'99 3.8 V6 randomly looses power - Mustang Evolution

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Old 08-20-2016, 09:25 PM   #1
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Location: York County
Region: Pennsylvania
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'99 3.8 V6 randomly looses power

I've a '99 Mustang 3.8 V6 with the 5 speed manual transmission. A problem has developed that has been slowly getting worse over time and I cannot figure it out. I'm experiencing random losses of power with no apparent rhyme or reason as to why.

Symptoms are as follows: I'll be driving along and go to pull a grade, or accelerate from a stop, and as I apply throttle the engine seems to bogg, miss, and hesitate. At times, fuel can be smelled from the exhaust, and fuel economy seems to be declining as well. When I depress the clutch to either upshift or downshift, the engine smooths out. When I release the clutch, and apply more throttle, the engine will again bogg, miss, and hesitate. The more throttle that's applied, the worse the symptoms. Now here's the kicker... If I turn the ignition off completely and immediately restart, the car runs normally. This trick works, especially when in heavy traffic, but the problem is returning more frequently as time goes on.

I've replaced the coil pack, since symptoms for a failing pack matched what I am experiencing. But that did not remedy the problem.

I've had the OBDII checked for codes, despite having no "check engine" or "service engine soon" lights. As expected, nothing was found.

Occasionally the "theft" light remains illuminated, and the odometer goes dark while driving, but these issues seem to have no correlation to the engine trouble.

The plug wires seem to be in very good condition as well. The insulation is in tact, is soft and supple, with the stamped markings still clearly legible. The rubber boots at either end of the wires are also in very good condition, as are the metal contacts.

I feel that if the spark plugs themselves were faulty, the symptoms would persist despite restarting the engine. But, maybe I'm wrong?

Has anyone else experienced a similar problem with their 3.8 V6? If so, how was the problem corrected? I'm rather mechanically inclined and not being able to figure this out is driving me crazy!

Thanks for taking the time to read this post!
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Old 08-20-2016, 09:36 PM   #2
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Location: Salinas
Region: California
Posts: 7,705
Have you done a fuel pressure test?
Fuel system pressure at idle should be 35-55 psi. The system should hold pressure with the key off for 5 minutes and lose less than 5 psi loss from the indicated operating pressure.
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