mistred

iTrader: (1)

I need help, I have a 2008 Impala SS 200K miles, Cylinder 4 misfire and random misfires Mostly with Cylinder 4 and others randomly!

Here is what I've done.
1) Replaced all New plugs (AC Delco 41-110 Gaped @ .40)
2) Replaced all New plug wires (Standard 27881)
3) replaced one new coil for cyl 4 (Standard UF413)

Same issue, P0300 along with service traction control.

3) Pulled the fuel rail and swapped #4 and #6 injectors.

Same codes.

4) Then I noticed that the throttle position % didn't match the peddle so I swapped both the Throttle body and the peddle with new.

5) Did an in place fuel injector clean using OTC Kit and 50% Seafoam 50% 93 octane gas.

Better idle and smoother engine but same codes...... So today I did a compression test, found next to no compression!

6) took off coils and valve cover and inspected all rockers, had a friend crank the engine and saw that the #4 intake rocker was not moving, so I pulled it and pulled the rod both were fine so I put the push rod back in and pushed on it to see if the lifter had collapsed, then had my friend crank the engine while I pushed on the rod. to my surprise it moved up and down. I then put the rod and rocker back on and had him crank it again. everything was working as it should visually! Did a compression check and had tons (maybe to much) Lots of fuel was spitting out. threw it all back together and .... now had a tic and same codes. Shut the car off and tighten the battery cable started it up and it was smooth as silk with full power and no misfires........ a mile down the road and got the code again.

What the hell am I missing?

2xLS1

iTrader: (25)

Does it have DOD/AFM? If it does #4 is a DOD cylinder. Probably have a bad DOD lifter. Pretty common problem on DOD engines.

mistred

iTrader: (1)

Just looked it up displacement on demand..... yes it does.
So it sounds like the lifter is bad.

mistred

iTrader: (1)

I assume this 5.3 is just like my lq4 and the head has to come off to change lifters?

G Atsma

ALL LS-based engines are the same that way

mistred

iTrader: (1)

I'm about to tare into this thing but before I do.

Could the ecu be the issue since this is one of the cylinders it shuts down for DOD? I ask because one minute it ran smooth (right after disconnecting and reconnecting the battery) and a mile latter it's back to running like crap.

Also I'm not sure I mentioned that the tic went away just as quickly as it started and at the same time it went away it started running good It has not come back. in fact I only ever heard the one time.

I'm just about done dumping money into this issue!