You could use the hose from the PCV or the vacuum hose for power steering to inject the smoke
You need to block off the opening to the throttle body

Also, could test if there is some exhaust leak that is pulling in air to confuse the 02 sensors
Put smoker into one of the muffler exhaust tips and plug up any others and also again block TB

Or if the engine has the smog pump is the hose from the pump to the check-valve into the exhaust manifold

 

Yup - seal the air intake at the throttlebody and use the PCV dirty air line.

What trouble codes are present in the car's diagnostic system? P 0171 P 0174.


Entirely possible that the intake manifold-to-throttlebody connector has failed.

 

Thanks all, OK I'll smoke test this weekend and post the results. Codes were for both banks too lean. My long term fuel trims are between +10-20% as well, and identical on both banks. So I have a problem somewhere.

I sprayed carb cleaner all around the manifold-throttle body connector and didn't detect a change in idle. However that trick has honestly never worked for me, which is why I bought the good old smoke machine.

Also, gas mileage is terrible. 13mpg. I owned this exact car before and I know it gets 18mpg.

 

Well I smoke tested today though the dirty PCV line and not a wisp of smoke escaped after 30 minutes or so.

So I will probably try @Team ZR-1 idea next.. thing is it is both banks that are running lean at identical measures.. so it has to be something that affects both

 

Being both B1 and B2 are reporting the same +10 to +20 % lean, then the problem is common to both
So you need to focus on what is common to both sides

1. MAF itself, faulty, dirty, not stock one ?
2. Did you smoke test with aircleaner off and blocked, so you could see if the airbridge between that and throttlebody has and unmetered leak ?
3. Put a fuel pressure gauge on fuel rail and see if the PSI reports normal for that engine ?
4. How old is the fuel filter, as there could be proper pressure but low gas volume flow ?
5. See if any senors are lying, does scanner show PCM going into "closed loop" if stays in open loop then PCM ignores feedback sensors and only uses predicted airmass via the VE table
6. If the LTFTs are reporting that lean, what are the STFTs reporting ?
7. if scanner supports bidirectional, once in closed loop, send command to clear fuel trims.
(if not disconnect battery just for few seconds)

Do the trims go right back to that lean just at idle ?
8. Do the fuel trims stay that lean at different driving conditions, or maybe just at idle ?

9. If fuel trims that lean, something has to tell PCM is that lean or,
so the O2 sensors should be reporting high values (rich) to get PCM to command fuel injector pulse width much longer

At closed loop idle, A/C OFF

MAF should report like 1-2 pounds of air (about 3,000 Hz)
MAP about 35 KPA, (if close to sea level) TPS around 10% angle
Injector pulse width around 3 mSecs
Upstream O2 sensors around 0.500 mVolts
If your scanner supports GM's fuel cells, at idle should report cell 16 or 17 with an auto tranny

Scanner should at least do I/M smog test results, are all in a complete state and
should be an O2 tests, are results correct ?

 

Being both B1 and B2 are reporting the same +10 to +20 % lean, then the problem is common to both
So you need to focus on what is common to both sides

1. MAF itself, faulty, dirty, not stock one ? Stock, not sure when replaced if ever.. now in the process of cleaning
2. Did you smoke test with aircleaner off and blocked, so you could see if the airbridge between that and throttlebody has and unmetered leak ? Yes
3. Put a fuel pressure gauge on fuel rail and see if the PSI reports normal for that engine ? Good point, I'll try this.. see if I can find my pressure gauge
4. How old is the fuel filter, as there could be proper pressure but low gas volume flow ? As far as I know, it is original. This is non-servicable, I believe
5. See if any senors are lying, does scanner show PCM going into "closed loop" if stays in open loop then PCM ignores feedback sensors and only uses predicted airmass via the VE table will have to check my data logs, I believe it goes into closed loop
6. If the LTFTs are reporting that lean, what are the STFTs reporting ? 0% at idle, and of course the change when engine load changes but they return to 0%
7. if scanner supports bidirectional, once in closed loop, send command to clear fuel trims.
(if not disconnect battery just for few seconds)

Do the trims go right back to that lean just at idle ?
8. Do the fuel trims stay that lean at different driving conditions, or maybe just at idle ? LTFT rise to +20% when engine speed is held at 2500rpm

9. If fuel trims that lean, something has to tell PCM is that lean or,
so the O2 sensors should be reporting high values (rich) to get PCM to command fuel injector pulse width much longer

At closed loop idle, A/C OFF

MAF should report like 1-2 pounds of air (about 3,000 Hz)
MAP about 35 KPA, (if close to sea level) TPS around 10% angle
Injector pulse width around 3 mSecs
Upstream O2 sensors around 0.500 mVolts
If your scanner supports GM's fuel cells, at idle should report cell 16 or 17 with an auto tranny

Scanner should at least do I/M smog test results, are all in a complete state and
should be an O2 tests, are results correct ?

Some answers above in bold, thanks for the list, I'll plug away on the rest. Curious as to fuel pressure.. I know these cars have fuel pump/relay problems. I checked my relay and while it was a little hot, none of the contacts were burned.

 

Fuel pressure checks? GM/Helm service manual.

 

Northstar was never DI - usual fuel pressure at the rail test port was 41 - 47 psi just after Key: ON or at idle.

The op's fuel rail, from pictures in Rock Auto, appears different from my 2002 version so perhaps the FPR is also different.

Although his smoke test was inconclusive the majority of Northstar P 0171 / P 0174 codes are (based on this site's threads history) caused by vacuum leaks on or near the intake manifold.

 

Possible the OP's smoker did not put out enough pressure and thus would not show small leaks
If possible, redo and up the smokers output pressure,
in any case, the scanner data of LTFTs and what O2 report at the same time would tell if unmetered air is the cause.
If vacuum leak, the readings of MAP would show that

 

My smoke tester has a regulator so I am limited as to how much pressure, but I did also spray water specifically at the manifold coupling when running, to see if anything was getting sucked in. No change in idle.

Also I should note, if I was not clear.. LTFT are always high, no matter the RPM. They seem to rise a bit when held at 2500rpm. But they are always high.

 

Cold start after cleaning MAF... adapter for my fuel rail pressure sensor won't be here until Friday

 

Does this scanner allow exporting the recording's raw data to like a TXT or CSV file, so it can be brought into Excel spreadsheet ?
As trying to scroll up/down on those screenshots, not easy to analyze data
Does this allow to show average values for that run cycle rather than looks like VALUE is that moment of time ?

How come it only show 3 O2 sensors, does this have the 2 upstream, then go to a Y pipe and then only 1 O2 after 1 CAT ?

Is this recording ONLY at idle and also not on the gas pedal ?

Fuel trim learn is ON and show in closed loop so that says PCM is happy with the feedback sensors
Also says using fuel trim cell 17, so if having an auto tranny then that is correct cell
Injector pulse width ON time 2.3 mSec for both heads, so balanced left/right and about correct for an idling V8 engine. So PCM is NOT commanding more fuel to bring down a lean LTFTs

MAP sensor reporting 98 KPa ?
Was that with engine running, if so MAP is the inverse of vacuum (I do not see vac PID)
so if MAP high means Vac low

IF at sea level, I would expect to see anywhere from maybe 35 to 45 KPa.

If that was 98 Kpa at idle, not on gas pedal, then either a vacuum leak, bad MAP sensor or wiring ?

 

Does this scanner allow exporting the recording's raw data to like a TXT or CSV file, so it can be brought into Excel spreadsheet ?
As trying to scroll up/down on those screenshots, not easy to analyze data
Does this allow to show average values for that run cycle rather than looks like VALUE is that moment of time ?

How come it only show 3 O2 sensors, does this have the 2 upstream, then go to a Y pipe and then only 1 O2 after 1 CAT ?

Is this recording ONLY at idle and also not on the gas pedal ?

Fuel trim learn is ON so that says PCM is happy with the feedback sensors
Also says using fuel trim cell 17, so if having an auto tranny then that is correct cell
Injector pulse width ON time 2.3 mSec for both heads, so balanced left/right and about correct for an idling V8 engine. So PCM is NOT commanding more fuel to bring down a lean LTFTs

Yes, 3 sensors on DTS, 2 upstream and 1 downstream

Yes let me see if I can upload the exported text file

 

Review what I just added to my last post
If that is now average and just real time values shown, hard to tell how both front B1/B2 are balanced or not

As it shows a 14% imbalance left/right

Coolant shows about 190 F deg, in closed loop and fuel trim learn on,
thus reading for the 1 downstream O2 is 0.489 mVolts which is about perfect stoch of around 14.7:1 AFR, if correct that is no where way lean so CAT it converting and functional

 

You're right, I need to grab average values here. The Map is 98 in one snapshot and 31 in another

 

How does this work, 3 O2 sensors

Have
B1S1
B2S1 and
B1S2, is that the downstream one ?

 

The post-1998 FWD Northstar cars have 3 O2 sensors - exhaust manifolds and one after-cat.

Manifolds to a Y-pipe, to a single cat, followed by a resonator. Phony dual exhaust.

Here's the after-cat O2 sensor bung - ahead of the resonator -

The left (front) bank sensor is in the exhaust collector; the right (rear) is in the top of the manifold.

......... and here's the phony rear section -

 

The post-1998 FWD Northstar cars have 3 O2 sensors - exhaust manifolds and one after-cat.

Manifolds to a Y-pipe, to a single cat, followed by a resonator. Phony dual exhaust.

Here's the after-cat O2 sensor bung - ahead of the resonator -

The left (front) bank sensor is in the exhaust collector; the right (rear) is in the top of the manifold.

They make it confusing as label it B1S2 when really is center to both B1 and B2 S1s

 

Damn those are small exhaust pipes, must have higher back pressure with that design
I have 3 inch from header collectors, right through 3 inch inlets of small mufflers on my Corvette

 

Damn those are small exhaust pipes, must have higher back pressure with that design
I have 3 inch from header collectors, right through 3 inch inlets of small mufflers on my Corvette

Probably sounds monstrous. My stock C6 is the quietest car on the planet.

 

Ref. Post 20 -

There is little or no backpressure in the original Northstar systems. It's a small 279 c.i. engine - the worst exhaust glitch for the FWD versions was the left bank crossunder pipe that forms the "Y" ahead of the cat flange. The header pipe itself and the method of joining it to the right (rear) bank leaves something to be desired. One trick is to Dremel out the excess flash from the left bank pipe where it sticks into the Y. Been there, done that.

The discontinued CORSA catback system frees up 16 hp at the top of the power curve - WOT shift area - nothing lower down. It's all 2.5" from the front of the cat back - no baffles anywhere - see the red carpet through the resonator? Those are 13 EEE shoes.

 

In the pre-2000 Northstar FWD setups there were 4 O2 sensors -

B1S1 = right (rear) bank - top center of exhaust manifold
B2S1 = Left (front) bank exhaust collector
B1S2 = pre-cat pipe
B1S3 = after-cat pipe.

 

Well I finally got my pressure tester adapter, running 43psi at idle which I believe is normal