07 Tahoe LTZ gas in the oil

[Hellacious tahoe]

Last fall, I bought this 07 tahoe and as soon as I made it home after a 200 km trek I changed the oil. At that time, I thought the oil was too thin, but dismissed it as overdue oil. After a double flush I poures 5w30 synthetic and a new fram filter. I spent the rest of the fall replacing the shocks and doing body work. There was a code pointing to the evap valve, which I replaced. Winter came and I stored the truck, but ran it at idle every 2 to 3 weeks while in storage. One cold February morning it made strange noises and the low oil pressure warning came up. I waited for the spring to address this, but spring came up and it ran like nothing ever happened. The evap code came back and after visually checking all the hoses, canister ect I dropped the tank and found a fuel pump from a prior generation Tahoe had been rigged in. I replaced the pump with the correct one and the evap code did not return. One day it made similar extrange noises, this time sounded like coming from the oil pump area . I drained the (new) oil and found it very thin with an obvious gas smell. I just dont know how gasoline is coming into the crankcase, since this truck does not have the high pressure pump that is notorious to leak on 2012 and newer models. I dont know what to do next and came into this forum pleading for a little help. In advance, I thank you for reading this long post and remain on standby for your input. Cheers

 

[Marky Dissod]

Post was not that long, no worries.
1st place I can think of where fuel sneaks into oil, is leaking fuel injectors.
2nd place methinks of where fuel sneaks into oil, is piston rings ... but those would betray excessive oil consumption, since fuel should literally wash oil off the walls ...
Having trouble thinking of the 3rd place ...

 

[Fless]

Put a good scanner on it and read the short- and long-term fuel trims. It may be overfuelling.

One cause of this -- if it's a flex fuel engine -- is that the PCM thinks it's running fuel with a high ethanol content (E85), and commands more fuel.

A good scanner will show you what it thinks the ethanol/alcohol percentage is, and that should roughly match the ethanol content of the gas you're putting in the tank (e.g., E0, E10, E15, E85). If you find out that there's a wild difference, the same scanner will likely allow you to reset the ethanol percentage, and the long-term fuel trims.

Please let us know what you find out. Video below for info specific to the cause and remediation.

 

[Hellacious tahoe]

Thanks Fless. I did a fuel leakdown test and from initial 55 psi it took over 20 minutes before it settled at about 40 psi, seemingly nrmal results. Fuel trims are negative at idle, climb up upon acceleration. Dont know about the ethanol percentage, pumps say up to 10%, will have to get back with that intel.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please. If we can't see it, it does not exist.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[strutaeng]

First question:

How was the previous generation fuel pump rigged?! The 07+ use the fuel pressure module to regulate the pump duty cycle via PWM, right? Whereas on the previous generation there's just a ON function? I guess the pump itself is still controlled by the fuel pump module?! I'm sorry, but not familiar with the later systems. Someone will chime in on that...

Second question:

It's obvious that fuel is making to the crankcase. That's really bad because the bearings will likely get damaged and the fuel washdown will cause piston rings to wear excessively into the bores. Whether the Jerry-rigged fuel pump is causing this, IDK?


General Comments and further questions:

The fuel trims are negative because the fuel vapors are getting sucked into the intake and the ECU is detecting this, and therefore dialing back fuel to the injectors.

Can you pop the fuel rail and prime the system to see if you have any injector(2) leaking fuel? That can also cause fuel wash and the cause fuel to enter the crankcase. Fuel pressure from 55 to 40 psi over 20 minutes seems too high for me? Need to find out where the system is losing pressure, if not that the injectors are leaking.

I hope this helps and welcome to the forum.

 

[Hellacious tahoe]

First question:

How was the previous generation fuel pump rigged?! The 07+ use the fuel pressure module to regulate the pump duty cycle via PWM, right? Whereas on the previous generation there's just a ON function? I guess the pump itself is still controlled by the fuel pump module?! I'm sorry, but not familiar with the later systems. Someone will chime in on that...

Second question:

It's obvious that fuel is making to the crankcase. That's really bad because the bearings will likely get damaged and the fuel washdown will cause piston rings to wear excessively into the bores. Where the Jerry-rigged fuel pump is causing this, IDK.


General Comments and further questions:

The fuel trims are negative because the fuel vapors are getting sucked into the intake and the ECU is detecting this, and therefore dialing back fuel to the injectors.

Can you pop the fuel rail and prime the system to see if you have any injector(2) leaking fuel? That can also cause fuel wash and the cause fuel to enter the crankcase. Fuel pressure from 55 to 40 psi over 20 minutes seems to high for me? Need to find out where the system is losing pressure, if not that the injectors are leaking.

I hope this helps and welcome to the forum.

Thanks for your attention strutaeng. Prior owner did the rig, plugged one of the 3 pipes on that pump, which was wider than the correct one, I had to break it in pieces to remove it. I also replaced the fuel pressure sensor for the tank. Vapors causing the pcm to dial back the injectors sounds like a normal thing, unless too muck of the vapor is being delivered. I did not see or smell any gas when I replaced the evap solenoid valve that lives under the left side of the beauty cover. The fuel pressure on the rail was measured with a new testing tool, I tend to trust it. Taking the injectors out seems risky, even the pigtail connectors were tough to remove when I tried to test injectors for the 5 and 7 cylinders, which are known to be frequently blamed for leaking. Cyl 5 injector resistance across terminals was normal. I could not disconnect cyl 7. I forgot to add that after removing the new, but diluted oil, I poured 5w40 and took the truck out for a 10 minute spin. As soon as it warmed up it gave me the low oil pressure warning, but no trouble code was set. Now you guys know the origing of the hellacious truck moniker. This thing is driving me insane.

 

[Hellacious tahoe]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please. If we can't see it, it does not exist.

You are already receiving sage advice from the knowledgeable folks on this Forum.

Thanks Joseph, for the warm welcome. I dont have any pics of the truck, will snap some for the forum next chance I get. For now Ill post pics of the wheels I got for the truck, which were peeled to metal, then painted with gunmetal appliance epoxy from Home depot. That is a tough coat that will not break the wallet, great for those in the 99%. I have a 97 Suburban to compare and Im impressed with the Tahoe's level of refinement, as compared with the Burb, which feels more "trucky" in terms of both steering and suspension. Ill be posting snapshots of the fuel trimmings and other findings once Im able to shake off the flu, which has made its rounds in my family.

 

[Hellacious tahoe]

Put a good scanner on it and read the short- and long-term fuel trims. It may be overfuelling.

One cause of this -- if it's a flex fuel engine -- is that the PCM thinks it's running fuel with a high ethanol content (E85), and commands more fuel.

A good scanner will show you what it thinks the ethanol/alcohol percentage is, and that should roughly match the ethanol content of the gas you're putting in the tank (e.g., E0, E10, E15, E85). If you find out that there's a wild difference, the same scanner will likely allow you to reset the ethanol percentage, and the long-term fuel trims.

Please let us know what you find out. Video below for info specific to the cause and remediation.

Here is a pic of the evap code it had before replacing the valve. It also shows the model of my scanner, which provides limited data.

One cause of this -- if it's a flex fuel engine --

How do I know if is a fuel flex engine?

 

[Fless]

P0452 relates to the data that the fuel tank pressure sensor is reporting to the ECM.

Your new pump should have come with a new fuel tank pressure sensor -- just to clarify, are you saying that you changed that sensor after installing the replacement pump?

 

[Fless]

Here is a pic of the evap code it had before replacing the valve. It also shows the model of my scanner, which provides limited data. View attachment 483110

How do I know if is a fuel flex engine?

Look inside the fuel filler door and there should be a sticker there. Or post the 8th digit of your VIN so we can tell which engine you have.

Sticker from a flex fuel:

 

[Marky Dissod]

post the 8th digit of your VIN so we can tell which engine you have.'

Z' = L59, Flex Fuel
Oops, my bad, Fless is absolutely correct.

 

[Fless]

Z' = L59, Flex Fuel

I seem to think that the FF 5.3L engine in 2007 would be the LMG, VIN code 0.

 

[swathdiver]

Winter came and I stored the truck, but ran it at idle every 2 to 3 weeks while in storage. One cold February morning it made strange noises...

That's your problem. The engine never gets hot enough to evaporate the fuel that gets into the oil. Don't do that, get a battery tender instead.

If you still experience too much fuel getting into your oil with regular use, check to see if the driver's side rocker cover is the improved design and then perform a compression test on the engine.

A lot of things can happen in 19 years.

 

[donjetman]

Here's the technical service bulletin link TSB 10-06-01-008M make certain its been done
and here's a pic showing the difference in valve covers when I did the TSB
Notice the location and shape of the pcv ports in each design.

 

[swathdiver]

Here's the technical service bulletin link TSB 10-06-01-008M make certain its been done
and here's a pic showing the difference in valve covers when I did the TSB
Notice the location and shape of the pcv ports in each design.
View attachment 483160

For those who come along later and see this, don't just buy the cover based on the part number you see in the photo. The 2009+ engines use a different one as the fitting for the hose is of a different size than the 2007-2008. Read the bulletin for the part numbers.

 

[Hellacious tahoe]

P0452 relates to the data that the fuel tank pressure sensor is reporting to the ECM.

Your new pump should have come with a new fuel tank pressure sensor -- just to clarify, are you saying that you changed that sensor after installing the replacement pump?

I did change the sensor together with the fuel pump. Just saw the flex fuel sticker on the fuel door. Today I replaced the oil pressure sensor and its screen. Since I must test the injectors, I took out the intake, will hook up a pump and a gauge to pressurize the fuel rack and check for leaks.

 

[Fless]

You may want to use new o-rings on the injectors when you reassemble.

Still need to determine if the alcohol percentage in the PCM matches the fuel that's being used.

 

[Hellacious tahoe]

Update: intake out to replace the oil pressure sensor and to test the injectors for leaks. I connected a fuel pump and a pressure gauge to the fuel rail, connected it to a battery. A second later, pressure went up to 100, then down to 80. All of the injectors are bone dry, so injector leaking may not be my issue

 

[Hellacious tahoe]

You may want to use new o-rings on the injectors when you reassemble.

Still need to determine if the alcohol percentage in the PCM matches the fuel that's being used.

You may be right Fless, the injectors dont leak. I havent taken any out of the intake. I plan to measure resistance across the 2 prongs on each one of them. After is all in one piece, I will try to see what the pcm thinks about the ethanol content. Thx for your support, to all of you.