3.4L LA1 faulty fuel overflow valve ? PLEASE HELP !!

[Zebe9]

As in subject plus IAC replaced w/working one,Fuel pressure regulator replaced also,still engine sluggish,hard start when hot(usually).Some guy suggested faulty overflow/return valve on fuel line..What is it and where to look for ?
What would be noticeable syptoms of its failure ?

[Juglenaut]

I didn't think there was a return over flow valve on the return fuel line. As far I as know the regulator controls this function.

I'd say it is more than a sensor or extrnal mechanical device that is causing this problem.

Have you tested fuel pressure yet??

A engine can run like that if it gets to much or not enough fuel. Most times if it is running rich the computer will compensate to a point, even it it doesn't, carbon in the exhaust and on the plugs will exsist, which is usually black, and the engine exhaust is cooler and smells somewhat more like gas. A good color is light grey with minimal tan or browning, but others have differently running engines and colors can vary. To lean and the spark plug burns hotter in turn so does the so does the combustion chamber mainly effects the exhaust side, but causes more heat over all.

unburt, or partially burt fuel burns black kind of like when you hold a lighter to the bottom of a aluminum can.

[Zebe9]

IAC replaced w/good(?) new(used) one,now...

still have intermittent slugishness problems.
Some two weeks my car runs SUPER fine,reacts immediately for acceleration then...as if there were five cylinders engaged,not six.
Sluggish,hesitates a bit-it takes me now a year to investigate it.
The only things remained(except of changing the car )
might be fuel pump(but pressure shows 45) or ignition coils(DIS system),
loose harnesses to some sensor ?
REAL PROFESSIONALS are KINDLY asked for HELP !!
This car drives me nuts.
I have counted so much on Made in USA quality,but....this car is unpredictable and hard to diagnose...
Help me change this oppinion.

Uhu,this NO DTC condition !

[Juglenaut]

Well fuel injectors or wiring to them can cause intermittent problems.

A crank position sensor can cause the computer to over and under compensate at regular intervals so that the computer doesn't trip a code.

If the ICM itself goes out it goes out and never comes back on ussually. However conditions in both wiring and in the computer can cause issues with drivability modes, spark advance, and timing.

TPS can cause blips in Throttle position as it is a potentiometer and can wear dead spots in the travel.

[manny]

Like Juglenaut mentioned - check your fuel injectors for misfiring or no pulse at all: first check your spark plugs. If any one of them is dirtier than the rest, I would concentrate on that cylinder for a bad injector. Do an ohms test on all of your injectors. I'm not sure of what your resistance should be, but the tolerances should all be pretty close. If any injector reads 0.0, it's gone. Also check your injector harness with a noid light. pull one harness at time, connect the noid light to the injector wiring and crank the engine, (or have someone crank it for you) the noid light should blink. check your spark plug wires after dark - any bad ones will show blue arcs where the insulation is failing.

also- hard starting when hot is a classic symptom of a failing ignition module for the DIS - have yours tested at your local autozone, murrays, napa etc...