Fuel Trim readings

[07TrailyLS]

Hey guys. I use torque throughout the entirety of all my drive cycles. I understand how to check for fuel trim levels. I'm just wondering if yours run anywhere like mine. So here we go.
Sitting in idle for 30 minutes with the truck completely warm my short term stayed between 0 an 3. But over time my long term crept upwards to 11%. And stayed. Now while driving, everything stays closer to 0 for short and long term. when I start my truck cold, summer or winter, I've ALWAYS had a terrible smell of fuel flowing through the exhaust. I'm just wondering if I have a stuck or overcompensating injector. The voltages on my 02 sensors read constant every second switching from .2-.7 volts. So both seem to be working. Can't figure out why she's trying to overcompensate in the fuel category. Thoughts appreciated guys
101k miles. The truck is very well kept. Mobil 1 every 3 thousand and the plugs were just changed. Dunno if it matters but she does burn 2 quarts every 3 thousand. Has done it since I bought her 3 years ago with 40000 miles on it. No misfires at all showing from torque. Thanks and sorry for the long ass post

 

[Chickenhawk]

Sounds like a lazy sensor to me. But your post is a bit confusing. A good pre-cat O2 sensor should bounce very rapidly, from .1 to .9 volts, several times a second. The post-cat sensor should be relatively steady.

Please post the two O2 readings and a description of how fast they change. There should be a SIGNIFICANT difference in how they read.

Also, post your coolant temperature when warm, and even a photo of your coolant temp gauge.

I am just speculating here but this is how we can tell if you are running too cool; if your cat is starting to go bad; or if your front O2 sensor needs replacing. We CAN'T tell if your cat is clogged, but if it does not accelerate very strongly, especially at highway speeds, then your cat is also clogged.

Also, you are wasting your money on oil changes. Stop that useless old-school oil change schedule, trust your oil life monitor, and spend the money on a new upstream O2 sensor. They should be changed at 100,000 miles with every plug change anyway, if for no other reason than they can corrode into the manifold and make it difficult to replace in the future.

Don't worry about changing the rear O2 sensor unless you get a code. They do not affect the performance and only serve to check the performance of the cat as far as emissions are concerned. (But not as far as clogging is concerned.)

 

[07TrailyLS]

Coolant stays steady at 198 degrees warmed up. I just replaced my thermostat a few months back. Noted on the oil changes. And I may as well replace the upstream 02 sensor when I change my trans and rear axle fluid in the next coming weeks. But the heavy smell of fuel through the exhaust doesn't concern you? Just curious. my truck spins the tires out of first without issue so I'm thinking there's no issue with a clogged cat. Thanks man!
Edit: I can throw a video up later of the 02 sensor reading in action. It would be easier to show than tell.

 

[budwich]

my guess would be poor fuel pressure resulting in insufficient fuel injection resulting in "more".... or you have a small intake leak somewhere again resulting in a "request" for more fuel.

 

[Chickenhawk]

Heavy smell of fuel is concerning but I would start with the easily replaced, and common wear, items first. There is a difference between "shotgunning" parts - which means randomly changing everything based on something read on the internet, versus changing some parts that might not be the cause of the problem, but are normal wear (or common problem-area) parts anyway.

My suggestion is do the easy stuff first and then report back. This means the front O2 sensor. Get the correct new part, cut off the wire of the old one and get a good deep socket to remove it. It may take a lot of torque to get it out. Soak it with PB Blaster on a cold engine every day for three days in advance.

You will need a special O2 sensor socket to install the new part. I don't recommend taking the old one out with the special socket, simply because they can slip if the sensor is really stuck inside the manifold.

We will know more once you post a video of course.

As for the cat, its not performance from standstill that is the most telling; it is performance on the highway. If it seems to lug a bit when accelerating to highway speeds, it is likely the cat is getting clogged. These trucks REALLY move out when you step on the gas on the highway.

Also, I know you did the thermostat (hopefully with an AC Delco) but that coolant temp is still low-ish. I would also replace the coolant temp sensor. It's a pain to get at, but should bring your temps up to the 210 area.

If you think about it, a 195-degree thermostat begins opening at 195, and normally runs at 205 to 210 when warm. So either your thermostat is opening too soon, or (more likely) the temp sensor needs replacing. (They live a pretty hard life immersed in coolant for years.)

 

[07TrailyLS]

Understood about the coolant sensor. And no I have 0 issue at highway speed. I manually shift 90 percent of the time unless I'm driving long highway runs. When I pass I still drop down to third or second to get by quickly. But even in automatic, highway speed is not suffering. The thermostat is ac delco. It's all I buy. When I check the oil it doesn't really smell like fuel. I've replaced oxygen sensors before. I'll order the special socket online for the install.

my guess would be poor fuel pressure resulting in insufficient fuel injection resulting in "more".... or you have a small intake leak somewhere again resulting in a "request" for more fuel.

So you're thinking the fuel pump isn't outputting enough fuel and could be worn out?

 

[gmcman]

You said it smells like fuel always when you start your truck cold, but how strong is the smell and how long does it wreak of unburned fuel?
The unburned fuel smell is normal when starting cold but I believe you have a legit concern if it's overly strong.

Check your intake manifold bolts, make sure there's no unmetered air going through....89 Inch pounds...not far past snug.

What are your fuel trims once the engine is up to temp, idling and driving steady?

 

[07TrailyLS]

As asked here is a 17 second video. This is 02 sensor voltage fluctuation for upstream and downstream, as well as long and short term fuel trims driving 35 miles per hour.

Sorry for the tablet talking in the background. Got all the kids watching paw patrol in the back. I'd say it smells like fuel for 3 to 5 minutes after cold start.

 

[budwich]

So you're thinking the fuel pump isn't outputting enough fuel and could be worn out?

check your fuel pressure to see if anything is amiss in the fueling domain. Doesn't mean the pump is bad, could be the regulator or other areas of fueling but it is a good place to start. From my limited experience, your long term trims don't "drift" to that high a positive unless there is an underlying issue either with leaking air or poor fuel "injection".

 

[gmcman]

Check your vacuum hoses, large hose under resonator and the small port in front of intake facing pass side, likely capped off, may or may not pull vacuum but check.

Check molded vacuum hose between #3&4 intake runner.

Get a 1/4" ratchet and short extension, 10mm socket and check your intake manifold bolts first.

If they are all snug, we can go from there.

 

[07TrailyLS]

Will do gmc. I'll report back sometime tomorrow

 

[AtlWrk]

Sitting in idle for 30 minutes with the truck completely warm my short term stayed between 0 an 3. But over time my long term crept upwards to 11%. And stayed. Now while driving, everything stays closer to 0 for short and long term. ass post

How long is "over time"? I.e. how long does it take to get the LTFT above 10?
30 minutes of idling is a relatively exceptional condition. LTFTs in the 3-5s during normal driving is perfectly normal (and actually quite good). Only if your LTFT creeps back up to 10+ within 2-3minutes of idling would I start looking for vacuum leaks. Point I'm getting at is: it doesn't sound like there's a problem here at all--at least not one worth chasing--for the fuel trims at least.

The smell of gas and burning 2 qts of every 3000miles is a different story...

 

[07TrailyLS]

Alt. It took me a full 30 minutes of idling to reach 11 in my ltft. And it's been in the negatives here in Ohio. I've done research and I've read ltft of 10 and below is good. So I don't know. As for the oil burning, I've been told from people on this site that if you drive your motor hard, this engine will burn it. When I changed my plugs at 100k they looked beautiful. So I'm not suspecting internal engine failure.

 

[AtlWrk]

Right. Conventional wisdom is anything in the double-digits indicates that something is wrong. But if takes 30 minutes of idling to get to that point how wrong can it be? If there's a real problem it will show up right away or during regular driving. I know that's not reassuring and there's no harm in doing all the checks discussed thus far--particularly snugging up all the intake manifold bolts but I wouldn't spend a whole lot of time chasing this.

 

[07TrailyLS]

I thought that if there was a problem it would present itself immediately as well. I was basically just trying to get others results and a comparison chart between the two. But I can tell you guys that the little cap for the LWB rear have is capped and not causing issues. As well as the large elbow hose just under the resonator is in very good condition. It did have some blow by in it last time I checked. I'm in the middle of a winter storm with winds chasing 40 mph and it's raining. So going outside today to even look at the intake manifold bolts would be stupid on my part. Just to update those involved in the thread. Thanks guys. And thanks @AtlWrk for the reassurance of don't chase this too far. Kinda eases my mind from what I read earlier in the post

 

[gmcman]

My long term fuel trims were around -7 for awhile, one thing I did was change the upstream O2 sensor and the fuel pressure regulator. I also religiously use BG 44K once and sometimes twice a year. Once after winter and once after fall but mainly after winter.

Here's a screenshot of my fuel trims and O2 sensor while driving a few days ago. The O2 sensor will have fewer updates when idling then more while driving.

I'll get a few more screenshot tonight but the trims have improved substantially. Mind you this is a new O2 sensor but my trims came back into check at the previous O2 service with the FPR. I just dont like to go over 80K on plugs and upstream sensor.

Also make sure the intake manifold bolts are snug with no leaks.

I've been checking them recently as my cat is original but could be getting close to needing a replacement. While the rear sensor is showing a working cat, the line isn't as steady as it should be when fully warmed up.

 

[gmcman]

Also, based on your screename I assume yours is a 2007?

Have you cleaned your MAF meter? Are you possibly using a K&N or any type of oil-soaked air filter?
Reason I ask is the thin wires can get oil residue on them affecting readings.

 

[budwich]

One of the reasons for the LTT to "drift" back to "equalized" when driving (steady state / speed) is that typically there is reduced vacuum and any leaks (air) are likely less than the amount of air being added by the throttle intake. At idle, the vacuum is large (larger), throttle is closed down and hence incoming metered air is less and thus any other leaks in proportion can become evident in the system and result in it "pushing" more fuel to compensate. The "standard check" with spray to detect change / stumble around areas of interest might help identify things as eyes usually can't see air ingression.

 

[07TrailyLS]

Update:
It was decent outside today so I decided to go out and mess with the truck. Took a couple extensions and reached in to the first IM bolt. I'll be damned if the first two in the back of the motor weren't loose as all hell. I think I turned them 7 or 8 full turns. The other three closest to the front of the motor were tighter but still were able to be turned s bit and torqued. After that I did the first start up of the day. I never mentioned this prior but the popping sound I was hearing out of my exhaust pipe is gone. Dunno if it was this vacuum leak that was causing it but it seems to be driving better. Throttle response has improved quite a bit. Anyway, I will fire up torque sometime this week and run through the fuel trim readings

 

[gmcman]

That's good news.

When the intake manifold bolts are loose, you run the risk of unmetered air entering the cylinders resulting in a lean mix. Problem is, not all the cylinders may end up lean, not every cylinder will get the extra air, but the O2 sensor will see a lean mix then add more fuel to all cylinders...resulting in a rich mix to other cylinders.

Then you get trim readings all over the place.

I would verify all bolts are tight, then reset your PCM, then drive for a tank and see what happens.