99 Tahoe w/ P0171, P0174, and P0305

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Chevychick

TYF Newbie
Joined
Apr 28, 2021
Posts
15
Reaction score
10
Location
NJ
I have P0171, P0174, and P0305 on my 99 Tahoe. I know the P0305 is misfire in cylinder 5 and I know that P0171 and P0174 are system too lean bank 1 and bank 2. I have been smelling coolant and my question is could a bad intake manifold gasket cause these codes? The truck also struggles going up hills with steep grades and I feel the misfires. Fuel pressure regulator was changed after I got a P0300 code and that code hasn't come back, distributor cap and rotor were just replaced, ignition coil was just replaced as well. Mass air flow sensor is new, fuel pump was installed in 2019/early 2020. 3 of the 4 O2 sensors have been replaced. Plugs and wires are fine. I don't want to just start throwing parts at it, I want to be able to fix it once and for all. Any insight would be much appreciated. This is the newest vehicle I've owned, I'm used to my 88 K5 I had or the 86 Monte Carlo SS and 84 Camaro I have lol. Thanks in advance!
 

east302

Full Access Member
Joined
Dec 21, 2016
Posts
1,557
Reaction score
1,381
Location
Mississippi
When were the intake gaskets last replaced?

Check for a coolant leak at seam between the intake and block (front and back) and along the valley between the intake and valve covers.
 
OP
OP
Chevychick

Chevychick

TYF Newbie
Joined
Apr 28, 2021
Posts
15
Reaction score
10
Location
NJ
When were the intake gaskets last replaced?

Check for a coolant leak at seam between the intake and block (front and back) and along the valley between the intake and valve covers.
I have no idea if or when they were replaced. I've had the truck for approximately 4 years and never changed them. I will check the area that you mentioned. I am using coolant because I do have to add some pretty frequently. Thanks!
 

east302

Full Access Member
Joined
Dec 21, 2016
Posts
1,557
Reaction score
1,381
Location
Mississippi
By now, they’ve likely been replaced. On my first 98, they went at 40k or so miles. Making it to even 100k on the original gaskets would probably be rare.

If you get to that point, there are two types of replacement gaskets. The ones to get are the ones with the metal reinforcement. They do still sell the stock original type, so those will have a shorter lifespan and would be the ones to avoid.

This type has the metal plate reinforcement…



54935DBB-B730-4EEC-B1C0-1A83D31AFDCD.jpeg
 
OP
OP
Chevychick

Chevychick

TYF Newbie
Joined
Apr 28, 2021
Posts
15
Reaction score
10
Location
NJ
By now, they’ve likely been replaced. On my first 98, they went at 40k or so miles. Making it to even 100k on the original gaskets would probably be rare.

If you get to that point, there are two types of replacement gaskets. The ones to get are the ones with the metal reinforcement. They do still sell the stock original type, so those will have a shorter lifespan and would be the ones to avoid.

This type has the metal plate reinforcement…



View attachment 349592
Thanks for the info! I no longer have the misfire code, BUT I consistently have the P0171 and P0174. When I drive the truck, I feel the misfires and they happen between 1300-1800 rpm. If I accelerate to 2000 rpm, it goes away, it doesn't always happen, but there is no rhyme or reason to it other than me catching the pattern of it occuring between those rpms. Could the EGR Valve or Throttle Position Sensor be a cause?
 

OR VietVet

Multnomah Falls
Supporting Member
Military
Joined
Oct 8, 2014
Posts
19,073
Reaction score
31,180
Location
Willamette Valley
The answer is yes, the intake gaskets could cause the leak and the misfire and the lean condition. You said 3 of the 4 O2 sensors have been replaced. Which one hasn't been replaced? If intake is leaking you could also get coolant in the oil. How old are the plugs? Have you removed them to check for problems?

Good recommendation by @east302 on the gaskets. I like Fel Pro gaskets.
 
OP
OP
Chevychick

Chevychick

TYF Newbie
Joined
Apr 28, 2021
Posts
15
Reaction score
10
Location
NJ
The answer is yes, the intake gaskets could cause the leak and the misfire and the lean condition. You said 3 of the 4 O2 sensors have been replaced. Which one hasn't been replaced? If intake is leaking you could also get coolant in the oil. How old are the plugs? Have you removed them to check for problems?

Good recommendation by @east302 on the gaskets. I like Fel Pro gaskets.
I don't remember which O2 sensor hasn't been replaced off the top of my head, but I believe it was one of the ones post cat. The thermostat gasket has been replaced which seems to have stopped the using of coolant and the coolant smell I was having. As for the plugs, they were removed and checked and looked ok, but they are 2-3 (closer to 3) years old. Also, the distributor cap and rotor were replaced, the ignition could was replaced, and timing was set via a reliable auto shop. I have the intake manifold gaskets, just haven't had a chance to do them, I've had 2 major back surgeries and a neck surgery since June of 2020. I'm going to attach pictures of the freeze frame I did and the live data I did, they are from 2 different days, but if you have any insight, I'd gladly take it! Thanks for your reply!
 

Attachments

  • Screenshot_20210911-164704_BlueDriver.jpg
    Screenshot_20210911-164704_BlueDriver.jpg
    115.3 KB · Views: 3
  • Screenshot_20210927-165615_BlueDriver.jpg
    Screenshot_20210927-165615_BlueDriver.jpg
    115.8 KB · Views: 3
  • Screenshot_20210911-164704_BlueDriver.jpg
    Screenshot_20210911-164704_BlueDriver.jpg
    115.3 KB · Views: 3
  • Screenshot_20210927-165615_BlueDriver.jpg
    Screenshot_20210927-165615_BlueDriver.jpg
    115.8 KB · Views: 3

OR VietVet

Multnomah Falls
Supporting Member
Military
Joined
Oct 8, 2014
Posts
19,073
Reaction score
31,180
Location
Willamette Valley
Since I have been out of the shops I ran for close to 13 years now, there are other sharper guys with this info than me. I don't want to steer you wrong with a WAG. They will chime in and help. IMO, the front O2's are the most important but would be best if all 4 were done and of good quality. Don't want to try and save a buck on O2's. The Genuine GM and Delphi are the way to go. Glad the coolant leak is now fixed for you. Careful with back and neck and let others help.
 
OP
OP
Chevychick

Chevychick

TYF Newbie
Joined
Apr 28, 2021
Posts
15
Reaction score
10
Location
NJ
Since I have been out of the shops I ran for close to 13 years now, there are other sharper guys with this info than me. I don't want to steer you wrong with a WAG. They will chime in and help. IMO, the front O2's are the most important but would be best if all 4 were done and of good quality. Don't want to try and save a buck on O2's. The Genuine GM and Delphi are the way to go. Glad the coolant leak is now fixed for you. Careful with back and neck and let others help.
Thank you! Any part I buy is AC Delco if available, if not then Delphi. My O2 sensors are Delco. I appreciate all your help!
 

Forum statistics

Threads
128,795
Posts
1,805,569
Members
91,779
Latest member
wilburMN
Top