Mechanics

VALVE CLATTER/HESITATION/LOW POWER/BAD MPG

2007 Chevrolet Impala • 154,300 miles

Ok so I've been battling this problem for a while to no avail:
My 07 impala 3.5 flex is making valve train noise after replacing intake manifold gasket, and replacing plugs and wires I've been told it may have something to do with pushrods and or hydraulic lifters here's my testing so far

Compression
1-198
2-202
3-195
4-203
5-201
6-200

Fuel pressure-
steady 58 psi running holds 50psi after key off
Fpr- operates fine

Vacuum-
Cranking 5"hg
Idle- 19 average but constantly fluctuates/flutter 3-4"hg
Snap throttle-0 and 25"hg high back to 19"hg slowly with a erratic fluctuation
1000rpm-20"hg pretty steady
2500rpm-22"hg

Good spark
Ac delco iridiums
Plugs gapped at 0.040"
Clean filter

Car has a weird loping feel at idle (very slight)
Can here constant ticking in car at idle
Idle is normally at 750-800rpm but intermittently it will drop about 100rpm or so when brakes are applied, and the engine begins to lope
I experience very inconsistent acceleration, loosing speed up hills
Doesn't want to hold rpms cruising in 2 or 3

The tranny isn't in the greatest condition but it has driven pretty much since the day I got it, and my problems got way worse after the manifold gasket replacement which is why I'm thinking valve train issues
Avatar
Pos07impala
March 1, 2012.




Any insight would be appreciated

Tiny
Pos07impala
Mar 1, 2012.
If you didn't have any problems until the intake gasket replacement then recheck your work or who ever did it. The pushrods are different lengths so could be int eh wrong positions as well as the gasket could be binding a pushrod. Your compression looks ok as high to low is only 8 # difference. Maybe the pushrods aren't adjusted correctly either.

Hmac300
Mar 1, 2012.
Well see that's where I'm stumped I personaly did the intake gasket, all pushrods in correct order, no wear on the gasket the first time I did it, second time I checked everything over againand I couldn't notice anything wrong, only thing I noticed was that the number 2 Pushrod looked a little stressed maybe bent very very slightly, but I don't see how that would cause such a lack in power, and its not missing.

I also don't think it has to do with the pushrods necessarily bc I have driven about 4000 miles on it like it is

Any other ideas?

Tiny
Pos07impala
Mar 1, 2012.
Also the rpms will jump when I LET OFF the gas cruising at like 45.
I just want to eliminate some possibilitys
A collapsed lifter would be noted in a loss off compression correct?
And if the Pushrod was indeed bent wouldn't it missfire?
Is there any way a rocker arm pedestal could be installed the wrong way?

Tiny
Pos07impala
Mar 1, 2012.
I mean jump as in 200-400 rpm once and then it decelerates as it should

Tiny
Pos07impala
Mar 1, 2012.
Scan for codes, check fuel pressure and clean throttle plate on both sides with choke cleaner. Then check for a vacuum leak with choke cleaner. Also clean iac valve and make sure duct work has no holes in it and connected to throttle body.

Hmac300
Mar 1, 2012.
No codes, fuel pressure at 58 steady, and fuel pressure responds as it should on acceleration, throttle plate cleaned alreAdy, and there is no iacv on this car, its a drive by wire so the throttle body is electric, and tps/iac are basically one unit

Tiny
Pos07impala
Mar 1, 2012.
I also searched everywhere for a vacuum leak to no avail, the ST AND LT fuel trims don't show any evidence of any cylinder(s) running lean due to a vacuum leak

Tiny
Pos07impala
Mar 1, 2012.
Without hearing this car it can only seem like a lifter problem. Maybe one is collapsing, and it seems to me like apushrod problem. The intake pushrods should have yellow stripes and exaust should have blue stripes. Or the intakes shold be 5.81 in long andexaust 6.1 in long. Also the rocker carms should have been torqued to 25 ft. Lb. As that is the adjustment. I'd recheck it once more to make sure they are right and torqued right.
AD

Hmac300
Mar 2, 2012.
One other thing, because of the valve clatter it is probably making your knock sensor go off and it's retarding the timing causing your low power.

Hmac300
Mar 2, 2012.

AD