07 yukon 5.3l flex p0300 after lots of money spent.

[mikechrisclark]

I have an 07 yukon 5.3l flex fuel with 195,000 miles. I know the P0300 code has been addressed a lot but mine may take the cake and I’m lost.

I spend $4800 to have lifters replaced by certified mechanics. Heads were milled and the repair was done correctly. I had 2 lifters go bad and had misfire and p0300 code. I got truck back and it was running great. Like new. I hardly use this truck except to tow camper and boat. It has only 3000 miles on engine after lifter repair. Not a daily driver. It has sat most of winter being started once a week for five minutes each time. When I finally decided to take it to the store it had no power, misfired, shifted hard and felt like it did before lifters were changed.

I removed valve covers. All rockers move, push rods move. Seems to be ok with lifters. So I have replaced, all coils, plugs, plug wires, fuel injectors, o2 sensors. Still not running right. I have a tuner to delete 4 cylinder mode but it has issues with tuner on or off.

I am at a lose for what’s next. I did notice when I changed fuel injectors the pressure relief valve on fuel rail didn’t even drip fuel when I pushed it in to take pressure off system. Will it still run, even like crap, with a bad fuel pump or clogged fuel filter? It should have sprayed out shouldn’t it? I’m in need of help. I have spent way more on engine and parts than the truck is worth at this point. Thank you for any advice.

 

[89Suburban]

I have an 07 yukon 5.3l flex fuel with 195,000 miles. I know the P0300 code has been addressed a lot but mine may take the cake and I’m lost.

I spend $4800 to have lifters replaced by certified mechanics. Heads were milled and the repair was done correctly. I had 2 lifters go bad and had misfire and p0300 code. I got truck back and it was running great. Like new. I hardly use this truck except to tow camper and boat. It has only 3000 miles on engine after lifter repair. Not a daily driver. It has sat most of winter being started once a week for five minutes each time. When I finally decided to take it to the store it had no power, misfired, shifted hard and felt like it did before lifters were changed.

I removed valve covers. All rockers move, push rods move. Seems to be ok with lifters. So I have replaced, all coils, plugs, plug wires, fuel injectors, o2 sensors. Still not running right. I have a tuner to delete 4 cylinder mode but it has issues with tuner on or off.

I am at a lose for what’s next. I did notice when I changed fuel injectors the pressure relief valve on fuel rail didn’t even drip fuel when I pushed it in to take pressure off system. Will it still run, even like crap, with a bad fuel pump or clogged fuel filter? It should have sprayed out shouldn’t it? I’m in need of help. I have spent way more on engine and parts than the truck is worth at this point. Thank you for any advice.

Can you rent a fuel pressure tester to get some readings?

 

[swathdiver]

I have an 07 yukon 5.3l flex fuel with 195,000 miles. I know the P0300 code has been addressed a lot but mine may take the cake and I’m lost.

I spend $4800 to have lifters replaced by certified mechanics. Heads were milled and the repair was done correctly. I had 2 lifters go bad and had misfire and p0300 code. I got truck back and it was running great. Like new. I hardly use this truck except to tow camper and boat. It has only 3000 miles on engine after lifter repair. Not a daily driver. It has sat most of winter being started once a week for five minutes each time. When I finally decided to take it to the store it had no power, misfired, shifted hard and felt like it did before lifters were changed.

I removed valve covers. All rockers move, push rods move. Seems to be ok with lifters. So I have replaced, all coils, plugs, plug wires, fuel injectors, o2 sensors. Still not running right. I have a tuner to delete 4 cylinder mode but it has issues with tuner on or off.

I am at a lose for what’s next. I did notice when I changed fuel injectors the pressure relief valve on fuel rail didn’t even drip fuel when I pushed it in to take pressure off system. Will it still run, even like crap, with a bad fuel pump or clogged fuel filter? It should have sprayed out shouldn’t it? I’m in need of help. I have spent way more on engine and parts than the truck is worth at this point. Thank you for any advice.

You'll want to check the fuel pressure from the rail. The fuel filter was deleted years ago. Running pressure ought to be in the mid-high 50s. When you turn off the engine, it ought to not lose more than 5 psi after about 5 minutes.

When the repairs to the engine were done, did they replace the lifter trays and VLOM with new GM OE units?

What codes are you getting now?

 

[mikechrisclark]

Yes the did replace everything with oem equipment. Not sure on lifter trays. Claim say it was replaced on my receipt of itemized parts. I’m looking at buying a fuel pressure tester now.

 

[Fless]

Lots of auto parts stores will 'rent' fuel pressure gauges; you just front them the cost with a credit card and they credit your account when you return it. If you don't return it, you bought it.

Do the prescribed fuel pressure tests with key on, engine off first. Then do the running test. Post up your readings in this thread. @swathdiver I thought that the running (regulated) fuel pressure was more like in the low-mid 40s -- 43, 44, something like that. I could be wrong; it happened once before...

If the fuel pressure values work out to be good it might be good to get a higher level scanner that will look at individual cylinder misfire counts.

 

[swathdiver]

Lots of auto parts stores will 'rent' fuel pressure gauges; you just front them the cost with a credit card and they credit your account when you return it. If you don't return it, you bought it.

Do the prescribed fuel pressure tests with key on, engine off first. Then do the running test. Post up your readings in this thread. @swathdiver I thought that the running (regulated) fuel pressure was more like in the low-mid 40s -- 43, 44, something like that. I could be wrong; it happened once before...

If the fuel pressure values work out to be good it might be good to get a higher level scanner that will look at individual cylinder misfire counts.

Not on the 2007s, they run the old way, can't even see the pressure with a scan tool, mechanical only.

I learned that trying to help a member on here at his house once.

 

[Fless]

Not on the 2007s, they run the old way, can't even see the pressure with a scan tool, mechanical only.

I learned that trying to help a member on here at his house once.

That's how I described it, I didn't mention using a scan tool except for misfire counts. Confused. What do you mean, 'Not on the 2007s'?

 

[swathdiver]

That's how I described it, I didn't mention using a scan tool except for misfire counts. Confused. What do you mean, 'Not on the 2007s'?

With the other year 900s, they have a Fuel Pump Control Module and run their fuel pressure at 43.5 psi. The 2007s are still set up like the GMT800s, the ECM controls the fuel pump at the old pressures and the Tech-2 cannot see the fuel pressure unlike the later years.