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Discussion Starter #1 (Edited)
Hey guys, i'm chasing down a low rpm miss and intake pop. Here is what I got:

*gt-40p heads (intake lightly ported, exhaust CNC ported)
*TrickFlow Street intake
*65mm FMS throttle body
*24lb FMS injectors
*80mm Pro-m mass-air
*Custom cam (buddy rawls)
*MAC 1 5/8" longtubes
*2.5" x-pipe & exhaust
*stock computer (A9L)

My fuel pressure is set at 37 with the vaccuum. I'm having a slight miss at low RPM and intake pop. I've tried lowering and raising fuel pressure but can't really shake the intake pop. It's rough < 2500 rpm and pops in the intake, then starts running good. The weird thing is, sometimes it runs fine under 2500, but then 2 minutes later, it will start running rough again.

EDIT: I should also mention the TPS is set at 0.090 i believe, and pretty much all sensors were replaced when new engine went in (2400 miles ago). I've also cleaned the 10-pin connectors.

Could my injectors be too big?

Any ideas?
 

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Check your plug wires, looking for cracks or wires touching. Might want to run the engine in the dark and look for wire arc. Just a thought.
 

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A bad wire could cause it as mentioned above as well as a cracked or carbon tracked distributor cap. But I am thinking it may be something in the valve train. Did you set the lifter preload correctly? If your rocker arm isn't shimmed correctly you could have an intake valve hanging open. That would cause a low RPM miss and roughness as well as popping through the intake.
 

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Subscribing to this thread.

I've got the same problem. When the motor's cold, it will stumble and pop through the intake w/ light throttle application.

Might be a slight lean condition as well.

Greg
 

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Discussion Starter #6
Thanks for the helps guys.

The plug wires (Taylor Pro) and distributor cap are new (when the engine was installed). However, I will double check them as I'm running gt-40p's with longtubes (very tight fit). I do have one plug wire that is stock that i had to put on b/c i broke one of the taylor wires installing some boot protectors.

I had a buddy that owns a shop set the lifter preload. I'm running Harland Sharp roller rocker with the stud conversion kit. If they were improperly set, would they make noise? They are pretty quiet and I did not have this problem in the past, which may be a stronger argument that one of my plug wires or something in my ignition is somehow messed up.
 

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A couple of years ago in my 89(similar setup as yours except for heads) I had the same problem. It wound up being a combo of 1 bad injector and a bad mass air sensor. The only difference is that it popped through the intake all the time not just at low rpm. just throwing that out there. Could also be vacuum leak.:confused:
 

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Discussion Starter #9
Something else i noticed from the last couple of days. It seems the car runs pretty good when cold but starts stumbling after it warms up. Does this point at anything in specific?
 

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What I found when mine was doing that was the pushrods were too short. Once I changed them to the correct length it went away. It happened more when it was cold. After it warmed up, things were better. Another problem I had was 38 psi fuel pressure wasn't enough for my 80mm MAF. I had to use at least 40 psi.
HTH
 

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I'm not getting rude at all. I just want to know why you guys put 80mm Mass Air Meters on in combination with 65mm throttle bodies? The problem is that the sensor, which is calibrated to the injectors, says this much air is coming through, but the throttle body only lets less air through. Now, my 87 mustang was converted to mass air still with stock intake. After installing this kit and making E303 cam, gt-40P head, and 1.7 roller rocker comb., I found it was popping like crazy through the intake. I had backfiring as well, but intake was bad. So, I added a C&L 76mm MAF for 24# injectors, 70mm Accufab TB, Ported Cobra upper intake, ported GT40 lower intake. I also replaced the Air Charge Temperature Sensor, The temp sensor, oxygen sensors, and ignition coil. Now it never pops through the intake. It would still backfire through the exhaust, but I adjusted the fuel pressure and now it runs good.
 

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Discussion Starter #13
blueovaldrew said:
I'm not getting rude at all. I just want to know why you guys put 80mm Mass Air Meters on in combination with 65mm throttle bodies? The problem is that the sensor, which is calibrated to the injectors, says this much air is coming through, but the throttle body only lets less air through. Now, my 87 mustang was converted to mass air still with stock intake. After installing this kit and making E303 cam, gt-40P head, and 1.7 roller rocker comb., I found it was popping like crazy through the intake. I had backfiring as well, but intake was bad. So, I added a C&L 76mm MAF for 24# injectors, 70mm Accufab TB, Ported Cobra upper intake, ported GT40 lower intake. I also replaced the Air Charge Temperature Sensor, The temp sensor, oxygen sensors, and ignition coil. Now it never pops through the intake. It would still backfire through the exhaust, but I adjusted the fuel pressure and now it runs good.
I have since sold the car, but I can tell you that every sensor was new on the car. Also, I had the C&L 76mm mass-air on the car before and it was much worse, that's why I switched to the Pro-m.
 

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I just ran into this problem in a Trick Flow heads/intake car. Full package, big cam, rockers, etc. Turned out to be the meter (Pro-M).

Threw on a C&L 76 and it runs like a raped ape. :D
 
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