Mechanics

CAR LOOSES POWER GOING UP HILLS

2007 Chevrolet Impala • 154,000 miles

The car has issues picking up speed from a stop, going up hills I will loose anywhere from
5-20mph unless I make the tranny downshift, the car will rev up just fine if you hit the gas good enough, but when I'm cruising it doesn't want to go above 2grand without a healthy downshift.

Tests-
Vacuum- at idle it fluctuated +/- 1 at 17"hg
1000rpm-18-19
2500rpm-20-21
Snap throttle- down to zero and up to 25"hg then very gradually returns to 17"hg fluctuating +/-1

Compression
1- 203psi
2- 195psi
3-205psi
4-201psi
5-198psi
6- 201psi

Tried-inatke manifold gasket upper and lower
Spark plugs (gapped right on.040)
Wires
Air filter
Tried swapping coils
Cleaning throttle body (needed it)
Fuel trim reset (after replacing any of the above)
Cam sensor
Maf cleaned

The issue- no CEL, no missfire (idle, cruising, heavy load)
Idles smooth but when I come to a stop it goes from 750-800 to about 575-600 when I'm holding the brake in drive. Rpms jump (only when I'm cruising and I let off the gas) tranny shifts fine, exhaust note is irregular (sounds rough) car gets ok gas mileage if I don't make it downshift too much, getting on the onramp at the beginning it feels as I'f I have a complete hesitation and no acceleration until I tap the gas a little more then it continues as. Usual.

Helpful information- when I. Did the intake I. Noticed one Pushrod was. Stressed more so then the other 11 and it was very very very slightly bent, I don't know if this has anything to do with it tho since compression was good. I do also have a little more valve train noise as apossed to normal operation. Idle sounds a little weird to with a constant lope sound/feel (very little if any rpm change(25-50rpm)
Avatar
Pos07impala
February 23, 2012.



Let me clarify the vacuum only fluctuated +/- 1 at idle
1000rpm- 19
2500rpm- 21

Tiny
Pos07impala
Feb 23, 2012.
Vac gauge to fluctuate like that could be just the valve over lap where both valves are open-could also be an exhaust restriction/also check the throttle position sensor/EGR valve

Rasmataz
Feb 23, 2012.
Ok and could one slightly bent pusrod cause this? And what would be a definitive test to rule out the tps? I'll pull the pre cat 02 later and see if it helps.

Tiny
Pos07impala
Feb 23, 2012.
A bent pushrod will affect the valve lash clearance and cause the valve not to open/close properly on time-You check the TPS closed and wide open throttle voltages

Rasmataz
Feb 23, 2012.