5.3 vortec envoy random misfire/ rough idle

2003 GMC envoy 200,xxx miles
Bought this truck with over 6 codes lit up
only issue was rough idle and misfire. P0449 p0300 p0134 p0135 p0154 p0442
What I fixed so far:
Injector bank 2 had a broken/ damaged wire (now I can hear all injector open and close)
Broken spark plug (#1) changed all driver side plugs still plan on charging the ones on the other side soon.
New plugs and seems like I’m getting spark from all wires.
Changed intake gasket and valve cover gaskets
New temperature sensor plug
New knock sensors and plugs.
Cleaned all injectors.
Now all the codes are gone. Except the random misfire code P0300.
New O2 sensors (previous owner had wired the O2 wrong)
O2 sensors bank 1 stays around .2V (recently found out it goes down to 0v at 2000 rpm
Bank 2 runs around .800/.900 V (still have to pull spark plugs to figure out what’s going on on that side.
I’m new to diagnostics and stilll trying to wrap my head around all this so all the help is well needed thanks guys.
Seems like it misfire got worse and now it pops. This is not my daily but would keep trying as soon as I get back home from being on the road.
 

Reprise

Lifetime VIP Supporter
Welcome to the forum! Not a ton of 5.3 owners, relative to the 4.2; always nice to have another one on board. Less than 3% of all consumer-owned vehicles get to 200,000 miles, so the previous owner(s) had to have taken somewhat good care of it.


When you go to replace the bank 2 (pass side) plugs; you may find it easier to go from underneath. Pull the wheel; you'll find a flap on the inner well housing toward the rear, by the frame rail. You can also pull the entire housing back a bit, and if you remove it outright (acknowledging that it's a bit of work), you'll have all kinds of room on that side.

I didn't have to fully remove mine, but I did pull it back a bit, and I had my spring out on that side as I was replacing shocks - that gives a lot of room to get to the front two.

Have a bunch of extensions ready. A bit of anti-seize on the plug threads will help for their next replacement; those heads are aluminum. Oh - and make sure you use the AC Delco iridiums (41-103; IIRC); I bought mine with Bosch plugs, and replacing them made all the difference in idle quality.

While you're ostensibly done with it now... on the driver's side, I did the plugs on that side from up top, and #1 was the worst of them, for me (wound up moving all that wiring and the bracket, and it was still difficult after that) I may have even moved the alternator, but can't remember, TBH.

P0300s can be tough to track down. You may find the below helpful...

Since you were going to replace all the plugs anyway, continue with that. Put in new wires, as well (didn't see you mention these). Next item in that area would be to measure voltage at the coil packs. Unfortunately, since it's a 0300, swapping the packs with one another won't tell you much. If you can get one new one, you can then swap that out with likely candidates to eliminate a bad pack.

If you find a bad coil via process of elimination, getting a 2nd new one to have as a spare can be a good idea, in case you lose another one down the line. Oh, and since you have an '03, like me, you'll likely have the 'square' versions (square heatsinks). Make sure someone didn't swap in a round style - not good to mix / match the versions, IMO.

The O2 sensors may play a part, especially since you said they were wired wrong, and you see voltage issues on both sides. Ignore the rear sensors for now; while they may be marginal and even throw a code, the *front* ones are the critical ones to make sure they're operating optimally. If not, they can toast your cat(s) (which can contribute to the P0300s)
Do a backpressure test on them if needed, to check.

You've cleaned the fuel injectors; if you're getting good pressure with all of them, that eliminates another cause of the misfires. If one is weak, check to make sure the fuel rail pressure is good at that outlet. If more than one is weak, and especially if on opposite sides, make sure your fuel filter has good throughput (you have the external type, on the D/S frame rail just behind the front door.) If it's weak there, the fuel pump may be marginal. Unfortunately, it's an in-tank design, and there's no access cover up top (unless you cut one out) - you'll need to drop the tank to replace it.

IIRC, there's a fuel pressure regulator to check out, too, but I forget where it is as I write this. Pretty sure it's nearer the fuel rail than the pump end.

At that point, the 'major' things have been pretty much eliminated / ruled out for the misfires, but there's a few left. Start with those, and let us know how you come out.

Also, there are others here besides myself who are more knowledgeable, so stay tuned to see if any of them proffer any potential solutions I haven't mentioned.
 

TollKeeper

Well-Known Member
What kind (brand) of O2 sensors did you use? I hope they are the ACDelco's, if not, you are going to have problems.

I would first finish up on doing a straight up tune up, dont use the cheapo spark plugs, they will cause nothing but problems. I personally recommend the ACDelco double platinum's, but have been told the AutoLite Double Plats work just as well. Using anything else is asking for headaches.
 
OP
OP
I
sorry guys between work and school I kinda gave up on trying to figure out what’s going on with this vehicle lol.... so far
I have replaced intake gaskets dealership said they think it’s the cause “NOT”
I currently have all brand new plugs , spark plug wires, and all coils seem to give enough spark.
After I put the intake and everything back together cleared the codes and started messin with the harness a little bit. Now I’m getting P0174 a bank 2 lean code with the p0300 multiple misfire also car pops and runs like crap, also could the Evaporate selinoid po449 somewhat related to what’s going on here ? . Pulled spark plugs “the new ones after letting it run for 40 minutes” and they have a ton of carbon deposit on them already. How can I test the harness for proper voltage ?
 

Mooseman

Moderator
P0449 is not likely to cause a lean condition. It's not giving an evap leak code.

Either one of two things might be causing a lean code. Either it has a vacuum leak or it's not getting enough fuel. @Reprise mentioned fuel pressure. Was this checked? For vacuum leaks, check with carb cleaner. Search for YouTube videos on how to do this.

Another thing to look for is water in the fuel. My son had bad misfires caused by this. We pumped out about 2 liters of water from the tank. We just disconnected the fuel line from the rail and ran the pump. Right away, we saw the water at the bottom.
 

MRRSM

Lifetime VIP Supporter
With 200,000 Miles on the Engine and with Carbon Clogged Spark Plugs you mentioned as another indicator... it might help to perform an ACDelco Top Engine Cleaner Treatment. While doing this task on the GM LL8 In-Line Six Cylinder Engine is very straightforward ...the V8 Engines may be a bit difficult .

However... after recently examining the 5.3L in my truck... I was thinking that by getting one of the Compression Kits from either Amazon (Skemidex Brand) or from Harbor Freight ... it would allow you the chance to Use just the Hose Threaded for the Spark Plugs from this Kit as the means to Guide the TEC Nozzle Spray into each Cylinder... and fill them up on both banks to the brim... without spilling a single drop.

https://www.amazon.com/dp/B07C9X163V/?tag=elightbars-20

SKEMIDEXXOMPTESTER.jpg

After leaving that stuff performing a "Cylinder Soak" for say... half a day when the vehicle can sit idle... to avoid Hydro-Locking the Engine... first pull out the Fuel Pump Relay ( on a Fully Charged Battery) ...and then crank the Motor over long enough to push out the gooey excess TEC and Black Carbon Mung from inside of the (8) Cylinders and catch that stuff with some packed in Scott Blue Shop Towels. Doing this TEC Treatment will definitely improve Ring Compression and re-establish the proper TDC "Quench" that the Carbon Build Up and Gas Gummy Lacquer in combo ruins the C/R, causing pre-ignition and misfires when the stuff gets accumulated in the tops of every cylinder and packs into the Ring Grooves trapping them tightly therein.

AFAIK... There are no contemporary Threads that cover this specific procedure for the GM Vortec V8's... but Carbon Buildup ...is Carbon Buildup, regardless of the the engine design ...and this TEC stuff might surprise you with Good Results. The longer you leave it inside of the cylinders... the better it works. If the Hose is used with this TEC Powerful Solvent... flush the Rubber Line clean with some Spray Brake Cleaner afterwards so the hose is not ruined... and then it can do double duty as an intended Compression Tester, too if needs be.

https://www.amazon.com/dp/B007Q102AE/?tag=elightbars-20

ACDELCOTEC1.jpg
 

Mooseman

Moderator
@MRRSM , have you tested TEC and how it affects rubber hoses like in compression testers? This stuff is powerful and may just turn the hose to goo.
 

MRRSM

Lifetime VIP Supporter
It just might... but for the minimal amount time the ACDelco TEC would be getting sprayed down through the Neck of the Air-Fitting Side of the Compression Hose and past the Spark Plug Holes... it probably will not have that much of an effect on the Rubber Lining ... especially as suggested earlier that the Compression Hose should get purged with Brake Cleaner immediately after topping off all (8) Cylinders.

But ... What The Hell... Let's Give it 'Real Test Try Out' to find out for sure... Yes?

I have assembled everything needed to do this scientifically as shown in the attached Images. As you can observe... it does become necessary to remove the OEM installed Schrader Valve... so the Tool shown ...or something like it ...will be needed open up the pathway for the TEC Spray.

I'll be using use the ACDelco TEC Foaming Spray as displayed and completely spray down and submerge the entire Hose inside of a Plastic Zip-Lok Baggie and leave it in there for 24 Hours. Of course, ordinarily... This is something I would NEVER do on purpose. But the Question you raise here is a valid one... and it does deserve a definitive Answer. I'll follow up on this within a Day or so and post up the Results with Images:

Uhhh.... The 'CAN ' of TEC will NOT be inside of the Baggie during the Test... Just the Foaming TEC of course... I just wanted to show it in there now... to convey the idea of what is about to happen... :>)

ACDELCOHOSETEST1.jpg

ACDELCOHOSETEST2.jpg

ACDELCOHOSETEST3.jpg

ACDELCOHOSETEST4.jpg

ACDELCOHOSETEST5.jpg
 
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OP
OP
I
I have never had to do a top end clean up... will look more into it will def help clean all that gunk out. Just found out that the cats been removed and installed straight pipes (could the downstream o2 cause fouled spark plugs) this creating all these issues ? Not related but I have a 1998 trans am with an ls3 swapped rear O2’s removed and never had any issues with it
 

Reprise

Lifetime VIP Supporter
OP - the Envoy s/b the same as the T/A, w/ regard to those downstream O2 sensors, I would imagine. However - if the converters have been removed (you have 2), that may (?) complicate the remedy somewhat, if emissions turn out to be the underlying cause.

Just a thought on the top engine cleaner, and putting it into the cylinders - I would think that having the associated cylinder at BDC would be beneficial when adding the cleaner - so doing this in at least *two* steps would give the best chance of freeing up more of the gunk?

If true, then I'd use one of those USB borescope cams (Amazon, eBay, et al) to determine which of the cylinders are at / near BDC... insert the cleaner in those cylinders only & wait the prescribed interval...then after extracting the cleaner from those, turn the crank so that the other half of the cylinders are at / near BDC, and then do those. I think you need 2 x 360 degree revolutions of the crank to get from TDC to BDC - the camera will help you determine that, though.
 

MRRSM

Lifetime VIP Supporter
Our Expert PCM Tuning Members @limequat and Kelly@PCMofNC can answer any questions about what can happen and what needs to be done to handle any changes caused by a CAT Delete.
 

Mooseman

Moderator
All the downstream O2 sensors do is report if the cats are working properly. To keep the CEL off, either the PCM was tuned or spacers (commonly called spark plug defoulers) were added to the sensors to pull them out of the exhaust stream and fake the cat's presence.

Sounds like you inherited a basket case with all these problems. Have you checked the basics? Vacuum leaks, fuel pressure, compression test?
 
OP
OP
I
I just got done doing a pressure test on all cylinders highest reading was 150 psi lowest was 133psi which is still sitting the 15% of the highest reading. After I changed the intake gasket I cleaned the valve covers from all the gunk and now room them back off to check to see if any lifter or valves are loose to find out there is this creamy stuff all over them almost looks more like water residue then oil got a sample of the fuel off the rails and no trace of water in there, no foul smell in oil from dip stick. And all cylinders are holding decent pressure
 

Attachments

Mooseman

Moderator
Is the coolant level stable? Not loosing any? Do you drive it enough to get it hot to burn off condensation?
 
OP
OP
I
the truck does not overheat at all, don’t loose coolant. I drove it for about 10 miles I’d think Its enough to burn all condensation. Is there a way to get all that stuff cleaned up ? I have noticed that a couple push rods are super dry compared to the others the video is too large to upload on here what could cause push rods to be dry ?
 

Mooseman

Moderator
I was asking about coolant level, not overheating. If coolant level is going down, it might be leaking into the engine. What does the oil itself look like? Maybe a flush might clean it out.

10 minute drives are not enough to fully get an engine to full temp and dry out condensation. What does the temp gauge show? Straight up or slightly to the left? Maybe the thermostat is defective. If that's the case, hopefully your cat is fine.
 

TollKeeper

Well-Known Member
Good compression.. So that only leaves a few possible options. So we all know the basic componets to a engine running, It needs air, spark, and a fuel source. So thats where I would start.

Is the coil operating, if the coil is operating, is that spark making it to the spark plug electrode, and what color is the spark (a nice bright blue is desired, not orange).

Is the fuel injector opening and closing, is fuel passing thru it when open, is fuel not passing thru it when closed, when pulsed open is the required amount of fuel passing thru it.

Is the intake valve opening, is the exhaust valve opening, is the intake runner for the cylinder possibly blocked.
 
OP
OP
I
Thank you guys for all the help you’ve all been awesome and provided allot of useful information. I just picked up an ly6 crate motor and will be installing a cam kit in it soon. Any threads on here on what all I need to do to make it work in my truck ? I know I have to get a vvt delete kit,will be installing a trunion upgrade kit with dual springs etc... Can I tune the cam/ crank sensors or should I just go with the lingerfter conversion box (like I did for my ls3 swap on my 98ws6)? Please direct me to the right thread if available or I can make a new thread thanks in advance peeps
 

Mike534x

Well-Known Member
I take it you went with the LY6 for power? A 5.3 LM7/L59 or 6.0 LQ4/LQ9 would have been cheaper and a straight plug and play drop in. Aside from getting the PCM re-programmed with no worries about deleting certain bits/rewiring to make everything work.
 
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Mooseman

Moderator
You'll need a PCM at the very least since the LY6 has a 58x reluctor whereas your LM7 is a 24x. I can see major wiring work and the BCM may not like talking to the new PCM given the changes between these generations.

So how did we go from a misfire and rough idle to an engine swap?
 

TollKeeper

Well-Known Member
OP
OP
I
I was already planing on swapping this motor out anyways and most likely doing a turbo build with it... I guess someone can buy this t/o motor if they need it. Im sick of running in circles took it to a couple mechanics and they couldn’t figure out (they said lifters probably bad). I’d rather start with a new motor then sit here trying to chase my tail I guess

You'll need a PCM at the very least since the LY6 has a 58x reluctor whereas your LM7 is a 24x. I can see major wiring work and the BCM may not like talking to the new PCM given the changes between these generations.

So how did we go from a misfire and rough idle to an engine swap?
Probably run a lingerfelter conversion box that way I don’t have to mess with tb and wiring
 

Traz

Well-Known Member
@ImmortalTechnique I would get a hold of RevHard, the mans a genius with these platforms. he swapped out his 4.2 for a 5.3 I'm sure he could give you some advice on how to get everything in and out easily. seriously hes a master,

also, me and capote are working on everything turbo for the 4.2 right now if you want to join in weve made considerable progress with a lot of the job
 
OP
OP
I
Good compression.. So that only leaves a few possible options. So we all know the basic componets to a engine running, It needs air, spark, and a fuel source. So thats where I would start.

Is the coil operating, if the coil is operating, is that spark making it to the spark plug electrode, and what color is the spark (a nice bright blue is desired, not orange).

Is the fuel injector opening and closing, is fuel passing thru it when open, is fuel not passing thru it when closed, when pulsed open is the required amount of fuel passing thru it.

Is the intake valve opening, is the exhaust valve opening, is the intake runner for the cylinder possibly blocked.
So I figured while I build this ly6 6.0 motor I can take a look at the 5.3 still sitting in the truck, allot of gunk on top of pistons and combustion chambers from. None of the push rods are bent and all lifters look fine (rollers are in good shape no cracks, not sure if there is a ) I tested valves they aren’t leaking either
Good compression.. So that only leaves a few possible options. So we all know the basic componets to a engine running, It needs air, spark, and a fuel source. So thats where I would start.

Is the coil operating, if the coil is operating, is that spark making it to the spark plug electrode, and what color is the spark (a nice bright blue is desired, not orange).

Is the fuel injector opening and closing, is fuel passing thru it when open, is fuel not passing thru it when closed, when pulsed open is the required amount of fuel passing thru it.

Is the intake valve opening, is the exhaust valve opening, is the intake runner for the cylinder possibly blocked.
Is the fuel injector opening and closing, is fuel passing thru it when open, is fuel not passing thru it when closed, when pulsed open is the required amount of fuel passing thru it.

Is the intake valve opening, is the exhaust valve opening, is the intake runner for the cylinder possibly blocked.
[/QUOTE]
So I figured while I build this ly6 6.0 motor I can take a look at the 5.3 still sitting in the truck, allot of gunk on top of pistons and combustion chambers from. None of the push rods are bent and all lifters look fine (rollers are in good shape no cracks, not sure if there is a ) I tested valves they aren’t leaking either. Will be putting it back together and figure out the root of this issue. I had the dealer check my coils and injectors. They said both were working fine. I checked the injectors to see if they opening and closing but I’d have to do a bench check to make sure they are spraying correctly. I took this truck to 3 different mechanics and a GM dealer they all told me I have a collapsed lifter. Do you know how to check for voltage at coil plugs ? And maybe I can check all the harness while it’s within reach. Thanks again fellas
 

Traz

Well-Known Member
 

HARDTRAILZ

Moderator
Avoid revhard. he is banned for good reasons. Actually it was his second time being banned and he is not one that I would trust to wash my truck, much less work on it.
 

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