P0101 + P0300 = ?

[menusk]

When I got those two codes. It was my knock sensors. And my intake manifold gaskets. When my took my I take manifolds off. They had a lot of carbon buildup. The fuel Injectors were covered in carbon as well. Like chunks. So when the fuel injector sprayed. Fuel would leak incorrectly out of them and leak from the carbon buildup on the intake manifold. I cleaned those all up. On top of that. I made sure any section where air can come through was tight. The air intake screws. From the filter box. And the screw to the throttle body. Then I made sure my oxygen sensors were tight as well. I don’t. Know which step exactly helped. But the code has never come back. Hopefully this helps.

 

[tlynch]

When I got those two codes. It was my knock sensors. And my intake manifold gaskets. When my took my I take manifolds off. They had a lot of carbon buildup. The fuel Injectors were covered in carbon as well. Like chunks. So when the fuel injector sprayed. Fuel would leak incorrectly out of them and leak from the carbon buildup on the intake manifold. I cleaned those all up. On top of that. I made sure any section where air can come through was tight. The air intake screws. From the filter box. And the screw to the throttle body. Then I made sure my oxygen sensors were tight as well. I don’t. Know which step exactly helped. But the code has never come back. Hopefully this helps.

Thanks for the insight. I'll ask how the intake manifold looked when the shop was doing the work.

I'll look for places downstream from the MAF that may have any sort of a leak. I have considered replacing all of the rubber and plastic pieces in the intake path.

 

[Monkeywrench78382]

Updates:

IAT reads at actual ambient temp.

I was able access misfire history. All cylinders had values at start up. Over 10-15 minutes running on my driveway, I saw increases in cylinders 3 (+16), 4 (+52) and 7 (+2).

Plugs and wires were replaced 5.5 years /23k miles ago. Throttle body was cleaned at the same time.

I have not yet started cleaning contacts or TB.

Are you getting a code for cat below threshold by chance? Pulse width changes like these would indicate a possible intake leak on 3 and 4 wider pulse width is the system trying to richen up. Vaccum leak at intake/heads it is advisable to do knocks and or dod if equipped.

 

[tlynch]

Are you getting a code for cat below threshold by chance? Pulse width changes like these would indicate a possible intake leak on 3 and 4 wider pulse width is the system trying to richen up. Vaccum leak at intake/heads it is advisable to do knocks and or dod if equipped.

Thanks for taking time to comment!

The only codes I have seen have been P0101 and P0300.

The intake manifold gaskets were just redone, and anti-knock sensors were replaced at the same time. Since then, the truck has run pretty smoothly. I have seen P0101 a couple of times (new AC Delco MAF a couple of months ago). No misfire code, but I have felt a couple of misfires. Nothing is racking up in the misfire history in the Torque app, though.

The shop that did the gaskets is a bit mystified. I assume the eventual explanation will include something that isn't common.

Thanks again for taking time.

 

[Monkeywrench78382]

Thanks for taking time to comment!

The only codes I have seen have been P0101 and P0300.

The intake manifold gaskets were just redone, and anti-knock sensors were replaced at the same time. Since then, the truck has run pretty smoothly. I have seen P0101 a couple of times (new AC Delco MAF a couple of months ago). No misfire code, but I have felt a couple of misfires. Nothing is racking up in the misfire history in the Torque app, though.

The shop that did the gaskets is a bit mystified. I assume the eventual explanation will include something that isn't common.

Thanks again for taking time.

I would ohm test injectors pre start up and once closed loop is acheived

 

[tlynch]

I would ohm test injectors pre start up and once closed loop is acheived

Thanks for the suggestion. I have a multimeter. When I have some time, I'll give this a try.

 

[ks03]

Do you have an egr?
Inspected the intake tube? I’ve seen OE air intake tubes leak / cracked where the silencer section attaches.

 

[tlynch]

Do you have an egr?
Inspected the intake tube? I’ve seen OE air intake tubes leak / cracked where the silencer section attaches.

Thanks. I'll do some research on this.

 

[tlynch]

I would ohm test injectors pre start up and once closed loop is acheived

Quick question. The connectors look pretty well sealed down into the pigtail. Is the test while running done by piercing the wires?

I pulled all the connectors and tested while stopped. All of them metered between 12.5 and 12.9

 

[tlynch]

No problem.

I added in checking fuel pressure above. You can rent tools from autozone or O’Reilly’s to check it.

If you can, post your fuel trim numbers (short trim and long trim from both banks) so we can review them. It may help point us to the right direction. Take readings when the engine is cold and after it has reached operating temp.

You win imaginary internet bonus points!

After a mere 5-month delay, I finally got around to borrowing a fuel pressure gauge from Autozone and hooked it up today.
50 psi, ignition on
44 psi ignition off
50 psi engine running

Looks like a fuel pump in my future.

 

[Fless]

A leaky injector or a bad fuel pressure regulator could cause the quick bleedoff of fuel pressure. How long does it take to drop to 44 when you turn the key off?

 

[tlynch]

A leaky injector or a bad fuel pressure regulator could cause the quick bleedoff of fuel pressure. How long does it take to drop to 44 when you turn the key off?

It dropped faster than it took me to walk from the driver's door to the engine compartment.

I looked at the fuel pressure regulator while I was checking injector resistance. It looked relatively new. At least it looked cleaner than everything around it. It may have been replaced at some point.

 

[tlynch]

I am tentatively declaring victory.

Over the last couple of weeks, my Tahoe has taken longer cranking to start, and would run rough for a couple of seconds before hitting its stride. Combined with the fuel pressure data, this definitely seemed to confirm fuel delivery issues.

Yesterday, I replaced the fuel pressure regulator, fuel pressure regulator vacuum line and fuel filter. Right after I was done, the truck started immediately. No hesitation. It sat for 32 hours, then started immediately again. Very nice change.

I wasn't smart enough to hang onto the borrowed fuel pressure gauge to measure the difference, but the experience is much improved.

Thanks again to everyone who shared their time and knowledge helping me.