fitting in one of the front 02 sensor bungs and start it up, should read no more than 5 psi (max)
I had a clogged cat and would get unexplained misfires and knock retard like a mofo, but at idle it was fine. it had got so bad it was causing lean codes and misfires, knock retard.
had no power, you could drive like gramma and it was fine, but if you went to say pass someone on the highway with some pedal it had nothing gutless wonder. anything at higher speed caused flashing cel, gutted the 3rd cat and it has been perfectly fine since.
not saying this is your issue, but it is worth checking, especially if the history of the truck is unknown, might cost you $30 for one from harbor freight.
other possibilities, chaffed wire on the coil/injector harness, if the wires are resting on anything and rubbing it can wear thru on the bottom part

 

[2009TahoeLT]

with 250k on it I would say the next step is a backpressure test, if a cat is clogged this would possibly explain the issue if everything else is good,
you can get a kit or make one from harbor freight
you stick the fitting in one of the front 02 sensor bungs and start it up, should read no more than 5 psi (max)
I had a clogged cat and would get unexplained misfires and knock retard like a mofo, but at idle it was fine. it had got so bad it was causing lean codes and misfires, knock retard.
had no power, you could drive like gramma and it was fine, but if you went to say pass someone on the highway with some pedal it had nothing gutless wonder. anything at higher speed caused flashing cel, gutted the 3rd cat and it has been perfectly fine since.
not saying this is your issue, but it is worth checking, especially if the history of the truck is unknown, might cost you $30 for one from harbor freight.
other possibilities, chaffed wire on the coil/injector harness, if the wires are resting on anything and rubbing it can wear thru on the bottom part

Just finally ordered a back pressure tester. Should be in within a few days. It’s now stalling if I let it warm up for about 20 mins. Key on, truck just shuts itself off. Doesn’t do it while driving though.. once I get the tester and test it. I’ll post the results here

 

[Babadook76]

Following. I have an 09 Tahoe with pretty rough idle that just started recently. It runs fine at speed. LTFT are showing close to negative 10 percent on both banks. No codes. New plugs and wires. Gonna smoke test it soon. Be curious to see how your back pressure test comes out. My Tahoe has 220k on it.

 

[2009TahoeLT]

Haven’t gotten to the back pressure test yet. Did the valve cover gaskets that were needed, while doing so. Took the coils off and noticed some of them are rotted on the back side. I honestly thought that metal case around them was part of the bracket haha. Ordering replacement coils for the broken ones and repairing the rust on the others. If that fails I’ll do the back pressure test after that

 

[rdezs]

I've never seen coils rusted like that. You must be in an area with high salt use in the winter?

That's a pretty good indicator to go around and clean all your ground connections.

 

[2009TahoeLT]

I've never seen coils rusted like that. You must be in an area with high salt use in the winter?

That's a pretty good indicator to go around and clean all your ground connections.

Yup. Massachusetts. But it depends on how bad the winter is haha. I’ve done a few grounds. Doubt it’s all of them lol

 

[rdezs]

I would check and clean the grounds at the back of the driver side cylinder head to the firewall, the one at the front of the passenger side cylinder head, and both ends of both battery cables. And don't forget the ground wire to the fuse/relay box. With that amount of corrosion, I would think it's worthwhile to pull out the fuse box, turn it over and see if it needs cleaning. I would also check all the fuses and relays for any signs of corrosion on the blades. Dielectric grease will probably be your friend.

They don't use road salt where I am... They use red volcanic cinders. Not corrosive, only leaves a red dusty film on everything that washes off. (Completely covers the back window to the point you can't see through it! And you definitely don't want to turn the rear wiper on until it's clean) Works great for melting ice in the daytime, as the sun heats up the cinders. Then if it refreezes at night, you have the granules mixed in with the ice for traction.

 

[2009TahoeLT]

I would check and clean the grounds at the back of the driver side cylinder head to the firewall, the one at the front of the passenger side cylinder head, and both ends of both battery cables. And don't forget the ground wire to the fuse/relay box. With that amount of corrosion, I would think it's worthwhile to pull out the fuse box, turn it over and see if it needs cleaning. I would also check all the fuses and relays for any signs of corrosion on the blades. Dielectric grease will probably be your friend.

They don't use road salt where I am... They use red volcanic cinders. Not corrosive, only leaves a red dusty film on everything that washes off. (Completely covers the back window to the point you can't see through it! And you definitely don't want to turn the rear wiper on until it's clean) Works great for melting ice in the daytime, as the sun heats up the cinders. Then if it refreezes at night, you have the granules mixed in with the ice for traction.

I’ve cleaned the drivers rear head to firewall. I’ve cleaned the pass front head ground, I may have missed the ground to the fuse box. I’ve cleaned both terminals on the battery. And cleaned other side of ground. Haven’t cleaned other end of positive. I’ll have to look into the fuse box. I went through fuses the other day because my fan wouldn’t shut off when vehicle was running. Turns out the fan 40a fuse blew. Checked the rest of them and they were good. I did have issues with the fuses a while back being absolutely stuck/melted/corroded in the fuse panel. Had to take a few fuses out in about 20-30 pieces. Replaced the fuses and all has been well with the fuses since.

 

[2009TahoeLT]

Finally got to doing a back pressure test. Back pressure at zero. I’m still at a loss