93 LT1 C4 Lean

Hey everyone, new here. Well this is an issue I have been trying to solve. I have made the car less lean that it was. Runs good, picks up great. 79k miles. All stock except for chambered cat back and taylor 8mm wires, lol. Interesting note, the car only runs lean in the city. Soon as I get up to freeway speeds, both BLM's are plus or minus 3 points of 128. If anyone wants to read my datalogs, I can email them to you.

Did a smoke test for vacuum leaks, found 3. Fixed that.

Exhaust leak at the driver side exhaust manifold. Fixed.

Fuel pressure is 42 psi when primed. 38-40 when running.

New fuel filter, new FIC injectors.

New Bosch 02's

Can anyone help? Oh, there is no check engine light, or any stored codes.

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Originally Posted by LT1C4

Hey everyone, new here. Well this is an issue I have been trying to solve. I have made the car less lean that it was. Runs good, picks up great. 79k miles. All stock except for chambered cat back and taylor 8mm wires, lol. Interesting note, the car only runs lean in the city. Soon as I get up to freeway speeds, both BLM's are plus or minus 3 points of 128. If anyone wants to read my datalogs, I can email them to you.

Did a smoke test for vacuum leaks, found 3. Fixed that.

Exhaust leak at the driver side exhaust manifold. Fixed.

Fuel pressure is 42 psi when primed. 38-40 when running.

New fuel filter, new FIC injectors.

New Bosch 02's

Can anyone help? Oh, there is no check engine light, or any stored codes.

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Is it actually running lean or is it just the fuel trims showing that it is lean. I have found many GM tunes to run a little leaner than you would otherwise expect at light throttle. My 1997 Express van ran so lean in stock form the tail pipe actually had rust showing inside it.

At least that's what the fuel trims are telling me. Left bank BLM at idle is 140-144. I know perfect is at 128. I only get like 13mpg city. But highway it is perfect, at 25 mpg. My IAC counts are at zero, when at warm idle. If I turn the AC on, the IAC counts come up to about 15.

First thing to do is close the throttle and get the IAC counts higher. You're saying left bank BLM so I suspect it's not balanced. Idle air has to go through the IAC to balance the banks.

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Originally Posted by lionelhutz

First thing to do is close the throttle and get the IAC counts higher. You're saying left bank BLM so I suspect it's not balanced. Idle air has to go through the IAC to balance the banks.

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Right bank does go lean, just not as much as the left bank. To be more clear, the right bank is lean as well, but for less time. At idle, right bank blm is around 120-124. Would that be adjusted through the throttle stop screw? And thanks for the response.

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Originally Posted by LT1C4

Right bank does go lean, just not as much as the left bank. To be more clear, the right bank is lean as well, but for less time. At idle, right bank blm is around 120-124. Would that be adjusted through the throttle stop screw? And thanks for the response.

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Yes that would be the correct way provided you have no vacuum leaks. I would would find someone with an Evap smoke leak tester and smoke test the intake if you have not already done it.

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Originally Posted by Fast355

Yes that would be the correct way provided you have no vacuum leaks. I would would find someone with an Evap smoke leak tester and smoke test the intake if you have not already done it.

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I'm not sure if my idle screw has been messed with. But here it is. Anyone know if that looks like it's been messed with?Attachment 10313
Does that sound like a vacuum leak? My idle is not high, nor does the car surge.https://youtu.be/o2n7NJY6u5A

the adjuster is on the other side. on an LT1 you want the plates to be closed as far as possible without binding in the bores.

that allows the idle passages to work with the iac and the air bypass hole (which feed the cylinders more evenly at low airflow)