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Old 07-13-2018, 11:24 AM   #2551
Jason7121
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Re: Crusty Rusty Leaky Squeaky 67 Step

Try unplugging the mass airflow sensor and take it for a drive see if it makes a change
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Old 07-13-2018, 11:26 AM   #2552
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Re: Crusty Rusty Leaky Squeaky 67 Step

If your filter is a type that requires oil sometimes that oil will get on the mass airflow sensor and skew the reading you can also try cleaning the mass airflow sensor with brake cleaner and Shop air
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Old 07-13-2018, 12:43 PM   #2553
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Re: Crusty Rusty Leaky Squeaky 67 Step

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Try unplugging the mass airflow sensor and take it for a drive see if it makes a change
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If your filter is a type that requires oil sometimes that oil will get on the mass airflow sensor and skew the reading you can also try cleaning the mass airflow sensor with brake cleaner and Shop air
The MAF looks like it did the day I installed it, clean as a whistle. However, unplugging it made a huge difference. It smoothed out at idle immediately and I was able to drive the short distance back home with no popping and banging. Do you believe this is due to a bad sensor or could it still be something in the tune?

I'm going to make another run and record data with the MAF unplugged. With it plugged in, STFT's were 25% on B1 and 28.1% on B2. Timing looked stupid too.
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Old 07-13-2018, 01:25 PM   #2554
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Re: Crusty Rusty Leaky Squeaky 67 Step

I sure hope it's something simple.....all this computer stuff is beyond me.
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Old 07-13-2018, 02:17 PM   #2555
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Re: Crusty Rusty Leaky Squeaky 67 Step

I think the majority of your issue is with the tuning. I would still clean the mass airflow sensor and blow it out there I don't think you have a bad sensor
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Old 07-13-2018, 02:34 PM   #2556
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Re: Crusty Rusty Leaky Squeaky 67 Step

what size is the intake tube? The tune needs to be modified if it is larger than stock size.
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Old 07-13-2018, 02:50 PM   #2557
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Re: Crusty Rusty Leaky Squeaky 67 Step

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I sure hope it's something simple.....all this computer stuff is beyond me.
Me too!
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I think the majority of your issue is with the tuning. I would still clean the mass airflow sensor and blow it out there I don't think you have a bad sensor
I'll give that a try. I think it would be surprising if the MAF became unstable with so few miles on it.
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what size is the intake tube? The tune needs to be modified if it is larger than stock size.
The 4" aluminum tube is from a kit made by Spectre. I modified it slightly with a 45 degree bend to relocate the filter, but the inside has been smoothed with a die grinder and cartridge rolls in the vicinity of the weld. I think it meets all the criteria WRT the placement of the MAF.

The second test drive with the MAF disconnected predictably set a DTC and the CEL was on the entire time but the truck drove great at all speeds and conditions. The trip to the tuner is 33 miles. I was planning to drive there if the truck would cooperate. Is there a downside to driving it without the MAF connected?
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Old 07-13-2018, 03:05 PM   #2558
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Re: Crusty Rusty Leaky Squeaky 67 Step

No it will be fine driving it. The ecm will compensate for lost signal as you can see with the fuel trim. It sounds like it runs to lean with maf connected. Keep us posted on the tune.
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Old 07-17-2018, 01:06 PM   #2559
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Re: Crusty Rusty Leaky Squeaky 67 Step

Not for nuthin- but it seems theres a bit of a block to the mount could it be the actual sensor isnt out in the airflow enough? Just a WAG from the peanut gallery
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Old 07-17-2018, 08:51 PM   #2560
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Re: Crusty Rusty Leaky Squeaky 67 Step

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No it will be fine driving it. The ecm will compensate for lost signal as you can see with the fuel trim. It sounds like it runs to lean with maf connected. Keep us posted on the tune.
Thanks, Jason, you've been a lifesaver!
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Not for nuthin- but it seems theres a bit of a block to the mount could it be the actual sensor isnt out in the airflow enough? Just a WAG from the peanut gallery
I'm not sure, Chip. The tube came as a kit from Spectre. The MAF mounting pad was already welded to the tube. I didn't make any changes other than cutting the tube and welding the halves back together 180 from stock so the MAF plug would be facing the engine. As you would surmise, I carefully ground the inside of the tube to be nice and smooth to avoid any turbulence. Should not have mattered, as that close to the wall it would be boundary layer anyway. But you know how OCD afflicted people are.

However, if that were a contributing factor, my mill could easily shorten up that pad. I'll see what Bryan has to say next week.
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Old 07-18-2018, 08:12 AM   #2561
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Re: Crusty Rusty Leaky Squeaky 67 Step

If it won't fit in the vise, I have one it will. Holler if you need anything.

Also, there's a related reply in my Big Black thread- http://67-72chevytrucks.com/vboard/s...d.php?t=767247

hope it helps.
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Old 07-18-2018, 06:18 PM   #2562
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Re: Crusty Rusty Leaky Squeaky 67 Step

Since you're talking about it, and I had a different but slightly similar issue when I first got my swap running, I'll throw this out there for you.

My STFT (short term fuel trims) were WAY off. I mean WAY WAY WAY off. They stored a 30-34 through all cells of my LTFT just to get my STFT in the 24-28 range. This is showing a severely lean condition. BUT... It smelled super rich. All things pointed to a vacuum leak, a bad connection to the O2 sensors, bad O2 sensors, or a bad MAF (although I could only fine one reference to a MAF sensor issue).

I replaced the MAF and had no change. Cleaned the old one and again, no change. Couldn't find a vacuum leak anywhere either.

So, I talked with my tuner, told him I had a larger intake (3.5" tube) than the van the motor came from, and wondered if he could play with the MAF tables to get it working. His first attemt was to bump it by 20% (so he told me) and it changed, but still in the low 20s for STFTs. 4 more revised tunes and I'm now at a LTFT of -3 to +4 (most at 0 to +1) and STFT of -4 to +11, most at about -3 or +5, depending on load.

All of my research said if you have fuel trims beyond a +/- 15, there are some major issues. Now, that's not to say you can't drive it, but the longevity of the engine would be compromised, however slightly. Talking with a local hotrod shop, they told me as long as I had my STFT in the high teens or low 20s I'd be okay for a short period, but definitely get it checked out before your first oil change.

I say all of this because you may very well have a tuning issue where the intake is allowing more air into the engine than the MAF can register due to the parameters in the tune. You may just need a good tuner to make some adjustments to the MAF tables and it COULD fix your issues.

Good luck!
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Old Today, 05:36 PM   #2563
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Re: Crusty Rusty Leaky Squeaky 67 Step

Thanks, Duane! I printed off a copy of your remarks and will add it to my list of topics to discuss with the tuner.
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