P0171-P0174 after plenum & T/B install - Ford Mustang Forum
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post #1 of 4 (permalink) Old 07-18-2010 Thread Starter
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P0171-P0174 after plenum & T/B install

96 GT with complete PI motor swap, shorty equal lengths, o/r x, flowmaster cat back, trickflow plenum, trickflow 75mm t/b, k&n intake. TPS sensor was set at 0.999, battery was reset and car idle high for alittle then surge then idle at ~800 then idle rough then threw codes P0171 and P0174. Checked for vaccum leaks as this was the most common result when researched none where found. Fuel filter was changed during motor swap (motor only has 2800 miles on it). Injectors where also cleaned during motor swap; was wondering if anybody had any suggestions on what it could be causing the problem? Codes where cleared and car still idles slightly rough and surges very slightly and when the fan kicks on the car idles so low that it seems like it wants to die?

Any suggestion would be appreciated.

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post #2 of 4 (permalink) Old 07-18-2010
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do you have a exaust leak before the o2's? if you have a good enough leak it might trick the car into thinking its lean causing it to dump too much fuel, but i would double check your gaskets and just double check for vaccum leaks, as you said thats the most common thing, if you didnt do it the first time spray some carb cleaner around the intake and the tb and see if the idle changes.

1993 lx hatch, 5 speed, all stock except american muscle cai, flowmaster mufflers, hids and a pro 5.0 shifter, more to come soon.
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post #3 of 4 (permalink) Old 07-18-2010
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I would try the carb cleaner spray and listen for and changes in your RPM`s sounds like you might have a vacum leak some where. Good Luck !!!!!

2003 Sonic Blue Cobra Convertible with Fidanza aluminum flywheel, Spec stage 2 plus clutch, DND 26 spline input shaft, UPR upper n lower non adj control arms,Ford racing rear cover on the 8.8 that was swapped when the IRS was removed, Eibach pro kit, 3:73 FRPP rear gear, 2.8 blower pully, Mack full lengths n Mac flow chamber..
Production number 914
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post #4 of 4 (permalink) Old 07-26-2010 Thread Starter
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So I finally got around to checking out my problem with my GT and I did some simple fuel pressure tests and came to the conclusion that my fuel pressure regulator gave out. After putting a fuel pressure gauge to my car it sat around 20 psi at idle; an easy way to tell wether your fuel regulator gave out on you is to pinch the return line and to watch the pressure gauge if it spikes your fuel pressure regulator is done if it doesn't move your fuel pump maybe causing the problem. NPI motors are supposed to be at 30-45 psi stock and PI motors are set at 40-70 psi from the factory and this is with the vacuum hose attached on the 96-97 models. I replaced the regulator with an Aeromotive adjustable regulator set it to 40 psi with the vacuum hose attached since I have the PI motor swap and all problems have been solved. Just thought if anyone else is having the same problem this might help; please check for vacuum leaks prior to conducting this test as normally these codes appear when there is vacuum leak and not an actual fuel related problem.
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