Need some help figuring out strange lean condition
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Need some help figuring out strange lean condition I have a 67 Chevelle that has a 427 Dart LS next block, trick flow heads forged internals etc.
running a ls7 intake manifold.
car was dyno tuned and ran great. Over the last week, the car has started to run poorly.. when data logging and using my wideband, I logged AFRs upwards of 18-19 so super lean.. this occurs under acceleration, like 19% throttle position and like 2300-3000 rpm. It’s intermittent. It happens sometimes are higher rpm.
I cleaned my fuel filter (magnafuel). Fuel pressure regulator gauge shows 58psi. Injectors are FIC 62lb/hr.
Also have a NW 92mm tb, Hooker 1.75” longtubes to a full 3” exhaust.
running a ls7 intake manifold.
car was dyno tuned and ran great. Over the last week, the car has started to run poorly.. when data logging and using my wideband, I logged AFRs upwards of 18-19 so super lean.. this occurs under acceleration, like 19% throttle position and like 2300-3000 rpm. It’s intermittent. It happens sometimes are higher rpm.
I cleaned my fuel filter (magnafuel). Fuel pressure regulator gauge shows 58psi. Injectors are FIC 62lb/hr.
Also have a NW 92mm tb, Hooker 1.75” longtubes to a full 3” exhaust.
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Update:
Yesterday I smoke tested the intake manifold for leaks. I’m doing so I removed the intake tube and unplugged the MAF.
Today, hooked my fuel pressure gauge up to see if I was dropping pressure which would cause the lean condition.
took the car on a drive and it ran perfect aside from dying when I come to a stop and hard starting..
No fuel pressure issues..
realized I left the MAF unplugged so I turned the engine off, plugged it in and cycled the key 2 times then started it. Accelerated and it went into a lean condition!
pulled over, unplugged the MAF and fired it up, and it ran fine again!
possibly dirty MAF? It’s brand new AC Delco LS7 maf maybe 350 miles on it. I do have a KN filter
Yesterday I smoke tested the intake manifold for leaks. I’m doing so I removed the intake tube and unplugged the MAF.
Today, hooked my fuel pressure gauge up to see if I was dropping pressure which would cause the lean condition.
took the car on a drive and it ran perfect aside from dying when I come to a stop and hard starting..
No fuel pressure issues..
realized I left the MAF unplugged so I turned the engine off, plugged it in and cycled the key 2 times then started it. Accelerated and it went into a lean condition!
pulled over, unplugged the MAF and fired it up, and it ran fine again!
possibly dirty MAF? It’s brand new AC Delco LS7 maf maybe 350 miles on it. I do have a KN filter
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From: Central Cal.
A dirty MAF might do that. Can't measure all the air, therefore won't command enough fuel. Sounds logical to me....
In all your playing around with the air system, did you run it sans filter for any time? OR did your system have any leaks after the filter?
In all your playing around with the air system, did you run it sans filter for any time? OR did your system have any leaks after the filter?
Last edited by G Atsma; Jul 19, 2021 at 11:18 AM.
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I cleaned it with MAF cleaner and now it is running lean upon start up whereas before it was under load about 2000rpm.
took the filter off and re cleaned and still runs bad with MAF plugged in.
Last edited by The0nlyon3; Jul 20, 2021 at 07:46 PM.
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p01 pcm hardware 411... put the new MAF in today, and it idles fine now but under accel it leans out again..
would opening up airflow to where the filter is (adding a headlight funnel and air vent) possibly have an effect on it??
May need to recalibrate the MAF after that change. Wouldn't hurt to datalog the MAF and see if it's off.
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maybe the air is too turbulent? I see some people using the honeycomb air straightener
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Here are two datalogs... The only labeled July 18 #4 was the last day using the old sensor. The one labeled July 21 is with the new sensor... Still having the same issues. it'll idle okay, but once the throttle is opened it starts to go lean. Also, the July 21 log started with the maf unplugged so the IAT shows -38. eventually in the log i plugged it back in.
Once again, this all seemed to start when I opened up the inner headlight hole to allow more outside air to the filter. I also added another airduct with a scoop in the bumper that feeds the filter. unfortunately, I can't cover those openings up to get it back to "how it was" before I started having issues...
Once again, this all seemed to start when I opened up the inner headlight hole to allow more outside air to the filter. I also added another airduct with a scoop in the bumper that feeds the filter. unfortunately, I can't cover those openings up to get it back to "how it was" before I started having issues...
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I did not run it with out the filter (i'm guessing that's what you meant by "sans").. and I smoke tested the intake and there is a TINY air leak on the throttle body shaft where the throttle cable is. I can't imagine that causing enough of a leak to lean it out this bad.
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ugh.. its a Nick Williams 92mm TB... I got it to replace a crap chinese holley TB that was giving me issues.... the NW TB fixed my issues I was having with idling.. doesn't have that much wear on it... I wonder if they have seals for these things??
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Nick Williams himself posted on a post regarding a 102mm shaft leak and stated that there is nothing wrong and that its not causing the OP's issues.
https://ls1tech.com/forums/generatio...ms-102-tb.html
https://ls1tech.com/forums/generatio...ms-102-tb.html
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here are two more logs from today. Not sure what is going on. Super frustrating.
July 22 is with maf plugged in... 22 #2 is with maf failed out at 100 Hz.. not as lean but still lean at higher rpm none the less...
July 22 is with maf plugged in... 22 #2 is with maf failed out at 100 Hz.. not as lean but still lean at higher rpm none the less...
Do have any logs of your setup before this issue started by any chance?
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unfortunately I do not.. new engine, new pcm with added maf and it was just tuned a month ago. Ran fine, little low on power but I was having IAT temps in the 140-150 range. I didn’t have any logs saved from when I had high IATs... just started logging when I noticed my wideband leaning out
unfortunately I do not.. new engine, new pcm with added maf and it was just tuned a month ago. Ran fine, little low on power but I was having IAT temps in the 140-150 range. I didn’t have any logs saved from when I had high IATs... just started logging when I noticed my wideband leaning out