Rough idle in drive, runs rich, catalyst P code

coleman

Original poster
Member
Dec 4, 2011
86
Got a strange issue on my 02 TB.

When in Drive at a light, most of the time the engine will shake. Some days it doesn't. This morning it didn't. I had the motor mounts replaced a few years ago. I don't think that's the problem. I've also lost MPG and the engine is running rich - so rich that when I start the car in the morning, all you can smell is gas from the exhaust pipe. Now, I got an SES of Catalyst Performing Below Threshold.

I think that running rich has screwed up the catalytic converter. The problem is, what's causing it? About a year or so ago, I had the exhaust manifold replaced. I believe it was starting to run rich before I replaced that, so I don't think an exhaust leak would be causing it.

As I got the SES on the way to work this morning, I took it to the shop. They haven't had a chance to take a good look at it yet, but said that I could need a new catalytic converter. That's probably true at this point, but what could be causing the problem that messed that up is what I'm trying to figure out.

Thanks!
 

The_Roadie

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Nov 19, 2011
9,957
Portland, OR
Stuck injectors or intake manifold vacuum leak would be my first two thoughts.
 

coleman

Original poster
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Dec 4, 2011
86
the roadie said:
Stuck injectors or intake manifold vacuum leak would be my first two thoughts.

Thanks, roadie. I've relayed that to the mechanic. I don't feel a loss if power at all, so I don't think the cat is clogged. I'll have to see tomorrow what they come up with. Hopefully it's not too expensive, whatever it is. Sure wish they'd announce when they're going to bring the TB back. I'm trying to make this one last a few more years in the hopes I can pick up a new one.
 

coleman

Original poster
Member
Dec 4, 2011
86
coleman said:
Thanks, roadie. I've relayed that to the mechanic. I don't feel a loss if power at all, so I don't think the cat is clogged. I'll have to see tomorrow what they come up with. Hopefully it's not too expensive, whatever it is. Sure wish they'd announce when they're going to bring the TB back. I'm trying to make this one last a few more years in the hopes I can pick up a new one.

Sorry for the late update. Been crazy here lately. The mechanic had it for a half day and wasn't able to find anything wrong. Of course, I get it back, and it shakes at a full stop. Strangely, it sometimes it's smooth as glass.

Today, the last couple of days now, my ABS light pops up and I lose engine power for a split second. That's happened four times. And today I got P0335 and P0336 crankshaft sensor codes. I seriously think that this truck is on its way out. Trying to hold on to see if the new TB is coming back in 2015, but I honestly don't think it's going to make it.

Edit: Slipped my mind that for some reason it's now starting to idle fast at a full stop. I restarted the engine at a light and it dropped down to where it should be and started shaking again. Almost got 155K on my TB.
 

CaptainXL

Member
Dec 4, 2011
2,445
coleman said:
Got a strange issue on my 02 TB.

I've also lost MPG and the engine is running rich - so rich that when I start the car in the morning, all you can smell is gas from the exhaust pipe.

In open loop all I can think of is... 1) Are all plugs firing? and 2) Have you ruled out the fuel pressure regulator as cause? The fpr is really the only thing that could "add" fuel to a cold engine in open loop aside from a bad coolant temp sensor or stuck injector.

To test the coolant temp sensor get a scan tool that can read the engine temp.

To test the injectors get a fuel pressure gauge and see if there is any pressure bleed-down
 

gmcman

Member
Dec 12, 2011
4,656
Coleman, what is the service history of your TB?

How many miles? Have the O2 sensors been changed, If so, which brand? Have you cleaned the TB?

Don't sweat these symptoms too much, hopefully worst case is you need a cat and aftermarket there not terribly expensive. Why could it be bad...it may be fine and the downstream O2 sensor is bad. I suspect something else as you probably do as well though.

When were the plugs changed and if they have, what plugs are in the motor? Should be AC 41-103 ONLY. The original plugs for the 2002 were platinums and the replacements are iridium (41-103).
 

gmcman

Member
Dec 12, 2011
4,656
coleman said:
Today, the last couple of days now, my ABS light pops up and I lose engine power for a split second. That's happened four times. And today I got P0335 and P0336 crankshaft sensor codes. I seriously think that this truck is on its way out. Trying to hold on to see if the new TB is coming back in 2015, but I honestly don't think it's going to make it.

This is why I don't take mine to anyone I wouldn't give the keys to my home. Not saying anyone is dishonest, but you don't know where they had their hands. The fact now you have crank sensor codes maybe the tech inspected the connector, I would make sure the connections are good and secure.

These vehicles are very reliable and your issue is likely something simple.
 

CaptainXL

Member
Dec 4, 2011
2,445
Hey gmcman. To avoid confusion I think it's best to approach the symptoms (as he described) when the vehicle is in open vs closed loop. Neither the O2 sensor or catalytic converter would present an extremely rich condition at cold startup. They are literally "out of the loop". Nip it in the bud at startup and the rest of the issues (if there are any left) can be approached in time.
 

gmcman

Member
Dec 12, 2011
4,656
I agree Cap't but why is it rich? I guess we need to get some scan data to see if it's staying in open-loop. That leads me to another question...what is the coolant temp needle resting at after driving it for about 15 min? If in open-loop that explains a lot but these motors switch to closed-loop rather quickly.
 

CaptainXL

Member
Dec 4, 2011
2,445
gmcman said:
I agree Cap't but why is it rich? I guess we need to get some scan data to see if it's staying in open-loop.

Exactly. I gave a list of possible reasons/things to check in my previous post.

gmcman said:
That leads me to another question...what is the coolant temp needle resting at after driving it for about 15 min? If in open-loop that explains a lot but these motors switch to closed-loop rather quickly.


Without getting too technical, there are a handful of parameters (that I know of) that must be met before the PCM enters closed loop.

I've read that closed loop is reached when the coolant gets to approximately 170F, the O2 sensor is heated and the proper amount of "engine run time" has elapsed. Don't quote me on this but it's something around those lines.
 

gmcman

Member
Dec 12, 2011
4,656
gmcman said:
I agree Cap't but why is it rich? I guess we need to get some scan data to see if it's staying in open-loop.

This is why I turned off the PC and went to bed..:yawn: It was a rough day and I was approaching delirium, this is why tired people should stay away from chainsaws...lol.
 

jbacklund

Member
Dec 16, 2012
118
gmcman said:
I agree Cap't but why is it rich? I guess we need to get some scan data to see if it's staying in open-loop. That leads me to another question...what is the coolant temp needle resting at after driving it for about 15 min? If in open-loop that explains a lot but these motors switch to closed-loop rather quickly.

If it takes too long to get into closed loop you'll get a trouble code.
 

coleman

Original poster
Member
Dec 4, 2011
86
gmcman said:
Coleman, what is the service history of your TB?

How many miles? Have the O2 sensors been changed, If so, which brand? Have you cleaned the TB?

Don't sweat these symptoms too much, hopefully worst case is you need a cat and aftermarket there not terribly expensive. Why could it be bad...it may be fine and the downstream O2 sensor is bad. I suspect something else as you probably do as well though.

When were the plugs changed and if they have, what plugs are in the motor? Should be AC 41-103 ONLY. The original plugs for the 2002 were platinums and the replacements are iridium (41-103).

155K. Top O2 sensor changed when I had to replace the exhaust manifold last year. Not sure of the brand. I had this problem before it was changed, though.

Plugs were changed at 75K and 125K. Yes, those are the plugs I used. I've had a couple instances where the coil packs went out. The first time, the error code was a specific coil pack. The second time, it kept throwing a "multiple coil packs" code and then suddenly gave me a cylinder so I changed the one that was identified.

Curious if a coil pack could be bad, but not throwing a code. That would be a pain in the butt to figure out, but it would definitely, I feel, fit the symptoms.
 

coleman

Original poster
Member
Dec 4, 2011
86
gmcman said:
This is why I don't take mine to anyone I wouldn't give the keys to my home. Not saying anyone is dishonest, but you don't know where they had their hands. The fact now you have crank sensor codes maybe the tech inspected the connector, I would make sure the connections are good and secure.

These vehicles are very reliable and your issue is likely something simple.

The guys I took it to are very reliable and honest. A month or so has gone by since I took it there. They checked it out for a half day and didn't charge me a penny.
 

gmcman

Member
Dec 12, 2011
4,656
jbacklund said:
If it takes too long to get into closed loop you'll get a trouble code.

Yeah, I totally spaced on that comment :biggrin:, open loop is crazy rich and Cap't just stated that. I was tired. :smile:


coleman said:
155K. Top O2 sensor changed when I had to replace the exhaust manifold last year. Not sure of the brand. I had this problem before it was changed, though.

Plugs were changed at 75K and 125K. Yes, those are the plugs I used. I've had a couple instances where the coil packs went out. The first time, the error code was a specific coil pack. The second time, it kept throwing a "multiple coil packs" code and then suddenly gave me a cylinder so I changed the one that was identified.

Curious if a coil pack could be bad, but not throwing a code. That would be a pain in the butt to figure out, but it would definitely, I feel, fit the symptoms.

Using the AC sensor is the best course of action to eliminate a variable.

When you changed the plugs, did you use a fair amount of dielectric grease between the plug tip and the coil lead?

Possible bad O2 sensor and high resistance at the plugs could very well account for some of the symptoms, especially burning the coil packs up, they are very reliable coils.


coleman said:
The guys I took it to are very reliable and honest. A month or so has gone by since I took it there. They checked it out for a half day and didn't charge me a penny.

That's cool. :thumbsup:
 

coleman

Original poster
Member
Dec 4, 2011
86
One other clue: If I pop it in neutral at a full stop, it's smooth. I just had the motor mounts changed out a few years ago with factory mounts. I can't believe that one or more may be worn again. A possibility?
 

coleman

Original poster
Member
Dec 4, 2011
86
And you there - as it happens...

Reset the computer this morning for grins. No change.

Drove it to a store a few miles away. Shopped for a 10 minutes, got in, drove to the edge of the parking lot, and it conked out on me. No warning, no SES, no nothing. It started right back up, but now it's idling high. Strange.

Sooner or later, my wife will have the final say in the matter. With a 1 yr. old, I can't afford to have an unreliable car/truck. As much as I love my truck, it may be gone soon.
 

gmcman

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Dec 12, 2011
4,656
When you changed the plugs, did you use the grease? This is important.

Have you ever cleaned the throttle body?
 

coleman

Original poster
Member
Dec 4, 2011
86
gmcman said:
When you changed the plugs, did you use the grease? This is important.

Have you ever cleaned the throttle body?

Yes, and yes. I've cleaned the throttle body three times I think. The last time I changed a coil pack and I took a look inside the throttle body and it was still nice and clean. Still, that wouldn't explain why the engine would just conk out. That's the second time it's done that. No warning, like someone just cut the juice. BTW, I changed the ignition switch before, too, while I was troubleshooting an issue with the truck not starting. That turned out to be the starter.
 

CaptainXL

Member
Dec 4, 2011
2,445
I would try driving it around with the O2 sensor disconnected and see if it stalls. This will force the computer to use default fuel tables. It could be a fuel metering issue, too lean or rich. The engine will also stall if the coolant temp sensor is bad. Check coolant temp using a scan tool while wiggling the harness connected to it.

In all honesty, unless the truck has been fixed or you explicitly state that there are problems with it then the truck will be tough to sell. Your best bet if all else fails would be to have a certified technician take a look and diagnose. It would be cheaper than getting another vehicle of similar age. Plus you would know the history that this vehicle has had proper maintenance and diagnostic work.
 

gmcman

Member
Dec 12, 2011
4,656
CaptainXL said:
I would try driving it around with the O2 sensor disconnected and see if it stalls. This will force the computer to use default fuel tables. It could be a fuel metering issue, too lean or rich. The engine will also stall if the coolant temp sensor is bad. Check coolant temp using a scan tool while wiggling the harness connected to it.

In all honesty, unless the truck has been fixed or you explicitly state that there are problems with it then the truck will be tough to sell. Your best bet if all else fails would be to have a certified technician take a look and diagnose. It would be cheaper than getting another vehicle of similar age. Plus you would know the history that this vehicle has had proper maintenance and diagnostic work.

That's good advice.

The motor sure sounds like it's getting too much fuel and stalling out. Like Roadie stated, stuck injectors could be a reason. The cat is apparently fried and if that's the case excess fuel likely was the culprit.

If the ignition system is functioning properly, ie, correct plugs, grease, then what's left to stall the motor, absence of fuel or air or abundance of either. Compression is good right? I would speculate it is.

Good advice has been given and has the crank sensor code come back?

If that were my vehicle I would pull each coil and inspect, then pull the plugs and inspect the electrodes. Did you try to gap them? Reason I ask is you cannot gap them. Note condition of plugs for normal operation, pics would help.

Then I would check the electrical connections of the sensors, make sure they are clean, use electronics cleaner.

Verify there is no crud, not even a spec around the thin edge of the throttle butterfly to hinder closing.

Are any vacuum lines cracked?

Is the large vacuum line under the intake resonator intact?

Is the molded vacuum line on the drivers side of the intake in the center cracked?

All intake bolts tight

You stated you were not sure of the O2 sensor brand. At you mileage on this sensor, I would change it if unsure, not much loss in $$$.

Is the air filter ok?

Do you have access to a real-time live data scan tool? This way you can monitor the O2 sensors and verify open or closed loop.

I would focus on the excess fuel, the FPR or the injectors first. This is what the technicians are going to do so save yourself the $$$.

coleman said:
The first time, the error code was a specific coil pack. The second time, it kept throwing a "multiple coil packs" code and then suddenly gave me a cylinder so I changed the one that was identified.

This still for some reason bugs me because these coil packs are very reliable. Why multiple misfires? I have to go back to the dielectric grease question and specifically ask if you applied to the tip or just around the boot?

Just throwing ideas out there.
 

seanpooh

Member
Jan 24, 2012
461
When ever I received the code Catalyst Performing Below Threshold, I ran some fuel injector cleaner (Lucas or Chevron) and it goes away by itself. Give it a try, won't hurt.

As for ruining the cat, I've drove on a open thermostat where my engine temp was 150 isn for thousands of miles... I was running so rich that Blackstone said my oil flashpoint was reduced and I had fuel dilution. After fixing the thermostat, no harm done to cat and I got back my great MPGs with no more fuel going into my oil. Don't let a shop bully you in paying for a new cat. For them to prove you need a new one, they would have to measure the back pressure.

As for ONLY using ACDelco plugs... I would like to call that a myth. I've used NGK IridiumIX for 150K miles (changes every ~75K miles) never gapped them myself and yet to have a misfire.

Try some type of fuel injector cleaner and see if there is a difference. (Lucas preferably since it always takes my code away)
 

coleman

Original poster
Member
Dec 4, 2011
86
All,
Thanks for the suggestions! I think this weekend I'm going to change out the spark plugs and regrease and clean the throttle body. I'll see what happens after that. I got a P1514 and a stall on the way home. And my inside door handle broke off. My TB isn't helping me win any arguments.

After I change everything out I'll post an update.
 

TangoBravo

Member
Dec 5, 2011
208
seanpooh said:
When ever I received the code Catalyst Performing Below Threshold, I ran some fuel injector cleaner (Lucas or Chevron) and it goes away by itself. Give it a try, won't hurt.



As for ONLY using ACDelco plugs... I would like to call that a myth. I've used NGK IridiumIX for 150K miles (changes every ~75K miles) never gapped them myself and yet to have a misfire.

Try some type of fuel injector cleaner and see if there is a difference. (Lucas preferably since it always takes my code away)
Just so you know, nobody running AcDelcos has had a problem directly related to AcDelcos(that wasn't thier screw up). While there are pages of well earned info(on THREE different trailblazer forums) on what happends when you don't use AcDelcos so you would be the only one I know of that has been able to use any other plug with no problems. However you just stated that you ACTUALLY do have a re-acurring issue that CAN be traced to plugs. You also say you change them at 75k while Delcos are good for 100k+ with you needing to change more often and having problems that can traced to plugs using NGK really doesn't seem too cost effective does it? FWIW I have 200k on my TB with no problems EVER traceable to plugs.... Now THAT is reliable.
 

CaptainXL

Member
Dec 4, 2011
2,445
Telling others to only use ACDelco is more of a quality check and to make sure nobody is using some off the shelf odd brand that is incompatible. It's basically a way of knowing a good plug was used in the troubleshooting stages.

From what I gather reading up on the company history, ACDelco doesn't make parts anymore. It's a brand label. From the little evidence I have gathered it seems that NGK and Denso both make the plugs.

In the end I would have to agree with seanpooh that using only ACdelco is just a myth. But don't tell that to your average Joe (non-mechanic type) who is asking for help. You can if you want but you likely will confuse the person asking for help. It's best to just state one brand to people who need help. ACDelco plugs have been tested to work with our vehicles. There is no reason to think that a good quality plug company didn't do the same due diligence in testing.
 

TangoBravo

Member
Dec 5, 2011
208
CaptainXL said:
Telling others to only use ACDelco is more of a quality check and to make sure nobody is using some off the shelf odd brand that is incompatible.

From what I gather reading up on the company history, ACDelco doesn't make parts anymore. It's a brand label. NGK and Denso both make the plugs.

And neither are worth a damn in our spacific platforms. Im not sayin they dont make a good product but when it comes to our platform if you search at all you will find that most times someone had a problem(that traced back to spark plugs) and needed help, they also had to fess up that they were using xyz brand and were promptly directed to use only Delcos, because thats what our TB's favor(regardless of who actually makes them now).
 

CaptainXL

Member
Dec 4, 2011
2,445
TangoBravo said:
if you search at all you will find that most times someone had a problem(that traced back to spark plugs) and needed help, they also had to fess up that they were using xyz brand and were promptly directed to use only Delcos, because thats what our TB's favor(regardless of who actually makes them now).

Could be due to a bunch of things. We must confess we just don't know half the time what the problem is. Replacing plugs often reminds the person needing help to reconnect that vacuum hose or reconnect that wire that they missed when changing the plugs the first time. They just don't tell us for fear they will be ridiculed. Hey...it happens. Not everyone is a top mechanic with impervious skills that knows how to properly installed plugs.

Basically we don't delve into this type of post mortem analysis. Half the time we can't see the persons plugs nor are we there to personally help.

There isn't a cut and dry answer here.

There are a lot of reasons people might have had problems with their plugs.

- Wrong plug type/incorrectly cross referenced
- Cheap/imitation
- Improperly tightened or installed
- Coil installed wrong
- Gapping a platinum or iridium plug
- Quality control issues
- Broken in box

etc....etc...
 

coleman

Original poster
Member
Dec 4, 2011
86
Just out of curiosity, should anything be connected to this nipple? Looks like a hose should be on there. ??

Thanks!

View attachment 28212
 

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gmcman

Member
Dec 12, 2011
4,656
coleman said:
Just out of curiosity, should anything be connected to this nipple? Looks like a hose should be on there. ??

Thanks!

View attachment 14636

Absolutely! That will cause a pile of issues. That's where I check manifold vacuum from. That will likely fix your problem.
 

gmcman

Member
Dec 12, 2011
4,656
We always tell people to check their vacuum with a gauge, why did we miss that this time? Roadie mentioned a manifold vacuum leak and we said to check vacuum hoses but no gauge. That's my first goto tool for a rough idle but I will admit fail on my part.

Fingers crossed it's your problem.
 

CaptainXL

Member
Dec 4, 2011
2,445
gmcman said:
We always tell people to check their vacuum with a gauge, why did we miss that this time?.

Probably cause we are so used to getting a funny look when we mention vacuum. Im sure the first thing that pops into peoples mind is a vaccum cleaner. By the way we cant always hold peoples hand and absolutely insist they buy a vacuum guage. A lot of times the people who come on this forum asking for help are talented using a computer to seach for answers yet functionally ignorant when it comes to automotive mechanics. Thats not a bad thing. Its just that people decide their time in life is better spent doing other things than reading auto repair manuals.
 

coleman

Original poster
Member
Dec 4, 2011
86
Okay, on the right track. Now, what goes on that nipple and where does it connect to??

Almost done with the spark plugs and the TB is all cleaned up. Don't want to start her up without this hose being in place. It's actually been that way for some time, actually.
 

coleman

Original poster
Member
Dec 4, 2011
86
Here's another pic so you guys can see what I'm looking at. Can't find any loose hoses that might need to be reattached. Grrrrr
View attachment 28213
 

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coleman

Original poster
Member
Dec 4, 2011
86
I just read in another thread that this isn't used on the 2002 and to just plug it up. Correct?
 

coleman

Original poster
Member
Dec 4, 2011
86
I taped up the nipple and hooked everything back up. The engine feels a lot better. A lot. There is still a bit of a shudder when stopped, but I'll drive it around for a few days and see how it goes. I'll also pick up some fuel additive and toss it in there, too. Definitely couldn't hurt. I'll report back either way.

Many thanks, guys. Hope my baby hangs in there!
 

gmcman

Member
Dec 12, 2011
4,656
On short wheelbase models it's capped off. After all your driveability issues, I would pull the NEG cable for about 30 min, allow the TB to relearn and then drive it.
 

coleman

Original poster
Member
Dec 4, 2011
86
Okay, guys, here's the status update.

New plugs, plenty o' grease, cleaned throttle body, new air filter (it was coming due), reset computer, Techron gas additive.

Ran great the first day, very smooth at full stop. I do not smell gas anymore when starting the vehicle.

The second day, it started shaking again. Some days it shakes less than others. Mind you, this is only in drive at a full stop. If I slow down sloooowly, I'll feel the vibrations come in just before the full stop.

I'm thinking that there were a couple things going on. There was probably a misfire, but I also think I have a worn motor mount. Once the truck is moving, it's very smooth. If I'm at a full stop and throw it in neutral, the shaking stops. I had my motor mounts replaced maybe 4 or 5 years ago years back with factory mounts, but maybe one of them is worn again.

Can't get it back to the shop until the middle of June and will see what happens then. Until then, at least I don't feel the engine trying to shut off.
 

gmcman

Member
Dec 12, 2011
4,656
Did you perform the relearn again? I feel after driving it with the big vacuum leak the ECM needs to be reset. Wouldn't hurt to ensure the TB is clean. If it were mine, I would unhook the NEG cable, clean the TB, and perform the relearn just to remove it from the equation, or hope to anyway.
 

coleman

Original poster
Member
Dec 4, 2011
86
gmcman said:
Did you perform the relearn again? I feel after driving it with the big vacuum leak the ECM needs to be reset. Wouldn't hurt to ensure the TB is clean. If it were mine, I would unhook the NEG cable, clean the TB, and perform the relearn just to remove it from the equation, or hope to anyway.

The TB was so sparkly you could eat off it. Yes, I also did a reset/relearn. I unhooked the negative battery terminal while I was playing under the hood.
 

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