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Old 10-06-2014, 07:30 AM   #1
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GT40P header issues

I recently jumped on the gt40p train. So I put the gt40p heads on with the Mac gr40p headers on I have 24lb injectors with C&L maf I have created a rich situation an when shifting from 1-2gear I'm getting a backfire any ideas how to correct this? Thanks.


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Old 10-06-2014, 01:58 PM   #2
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Backfire....check for timing issue.
Then check for vacuum leak issue.
Maybe a header leak issue also.


If that all checks out then we will try step 2.
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Old 10-06-2014, 02:02 PM   #3
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I have tried all of that my brother what is step 2?
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Old 10-06-2014, 02:07 PM   #4
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Where is the backfire coming from?


Like I said that is usually a timing issue so check to make sure the balancer is in good shape meaning you have the right timing.


How do you know it is running rich?


Did you run your codes?


Swap to 19's and change out the calibration tube (I know more work and it sucks) and see what happens then.
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Old 10-06-2014, 02:10 PM   #5
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Cool brother I will check timing again after work thanks for all of your help I will keep you posted.


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Old 10-06-2014, 02:12 PM   #6
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Try not to get overwhelmed and try not to throw parts at it.


Go over the simple things as sometimes they get overlooked.


I had a vacuum leak I could not find and it turned out when they machined the heads the intake no longer fit flush and it was causing a tiny little vacuum leak. Took me 3 intake gasket sets to figure it out LOL.
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Old 10-06-2014, 02:18 PM   #7
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so a simple leak will cause it to backfire was not doing it before i changed out the headers to bigger headers had the cast iron headers before that came off the explorer now have Mac shortly headers and she backfires.
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Old 10-07-2014, 10:19 PM   #8
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Hey just wondering what kind of gaskits did you use for your gt40p heads?

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Old 10-07-2014, 10:22 PM   #9
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Standard not the brass ones.


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Old 10-07-2014, 11:14 PM   #10
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Like for the header gaskit and intake gasket where did u buy them?

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Old 10-07-2014, 11:15 PM   #11
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Autozone.


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Old 10-08-2014, 07:11 AM   #12
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So an update I have fixed the backfiring. Put the 19lb injectors an sample tube back in the car an played with the timing it's not perfect yet throttle responds is a little sluggish but no backfiring I will keep playing with the timing to get it perfect but I was wondering what I need to do to put the 24lb injectors back in the car an not bring the backfiring back any ideas would be greatly appreciated. Thx fellas.


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Old 10-08-2014, 01:10 PM   #13
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You need to tune the computer for 24s. Actually, you need a tune period.
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Old 10-08-2014, 04:46 PM   #14
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How are you timing this thing? You shouldn't be playing with it.


Now the sluggishness could be from the timing also as it is too low.


You wanna run 24 lb injectors....make 300 hp and your car will need it.
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Old 10-08-2014, 04:56 PM   #15
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i have always done my own timing i built the motor myself. i dont have the cash to pay another person to do what i can. when i have the 24lb injectors is when i was getting a loud loud backfire so i put the stock ones back in it and played with the timing and it went away but it is now sluggish in 3-4 gear not like it was before i put the headers on it. who should do my timing.
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Old 10-08-2014, 07:09 PM   #16
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So you are just going from 19s to 24s and trying to make it work with timing? You do know how mass air efi cars work right?

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Old 10-09-2014, 09:51 PM   #17
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I just put new plugs an wires in the beast an timed her she now runs like a raped ape oh yeah feels good when u work hard for something an it does what u want thanks for all of ur help.


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Old 10-10-2014, 08:41 AM   #18
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Ok I re-read your OP, you have a C&L MAF which I'm guessing is "calibrated" for 24s, not 19s. That will be fine, set timing to 14 degrees advanced with the spout out and run 93 octane and it should **** and git.

As long as the cam is stock you won't need a tune, not with a fox computer.
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Old 10-10-2014, 10:19 AM   #19
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It's has an f303 racing cam.


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Old 10-10-2014, 09:13 PM   #20
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Then it will benefit greatly from a tune.
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