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Discussion Starter · #1 · (Edited)
'97 vulcan, 209k miles

Several weeks ago was getting both P0171 & P0174, now only P0171. Rough idle, sputtering, occasional misfire and a stumbling sound.

Leak detector flow meter indicated a large leak.

In the past few days, I replaced gaskets for EGR, IACV, LIM, UIM, TB & valve covers. Rubber hoses have also been replaced. Hard plastic lines appear to be fine. After replacing gaskets and removing IAC, EGR and closing off various hoses the leak detector flow meter still indicates a large leak.

Fuel filter & pump also replaced due to weak pressure & inaccurate gauge.

Exhaust system smoke test - looking under car and finding no leak other than muffler.

Connected detector directly to brake booster hose - no leaks found - psi was building up.

Owned this car for nearly 12 years and the past couple of weeks I've have had so many problems happen at once. Don't know what else to do.

I have read many many postings here and articles & videos elsewhere regarding P0171.

Hope to hear ideas or recommendations from the great people here.

Ray
 

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'97 vulcan, 209k miles

Several weeks ago was getting both P0171 & P0174, now only P0171. Rough idle, sputtering, occasional misfire and a stumbling sound.

Leak detector flow meter indicated a large leak.

In the past few days, I replaced gaskets for EGR, IACV, LIM, UIM, TB & valve covers. Rubber hoses have also been replaced. Hard plastic lines appear to be fine. After replacing gaskets and removing IAC, EGR and closing off various hoses the leak detector flow meter still indicates a large leak.

Fuel filter & pump also replaced due to weak pressure & inaccurate gauge.

Exhaust system smoke test - looking under car and finding no leak other than muffler.

Connected detector directly to brake booster hose - no leaks found - psi was building up.

Owned this car for nearly 12 years and the past couple of weeks I've have had so many problems happen at once. Don't know what else to do.

I have read many many postings here and articles & videos elsewhere regarding P0171.

Hope to hear ideas or recommendations from the great people here.

Ray
You will need data. Fuel trims at idle, actual not what the code tells. Pic attached shows chart of vac leak, as fuel trim high at idle and OK under power. This pattern confirms a vac leak. Good code reader will have "live data". Car running and look at long term fuel trims. Look at bank 1 then bank 2. Both similar and the leak is where it effects both banks.
-chart-
 

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You will need data. Fuel trims at idle, actual not what the code tells. Pic attached shows chart of vac leak, as fuel trim high at idle and OK under power. This pattern confirms a vac leak. Good code reader will have "live data". Car running and look at long term fuel trims. Look at bank 1 then bank 2. Both similar and the leak is where it effects both banks.
-chart-
Pic of code reader in live data. Those numbers are always changing so pic is one snap shot. Do not be concerned about short trims. LTFT = long term fuel trims should be near the same value bank to bank +/- 5% or so but not exact numbers. +10% is fine, maybe a very tiny leak effecting both banks. If those near 20% then significant leak. Test done engine warm, idling in "N" A/C off.
If anyone expects to do their own work, then a good reader is critical. Another use of this reader is "pending codes". You can have a problem, like misfire but no codes. Finding which cylinder is missing with no codes is a pain. My case, #3 had pending misfire code. #3 was bad coil.
-chart-
 

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Discussion Starter · #6 ·
Hi Chart,

I appreciate your quick reply.

I performed several leak tests with a smoke machine. The only areas smoke is revealed is the IACV vent, throttle body (butterfly shaft bushing where the spring is at) and the bottom of EGR valve. From what I've read it is normal for smoke to seep from these areas during a test. I even removed these parts, sealing/covering hole completely and machine "leak size" gauge still indicates a large leak.

Performed test on the brake booster and it appears to have no leaks. Performed a exhaust test through muffler and found several leaks at the muffler & flex pipe so I sealed them up.

In all the years of owning car, this problem has been the most challenging. Problem has been going on for several weeks.

Ray
 

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Hi Chart,

I appreciate your quick reply.

I performed several leak tests with a smoke machine. The only areas smoke is revealed is the IACV vent, throttle body (butterfly shaft bushing where the spring is at) and the bottom of EGR valve. From what I've read it is normal for smoke to seep from these areas during a test. I even removed these parts, sealing/covering hole completely and machine "leak size" gauge still indicates a large leak.

Performed test on the brake booster and it appears to have no leaks. Performed a exhaust test through muffler and found several leaks at the muffler & flex pipe so I sealed them up.

In all the years of owning car, this problem has been the most challenging. Problem has been going on for several weeks.

Ray
Most vacuum leaks effect both banks. With bank 2 normal and bank 1 way out of control, might look for some other cause. Like fuel injector. What year, what engine? Might pull the plug wire on one cylinder at a time on bank 1 and look for a cylinder that does not drop the rpm, like it isn't firing.
-chart-
 

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Why not just pull the plugs and see what they look like? No better way to see what's going on inside the combustion chambers.
Put a stethoscope (or screwdriver) on the injectors and see if they all sound the same.
 

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