Bet you cant figure it out - SOLVED

[shauno]

So I have searched and read for days but I hope we can figure this out and help others who have had a ghost like this .

Let's start with the vehicle
2009 yukon xl 5.3 4l80e
The issue is a miss at idle that slows off idle
Yes the afm has been deleted with gm parts
My background is cars . I was a tech for nearly 20 years doing diag and for this to stump me is borderline embarrassing. With that let's get into the issue

This vehicle was purchased not running after an afm lifter failure . I pulled the engine that was only a year old reman and completely rebuild it from the ground up new everything other than coils . Everything is clean . All the parts used were gm or better . Got everything in and the truck ran great for nearly a month .

Now it has a missfire on cylinder 3 . So I go down the rabbit hole . I check the plugs wires coil injector all are working properly . Do a compression test both stadic and dynamic , both are normal and close to all the adjacent cylinders . Do a leak down test , no abnormalities there either . At this point im lost . So I start grasping at straws . Pull the plenum and replace the whole intake . No changed .

Now we get into the programming . Hp tuners was used to deactivate the afm . So I pull up the original tune that was read from the computer, build a new tune and wipe the old tune . Everything is the same still missing on 3 .

Now the weird . I install the base factory tune and the truck is missfiring on cylinder 1746 but I have 3 back . So I think maybe its the tune . From this point I use techline connect (gm software) to do a full reprogram with updates and then turn off the afm again through hptuners . Still missing on 3 .
At this point im banging my head against the wall so I leave my noid light hooked to cylinder 3 while its running and the light stops blinking . So I found the problem , right? . Nope

I have narrowed it to the signal wire , I have voltage to the injector but the trigger signal will drop out . The wire to the injector has been checked all the way to the ecm with my signal tracer . No internal brakes . The odd part is if I disconnect the injector on cylinder 1 then the signal for 3 comes back . Per the wiring diagram 1&3 share a main fuse . I have supplied power to the injector thinking injector circuit 1 was drawing power away from 3 but no change . I am at a total loss we replaced the ecm with another known good ecm still no change.

This has me completely baffled . Im open to ideas or help and before you say ground I have checked all the grounds the gen4 computers have one main ground in the harness and I have supplied ground to the circuit directly at the ecm .

Im stumped , my gm tech friends are stumped . Im open to ideas up to and including a bonfire

 

[Fless]

Just spitballin....

Do a CASE relearn just to rule it out; that's stored in the ECM so every time that's changed a relearn should be done. Swap injector #3 with #5 to see if the miss follows.

 

[shauno]

Just spitballin....

Do a CASE relearn just to rule it out; that's stored in the ECM so every time that's changed a relearn should be done. Swap injector #3 with #5 to see if the miss follows.

Case relearn? . Do you mean crank sensor
The injectors have been swapped around and no change.

 

[j91z28d1]

have you checked the resistance across each injector? I had one that was higher than the rest for years on a ls3 and didn't even know it, caught it on a hptuners log file looking at o2 voltage. oddly I replaced the set of injectors and I sware it idles rouger haha. but the miss in the o2 voltage was gone. so eh.


I believe I've read somewhere that the ecm can shut the fuel off to a cyl if it's missing badly to try and save it from washing down. how bad is the miss, like a completely dead hole?

since you have hptuners, can you disable the knock sensors completely and see what happens? I believe you can unplugged them and then turn off the fault code for everything kncok sensor related. but you might want to do a quick search

 

[shauno]

have you checked the resistance across each injector? I had one that was higher than the rest for years on a ls3 and didn't even know it, caught it on a hptuners log file looking at o2 voltage. oddly I replaced the set of injectors and I sware it idles rouger haha. but the miss in the o2 voltage was gone. so eh.


I believe I've read somewhere that the ecm can shut the fuel off to a cyl if it's missing badly to try and save it from washing down. how bad is the miss, like a completely dead hole?

since you have hptuners, can you disable the knock sensors completely and see what happens? I believe you can unplugged them and then turn off the fault code for everything kncok sensor related. but you might want to do a quick search

Ive checked the injectors even moved them in the rail to isolate a possible issue . The fuel trims dont show enough of a variant to warrant a lean or rich code so even if the ecm was set to shut off an injector there would need to be a correlating code to merit the action . The nock sensors show no activity on either bank for faults and the only codes present are a p0303 miss on cylinder 3 .

The miss is a dead hole at idle and goes away off idle . You can watch the missfires on the data stream slowly go to zero as the rpms come up them at idle the miss comes back .
No noise in the valve train and ive checked the pushrods and rockers . Ran the engine with the cover off to verify the valves are coming to full open as much as I visually can tell . Ive also backed off the rocker bolt to check the lifter and that it had good preasure . No issue on the intake or exhaust side .

 

[j91z28d1]

if it's enough to set the miss fire fault code, it's probably enough for what you saw on the noid light.

very weird that it goes away. is it possible the cam timing moved or is off a tooth. a guy on a face book group just had that happen. hit a big bump on the interstate, I guess the timing chain tensioner was badly worn and let the chain move to much.


byond that? new cam and crank sensor and do a relearn. see what happens?

 

[rdezs]

We're missing some data:

1. Does this misfire occur only when cold, hot or at all EOT temperatures at idle?
2. How is your oil pressure at a hot idle? And what viscosity oil are you using?
3. When doing the AFM delete, did you retain VVT? If so, did you use the timing chain tensioner upon reinstall? Or did you go with the earlier style to bolt dampener? (VVT has been known to have issues if not running the OEM style tensioner, usually the issue occurs at idle when slack occurs on the passenger side of the timing chain)
4. When you ran the engine with the valve covers off, was the engine oil up to full temperature?
5. Did you plug the towers under the valley cover either with steel plugs, or threaded plugs? And not just rely on the o-rings that come with the flat valley cover?
6. Oil pressure relief valve in the oil pan was plugged?
7. If VVT was retained, was a new actuator and solenoid used? The actuator is a one-time use, TTY.

Reading everything you have done, sounds pretty damn thorough. Personally, I would replace both the camshaft and crankshaft position sensors with genuine GM, start it up.... When up to normal operating temperature run the CASE relearn. I ran across those sensors that test out okay, yet end up being defective. Usually it's the camshaft sensor.

That's based on the assumption that the number three misfire happens wether the engine is warm or cold.

If it only does it when the engine is warmed up, I would be leaning towards some mechanical issue with the oil supply to the number three lifters. That could implicate the number two camshaft bearing clearance, a defective lifter, or excess clearance in the lifter bore. Bad lifters don't always make noise. Sometimes they have enough pressure to keep the slack out, but not enough to fully operate the valves.

My gut instinct is it's actually mechanical in nature, but before digging into it I would want to make sure the cam and crank sensors are good.

 

[rdezs]

As a side note.... You might also do an oil change with some 10w40, and see if that changes the symptoms. If it does, then you have your answer regarding something with excess clearance.

 

[shauno]

We're missing some data:

1. Does this misfire occur only when cold, hot or at all EOT temperatures at idle?
2. How is your oil pressure at a hot idle? And what viscosity oil are you using?
3. When doing the AFM delete, did you retain VVT? If so, did you use the timing chain tensioner upon reinstall? Or did you go with the earlier style to bolt dampener? (VVT has been known to have issues if not running the OEM style tensioner, usually the issue occurs at idle when slack occurs on the passenger side of the timing chain)
4. When you ran the engine with the valve covers off, was the engine oil up to full temperature?
5. Did you plug the towers under the valley cover either with steel plugs, or threaded plugs? And not just rely on the o-rings that come with the flat valley cover?
6. Oil pressure relief valve in the oil pan was plugged?
7. If VVT was retained, was a new actuator and solenoid used? The actuator is a one-time use, TTY.

Reading everything you have done, sounds pretty damn thorough. Personally, I would replace both the camshaft and crankshaft position sensors with genuine GM, start it up.... When up to normal operating temperature run the CASE relearn. I ran across those sensors that test out okay, yet end up being defective. Usually it's the camshaft sensor.

That's based on the assumption that the number three misfire happens wether the engine is warm or cold.

If it only does it when the engine is warmed up, I would be leaning towards some mechanical issue with the oil supply to the number three lifters. That could implicate the number two camshaft bearing clearance, a defective lifter, or excess clearance in the lifter bore. Bad lifters don't always make noise. Sometimes they have enough pressure to keep the slack out, but not enough to fully operate the valves.

My gut instinct is it's actually mechanical in nature, but before digging into it I would want to make sure the cam and crank sensors are good.

Oil pressure is 55 60 cold 30 35 warm all at idle . Off idle pressure is over 40 warm at 1500 rpms.
The miss is constant at all temps . Off idle it is less noticeable and slows on the scanner with rpms

The timing assembly is new and the cam and lifters are new all gm . No vvt installed
Running valvoline 10-30 as I live in fl and it gets hot out . The afm ports in the block were tapped and set screws were installed in each port . The oil pressure relief valve was plugged in the pan and I am running the larger delco filter with the higher bypass pressure like I do on most of my trucks .

Ive done the relearn multiple times . All the sensors are new and have been replaced a second time to eliminate that out of possible causes .

Its definitely not mechanical , its losing pulse on 3 and if I unplug 1 the pulse comes back weak . Its not the voltage as I bypassed the fuse and supplied voltage directly to the injector .

Its something in the signal wire to the injector . At this point I wish I had a schematic of the ecm to isolate any cross over from other modules or sensors .

This is a ghost for sure . Alao to add my fuel pressure is 55 - 60 priming and 44 running which is in spec per prodemand .

Alao running the engine at full temp with the valve covers off the valve train seems to be operating normal . All the rockers have the same or similar travel and there doesnt seem to be any valve float or spring abnormalities .

Keep in mind this truck ran flawless for over a month before this failure presented it self . Its hard for me to blame the tune because I have 3 other vehicles that have had the same work done with the same tunes on them and all of them run flawless with no issues and have for years .

 

[j91z28d1]

are you looking for the wiring diagram for the injector harness? I can look that up for you but I'm sure it doesn't run to any other module but the ecm.

my thought was weak driver in the ecm, but these don't share drivers like the old batch fire stuff and you've already replaced ecm.

at this point just back probe and run a jumper wire from the ecm pin to the injector and rule out wiring harnesses issue to injector one and 3.

I'm guessing you've checked all the grounds, especially the ecm ground? all the injector drivers in the ecm need to ground thru it. can be a bit of a load. I don't know if you can active a injector stady state with the scanner and check for a voltage drop while there too. guess you could unplug the ecm, ground the ecm side to open the injector and use the back probe to look for voltage drop.

I mean if you've replaced the ecm and it's dropping power enough that it's unable to open an injector and your light stops flashing. gotta be something in the tune shutting off the signal?

 

[Fless]

Case relearn? . Do you mean crank sensor
The injectors have been swapped around and no change.

Yes, Crankshaft Position Variation Relearn (CASE Relearn)

 

[Fless]

You may have already carefully inspected the ECM connectors, but it wouldn't hurt to verify pin tension and fitment, especially for the injector control pins. Maybe a flexed wired by the connector has been compromised.

Hit this site and verify your vehicle, then scroll to the bottom for the injector diagram:

Electrical Diagrams — 2009 GMC Yukon XL 2WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2009 GMC Yukon XL 2WD V8-5.3L.

charm.li

 

[j91z28d1]

You may have already carefully inspected the ECM connectors, but it wouldn't hurt to verify pin tension and fitment, especially for the injector control pins. Maybe a flexed wired by the connector has been compromised.

Hit this site and verify your vehicle, then scroll to the bottom for the injector diagram:

Electrical Diagrams — 2009 GMC Yukon XL 2WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2009 GMC Yukon XL 2WD V8-5.3L.

charm.li

View attachment 467125

I like that idea, pin got loose and making weak connection.

 

[strutaeng]

4L80e in a 2009 SUV? Is this a 2500 SUV? Or was that a typo?

Should be a 6L80/6L90 for a GMT900. Or they swapped that transmission in it? I believe the only GMT900 that got the 4L80e was the first year 2500 SUV GMT900 (2007)?

 

[shauno]

As a side note.... You might also do an oil change with some 10w40, and see if that changes the symptoms. If it does, then you have your answer regarding something with excess clearance.

The oil pressure definitely is not the issue .

4L80e in a 2009 SUV? Is this a 2500 SUV? Or was that a typo?

Should be a 6L80/6L90 for a GMT900. Or they swapped that transmission in it? I believe the only GMT900 that got the 4L80e was the first year 2500 SUV GMT900 (2007)?

6l80e sorry typo .

 

[shauno]

I like that idea, pin got loose and making weak connection.

Ive checked the pigtail connection to the injector . Either way my noid light fits firm in the plug and ive wiggled it to double check it wasnt loose .

To address the voltage drop across the circuit ive put a jumper wire to the injector with direct power to rule out injector 1 pulling amperage from injector 3 .

Ive verified the entire wire from the injector to the ecm with a frequency tracer (sends traceable frequency down the wire to check for internal breaks) . Ive also pushed on and reset the pins on the injector wire at thr ecm

To the guy who drop the schematic i have pro demand to pull schematics i was looking for an internal schematic for the ecm to see if there was a cross over or share circuit inside the board . But thank you good looking out on the wiring diagrams

 

[Marky Dissod]

The odd part is if I disconnect the injector on cylinder 1 then the signal for 3 comes back.
Per the wiring diagram 1&3 share a main fuse.
I have supplied power to the injector thinking injector circuit 1 was drawing power away from 3 but no change.

I have this odd sensation in my left arm and hand, feels like my hand or arm has its tongue licking a 9V batt, but the sensation moves up & down my hand and arm.
After a year of not being able to do ANYTHING about this sensation, I went to a chiropractor / masseur, who adjusted my upper SPINE,
which IMMEDIATELY reduced the intensity of the buzz in my arm by at least 2 orders of magnitude.
Point is, the problem FELT like it was in my arm or my hand, but it was in my upper spine.

"if I disconnect the injector on cylinder 1 then the signal for 3 comes back."
This kind of symptom correction coupled with your persistent cylinder 3 miss, leads me to say something like
Replace the entire driver side fuel injector wiring harness.

 

[mikez71]

Maybe swap injector 1 to test as well..

That is really weird with AFM disabled tune changing things..

 

[Marky Dissod]

Depending on the injectors' (plural) mileage ...
Every injector does something that is not easy to explain, but here goes ...

Most people get that, for 'x' amount of energy supplied to an injector (at sufficient force), a reliably consistent amount of fuel comes out,
and if the amount of energy is reduced or increased, the amount of fuel reduces or increases PROPORTIONATELY ...
HOWEVER!
There is a lower level under which that proportional relationship changes for 'the worse' -
it is proportional, but it is a different less favorable proportion.
People who know more about injectors than we do call this the injector's 'knee'.

It is possible that the injector is old enough, that its behavior 'under the knee' has aged worse than its behavior above it.
It is also possible that the wiring to that injector falters at very low currents / voltages / whatever.
Both are also possible - all the stuff involved is over 15 years old ...

 

[mikez71]

i have pro demand to pull schematics i was looking for an internal schematic for the ecm to see if there was a cross over or share circuit inside the board .

Sorry if I missed it, but was a new crank sensor tried?

Saw this video on checking injector drivers.. Looks like you need a scope to check...