2005 Chrysler Town & Country 3.8 no power upon initial acceleration

no check engine light.
spark plugs replaced
wires replaced.

originally, i had cylinder 3 misfire, but once i changed the plugs and wires, the code went away.
the cat is not clogged. symptom is that when you mash on the gas, the minivan doesn't get up and go like before.
Can someone give some direction as to the road in making this repair.
most of the other old plugs looked good. I know is kind of broad what i'm mentioning, but that is all I got to go for now.

thanks fellow techs

Are you able to get Fuel Trim data at idle, 1500, 3500 rpm?

Are you able to check the fuel pressure with a guage? 58 psi is the spec. Does it drop on snap throttle.

Is the power loss only on initial acceleration, then the motor accelerates normally?

Based on what you said, I would do a quick fuel pressure test, just to rule that out.

I was able to get fuel trim data. this is what it revealed.

Idle
STFT = -3.9%
LTFT = -0.7%

1500 RPM
STFT = -6.2%
LTFT = -7.8%

2500 RPM
STFT = -7.0%
LTFT = -3.9%

Obviously if I'm interpreting this readings correctly, there's a fuel system issue. the computer continuously is taking away fuel. something in the system is adding fuel. Don't know what it is. Can you help me interpret these readings correctly? The 3 other questions I will answer during the week as time allows. But I will answer all 3 of them. thank you Weycraze



LTFT = - 3.9%

my next test will be fuel pressure. I know the 3.8 does not have a schroeder valve. any suggestions as to the proper tool and I can use to tap into the system?

how do i upload photos to here? thank you

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how do i upload photos to here? thank you

Is the power loss only on initial acceleration, then the motor accelerates normally?
no, during acceleration acceleration and also during the drive cycle when I'm attempting to pass another vehicle, there's no power at all. thanks.

You're sure about the cat not being plugged? :huh: Because that sounds exactly like an exhaust restriction. The rich fuel trims would tend to support that.

I wouldn't bother with a fuel pressure test, as the rich trims tell you it's getting enough fuel. I'd suggest a WOT run through first gear while watching the upstream O2 and the MAP. If the MAP shows atmospheric pressure, and the O2 stays rich, then fuel and the intake are not at fault.

I agree with Tyler after seeing those fuel trims, and the possible plugged exhaust.

I would pull out the front 02 sensors, and try an open loop acceleration road test, if thats possible. Don't burn you harnesses!

One thing that really bugs me is the Calculated engine loads.

42.3% @ 762 rpm
34.1% @ 1763
35.6% @ 2405

I have a question for Tyler, do these numbers further support a possible plugged exhaust? I would expect Calc LD to increase with rpm.
This is high at idle, low, then high!

I think that's directly related to the MAP sensor behavior? In his pictures, you can see the MAP is lowest at idle, and improves off idle. That's typical intake vaccum behavior, IMO.

Not super familiar with MAP sensor Load calculations, TBH. :blush: It's not a PID I normally use on speed density systems.

I still feel exhaust coming out the tail pipe. Can I have a partial exhaust blockage that produce these fuel trim numbers?
I don’t have a fancy exhaust back pressure tester to test the system.
So the next test I will perform is removing the front 02 and perform a test drive and see what happens. As you suggested.

It only takes 2psi of exhaust backpressure and you have lack of power at all ranges. Does the exhaust smell rich? (unburnt fuel), as this would suggest excessive fuel pressure.



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