Maf sensor and headers

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Joeyk94

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Ok so I put long tube headers on my truck in march along with a 3 inch y pipe to a 3 inch flowmaster. I HAVE NOT TUNED IT YET. Ever Since then the truck only like to stay running if you leave the maf sensor and intake temp sensor unplugged. If you plug those in it starts running rough and if you try slowly revving it just falls on its face. It ran fine when it had the stock exhaust on it. Is this because the tune is off and doesn't have downstream o2 sensors?

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Christian Steffen

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Downstream o2's shouldn't make a difference, they're just there to make sure the cats are working. I'm doubting that unplugging the IAT is doing anything to help it run, have you tried just unplugging the MAF?

You still have the upstream o2s hooked up right? Have you tried letting it run long enough to enter closed loop? What engine is this?
 

Joeyk94

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I have tried it with just the mad itself it clears up a little bit but not as much as if they were both unplugged. When I put the headers on a week later or so I put new upstream o2s in. Its my daily driver so I'm sure its entered closed loop. Its just a 5.7 vortec. I didn't even think about it till rightnow same time this problem started I put an accel coil in it. What are the chances its that?

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Jorge6.5

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Yep it's that coil.

Changing up the exhaust like that really can't affect how it runs all that much. I did custom exhaust on my truck along with deleting rear o2 sensors and she purrs. No tuning either
 

Joeyk94

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So I changed the coil back to the stock. When I started it ran super smooth. When I rev it, its clean and crisp. As soon a I plug the maf and iat in and start it. It acts like it has a huge cam in it and the idle gets very rough and really choppy I try and see if I can find an rpm where it cleans up. All it does is spit and spudder like its out of fuel or I unplugged 6 of 8 plug wires. When I let it idle after that it just lopes from 300 rpm to 900 rpm until it just stalls (sounds cool at first but I know its not good haha). With it unplugged it runs fine but at higher rpm(4k to stock shift point) it acts like its either staving for fuel or timing is off because it will slowly climb in rpm versus how quick during (idle to 4k)

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Tom P

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What brand of O2 sensors did you use? I have always had good luck with delco or denso, and very crappy luck with bosch sensors. A similar thing happened to me on a little toyota pickup. Engine ran great and then I installed a header and new exhaust system and a bosch O2 sensor. Less than an hour after running with the new exhaust, the truck ended up with almost the same issues you're talking about. I went to a local mechanic who was good with 22RE's and he said before he'd touch it I needed to change back to a denso O2 sensor and run a can of seafoam through the fuel system and drive it like I stole it. I took his advise and 35 miles later the thing purred like a kitten and never gave me any troubles again. Granted, this was a completely different truck but it does have the same basic components.

My K3500 was giving me similar fits as well but only after making it in to closed loop. That issue was solved by new O2 sensors and spark plug wires.
 
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