Help (!/?) [UPDATED - AT BOTTOM]

"Smallbear wants a modern Syclone, local Maple Leafs spammer" (smallbear94) 08/01/2019 at 09:01 • Filed to: None

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My truck has some issues... BESIDES the fact that it’s a 1st Gen Colorado. Beat you to it. You know who you are. Internet Diagnosis plz? (WebMD says it has cancer.)

(Video for thumbnail purposes as I cannot upload pics anymore)

The Facts:

- 2010 Chevy Colorado, LH9 5.3L V8, ~145,000KMS, has been tuned

- !!!error: Indecipherable SUB-paragraph formatting!!! I started getting a P0420 code. I just kept clearing it, on the basis that if the cat was fucked I couldn’t be bothered un-fucking it until it was actually causing drivability issues... and if it was the downstream sensor that had issues, I wasn’t terribly worried because the downstream O2 sensor is really only there to see if the cat is working or not. Plus, it only came on every couple weeks or so.

- Truck has had a slight stutter at 3500-4000 RPM for some time now. Recently this got much worse, but still went away after crossing the 4000RPM mark.

- A few weeks ago I started getting P0420 again. This time it was much more persistent, a couple times a week up to an almost daily CEL.

- Shortly after the P0420 came back, I had a very brief misfire at 5100RPM that set a P0300.

- After the P0300 came on I ran a couple bottles of injector cleaner through for shits and giggles to see if it would do anything at all.

- On the tail end of the second injector cleaner tank I was accelerating uphill on the highway, AC on, again at roughly 5100RPM, and I got a very definite misfire (I throttled back as much as possible, but had to more or less stay in it as had a person behind me catching up).

- The “person behind” also happened to be in convoy with me... and remarked that the truck smelled like no cats when I was on the gas.

- Timing the truck 0-60 indicates I’ve lost between 1-1.5 seconds over the last 3 years. (Admittedly with several different timing methods) Also looks like 1 second in the last year. So it definitely was down on power.

- Seemed to me the best thing to do was to change all the easy things that could be suspect... on the basis that for the cost of getting a proper diagnosis, I could install the parts myself. Seemed like I had a good shot at fixing the problem and I’d have new parts where they were probably ready for a change anyway. So, I ordered new O2 sensors, plugs and wires.

- New plugs and wires seemed to make a slight difference, in that the mid-range chatter subsided a little and the high RPM misfire went from ~5100 to ~5600RPM. Also cleaned the MAF, that seemed to completely erase the mid-range chatter... at least around town.

- Plugs had a little carbon buildup around the flat area at the very end of the threads (facing directly into the cylinder), but the electrodes and the insulator were a beautiful light brown. However the threads on all 8 were wet. *shrug*

- Next day, get on the highway... no. At highway speeds, it still chattered under load, and while there was definite improvement, it was quite slight. Did seem to edge the 0-60 numbers in the right direction, but the margin of error is so huge I’m not really putting much faith in that.

- Remember that bit about changing stuff myself so I paid for new parts instead of a diagnosis? Yeah... at least a couple O2 sensors were stuck so hard I had to take it to a pro anyway. Oh well. Anyway, part of the reason I bought them was that not only were they a possible cause of the P0420, the voltage output from one of them was erratic enough that I didn’t trust it anyway.

- New sensors went in this Tuesday. The O2 voltages were slightly different from the old ones, so something was going on for sure. Also, the fact that the engine light hasn’t come back on is a giveaway.

- Old O2 sensors varied from side to side. The Bank 2 sensors had a thin wispy white layer on them, no carbon. The Bank 1 upstream sensor had carbon on the base but the tip was clean. It had been too stuck for me to handle but came out OK for the mechanic. Bank 1 downstream had been totally seized and had shredded it’s threads on the way out. It had more carbon around the base, and evidence of physical damage on the tip. Scratches and debris inside (Could have been from removal, or maybe the mechanic dropped it... but I have an idea this was all there before removal).

However. Problem NOT solved.

- Midrange chatter is gone or almost gone. So that’s nice.

- Top end(5100RPM+) misfire appears to be drastically lessened, but still present.

- I haven’t rechecked acceleration yet (which is basically my only measure of power loss).

- Downstream sensors are reading roughly 0.6-0.7v which is pretty much what I’ve always seen when the truck has been running right.

- Fuel trims are within the +/- 10% range—I haven’t done the proper idle/1500/2500RPM check yet—but LTFT on both banks is generally positive (Bank 1 more so than Bank 2) at idle and dips negative the second any throttle is applied. I found diagnostic charts for other LTFT behaviours, but nothing matching that. STFT I can’t say much about as it adjusts too fast... but I can see that the combined STFT and LTFT combined generally stays well within the +/- 10%. Not sure what any of that means and would be glad of help. Maybe it’s normal. I’ll do a proper test and update this.

- I have not checked into the PCV system, EVAP system or injectors. I do tend to run the tank to the LOW FUEL light and when filling I do two extra clicks, after giving the fuel time to settle between them (as suggested to me by an Oppo as a way to normalize fuel economy numbers between different pumps).

- There has been a noise at idle on the drivers side (as best as I can tell) for quite some time. I’ve asked the dealer to have a look before and they came up empty. WAG’s about what it may be include an injector (*shrug*), a lifter (I don’t have AFM, but it’s still not unheard of for a 5.3 to have lifter noise), weak valve spring (really doubt it, but...), piston slap (again, typical 5.3 noise apparently), small exhaust manifold crack. Anything from a “tsht tsht tsht” to sounding kinda like a really quiet 7.3 Power Stroke.

!!! UNKNOWN CONTENT TYPE !!!

My going theory is that a fluffy Bank 1 upstream O2 sensor messed with the mixture long enough to fry the cat, and the downstream sensor caught in the debris as it let go. And now the added restriction is causing the top end misfire to persist. Dunno, I’m not a mechanic. I’ll try to get more info if it’ll help.

Help please?

!!! UNKNOWN CONTENT TYPE !!!

- So the P0420 code did come back after about a week, and then every couple days after that. The misfire was nowhere near as bad, but it was still there when I ratted it to 5100+RPM on the highway. All in all I’m convinced the sensors were bad for it to improve that much.

- Also noticed that at idle, it was bouncing in and out of closed loop. As soon as I moved anywhere, it would switch back to closed loop and stay there until the next stop.

- I got the rear cat removed and the front cats gutted yesterday. Much better throttle response, pulls clean all the way up, doesn’t make a horrible racket either... at WOT.

- Part throttle is another story. At 1800 to 2500RPM - ie, the exact range I need for DD purposes, it’s obnoxious and sounds like shit. Most likely because of the big hollow shell it get to play in now. So that’s a thing I’ll have to work on. Oh well, I guess #neverlift?

atfsgeoff > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/18/2019 at 15:32

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Unbolt exhaust, physically inspect catalyst.

Michael > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/18/2019 at 15:47

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Italian tuneup. Load up the bed, pull a trailer and get everything good n’ hot.  After inspecting the catalyst like aftsegeoff said

Smallbear wants a modern Syclone, local Maple Leafs spammer > atfsgeoff 07/18/2019 at 15:53

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Thanks.

Also, shit. This thing is tighter than a frightened nun to work on since it was never meant to have a V8. This is where I have to start paying people I think.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Michael 07/18/2019 at 15:56

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I should have said I’d been doing Italian tuneups (kinda—holding 2nd or 3rd gear most of the time and beating on it a bit) for 2-3 weeks when I first got the P0300.

I guess I’ll have to slide a camera in the O2 sensor hole and see what’s going on. If I can’t see then this is where I start paying others to do my dirty work—like I replied to aftsegeoff it’s tighter than a frighened nun down there.

Michael > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/18/2019 at 16:00

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Any rattling when you knock on the catalytic converters?

ITA97, now with more Jag @ opposite-lock.com > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/18/2019 at 16:06

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Have troubleshooted the fuel system? I’d be curious if that high RPM misfire isn’t a momentary lean condition. Fuel filter or weak pump on its way out?  I’d stick a fuel pressure gauge on it. Beyond the standard pressure test, it can sometimes be worthwhile to stick the gauge under the windshield wiper where you can see it and take test drive. I’ve seen an occasional weak fuel pump that met the specs of a static or idle test, but couldn’t deliver enough under load and you could watch fuel pressure drop under high RPM/high load situations.

merged-5876237249235911857-hrw8uc > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/18/2019 at 16:07

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Yeah you really need to check out the cat.This is from a G6 that was misfiring for a while.  Can’t imagine it breathes too well with that type of restriction.  

Long_Voyager, Now With More Caravanny Goodness > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/18/2019 at 16:09

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It’s very likely a bad cat is/has been causing the 420 code from the start....

Long_Voyager, Now With More Caravanny Goodness > atfsgeoff 07/18/2019 at 16:10

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Unbolt exhaust, throw away cat, install straight pipe.

Probably still be cleaner then how you’v e been running it the last 3 years.

Highlander-Datsuns are Forever > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/18/2019 at 16:32

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Plugged cat/exhaust.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Highlander-Datsuns are Forever 07/18/2019 at 17:15

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Here’s hoping not, but isn’t a very strong one.

Next question after that would be whether that's a symptom or a cause.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Long_Voyager, Now With More Caravanny Goodness 07/18/2019 at 17:19

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But if that was the case, why would it a) go away for 6 months and b) not come back with the new sensors installed?

Not saying you’re wrong, because frankly I really don’t know much and I’m out my depth. But is that possible?

Anyway, I’m pretty much convinced that cat is bad for sure now, but I wanted Oppo’s thoughts on whether a bad cat would be the cause of the problems, or a symptom of something else.

Thanks for the input.

Highlander-Datsuns are Forever > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/18/2019 at 17:22

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C ause. I had a plugged exhaust, replaced it and all was good.

Smallbear wants a modern Syclone, local Maple Leafs spammer > merged-5876237249235911857-hrw8uc 07/18/2019 at 17:22

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Eek. Did that cat just go bad on its own though, or was it a symptom of another problem? If possible I’d like to figure that out before dropping $700 on a cat. I don’t want to end up replacing it twice if I don’t have to.

That said, Ontario has scrapped the emissions testing for private vehicles, so I could just gut it if it came to that...

Smallbear wants a modern Syclone, local Maple Leafs spammer > ITA97, now with more Jag @ opposite-lock.com 07/18/2019 at 17:26

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I haven’t gone in depth , mainly because I don’t know where to start. All I’ve done is check fuel pressure via OBD2, 56psi Key On Engine Off, 43.5psi with engine on. All of which is apparently normal.

I have been suspicious of an injector for a long time (because of the noises I mentioned in the post) but I don't know where to go with that as far as diagnostics go.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Michael 07/18/2019 at 17:27

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Haven’t tried. Good call, I’ll check that.

Thanks!

Smallbear wants a modern Syclone, local Maple Leafs spammer > Highlander-Datsuns are Forever 07/18/2019 at 17:29

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Good to know. Just asking because pretty much every article/forum/insertsourcehere I’ve come across is saying the cat usually is the victim of something else that needs fixing and you’ll end up doing the job twice.

Thanks!

Smallbear wants a modern Syclone, local Maple Leafs spammer > Long_Voyager, Now With More Caravanny Goodness 07/18/2019 at 17:44

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I like this thought. Conveniently, Ontario recently did away with private vehicle emissions testing...

TheRealBicycleBuck > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/18/2019 at 18:07

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I used to top off my tank like you describe, but I stopped after reading several articles about how it can screw up the evap system and cause engine problems. I asked a couple of mechanics I know and trust (one is a good friend and the other is my cousin). Both of them confirmed it.

If you want consistency, try to use the same pump with the same procedure all the time.

Besides, how much fuel do you really get by topping off? It can’t be more than a pint, maybe two. That’s less than 1% in a 14 gallon tank.

Smallbear wants a modern Syclone, local Maple Leafs spammer > TheRealBicycleBuck 07/18/2019 at 18:30

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I’ve got a couple hundred ml in after the initial shutoff, I’ve got over two litres. All depends on the pump I think.

Doesn’t matter, everything you say is accurate... And in the long run—heck, after 3-4 tanks—you’ll get your true mpg figured out. I also fill up at the same pump when possible. I happen to be anal about stuff though and it’ll eventually cost  me if I can't bust the habit

merged-5876237249235911857-hrw8uc > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/18/2019 at 20:53

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It was misfiring due to needing new plugs and maybe a coil pack but it was from the misfires that killed it.

DipodomysDeserti > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/18/2019 at 21:50

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Does your truck have cylinder deactivation? If so there’s an updated valve cover. The original one would drip oil right into one of the cylinders causing misfires. I replaced my dad’s on his ‘10 Silverado a few years ago. The new cover and gasket were around $50. Took me maybe 45 minutes.

Smallbear wants a modern Syclone, local Maple Leafs spammer > merged-5876237249235911857-hrw8uc 07/18/2019 at 22:07

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This sounds like it could be very relevant

Smallbear wants a modern Syclone, local Maple Leafs spammer > DipodomysDeserti 07/18/2019 at 22:11

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Nope. Colorado never got that. LH9 was updated from the LH8 by adding VVT, but AFM never made it.

Long_Voyager, Now With More Caravanny Goodness > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/19/2019 at 06:52

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When the front cat was failing on our Stratus I would get an intermittent code. Installed new sensors, code went away for a while. When it came back it was accompanied by misfires and severe performance loss. Imagine the surprise when it was found to be 80% clogged.

Needless to say I wasn’t spending $1800 to replace the cats, so $1k later I had custom 3-1 headers, full exhaust, and a tune.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Long_Voyager, Now With More Caravanny Goodness 07/19/2019 at 07:16

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IMO t hat runs counter to any logical thought... So it’s good to know it can happen. Thanks tons.

Long_Voyager, Now With More Caravanny Goodness > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/19/2019 at 07:41

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Yes and no. That po420 code is coming on for a reason, that reason can be that the reading difference between the front and rear O2s is too far out of range, a sign that the Cat isn’t working properly. Most of the time an O2 code isn’t actually an O2, it’s thrown by something like a faulty cat/MAP/MAF/Injector etc causing the vehicle to run out of range. The O2 in turn picks up this out of range and throws a code saying “hey, shit’s not running right here bro!”.

If you replace the O2s, it can take some time for the ECM to “retune” for the new sensors combined with new sensors giving different readings, it can sometimes take quite a while to tune and throw a code again.

All the while you are driving around with an improperly tuned vehicle, making the initial problem even worse. Once the cat gets bad enough, the excess backpressure can cause misfires due to the cylinders not being able to evacuate properly.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Long_Voyager, Now With More Caravanny Goodness 07/19/2019 at 08:18

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Did the Stratus initially run better after changing the sensors?

Long_Voyager, Now With More Caravanny Goodness > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/19/2019 at 10:08

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It seemed to, yes, until it got significantly worse.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Long_Voyager, Now With More Caravanny Goodness 07/19/2019 at 10:23

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Well then.

Long_Voyager, Now With More Caravanny Goodness > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/19/2019 at 12:27

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IIRC the ultimate cause of the cat failing was a faulty MAF, which would cause it to burn rich/lean depending on conditions, but the cat is what ended up wreaking havoc.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Long_Voyager, Now With More Caravanny Goodness 07/19/2019 at 16:37

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That didn’t seem dirty, but I cleaned it anyway. So if that was causing the problem, it should be fixed now.

The concensus is pretty clear here though that whatever caused it, the cat is the current issue. So I'll be looking after that.

Long_Voyager, Now With More Caravanny Goodness > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/19/2019 at 16:59

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It’s a GM, the MAF can be brand new and be junk. I have no hate for GM, but their MAF sensors are terrible.

I would definitely start at the Cat regardless.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Long_Voyager, Now With More Caravanny Goodness 07/19/2019 at 20:25

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$ 60-80 part... I’d be kinda pissed if I messed with the cat and it was the maf all  along, but I'm going to start at the cat anyway I think

Long_Voyager, Now With More Caravanny Goodness > Smallbear wants a modern Syclone, local Maple Leafs spammer 07/22/2019 at 07:02

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The joyous part is the MAF will cause it to throw O2 codes because it throws off the A/F mixture.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Long_Voyager, Now With More Caravanny Goodness 08/01/2019 at 09:04

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Went with gutting the cats. Sounds like shit under part throttle but the response and top end power is back. I need to get someone to run a straight pipe through the cat I guess.

Work in progress, but better than a strangled engine.

Grindintosecond > Smallbear wants a modern Syclone, local Maple Leafs spammer 08/01/2019 at 10:01

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Is your computer truck is plugged in to an outlet ?

Have you turned your computer truck on?

please have the operating system disk insert to your computer truck.

What? Oh, yessir. The weather is mild today  in India Indiana.

Grindintosecond > Smallbear wants a modern Syclone, local Maple Leafs spammer 08/01/2019 at 10:05

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On a serious reply, is it the same with a reset to normal tune? I had a focus act like that when the coil pack melted a tower for a plug wire. But that was the easy one. I had a Bosh K-jet powered Volvo do that kind of misery when the whole fuel injection manifold and all the injection gaskets and o-rings started leaking air. I t behaved badly rich in all the weird places. I can’t help on this, but going back to factory fresh tune to begin with should help remove another variable for testing/checking ignition and fuel sy stems individually.

Long_Voyager, Now With More Caravanny Goodness > Smallbear wants a modern Syclone, local Maple Leafs spammer 08/01/2019 at 10:06

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I straight piped our 04 Colorado with the 3.5L. It had an interesting sound, kinda ricey down low, raspy in the higher revs. I can’t imagine a 5.3L would sound bad with gutted cats. Maybe just add in a resonator of sorts to mellow out the sound?

WildlyMild > Smallbear wants a modern Syclone, local Maple Leafs spammer 08/01/2019 at 10:22

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Exhaust manifold bolt on the head is common at that mileage. Also creates a ticking noise. Most prominent on cold starts.   Also possible intake leak after MAF could be giving you those symptoms. Dont see cats very often.

But I only see the broken cars so my perspective may be a bit skewed.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Grindintosecond 08/01/2019 at 10:35

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Dammit, I knew I forgot something. Should’ve figured it out from the CD dangling out of the dash.

Smallbear wants a modern Syclone, local Maple Leafs spammer > WildlyMild 08/01/2019 at 10:50

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I have to admit I’ve wondered, but I had it in at the dealer for other reasons (semi-annual, oil change and tire swap because I’m lazy ) a couple weeks after it started making the noise, *couldn’t duplicate*. Of course this is the same place that didn’t catch a filthy MAF on my brother’s car so their word doesn’t carry a ton of weight.

As far as an intake leak goes, since yesterday’s cat gut I’ve noticed that it whistles/whines a little bit at or just off idle. It’s not an unfamiliar noise, I’ve heard 5.3's make that noise before... but it’s funny that it showed up immediately after the cats were eliminated. I don’t remember if the noise was there when I first got the truck or not, and it’s been about a year since my first P0420—maybe the *new* noise comes as a result of the increased airflow out the ass end? In that case do you think it’s plausible that there is an intake leak and that with the front cats clogged it couldn’t suck enough air to hear it?

I’m almost positive it’s a normal 5.3 noise I’ve heard before though.

Grindintosecond > Smallbear wants a modern Syclone, local Maple Leafs spammer 08/01/2019 at 11:05

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intake leaks....on my volvo with the problems it had, all they had to do was spray ether at the engine bay with the hood up, just lazy around the engine, and it would bog down, meaning it had a pretty bad intake leak.

Smallbear wants a modern Syclone, local Maple Leafs spammer > Long_Voyager, Now With More Caravanny Goodness 08/01/2019 at 11:08

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Conveniently, there’s a stretch of straight pipe where the secondary cats were. I p lan to do something there if the noise doesn’t grow on me.

I know it’s not the task of a resonator, but do you have any idea how much volume they’ll cut? Frankly it’s too loud right now for my liking. I was thinking originally to throw a couple really small mufflers in there but that wouldn’t be likely to solve drone would it?

Kinda funny (and also irritating), earlier this year the cheap muffler install had reached it’s 3-year non-stainless life expectancy and fell off. I hadn’t been completely satisfied with the volume I got from the Borla (tone was fantastic) so I stepped up to a Magnalow, which had about a perfect volume. Maybe a little quiet still but all in all really nice. Now it looks like I should’ve just stuffed a Borla back in :D/:(

Smallbear wants a modern Syclone, local Maple Leafs spammer > Grindintosecond 08/01/2019 at 11:15

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No idea. I really don’t want to do that if I can avoid it since the guy who did the tune is an hour or more away and not readily available. Not many guys closer either, and most of them specialize in Euro stuff.

I’ve though about the possibility of a sticky inject or because of the noise and the fact that the symptoms are so vague that it could be literally anything underhood, but I never thought about bad gaskets on the injectors. Interesting.

Long_Voyager, Now With More Caravanny Goodness > Smallbear wants a modern Syclone, local Maple Leafs spammer 08/01/2019 at 12:30

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The resonator will cut out tones and cut some volume. Generally if people don’t like their exhaust sound, adding a resonator is my go to, 9 times outta 10 it works perfectly.