Weird voltage fluctuations

[Mike534x]

@Mooseman Thank you! For safe measure, I emailed PCM of NC as well to see if they perhaps know what the idle speeds may be for the 5.3. The steps in the video were what I used during the first round to get the idle to settle down. Should I still attempt that, or force the PCM to relearn on its own by driving around for a few days? Also what kind of values should I be looking for that are considered normal for the 5.3?

 

[Mooseman]

I'd do the relearn just to cover the bases.

Also what kind of values should I be looking for that are considered normal for the 5.3?

Which values? Idle should be between 600-650. Trims shouldn't go no higher or lower than -/+10 although I would start looking at it around +/- 7 or 8. Check for vacuum leaks using carb cleaner.

 

[Mike534x]

I'd do the relearn just to cover the bases.



Which values? Idle should be between 600-650. Trims shouldn't go no higher or lower than -/+10 although I would start looking at it around +/- 7 or 8. Check for vacuum leaks using carb cleaner.

So thats interesting, I completely disconnected the battery left for a half hour. Came outside hooked it all up and the idle is still practically the same. Well its staying more at 550ish now. It still stumbles when giving it gas but its not fully stalling out like it was before. Interesting thing I noticed is that when it stumbles I can hear the whine from the alternator. I'm sorry I meant to put what values were the fuel trims are supposed to be.


I attached screenshots of my fuel trims, they look like they're within spec? At least they seem to be above 7. I'm not sure if I should expect different results from the LH6, but I tried comparing it to my Avalanche with the LM7 and the idle is about 550ish as well, and the throttle is showing 8% at idle whereas mine is at 15% on the Envoy. I'm off to the store in a bit to get some carb cleaner. One thing I'm curious about is, I know the MAP sensor reads and helps the MAF and the throttle body but I pulled it out of curiosity and found it was fouled with oil. This wouldn't by chance cause any issues would it?

 

[budwich]

although the captures are "good", you need to monitor some of these with "displays" to get a better understanding of where they are when.

Further, I am not so sure that those values for long term trim are good... I guess it depends on what the engine was doing at the time. At "normal operating", I would expect idle values to "mimic" zero levels as the engine would have learned how to operate at "no load / idle" well and "zero" is well "zero" meaning no compensation. Of course, I am speaking from 4.2 experience and monitoring trims all the time during trips pulling "heavy".

My guess, given what I would consider low idle speed, is you aren't getting enough air... causing the system to lean out the mixture.

 

[mrrsm]

If you decide to Test the MAF Sensor:

https://easyautodiagnostics.com/gm/4.8L-5.3L-6.0L/testing-the-maf-sensor-1

 

[Mooseman]

Yeah, a bit more data would be good. Maybe doing a log of the trims, rpm, speed would be good.

But even just look at the bits you got, getting that close to -10 is not good. It's taking fuel away as if it's getting too much fuel or not enough air. In other words, it thinks it's running rich.

 

[Mike534x]

although the captures are "good", you need to monitor some of these with "displays" to get a better understanding of where they are when.

Further, I am not so sure that those values for long term trim are good... I guess it depends on what the engine was doing at the time. At "normal operating", I would expect idle values to "mimic" zero levels as the engine would have learned how to operate at "no load / idle" well and "zero" is well "zero" meaning no compensation. Of course, I am speaking from 4.2 experience and monitoring trims all the time during trips pulling "heavy".

My guess, given what I would consider low idle speed, is you aren't getting enough air... causing the system to lean out the mixture.

I'm not all too familiar with fuel trims, so this is new territory for me sadly. I had made a mention that when I removed the MAP sensor from the intake it was fouled with oil. I'm just wondering if it being fouled (I cleaned it) could play a part in the readings being what they are? I know its used to monitor air flow and adjust fuel usage. My thoughts are maybe the sensor being bad comes into play here?

If you decide to Test the MAF Sensor:

https://easyautodiagnostics.com/gm/4.8L-5.3L-6.0L/testing-the-maf-sensor-1

Thanks for the link! I'll have to test it out, I was also wondering if the MAF sensor was going. I know the MAP sensor was fouled with oil, and was wondering if that could affect the system in anyway.

Yeah, a bit more data would be good. Maybe doing a log of the trims, rpm, speed would be good.

But even just look at the bits you got, getting that close to -10 is not good. It's taking fuel away as if it's getting too much fuel or not enough air. In other words, it thinks it's running rich.

I'll try to keep logs going and see if any changes appear. What are the odds of it being a MAF or MAP sensor being the issue?

 

[Mooseman]

The MAP is a definite possibility. You could try cleaning it with carb cleaner but for the cost, I'd just replace it. If you cleaned the MAF, it should be good.

Could also be a lazy or old O2 sensor that's throwing things off. Try the cheaper stuff first though.

 

[Mike534x]

The MAP is a definite possibility. You could try cleaning it with carb cleaner but for the cost, I'd just replace it. If you cleaned the MAF, it should be good.

Could also be a lazy or old O2 sensor that's throwing things off. Try the cheaper stuff first though.

I tried cleaning it but it didn't seem to have an effect. I ordered one off Amazon, its cheap so might as well give it a shot. I didn't think an O2 sensor could cause things to get "wacky". If I have to replace it, good thing I got a brand new one lying around somewhere. I should be able to get away with connecting the MAP sensor without doing another reset hopefully?

 

[Mooseman]

I should be able to get away with connecting the MAP sensor without doing another reset hopefully?

Yes, it's just a straight sensor. If you replace the O2 sensors, then it should be reset.

 

[Mike534x]

Yes, it's just a straight sensor. If you replace the O2 sensors, then it should be reset.

Alright, thanks Mooseman! I'll post updates on what I find out with the battery and if the MAP sensor helps at all.

 

[budwich]

It would appear (based on a quick internet scan) that potentially, idle for "some" on V8 blocks might be lower as you confirm via the comparison with your other truck.... although others comment / complain of idle below 600 as being not very good and having reprogrammed to move towards 600. The idle speed maybe an issue for the alternator but not for motor / vehicle operation. However, I don't believe the trim values are good as I would expect them to be neutral (near neutral) during idle. Further, although I use torque, I ain't no expert.... I am not sure that using the "table" as a "reading display / troubleshooting " is appropriate. That display is basically for determining what PIDs are available to be displayed in other functions. I don't believe that the information that is presented in the table is classified as "real time data" and as such I am not sure that it is reliable for "active" monitoring in terms of finding issues.

One thing, as suggested, if you are still doing stuff towards the alternator / powering, you need to measure the voltage at the ON/OFF pin / connection with the key on / engine off.

 

[Mike534x]

Yeah PCM of NC also said the factory idle speed is 550 as well. Well this interesting and the MAF issue might be something I did wrong. I went to look back under the hood while on my lunch break and noticed I don't have the arrows lined up with the MAF sensor with the ones on the tube leading to the intake. Oops. I suppose that could probably throw everything off then haha. I assume I should go ahead and disconnect the battery again huh? Or drive it around and see if it relearns without the reset?

 

[Mooseman]

I doubt it will make a difference but can't hurt.

One thing you could try is unplug the MAF. It will run on preset values according to the MAP and other parameters. If it improves, it might be defective despite not having a code for it.

 

[Mike534x]

I doubt it will make a difference but can't hurt.

One thing you could try is unplug the MAF. It will run on preset values according to the MAP and other parameters. If it improves, it might be defective despite not having a code for it.

You know....I didn't think to even try that. I just received the new MAP sensor to replace the old fouled one with no noticeable change. I was going to hook up torque and pull in the readings from it to see if they're in line with how its suppose to be.

 

[mrrsm]

Just curious... since the MAP Sensor actually behaves sort of like a BPG (Barometric Pressure Gauge) and uses ambient air pressure to help the PCM calculate the Fuel/Air Tables.... at what Elevation are you situated? By the way... One of our Experienced Members @limequat ALSO does Professional Quality PCM Tunes and Deletes as necessary.... if you need that sort of assistance... you can always PM him.

 

[Mike534x]

I doubt it will make a difference but can't hurt.

One thing you could try is unplug the MAF. It will run on preset values according to the MAP and other parameters. If it improves, it might be defective despite not having a code for it.

I unplugged the MAF sensor, it was stumbling and idling rough and smoothed out after a few minutes. I took it around the block and it still seemed to do it. I'm gonna leave it unplugged and drive it around a bit longer to see if it changes.

Just curious... since the MAP Sensor actually behaves sort of like a BPG (Barometric Pressure Gauge) and uses ambient air pressure to help the PCM calculate the Fuel/Air Tables.... at what Elevation are you situated? By the way... One of our Experienced Members @limequat ALSO does Professional Quality PCM Tunes and Deletes as necessary.... if you need that sort of assistance... you can always PM him.

I think I'm at 577-610 ft. I forgot about limequat! haha, it didn't even cross my mind. I'm so used to PCM of NC.


Could a bad or failing cat have any effect on the idle and my fuel trim levels by chance? The one on the passenger side makes some noise when driving around and banging on it sounds like I'm hitting a coffee can of screws. I chopped it up to being a loose heat shield, its been making noise since late Fall, and seems to have gotten worse since then.

I also have a screenshot from Torque, are these lines supposes to be going up and down? Or are they suppose to be a steady line? I can get a good deal on a new MAF sensor locally, and I assume I should unplug the battery again to reset the PCM when testing the new one?

 

[limequat]

Since both banks are reading similar trims, I'd be looking up stream. Aftermarket filter or intake tube? Or even clogged filter?

 

[Mike534x]

Since both banks are reading similar trims, I'd be looking up stream. Aftermarket filter or intake tube? Or even clogged filter?

I'm using a purolator filter and the stock air box and intake. I just attached the readings I'm getting from the MAF sensor. I can't really think of what else could be the issue besides maybe the throttle body?

 

[mrrsm]

If you have suspect CAT(s) making that "Jingle-Tinkle" sound... it will be pieces of the extremely brittle and hard Ceramic Honeycomb that have fractured enough to make contact with either the side of the S/S 'tin can' and ringing like a Bell ...or actual pieces of the stuff that have broken clean off and settled down into the bottom of the CAT Can. The easiest way to confirm or eliminate this possibility is to do the following:

(1) Park the Vehicle on a level surface and allow the engine to go Stone Cold.
(2) Take a"Dead Blow" Steel-Shot Filled Hammer and LIGHTLY strike the bottom of the CAT Can.
(3) If there are any loose pieces,the energy imparted by the hammer taps bounces the pieces.
(4) The Rebound from the Ceramic Chunks will cause a distinct "loose change on metal" sound.
(5) The Broken pieces of the Ceramic Honeycomb CAN cause an Exhaust Gas Flow disruption.
(6) If performances suffers... an R&R of the CAT might be called for.
(7) This is Important... Fractured, Vibrating CAT pieces can emulate the sound of a CRACKED FLEX-PLATE.

Amazon carries this Inexpensive Tool (among others) here:

https://www.amazon.com/dp/B000QYC26K/?tag=gmtnation-20

 

[budwich]

maybe check your fuel pressure. if fuel pressure is poor, burn is poor reulting in leaning.

 

[Mooseman]

It's actually running rich. PCM is taking fuel away. Maybe not enough air or erroneous readings.

 

[budwich]

yes... the "leaning" is the action taken by the trims to try reduce the richness that the sensors are seeing.

 

[Mooseman]

Ah, thought you meant it was running lean

 

[BRomanJr]

Don't remember the Fuel Trims I had when my 5.3 was idling rough (not bad but it bothered me) I ended up replacing both upstream O2 sensors, some improvement. I cleaned the Throttle body once at 170k shortly after purchase, but it was barely dirty as other V8 owners have noted.
After a few weeks more I decided to try replacing coils, first purchased (4) to start eliminating possible bad ones. This got me nowhere as overall it improved but was difficult to blame any particular coil(s) even after some logical swapping.

Ended up replacing last 4, all Delco/Dephi parts. The result was improved overall idle smoothness (214,000 or so miles at that time) not perfect, but improved.

Not sure if you or others replaced the upstream O2 sensors at any point in your trucks life, worth checking. Also, I replaced my Alternator just before this because of noisy bearings (bought new Delco because original went over 200k), no voltage issues before that I can remember.

Definitely check fuel pressure, so many strange symptoms. I've read that low fuel pressure can cause fuel not to spray properly and droplets don't burn efficiently and cause O2 sensors to "think" it is running rich.

Hope you track it down soon.

 

[Mike534x]

Sorry I haven't updated this in the past week, lots of family things going on that has had me leave out of town.

I took it to the Chevy dealer down the street to have our buddy check it out for the weekend while gone. Fuel pressure is showing up good, I don't remember the exact numbers but it was 55-57 PSI, Upstream O2 sensors appear to still be functioning, maybe they're getting lazy with 184k on the clock. I have one 02 sensor made by Delphi when the the one was going bad on my TB's 5.3 but never got the chance to install it. The passenger side does sound like it has something rattling around but it passed the back pressure test. The thought the PCM needed updating, it has a few updates available but none that pertain to my exact issue. I should have asked for a print out or something along those lines to see what was listed for the newest software version.

Go figure the truck wouldn't stall out for them, while I was able to get it to do it once in the parking lot, and the other times with the idle dropping to nearly stall it. They tested for vacuum leaks but there was nothing.

Could a partially clogged fuel injector be an issue? When they tested the fuel pressure, I think it was done under the truck to see if it was a fuel pump issue. Since its not throwing any trouble codes when it does stall out, I was given the drive it until the light comes on or bring it in when it does break down.

 

[mrrsm]

Same Engine ...Different Problem (Misfires) with a Different Year and Truck Series ... But the Clogged EFI Issue is well covered and the VOP (Video Original Poster) provides some novel ideas on how to deal with the problem:

 

[budwich]

I would expect a clogged injector to cause some misfire counts against that cylinder.

On a recent trip, I changed out the air filter. I saw about a 50% "improvement" in the "leaning action" at normal speeds, average throttle load... going from about -3.1 to about -1.6

When was the last time you changed out the air filter? Mine had about 1.5 years and about 35kkm on it. I looked reasonably clean but maybe not at the "microscopic level".

 

[Mike534x]

I may give cleaning the injectors a shot to see what happens this weekend!

Unfortunately no misfires or any of the sort. I changed out the air filter and cleaned the MAF sensor when I did the alternator swap. So about 20 miles on the new filter.

 

[budwich]

thanks... :-(
back to your "graph of the maf"... if you look at the graph... basically the legend on the values is very small so the graph is "moving" because you are asking for a "plot" of "1/10ths" of grams/s (I think that's the measure). Anyways, the "5.3" seems rather "thin" / low. At idle, I normally see around 6 or above. Bases on the lower reading, it would appear, you are getting relatively low intake of air and hence the system has to lean out your fuel trims to maintain the ratio.

 

[Mike534x]

Update:

I took the truck over to interstate, the battery puts out 750 CCA, and its rating at 800 something on their test machine. They charged it and the cells appear to be healthy since its holding a charge. But it got a clean bill of health by Interstate.

I'm also wondering if my upstream 02 sensors are going bad. I attached screenshots from Torque with readings from Bank 1 sensor 1 and Bank 2 sensor 1. They seem to be rapidly changing from 0.1-.073 in rating, unless that is normal? Bank 1 sensor 2 and Bank 2 sensor 2 are holding steady ratings without really any changes whatsoever. The first screenshot seems to be somewhat consistent, but the Bank 2 sensor is very erratic. There is also a slight MPG loss at the moment, I would easily get about 20 on the highway on the same commute out of town and but I'm getting 18.5 right now.

 

[mrrsm]

ScannerDanner's Video might be helpful at this point:

 

[mrrsm]

...and maybe scouting eBay at this link for some OEM (Chinese on some...?) EFIs just to have them on hand via eBay would eliminate any hassles from having to clean any ...one way or another ...of all that build up from years of driving , As matched sets these can be had for not too much "Bread":

https://www.ebay.com/sch/i.html?LH_...sacat=&_sadis=&_sop=12&_udhi=&_udlo=&_fosrp=1


Like this set... some will be the REAL OEM Delphis, too:

 

[Sparky]

Upstream sensors should bounce constantly like that. Downstream should be pretty steady. Your bank 2 sensor 1 (passenger upstream) could be getting a little lazy though, perhaps, and that could affect things a little.

 

[Mike534x]

...and maybe scouting eBay at this link for some OEM (Chinese on some...?) EFIs just to have them on hand via eBay would eliminate any hassles from having to clean any ...one way or another ...of all that build up from years of driving , As matched sets these can be had for not too much "Bread":

https://www.ebay.com/sch/i.html?LH_...sacat=&_sadis=&_sop=12&_udhi=&_udlo=&_fosrp=1


Like this set... some will be the REAL OEM Delphis, too:

I'm honestly surprised to see Delphis in some of the listings, admittingly $78 seems like a fair price for a set of 8 compared to getting 4 Delcos from RA for roughly the same price. I may look into getting a set and experimenting. I threw 1 1/2 bottles of the techron concentrate plus to help a little bit of the build up until I can get these.

Upstream sensors should bounce constantly like that. Downstream should be pretty steady. Your bank 2 sensor 1 (passenger upstream) could be getting a little lazy though, perhaps, and that could affect things a little.

I wasn't entirely sure how the fronts were supposed to read, I've never had to check them or replace them before. I imagine getting one of them free is not going to be easy, I guess a weeks worth of spraying with PB blaster and a decent size breaker bar could help.

 

[Sparky]

Best thing you can do for O2 sensors is really spray them and heat cycle them and spray again. Do that for a week, driving it as usual, and it helps to break them free.

 

[Mike534x]

Voltage update:

So there has been no change with how the voltage fluctuates. It now does it regardless of the heat or A/C being on. Left a buddy's place last night and noticed "micro/mini" pulsations. Its hard to describe but while driving I could see the headlights dimming/lighting up quickly in rhythm of the pulsations I was seeing on the gauge cluster, radio and climate controls. I have never seen that happen before, it never did this with the old alternator either. It was about 30 degrees out and of course, I see the voltage gauge drop to its usual 11.5-12V and "jump" up to 14 and the pulsations went away. The pulsations happened within the first 6-7 minutes of the drive, and then once the gauge dropped and shot back up that is when it stopped. All grounds in the engine bay look to be good, not much corrosion if any. I jacked up the truck this morning and cleaned up the ground under the driver seat which did have a pretty hefty build up of crud and what not. Took the wire brush and made sure the contact surface with the frame and eye connector were as clean as can be.

Trip #2 to the Interstate facility showed the battery is still coming up in good health, just a little bit low. The only thing I can really think of is that maybe the problem lies within the "reman" alternator. The voltage issue still existed with the original 185k OEM, but the pulsations were never there.

Idle update:

I purchased the reman Delphi fuel injectors in the link @MRRSM posted, have yet to get a chance to do any "under the hood" work. The weather took a quick turn from being a moderate 60-70 degrees up until a week ago, and now its been hovering in the 30-40 degree range. Gotta love the Chicago/NWI weather system. I'll post back about this portion the moment I get a chance to swap injectors, but the truck still wants to come close to stalling out when you try to give it gas while idling. MIght need to put off the 02 sensors until Spring.