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Discussion Starter #1
I have a new bug to figure out on my 91 GT. For the last couple weeks when I crank 'er up to 5500 the car falls off flat on its face and starts to backfire and sputter. I have new AFR 165's and the Holley Systemax upper and lower intake on a stock bottom end. Not boosted or NOS'd. Do I have a fuel delivery problem? I also installed an adjustable regulator and a 255 lph pump. Or possibly a broken valve spring? The car drives perfectly under 5500 but every time, right @ 5500 it falls off. I installed the intake and heads almost a year ago and this is the first problem.
 

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distr and coil, also powers to them
 

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Also could be weak valvesprings. This would not happen all of a sudden, and it would not happen until a higher RPM when the engine was cold.

Steve
 

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Discussion Starter #5
I'm kinda leaning towards the valvesprings also. The car used to run flawlessly until the factory rev limiter until a week or so ago. I checked all of the plugs, and the cap and rotor are clean. There appears to be no excess play in the distributor either.
 

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What cam are ya runnin??? If its stock why r ya tryin to take it to 5500??? And what is tellin ya that u r shiftin at 5500?? Anywho....do u have acess to a vacuum pump gauge??? If so here is to tell if the valvesprings are weak, or broken...with the pump hooked up the needle will fluctuate between 10"-21"Hg at idle rapidly. Of course, the fluctuations will increase with engine speed. And this will happen whenever the valve attempts to close.
 

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Discussion Starter #7
I usually run it up towards 6000 because with the heads and intake the beast would pull right up 'til the limiter. I know I'm not the only one either! How do I know I'm shifting @ 5500? Good ol Auto Meter instrumentation. I do have a vacuum gauge onboard but it hasn't shown a difference the whole time. So am I looking at spark or fuel delivery issues now?
 

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Discussion Starter #9
Fp is set at 41 psi, stock 19 lb/hr injectors (I know they're small but I do plan in upgrading once I get this bug worked out), stock rails, filter is about 6-8 months old. No ignition mods. I'm starting to wonder if there might be some deflection in the stock distributor or if one of the gears might be wearing?
 
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